CA2278317A1 - Method and system for dynamic allocation of bandwidth in asynchronous transfer mode (atm) switching systems - Google Patents
Method and system for dynamic allocation of bandwidth in asynchronous transfer mode (atm) switching systems Download PDFInfo
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- CA2278317A1 CA2278317A1 CA002278317A CA2278317A CA2278317A1 CA 2278317 A1 CA2278317 A1 CA 2278317A1 CA 002278317 A CA002278317 A CA 002278317A CA 2278317 A CA2278317 A CA 2278317A CA 2278317 A1 CA2278317 A1 CA 2278317A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L49/00—Packet switching elements
- H04L49/30—Peripheral units, e.g. input or output ports
- H04L49/3081—ATM peripheral units, e.g. policing, insertion or extraction
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing
- H04Q11/0428—Integrated services digital network, i.e. systems for transmission of different types of digitised signals, e.g. speech, data, telecentral, television signals
- H04Q11/0478—Provisions for broadband connections
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/54—Store-and-forward switching systems
- H04L12/56—Packet switching systems
- H04L12/5601—Transfer mode dependent, e.g. ATM
- H04L2012/5629—Admission control
- H04L2012/5631—Resource management and allocation
- H04L2012/5632—Bandwidth allocation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/54—Store-and-forward switching systems
- H04L12/56—Packet switching systems
- H04L12/5601—Transfer mode dependent, e.g. ATM
- H04L2012/5629—Admission control
- H04L2012/5631—Resource management and allocation
- H04L2012/5632—Bandwidth allocation
- H04L2012/5635—Backpressure, e.g. for ABR
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- Computer Networks & Wireless Communication (AREA)
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- Data Exchanges In Wide-Area Networks (AREA)
Abstract
The present invention is directed to a method and system for dynamically adjusting the total bandwidth that an asynchronous transfer mode (ATM) switching system (105) can make available to Available Bit Rate (ABR) virtual circuits by determining the total bandwidth allocated to the inactive ABR
virtual circuits in the switching system (105), and making available the bandwidth allocated to the inactive ABR virtual circuits to the active ABR
virtual circuits in the switching system (105). When transmission of cells resumes for an inactive ABR virtual circuit, the switching system allocates new bandwidth to the virtual circuit. Furthermore, the switching system (105) dynamically adjusts the total bandwidth that the switching system (105) can make available to ABR virtual circuits by recomputing, at fixed time intervals, the total bandwidth that is available to the active ABR virtual circuits that are bottlenecked at the switching system (105).
virtual circuits in the switching system (105), and making available the bandwidth allocated to the inactive ABR virtual circuits to the active ABR
virtual circuits in the switching system (105). When transmission of cells resumes for an inactive ABR virtual circuit, the switching system allocates new bandwidth to the virtual circuit. Furthermore, the switching system (105) dynamically adjusts the total bandwidth that the switching system (105) can make available to ABR virtual circuits by recomputing, at fixed time intervals, the total bandwidth that is available to the active ABR virtual circuits that are bottlenecked at the switching system (105).
Description
METHOD AND SYSTEM FOR DYNAMIC ALLOCATION OF BANDWIDTH IN
ASYNCHRONOUS TRANSFER MODE (ATM) SWITCHING SYSTEMS
WO 98!31156 PCT/US98/00781 BACKGROUND OF THE INVENTION
The present invention relates generally to asynchronous transfer mode (ATM) switching systems, and more particularly, to a method and system for dynamically allocating bandwidth to Available Bit Rate (ABRI virtual circuits in ATM
switching systems.
In an ATM network, a virtual source (VS) transmits data in the form of fixed sized cells to a virtual destination (VD) through a connection (referred to as virtual circuit) established between the virtual source and the virtual destination.
The virtual source and virtual destination may be a telephone. video equipment, facsimile, computer. edge-router, edge-switch, etc. The cells may include any type of digitized information. including audio. computer data, video, multimedia, Internet data, etc.
For example, in a network that uses Transmission Control Protocol/Internet Protocol (TCP/IP) over ATM, a virtual source may be an edge-router at the entry to an ATM
network. An entry edge-router segments the incoming TCP/IP data packets into one or more ATM cells before transmitting each cell to the ATM network. Similarly, a virtual destination may be an edge router at the exit of the ATM network. An exit edge-router reassembles incoming ATM cells into TCP/IP data packets before transmitting each packet to its destination.
When establishing a virtual circuit through an ATM network, a virtual source can select one of five different categories of service: Constant Bit rate (CBR), Variable Bit Rate - Real Time (VBR-RT), Variable Bit Rate - Non Real Time (VBR-NRT), Available Bit Rate (ABR), and Unspecified Bit Rate (UBR). ATM Forum Traffic Management Standard of tm-0056.00 describes each of these services.
The ABR service determines excess bandwidth in the network and uses network management methods to reallocate the excess bandwidth among the virtual circuits in the network to reduce network congestion and cell loss. In negotiating an ABR virtual circuit, a virtual source negotiates a peak cell rate (PCR) and a minimum cell rate (MCR) with the ATM network. PCR is the maximum cell rate a virtual circuit can support. MCR is the minimum cell rate that a virtual source requires a virtual circuit to support. The ABR service uses the negotiated PCR and MCR
parameters to provide a guaranteed quality of service concerning bandwidth .r i availability and cell loss in a virtual circuit.
When a virtual source selects the ABR service, the virtual source periodically generates a resource management (RM) cell to get feedback from the network on the rate at which the virtual source can transmit cells on a virtual circuit without causing loss of cells due to network congestion. Typically, a virtual source generates an RM
cell for every thirty-one cells it transmits or at the expiration of a fixed time interval, whichever occurs first. The network processes the RM cell, updates virtual circuit bandwidth information in the RM celi, and returns the RM cell to the virtual source.
The virtual source then dynamically adjusts its rate of cell transmission based on the bandwidth information contained in the RM cell.
An RM cell generated by a virtual source is referred to as a Forward RM cell.
The Forward RM cell passes through one or more switching systems in the network before reaching a virtual destination. The virtual destination processes the Forward RM cell and returns a Backward RM cell to the virtual source. The Backward RM
cell passes through one or more switching systems in the network before reaching the virtual source.
A virtual source maintains the MCR, current Allowed Cell Rate (ACR), and the PCR associated with the virtual circuit. ACR is the rate at which the network allows the virtual source to transmit cells on a virtual circuit. When a virtual source receives a Backward RM cell, based on the bandwidth information in the Backward RM cell, the virtual source computes a new ACR. Consequently, ACR dynamically changes as the network traffic changes and as the virtual source receives feedback from the network.
A Forward RM cell includes an MCR field, can ent cell rate (CCR) field, and an explicit rate (ER) field. CCR is the rate at which a virtual source is transmitting cells on a virtual circuit at the time the virtual source generates a Forward RM cell.
ER is the rate at which the virtual source wishes to transmit cells on a virtual circuit.
A virtual source cannot set the ER field in a Forward RM cell to be greater than PCR.
After generating a Forward RM cell and setting the MCR, CCR, and ER fields in the Forward RM cell, the virtual source transmits the Forward RM cell to the network.
When a virtual source transmits a Forward RM cell, the Forward RM cell passes through each switching system on the path of the virtual circuit to the virtual destination. Each switching system on the path can either keep the ER in Forward RM cell the same or decrease the ER to a lower rate. However, according to ATM
Forum Traffic Management Standard of tm-0056.00, a switching system cannot decrease the ER below the MCR for the virtual circuit. Furthermore, a switching system cannot increase the ER for the virtual circuit. A switching system that allocates bandwidth to a virtual source by setting the ER field in an RM cell is referred to as an ABR Explicit Rate (ABR-ER) switching system.
When a Forward RM cell associated with a virtual circuit arnves at an ABR-I 0 ER switching system, the switching system determines an upper threshold (referred to as "Cutoff ') for the bandwidth that can be made available to the virtual circuit in the switching system. If the switching system determines that the computed Cutoff for the virtual circuit sets the ACR in the virtual source (i.e, the switching system computes the smallest Cutoff among all of the switching systems on the path of the 15 virtual circuit), then the switching system considers the virtual circuit to be "bottlenecked here" or bottlenecked in the switching system. If the switching system determines that the computed Cutoff does not set the ACR in the virtual source (i.e, the switching system does not compute the smallest Cutoff among all of the switching systems on the path of the virtual circuit), then the switching system identifies the 20 virtual circuit as "bottlenecked elsewhere."
The switching system determines a new bandwidth that it can allocate to the virtual circuit by determining a new ER for the virtual circuit and setting the new ER
in the Forward RM cell. The switching system then determines an estimated rate (Exp Rate) at which the switching system "expects" the virtual source to transmit 25 data cells after the virtual source adjusts its ACR based on the newly set ER. Finally, the switching system sends the Forward RM cell to the next switching system on the path of the virtual circuit.
When the Forward RM cell reaches the virtual destination, the virtual destination returns the Forward RM cell as a Backward RM cell. The Backward RM
30 cell passes through one or more switching systems on the path of the virtual circuit without any further modification to the bandwidth information set in the Forward RM
ASYNCHRONOUS TRANSFER MODE (ATM) SWITCHING SYSTEMS
WO 98!31156 PCT/US98/00781 BACKGROUND OF THE INVENTION
The present invention relates generally to asynchronous transfer mode (ATM) switching systems, and more particularly, to a method and system for dynamically allocating bandwidth to Available Bit Rate (ABRI virtual circuits in ATM
switching systems.
In an ATM network, a virtual source (VS) transmits data in the form of fixed sized cells to a virtual destination (VD) through a connection (referred to as virtual circuit) established between the virtual source and the virtual destination.
The virtual source and virtual destination may be a telephone. video equipment, facsimile, computer. edge-router, edge-switch, etc. The cells may include any type of digitized information. including audio. computer data, video, multimedia, Internet data, etc.
For example, in a network that uses Transmission Control Protocol/Internet Protocol (TCP/IP) over ATM, a virtual source may be an edge-router at the entry to an ATM
network. An entry edge-router segments the incoming TCP/IP data packets into one or more ATM cells before transmitting each cell to the ATM network. Similarly, a virtual destination may be an edge router at the exit of the ATM network. An exit edge-router reassembles incoming ATM cells into TCP/IP data packets before transmitting each packet to its destination.
When establishing a virtual circuit through an ATM network, a virtual source can select one of five different categories of service: Constant Bit rate (CBR), Variable Bit Rate - Real Time (VBR-RT), Variable Bit Rate - Non Real Time (VBR-NRT), Available Bit Rate (ABR), and Unspecified Bit Rate (UBR). ATM Forum Traffic Management Standard of tm-0056.00 describes each of these services.
The ABR service determines excess bandwidth in the network and uses network management methods to reallocate the excess bandwidth among the virtual circuits in the network to reduce network congestion and cell loss. In negotiating an ABR virtual circuit, a virtual source negotiates a peak cell rate (PCR) and a minimum cell rate (MCR) with the ATM network. PCR is the maximum cell rate a virtual circuit can support. MCR is the minimum cell rate that a virtual source requires a virtual circuit to support. The ABR service uses the negotiated PCR and MCR
parameters to provide a guaranteed quality of service concerning bandwidth .r i availability and cell loss in a virtual circuit.
When a virtual source selects the ABR service, the virtual source periodically generates a resource management (RM) cell to get feedback from the network on the rate at which the virtual source can transmit cells on a virtual circuit without causing loss of cells due to network congestion. Typically, a virtual source generates an RM
cell for every thirty-one cells it transmits or at the expiration of a fixed time interval, whichever occurs first. The network processes the RM cell, updates virtual circuit bandwidth information in the RM celi, and returns the RM cell to the virtual source.
The virtual source then dynamically adjusts its rate of cell transmission based on the bandwidth information contained in the RM cell.
An RM cell generated by a virtual source is referred to as a Forward RM cell.
The Forward RM cell passes through one or more switching systems in the network before reaching a virtual destination. The virtual destination processes the Forward RM cell and returns a Backward RM cell to the virtual source. The Backward RM
cell passes through one or more switching systems in the network before reaching the virtual source.
A virtual source maintains the MCR, current Allowed Cell Rate (ACR), and the PCR associated with the virtual circuit. ACR is the rate at which the network allows the virtual source to transmit cells on a virtual circuit. When a virtual source receives a Backward RM cell, based on the bandwidth information in the Backward RM cell, the virtual source computes a new ACR. Consequently, ACR dynamically changes as the network traffic changes and as the virtual source receives feedback from the network.
A Forward RM cell includes an MCR field, can ent cell rate (CCR) field, and an explicit rate (ER) field. CCR is the rate at which a virtual source is transmitting cells on a virtual circuit at the time the virtual source generates a Forward RM cell.
ER is the rate at which the virtual source wishes to transmit cells on a virtual circuit.
A virtual source cannot set the ER field in a Forward RM cell to be greater than PCR.
After generating a Forward RM cell and setting the MCR, CCR, and ER fields in the Forward RM cell, the virtual source transmits the Forward RM cell to the network.
When a virtual source transmits a Forward RM cell, the Forward RM cell passes through each switching system on the path of the virtual circuit to the virtual destination. Each switching system on the path can either keep the ER in Forward RM cell the same or decrease the ER to a lower rate. However, according to ATM
Forum Traffic Management Standard of tm-0056.00, a switching system cannot decrease the ER below the MCR for the virtual circuit. Furthermore, a switching system cannot increase the ER for the virtual circuit. A switching system that allocates bandwidth to a virtual source by setting the ER field in an RM cell is referred to as an ABR Explicit Rate (ABR-ER) switching system.
When a Forward RM cell associated with a virtual circuit arnves at an ABR-I 0 ER switching system, the switching system determines an upper threshold (referred to as "Cutoff ') for the bandwidth that can be made available to the virtual circuit in the switching system. If the switching system determines that the computed Cutoff for the virtual circuit sets the ACR in the virtual source (i.e, the switching system computes the smallest Cutoff among all of the switching systems on the path of the 15 virtual circuit), then the switching system considers the virtual circuit to be "bottlenecked here" or bottlenecked in the switching system. If the switching system determines that the computed Cutoff does not set the ACR in the virtual source (i.e, the switching system does not compute the smallest Cutoff among all of the switching systems on the path of the virtual circuit), then the switching system identifies the 20 virtual circuit as "bottlenecked elsewhere."
The switching system determines a new bandwidth that it can allocate to the virtual circuit by determining a new ER for the virtual circuit and setting the new ER
in the Forward RM cell. The switching system then determines an estimated rate (Exp Rate) at which the switching system "expects" the virtual source to transmit 25 data cells after the virtual source adjusts its ACR based on the newly set ER. Finally, the switching system sends the Forward RM cell to the next switching system on the path of the virtual circuit.
When the Forward RM cell reaches the virtual destination, the virtual destination returns the Forward RM cell as a Backward RM cell. The Backward RM
30 cell passes through one or more switching systems on the path of the virtual circuit without any further modification to the bandwidth information set in the Forward RM
.. ~. _.
cell. When the Backward RM cell reaches the virtual source, the virtual source uses the new ER in the RM cell to determine a new ACR. Based on the new ACR, the virtual source adjusts the rate at which it transmits cells.
Every time a switching system determines a Cutoff and ER for a virtual circuit, the switching system also recomputes certain global bandwidth parameters for the virtual circuits that the switching system handles. These global bandwidth parameters include the total bandwidth available to all ABR-ER virtual circuits, the total Exp Rate for ABR-ER virtual circuits that are bottlenecked elsewhere, the total number of ABR-ER virtual circuits that are bottlenecked elsewhere, and the total number of ABR-ER virtual circuits that are bottlenecked at the switching system.
Methods for determining and updating the global bandwidth parameters in an ABR-ER switching system are known. However, these methods have the disadvantage that every time a switching system recomputes the global bandwidth parameters that the switching system maintains on its virtual circuits, the computations introduce errors in the form of round-off errors into the global bandwidth parameters. Over the life of the virtual circuits, as the switching system recomputes the global bandwidth parameters, the round-off errors can accumulate, and as a result of the accumulated errors, the parameters gradually become inaccurate.
When an ABR-ER switching system maintains inaccurate global bandwidth parameters, the switching system fails to allocate an optimum bandwidth to each virtual circuit. Specifically, a switching system allocates an optimum bandwidth to a virtual circuit when the virtual source uses the entire or nearly the entire bandwidth allocated to the virtual circuit. If the global bandwidth parameters are inaccurate, the switching system may allocate an insufficient amount of bandwidth to a virtual circuit, even though the switching system may in fact have sufficient bandwidth available. Similarly, the switching system may allocate an excessive amount of bandwidth to a virtual circuit, even though the switching system may in fact have insufficient bandwidth available. In either case, the switching system would fail to allocate an optimum bandwidth to the virtual circuit.
The methods known prior to the present invention for determining and updating the global bandwidth parameters in an ABR-ER switching system have the -S-additional disadvantage that, when a virtual circuit does not use the entire bandwidth a switching system allocates to it, the switching system cannot dynamically identify and reallocate the unused bandwidth to other virtual circuits in the switching system. For example, when a virtual source stops transmitting cells on a virtual circuit or transmits cells at a much lower rate than the bandwidth allocated to the virtual circuit permits, the virtual source does not use the bandwidth allocated to the virtual circuit in an optimum fashion.
Furthermore, the methods known prior to the present invention for allocating bandwidth to an ABR virtual circuit have the disadvantage that a switching system may allocate more bandwidth to the virtual circuit than a virtual source could use. For example, when a virtual source requests an ER that is below the MCR for a virtual circuit, the switching system cannot decrease the ER below the MCR.
Therefore, it is desirable to have a method and system for correcting, within a fixed time interval, the accumulation of computational errors in the global bandwidth parameters maintained in an ABR-ER switching system, identifying the unused bandwidth in virtual circuits, allocating the identified unused bandwidth to other virtual circuits in the switching system, and increasing the total bandwidth that the switching system can make available to virtual circuits.
DESCRIPTION OF THE INVENTION
The present invention comprises a method and system for dynamically adjusting the total bandwidth that an ABR-ER switching system can make available to ABR virtual circuits in the switching system by recomputing, at fixed time intervals, the total bandwidth that the switching system can make available to active ABR
virtual circuits that are bottlenecked in the switching system. The method and system classifies the ABR virtual circuits that are established through an output port of the switching system into three categories of "recently active," "active," and "inactive"
virtual circuits. An ABR virtual circuit is "recently active" if an output port receives at least one RM cell for the virtual circuit since the most recent recomputation of the total bandwidth that the switching system can make available to active ABR
virtual circuits that are bottlenecked in the switching system (hereinafter referred to as ., "bandwidth allocation update"). An ABR virtual circuit is "active" if an output port receives at least one RM cell within the two most recent bandwidth allocation updates. An ABR virtual circuit is "inactive" if an output port does not receive at least one RM cell within the two most recent bandwidth allocation updates.
The present invention further comprises a method and system for dynamically adjusting the total bandwidth that an ABR_ER switching system can make available to ABR virtual circuits in the switching system by determining the total bandwidth allocated to inactive A.BR virtual circuits in the switching system without explicitly identifying the inactive ABR virtual circuits, and making available the bandwidth allocated to inactive ABR virtual circuits to active ABR virtual circuits that are established through the switching system. When transmission of cells resumes in an inactive A.BR virtual circuit, the switching system reallocates new bandwidth to the virtual circuit.
Specifically, at each fixed time interval, the switching system sets the total 1 S expected rate (Exp Rate) for active ABR virtual circuits that are bottlenecked elsewhere equal to the total expected rate for recently active ABR virtual circuits that are bottlenecked elsewhere, sets the total number of active ABR virtual circuits that are bottlenecked at an output port of the switching system equal to the total number of recently active ABR virtual circuits that are bottlenecked in the output port of the switching system, resets to zero the total expected rate for recently active ABR virtual circuits that are bottlenecked elsewhere, and resets to zero the total number of recently active ABR virtual circuits that are bottlenecked at the switching system.
The present invention further comprises a method and system for allocating bandwidth to an ABR virtual circuit that is established through an ABR-ER
switching system by allocating an explicit rate (ER) to the virtual circuit that is less than the minimum cell rate (MCR) for the virtual circuit, when the switching system receives a resource management (RM) cell with an explicit rate that is less than the minimum cell rate for the virtual circuit.
The description of the invention and the following description for carrying out the best mode of the invention should not restrict the scope of the claimed invention.
Both provide examples and explanations to enable others to practice the invention.
_7_ WO 98!31156 PCT/US98l00781 The accompanying drawings, which form part of the description for carrying out the best mode of the invention, show several embodiments of the invention, and together with the description, explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure la is a block diagram of an asynchronous transfer mode (ATM) communications network.
Figure 1 b is a block diagram of an end-to-end path of a virtual circuit that passes through N switching systems in an asynchronous transfer mode (ATM) communications network.
Figure 2 is a block diagram of a switching system in accordance with an embodiment of the invention.
Figure 3 is a block diagram of an output port in a switching system in accordance with an embodiment of the invention.
Figure 4 is a flow chart of the steps a switching system performs to process a resource management cell in accordance with an embodiment of the invention.
Figure 5 is a flow chart of the steps a switching system performs to process a resource management cell in accordance with an embodiment of the invention.
Figure 6 is a flow chart of the steps a switching system performs to determine bandwidth parameters for an output port and a virtual circuit in accordance with an embodiment of the invention.
Figure 7 is a flow chart of the steps a switching system performs to determine a new explicit rate for a virtual circuit in accordance with an embodiment of the invention.
Figure 8 is a flow chart of the steps a switching system performs to determine the total expected rate for active Available Bit Rate virtual circuits that are bottlenecked elsewhere in accordance with an embodiment of the invention.
Figure 9 is a flow chart of the steps a switching system performs to determine a the total expected rate for recently active Available Bit Rate virtual circuits that are bottlenecked elsewhere in accordance with an embodiment of the invention.
Figure 10 is a flow chart of the steps a switching system performs to determine _g_ ~r the total number of active Available Bit Rate virtual circuits that are bottlenecked at an output port of the switching system in accordance with an embodiment of the invention.
Figure 11 is a flow chart of the steps a switching system performs to determine the total number of recently active Available Bit Rate virtual circuits that are bottlenecked at an output port of the switching system in accordance with an embodiment of the invention.
Figure 12 is a flow chart of the steps a switching system performs to determine the total bandwidth available to active Available Bit Rate virtual circuits that are bottlenecked at an output port of the switching system in accordance with an embodiment of the invention.
Figure 13 is a flow chart of the steps a switching system performs to make available a new total bandwidth to active Available Bit Rate virtual circuits that are bottlenecked at an output port of the switching system in accordance with an embodiment of the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.
Wherever possible) the same reference numbers will be used throughout the drawings to refer to the same or like parts.
Figure 1 a illustrates a block diagram of an asynchronous transfer mode (ATM) communications network in accordance with an embodiment of the invention.
Virtual source (VS) 100 interfaces with ATM network 160 via transmission link 120.
Virtual destination (VD) 110 interfaces with ATM network 160 via transmission link 125. In establishing a connection between VS 100 and VD 110, ATM network 160 sets up a virtual circuit (VC) (not shown) between VS 100 and VD 110. During the set-up phase of the connection, VS 100 negotiates with ATM network 160 for an Available Bit Rate-Explicit Rate {ABR-ER) service.
After completion of the set-up phase of the connection, VS 100 generates Forward resource management {RM) cell 130 and transmits it on transmission link 120. Forward RM cell 130 passes through ATM network 160 and transmission link 125, and arnves at VD 110. VD 1 IO processes Forward RM cell 130, and generates Backward RM cell 140 in response to Forward RM cell 130. VD 110 then transmits Backward RM cell I40 on transmission link I25. Backward RM cell 140 passes through ATM network 160 and transmission /ink 120, and arrives at VS I00.
VS I00 generates data cell 150 and transmits it on transmission link 120. Data cell 150 passes through ATM network 160 and transmission link 125, and arrives at VD 110. Similarly, VD 110 generates data cell 150 and transmits it on transmission link I25. Data cell 150 passes through ATM network I60 and transmission link I20, IO and arrives at VS 100.
Figure Ib illustrates a block diagram of the end-to-end path of VC in ATM
network 160 in accordance with an embodiment of the invention. The path of the VC
established between VS 100 and VD 110 passes through N switching systems 105, through I05,~. Accordingly, when VS 100 transmits Forward RM cell 130 on transmission link 120, Forward RM cell passes through N switching systems 105, through 105,. Each switching system 105, through 105N connects to its adjacent switching system via a corresponding transmission link. For example, switching system 105, connects to switching system I05z via transmission link 121.
Switching System Figure 2 illustrates a block diagram of a switching system, for example switching system 1052, in accordance with an embodiment of the invention. As shown, switching system 1052 comprises M input ports 240, through 240,. Each input port interfaces with an input line, which can carry K virtual circuits.
For example, input port 240M interfaces with input line 121 M, which can carry K
virtual circuits (not shown). Input ports 240, through 240,, preferably interface with a cross-point switch fabric 250 via input links 220, through 220M respectively.
Alternatively, switch fabric 250 may be a Batcher-Banyan switch network, Sunshine switch, or any other switch fabric capable of switching ATM cells.
Switch fabric 250 interfaces with N output ports 260, through 260, via output links 230, through 230, respectively. For example, output port 260; interfaces with __. ~. ... _.. ..m ....
w, r switch fabric 250 via output Iink 230,. Each output port interfaces with an output line, which can carry K virtual circuits. For example, output port 260N
interfaces with output line 122N, which can carry K virtual circuits (not shown).
Output Ports Figure 3 illustrates a preferred embodiment for each output port 260, through 260N in accordance with an embodiment of the invention. As shown, each output port, for example output port 260N, preferably has access to central processing unit 310 (CPU), memory unit 360, controller 390, secondary storage 380, and high speed buses 370, 371, and 372. CPU 310 interfaces with controller 390 via high speed bus 372. Controller 390 interfaces with memory unit 360 and secondary storage 380 via high speed buses 370 and 371 respectively.
Memory unit 360 preferably includes VC Handler 320, Port Handler 330, Bandwidth Allocation Update 340, and Buffer 350. VC Handler 320, Port_Handler 330, Bandwidth Allocation Update 340, and Buffer 350 each preferably include a set of instructions in the form of software, which CPU 310 executes. VC_Handler receives and processes RM cells for VCs in output port 260N. Specifically, Port Handler 330 deterniines a new ER and Exp Rate for a VC, and recomputes the global bandwidth parameters for the VCs in output port 260;x, when a VC
receives an RM cell. At fixed time intervals, Bandwidth Allocation Update 340_ recomputes the total bandwidth that output port 260y can make available to active VCs that are bottlenecked at output port 260N. Buffer 350 stores cells (i.e, data cells and RM
cells) that arrive at output port 260N in queues (not shown), which are in memory unit 360. Alternatively, each VC Handler 320, Port Handler 330, Bandwidth Allocation Update 340, and Buffers 350 may be implemented in hardware using hardware technology known to one of ordinary skill in the art.
Secondary storage 380 includes disk drive unit 382 and tape cartridge 381.
Stored in disk drive unit 382 are software and data for switching system 105,.
For example, disk drive unit 382 contains software for VC Handler 320, Port_Handler 330, Bandwidth Allocation Update 340, and Buffer 350. Secondary storage 380 can copy software and data for switching system 105, from tape cartridge 381 into disk drive unit 382. Controller 390 can then upload the software and data from disk drive unit 382 into memory unit 360. Similarly, controller 390 can download software and data from memory unit 360 into disk drive unit 382. Secondary storage 380 can then copy the downloaded software and data from disk drive unit 382 into tape cartridge 381.
VC Handler A VC Handler processes and stores data specific to each VC in an output port.
Specifically, a VC Handler preferably stores for each VC a MCR, the time that an RM cell last arrived for the VC, an Exp Rate, and a Bottlenecked Elsewhere indicator. VC,Handler sets Bottlenecked Elsewhere indicator to a logical value of l, when at the time VC Handler receives an RM cell for a VC, the VC is bottlenecked elsewhere. If the VC is instead bottlenecked at an output port of the switching system, then VC Handler sets Bottlenecked Elsewhere indicator to a logical value of 0.
Figure 4 illustrates a flow chart of the steps a VC Handler, for example VC Handler 320, preferably performs to process an- RM cell, for example RM
cell 130, for a VC. VC Handler 320 receives RM cell 130 VC from switch fabric 250 (step 400). VC Handler 320 then generates an RM Cell Request (step 405). An RM-Cell Request includes a MCR, Bottlenecked_Elsewhere indicator, current Exp'Rate for VC, CCR, and a current ER for VC.
VC Handler 320 then sends the RM Cell Request to Port Handler 330 (step 410). Port Handler 330 computes a new ER, Exp Rate, and Bottlenecked Elsewhere indicator, and incorporates them in RM Cell Request.
VC Handler 320 waits until it receives the RM_Cell Request back from Port Handler 330 (step 415). If VC Handler 320 does not receive the RM_Cell Request back from Port_Handler 330 (step 415), then VC Handler continues to wait until it receives the RM Cell Request from Port-Handler 330 (step 420). If VC Handler 320 receives the RM Cell Request back from Port Handier 330, then VC Handler 320 resumes the processing of the- RM-Cell Request (step 425).
~Y ...
VC Handler 320 stores the new ER, Exp Rate, and the Bottlenecked Elsewhere indicator in memory unit 360 (step 430}. Alternatively, VC Handler 320 may store each of these values in a register. Finally, VC_Handler 320 replaces the current ER in RM cell 130 with the new ER in RM_Ceil Request (step 435). VC Handler 320 then sends RM cell 130 to Buffer 350 in output port 260N (step 440).
Port Handler A Port_Handler determines a new ER and Exp Rate for a VC, and recomputes the global bandwidth parameters for VCs in an output port. Specifically, a Port Handler preferably stores the time of the most recent bandwidth allocation update, the time of the second most recent bandwidth allocation update, the total bandwidth available to all VCs (i.e., CBR, VBR, ABR, and UBR VCs) in the output port, the total bandwidth available to all ABR VCs (i.e., active and inactive ABR
VCs), the total Exp Rate for active ABR VCs bottlenecked elsewhere, total Exp Rate for recently active ABR VCs bottlenecked elsewhere, the total bandwidth available to ABR VCs bottlenecked at the output port, the total number of active ABR VCs bottlenecked at the output port, and the total number of recently active ABR
VCs bottlenecked at the output port. When the Port_Handler receives an RM_Cell Request from a VC Handler, the Port Handler- _ recomputes the above mentioned global bandwidth parameters.
Figure 5 illustrates a flow chart of the steps a Port_Handler, for example Port_Handler 330, preferably performs to process an RM-Cell Request.
Pol-t_Handler 330 receives RM-Cell Request from VC Handler 320 (step 500).
Port Handler 330, as explained below,- recomputes global bandwidth parameters for output port 260N, and new ER and Exp'Rate for VC (step 505). Port_Handler 330 stores the new global bandwidth parameters for output port 260, in memory unit (step 510). Port Handler 330 sets the global bandwidth parameters for VC in the RM Cell Request (step 515). Port Handler 330 then returns the updated RM_Cell Request to VC Handler 320 (step 520).
Figure 6 illustrates a flow chart of the steps a Port Handler, for example Port-Handler 330, preferably performs to determine new global bandwidth parameters for an output port, for example output port 260N, and a VC. Port Handler 330 determines whether the last RM cell for VC arrived at output port 260N within the two most recent bandwidth allocation updates in output port 260N (step 600).
If Port Handler 330 determines that the last RM cell for VC arrived at output port 260N before the two most recent bandwidth allocation updates in output port 260N
(step 610), Port Handler 330 resets the current Exp Rate for VC to zero (step 615), and determines that VC is bottlenecked elsewhere and sets the Bottlenecked Elsewhere indicator in the RM Cell Request equal to a logical 1 (step 620). Port-Handler then determines whether VC is bottlenecked elsewhere (step 625).
If Port_Handler 330 determines that the last RM cell for VC arrived at output port 260, within the two most recent bandwidth allocation updates in output port 260, (step 605), then Port-Handler 330 determines whether VC is bottlenecked elsewhere (step 625).
If Port Handler 330 determines that VC is bottlenecked elsewhere (step 640), then Port Handler 330 determines an upper threshold, namely "Cutoff," for the amount of bandwidth that output port 260N can make available to VC. Port Handler 330 preferably determines the Cutoff for VC by dividing the total bandwidth available to active ABR VCs bottlenecked at output port 260; plus the current Exp Rate for VC by the total number of active ABR VCs bottlenecked at output port 260, plus one (step 645). Step 645 may alternatively be expressed as follows:
Cutoff = (Total Bandwidth Available to Active ABR VCs at Output Port 260N + Current Exp Rate for VC) / (Total Number of Active ABR VCs Bottlenecked at Output Port 260N + 1 ) If Port Handler 330 determines that VC is bottlenecked at output port 260N
(step 630), Port Handler 330 sets the Cutoff for VC equal to the total bandwidth available to active ABR VCs bottlenecked at output port 260, divided by the total number of active ABR VCs bottlenecked at output port 260; (step 650).
Port Handler 330 then, as explained below, determines a new ER for VC (step ~, ~
655), a new ExpTRate for VC (step 660), a new total Exp Rate for recently active ABR VCs bottlenecked elsewhere (step 665), a new total Exp Rate for active A.BR
VCs bottlenecked elsewhere (step 670), a new total number of recently active ABR
VCs bottlenecked at output port 260N (step 675), a new total bandwidth that output port 260N can make available to active ABR VCs bottlenecked at output port (step 680), and a new total number of active ABR VCs bottlenecked at output port 260N (step 685).
Figure 7 illustrates a flow chart of the steps a Port_Handler, for example Port Handler 330, preferably performs to determine a new ER for a VC.
Port_Handler 330 determines whether the Cutoff for VC is less than or equal to MCR
for VC (step 700). If Port-Handler 330 deterTnines that Cutoff for VC is greater than MCR (step 710), Port_Handler 330 sets the new ER equal to the minimum of the current ER and MCR (step 715). Port Handler 330 then determines that VC is bottlenecked elsewhere, and sets the Bottlenecked Elsewhere indicator in the 1 S RM_Cell Request to a logical 1 (step 755).
If Port Handler 330 determines that Cutoff for VC is less than or equal to MCR for VC (step 705), Port Handler 330 determines a most likely new Exp Rate for VC (step 720). Port Handler 330 selects the maximum of CCR and MCR for VC, and sets the most likely new Exp Rate to the minimum of that maximum value and the current ER for VC.
Port-Handler 330 determines whether the Cutoff for VC is greater than the most likely new Exp Rate for VC (step 725). If Port Handler 330 determines that the Cutoff is not greater than the most likely new Exp Rate (step 735), then Port_Handler 330 sets the new ER for VC to the minimum of current ER and the Cutoff (step 740).
Port Handier 330 then determines that VC is bottlenecked elsewhere and sets the Bottlenecked Elsewhere indicator in the RM Cell Request to a logical 1 (step 755).
If Port Handler 330 determines that the Cutoff for VC is greater than the most likely new Exp Rate (step 730), Port_Handler 330 sets the new ER equal to the Cutoff (step 745). Port_Handler 330 then determines that VC is bottlenecked at output port 260,x, and sets the Bottlenecked Elsewhere indicator in the RM_Cell Request to a logical 0 (step 750).
Figure 8 illustrates a flow chart of the steps a Port Handler, for example Port Handler 330, preferably performs to determine a new total Exp Rate for active ABR VCs that are bottlenecked elsewhere. Port-Handler 330 determines whether a VC is currently bottlenecked elsewhere (step 800). If Port-Handler 330 determines that VC is bottlenecked at output port 260, (step 810), then Port Handler 330 determines whether, when last time output port 260N received an RM cell for VC, VC
was bottlenecked elsewhere (step 815). If Port-Handler 33 determines that last time VC was bottlenecked at output port 260, (step 820), then Port Handler 330 determines that the total Exp Rate for active ABR VCs that are bottlenecked elsewhere remains unchanged (step 82S).
If Port Handler 330 determines that, when last time output port 260, received an RM cell for VC, VC was bottlenecked elsewhere (step 830), then Port Handler 330 decreases the total Exp Rate for active A.BR VCs that are bottlenecked elsewhere by the current Exp Rate for VC (step 835).
1 S If Port-Handler 330 determines that VC is currently bottlenecked elsewhere (step 80S), then Port Handler 330 determines whether, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 840). If Port Handler 330 determines that last time VC was bottlenecked at output port 260, (step 84S), Por-t_Handler 330 increases the total Exp Rate for active ABR VCs that are bottlenecked elsewhere by the new Exp Rate for VC (step 8S0).
If Port-Handler 330 determines that last time VC was bottlenecked elsewhere (step 85S), the Port Handler 330 decreases the total Exp Rate for active- ABR
VCs by the current Exp Rate for VC and increases the total Exp Rate for active- ABR
VCs by the new Exp Rate for VC (step 860).
2S Figure 9 illustrates a flow chart of the steps a Port Handler, for example Port Handler 320, preferably performs to determine a new total Exp Rate for recently active. ABR VCs that are bottlenecked elsewhere. Port Handler 330 determines whether the last RM cell for a V C arrived at output port 260; after the most recent bandwidth allocation update in output port 260N (step 900).
If Port Handler 330 determines that the last RM cell for VC arrived at output port 260N before the most recent bandwidth allocation update in output port 260N (step *~
905), then Port_Handler 330 determines whether VC is currently bottlenecked elsewhere (step 920). If Port_Handler determines that VC is currently bottlenecked elsewhere (step 920), the Port-Handler 330 increases the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere by the new Exp Rate for VC
(step 980).
If Port Handler 330 determines that VC is currently bottlenecked at output port 260N (step 915), then Port Handler 330 determines that the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere remains unchanged (step 925).
If Port Handler 330 determines that last- RM cell for VC arrived after the most recent bandwidth allocation update in output port 260v (step 930), then Port_Handler 330 determines whether VC is currently bottlenecked elsewhere (step 935). If Port_Handler 330 determines that VC is bottlenecked at output port 260N (step 940), then Port Handler 330 determines whether, when last time output port 260N
received an RM cell for VC, VC was bottlenecked elsewhere (step 950). If Port_Handler determines that last time VC was bottlenecked at output port 260N (step 955), then Port Handler 330 determines that the total Exp Rate for recently active ABR
VCs that are bottlenecked elsewhere remains unchanged (step 925).
If Port_Handler 330 determines that VC is bottlenecked at output port 260N
(step 940) and determines that, when last time output port 260N received an RM
cell for VC, VC was bottlenecked elsewhere (step 960), then Port-Handler 330 decreases the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere by the current Exp Rate for VC (step 965).
If Port Handler 330 determines that last RM cell for VC arrived after the most recent bandwidth allocation update in output port 260N (step 930) and determines that VC is currently bottlenecked elsewhere (step 945), then Port_Handler 330 determines whether, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 970). If Port_Handler determines that last time VC was bottlenecked at output port 260, (step 975), then Port_Handler 330 increases the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere by the new Exp Rate for VC (step 980).
If Port-Handler 330 determines that last RM cell for VC arnved after the most recent bandwidth allocation update in output port 260N (step 930), determines that VC
is currently bottlenecked elsewhere (step 945), and determines that, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 985), then Port_Handler 330 decreases the total Exp Rate for recently active ABR
VCs that are bottlenecked elsewhere by the current Exp Rate for VC and increases the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere by the new Exp Rate for VC (step 990).
Figure 10 illustrates a flow chart of the steps a Pol-t_Handler, for example Port Handler 330, preferably performs to determine the new total number of active ABR VCs that are bottlenecked at an output port, for example output port 260N.
Port Handler 330 determines whether a VC is currently bottlenecked elsewhere (step 1000). If Port-Handler 330 determines that VC is currently bottlenecked at output port 260, (step 1005), then Port Handler 330 determines whether, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 1015). If Port Handler 330 determines that last time VC was bottlenecked at output port 260N (step 1020), then Port Handler 330 determines that the total number of active ABR VCs that are bottlenecked at output port 260N remains unchanged (step I050).
If Port Handler 330 determines that VC is currently bottlenecked elsewhere (step 1010), then Port-Handler 330 determines whether, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 1030). If Port Handler 330 determines that last time VC was bottlenecked at output port 260h (step 1040), then Port Handler 330 decreases the total number of active- ABR
VCs that are bottlenecked elsewhere by one (step 1045).
If Port-Handler 330 determines that VC is currently bottlenecked elsewhere (step 1010) and determines that, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 1035), then Port Handler 330 determines that the total number of active ABR VCs that are bottlenecked at output port 260, remains unchanged (step 1050).
Figure 11 illustrates a flow chart of the steps a Port Handler, for example ., Port_Handler 330, preferably performs to determine the new total number of recently active A.BR VCs that are bottlenecked at an output port, for example output port 260N.
If Port Handler 330 determines that the last RM cell for a VC arrived before the most recent bandwidth allocation update (step 1105), then Port_Handler 330 determines whether VC is currently bottlenecked elsewhere (step 1115). If Port_Handler determines that VC is currently bottlenecked at output port 260, (step 1120), then Port Handler 330 determines that the total number of recently active- ABR VCs that are bottlenecked at output port 260N remains unchanged (step 1165).
If Port_Handler 330 determines that the last RM cell for VC arrived before the most recent bandwidth allocation update (step 1105) and determines that VC is currently bottlenecked elsewhere (step 1125), then Port Handler 330 increases the total number of recently active A.BR VCs that are bottlenecked at output port 260N by one (step I 130).
If Port-Handler 330 determines that last RM cell for VC arrived after the most recent bandwidth allocation update (step 1110), then Port_Handler 330 determines whether, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 1135). If Port Handler 330 determines that last time VC
was bottlenecked elsewhere (step I 140), then Port_Handler 330 determines whether VC is currently bottlenecked elsewhere (step 1115). If Port_Handler 330 determines that VC is currently bottlenecked at output port 260N (step 1120), then Port_Handler 330 determines that the total number of recently active ABR VCs that are bottlenecked at output port 260N remains unchanged (step 1165).
If Port Handler 330 determines that, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 1140) and determines that VC is currently bottlenecked elsewhere (step 1125), then Port-Handler 330 increases the total number of recently active ABR VCs that are bottlenecked at output port 260.
by one (step 1130).
If Port Handler 330 determines that the last- RM cell for VC arrived after the most recent bandwidth allocation update (step 11 IO) and determines that VC
was bottlenecked at output port 260N (step 1145), then Port Handler 330 determines whether VC is currently bottlenecked elsewhere (step 1150). If Port Handler determines that VC is currently bottlenecked at output port 260N (step 1155), then Port Handler 330 determines that the total number of recently active ABR VCs that are bottlenecked at output port 260N remains unchanged (step 1165).
If Port Handler 330 determines that last RM cell for VC arrived after the most recent bandwidth allocation update (step 1110), determines that, when last time output port 260, received an RM cell for VC, VC was bottlenecked at output port 260N
(step 1145), and determines that VC is currently bottlenecked elsewhere (step 1160), then Port-Handler 330 decreases the total number of active ABR VCs that are bottlenecked at output port 260N by one (step 1170).
Figure 12 illustrates a flow chart of the steps a Port_Handler, for example Port Handler 330, preferably performs to determine the new total bandwidth that an output port, for example output port 260N, can make available to active ABR
VCs that are bottlenecked at output port 260N. Port_Handler 330 determines whether a VC
is currently bottlenecked elsewhere (step 1200). If Port_Handler 330 determines that VC is bottlenecked at output port 260, (step 1205), then Port Handler 330 determines whether, when last time output port 260, received an RM cell for VC, VC was bottlenecked elsewhere (step 1215). If Port Handler 330 determines that last time VC
was bottlenecked at output port 260, (step 1220), then Port Handler 330 determines that the total bandwidth that output port 260N can make available to active ABR VCs at output port 260, remains unchanged (step 1230).
If Port-Handler 330 determines that VC is bottlenecked at output port 260, (step 1205) and determines that, when Iast time output port 260y received an RM cell for VC, VC was bottlenecked elsewhere (step 1225), then Port Handler 330 increases the total bandwidth that output port 260N can make available to active ABR VCs that are bottlenecked at output port 260N by the current Exp Rate for VC (step I235).
If Port_Handler 330 determines that VC is bottlenecked elsewhere (step 1210), then Port Handler 330 determines whether, when last time output port 260N
received an RM cell for VC, VC was bottlenecked elsewhere (step 1240). If Port Handler determines that last time VC was bottlenecked at output port 260, (step 1245), then Port Handler 330 decreases the total bandwidth available to active ABR VCs that are bottlenecked at output port 260; by the new Exp Rate for VC (step 1255).
_, If Port Handler 330 determines that VC is bottlenecked elsewhere (step 1210) and determines that, when last time output port 260N received an RM cell for VC, VC
was bottlenecked elsewhere (step 1250), then Port Handler 330 increases the total bandwidth that output port 260N can make available to active ABR VCs that are bottlenecked at output port 260N by the current Exp Rate for VC and decreases the total bandwidth that output port 260N can make available to active ABR VCs that are bottlenecked at output port 260N by the new Exp Rate for VC (step 1260).
Bandwidth Allocation Update An output port, for example output port 260N, invokes, at preferably fixed time intervals, Bandwidth Allocation Update 340. Bandwidth Allocation Update 340 preferably stores the time interval between each invocation in a static memory. The manufacturer of a switching system may set a default for the fixed time interval, which a switching system administrator or network administrator may subsequently reconfigure.
The time interval between each invocation may preferably be twice the upper bound for the time interval between each RM cell generated by an active virtual source. The upper bound may preferably be in the range of 2'S milliseconds to milliseconds. Alternatively, the time interval between each invocation may be less than twice the upper bound for the time interval between each RM cell, in which case the time interval between each invocation must still be sufficiently large to allow for arrival of at least one RM cell between two consecutive invocations of Bandwidth Allocation Update 340.
Bandwidth Allocation Update 340 preferably has access to the global bandwidth parameters stored in memory unit 360 by Port_Handler 330.
Specifically, Bandwidth Allocation Update 340 has access to the time of the most recent bandwidth allocation update, the time of a second most recent bandwidth allocation update, the total bandwidth available to all ABR VCs (i.e., active and inactive ABR
VCs), the total Exp Rate for active ABR VCs bottlenecked elsewhere, the total Exp Rate for recently active ABR VCs bottlenecked elsewhere, the total bandwidth available to active ABR VCs bottlenecked at output port 260N, the total number of active ABR VCs bottlenecked at output port 260N, and the total number of recently active ABR VCs bottlenecked at the output port 260N.
Figure 13 illustrates a flow chart of the steps a Bandwidth Allocation Update, for example Bandwidth Allocation Update 340, preferably performs to make available a new total bandwidth to active ABR VCs that are bottlenecked at an output port, for example output port 260N. Bandwidth Allocation Update 340 sets the total Exp Rate for active ABR VCs that are bottlenecked elsewhere equal to the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere (step 1300).
Next, Bandwidth Allocation Update 340 sets the total number of active- - ABR
VCs that are bottlenecked at output port 260N equal to the total number of recently active ABR VCs that are bottlenecked at output port 260, (step 1305).
Bandwidth Allocation Update 340 then sets the total bandwidth that output port 260, can make available to active ABR VCs that are bottlenecked at output port 260N equal to the difference between the total bandwidth available to all ABR
VCs 1 S (i.e., active and inactive ABR VCs) and the total Exp Rate for recently active ABR
VCs that are bottlenecked elsewhere (step 1310).
Next, Bandwidth Allocation Update 340 resets the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere (step I315).
Bandwidth Allocation Update 340 then resets the total number of recently active ABR VCs that are bottlenecked at output port 260N (step 1320). Finally, Bandwidth Allocation Update 340 sets a timer for the next update to the total bandwidth that output port 260N can make available to active ABR VCs that are bottlenecked at output port 260N (step 1325).
To prevent reallocation of bandwidth from a VC when an RM cell for the VC
is lost, for example, due to network congestion for an extended period of time, an ATM network may assign a high priority to RM cells. Alternatively, by keeping the time interval between the updates to the global bandwidth parameters (i.e., invocation of Bandwidth Allocation Update) sufficiently large, if an RM cell is lost due to network congestion, the impact to allocation of an optimum bandwidth to the VC
would be minimal.
While it has been illustrated and described what are at present considered to be ,. f. ..
preferred embodiments and methods of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the invention.
In addition, many modifications may be made to adapt a particular element, technique or implementation to the teachings of the present invention without departing from the central scope of the invention. Therefore, it is intended that this invention not be limited to the particular embodiments and methods disclosed herein, but that the invention include all embodiments falling within the scope of the appended claims.
cell. When the Backward RM cell reaches the virtual source, the virtual source uses the new ER in the RM cell to determine a new ACR. Based on the new ACR, the virtual source adjusts the rate at which it transmits cells.
Every time a switching system determines a Cutoff and ER for a virtual circuit, the switching system also recomputes certain global bandwidth parameters for the virtual circuits that the switching system handles. These global bandwidth parameters include the total bandwidth available to all ABR-ER virtual circuits, the total Exp Rate for ABR-ER virtual circuits that are bottlenecked elsewhere, the total number of ABR-ER virtual circuits that are bottlenecked elsewhere, and the total number of ABR-ER virtual circuits that are bottlenecked at the switching system.
Methods for determining and updating the global bandwidth parameters in an ABR-ER switching system are known. However, these methods have the disadvantage that every time a switching system recomputes the global bandwidth parameters that the switching system maintains on its virtual circuits, the computations introduce errors in the form of round-off errors into the global bandwidth parameters. Over the life of the virtual circuits, as the switching system recomputes the global bandwidth parameters, the round-off errors can accumulate, and as a result of the accumulated errors, the parameters gradually become inaccurate.
When an ABR-ER switching system maintains inaccurate global bandwidth parameters, the switching system fails to allocate an optimum bandwidth to each virtual circuit. Specifically, a switching system allocates an optimum bandwidth to a virtual circuit when the virtual source uses the entire or nearly the entire bandwidth allocated to the virtual circuit. If the global bandwidth parameters are inaccurate, the switching system may allocate an insufficient amount of bandwidth to a virtual circuit, even though the switching system may in fact have sufficient bandwidth available. Similarly, the switching system may allocate an excessive amount of bandwidth to a virtual circuit, even though the switching system may in fact have insufficient bandwidth available. In either case, the switching system would fail to allocate an optimum bandwidth to the virtual circuit.
The methods known prior to the present invention for determining and updating the global bandwidth parameters in an ABR-ER switching system have the -S-additional disadvantage that, when a virtual circuit does not use the entire bandwidth a switching system allocates to it, the switching system cannot dynamically identify and reallocate the unused bandwidth to other virtual circuits in the switching system. For example, when a virtual source stops transmitting cells on a virtual circuit or transmits cells at a much lower rate than the bandwidth allocated to the virtual circuit permits, the virtual source does not use the bandwidth allocated to the virtual circuit in an optimum fashion.
Furthermore, the methods known prior to the present invention for allocating bandwidth to an ABR virtual circuit have the disadvantage that a switching system may allocate more bandwidth to the virtual circuit than a virtual source could use. For example, when a virtual source requests an ER that is below the MCR for a virtual circuit, the switching system cannot decrease the ER below the MCR.
Therefore, it is desirable to have a method and system for correcting, within a fixed time interval, the accumulation of computational errors in the global bandwidth parameters maintained in an ABR-ER switching system, identifying the unused bandwidth in virtual circuits, allocating the identified unused bandwidth to other virtual circuits in the switching system, and increasing the total bandwidth that the switching system can make available to virtual circuits.
DESCRIPTION OF THE INVENTION
The present invention comprises a method and system for dynamically adjusting the total bandwidth that an ABR-ER switching system can make available to ABR virtual circuits in the switching system by recomputing, at fixed time intervals, the total bandwidth that the switching system can make available to active ABR
virtual circuits that are bottlenecked in the switching system. The method and system classifies the ABR virtual circuits that are established through an output port of the switching system into three categories of "recently active," "active," and "inactive"
virtual circuits. An ABR virtual circuit is "recently active" if an output port receives at least one RM cell for the virtual circuit since the most recent recomputation of the total bandwidth that the switching system can make available to active ABR
virtual circuits that are bottlenecked in the switching system (hereinafter referred to as ., "bandwidth allocation update"). An ABR virtual circuit is "active" if an output port receives at least one RM cell within the two most recent bandwidth allocation updates. An ABR virtual circuit is "inactive" if an output port does not receive at least one RM cell within the two most recent bandwidth allocation updates.
The present invention further comprises a method and system for dynamically adjusting the total bandwidth that an ABR_ER switching system can make available to ABR virtual circuits in the switching system by determining the total bandwidth allocated to inactive A.BR virtual circuits in the switching system without explicitly identifying the inactive ABR virtual circuits, and making available the bandwidth allocated to inactive ABR virtual circuits to active ABR virtual circuits that are established through the switching system. When transmission of cells resumes in an inactive A.BR virtual circuit, the switching system reallocates new bandwidth to the virtual circuit.
Specifically, at each fixed time interval, the switching system sets the total 1 S expected rate (Exp Rate) for active ABR virtual circuits that are bottlenecked elsewhere equal to the total expected rate for recently active ABR virtual circuits that are bottlenecked elsewhere, sets the total number of active ABR virtual circuits that are bottlenecked at an output port of the switching system equal to the total number of recently active ABR virtual circuits that are bottlenecked in the output port of the switching system, resets to zero the total expected rate for recently active ABR virtual circuits that are bottlenecked elsewhere, and resets to zero the total number of recently active ABR virtual circuits that are bottlenecked at the switching system.
The present invention further comprises a method and system for allocating bandwidth to an ABR virtual circuit that is established through an ABR-ER
switching system by allocating an explicit rate (ER) to the virtual circuit that is less than the minimum cell rate (MCR) for the virtual circuit, when the switching system receives a resource management (RM) cell with an explicit rate that is less than the minimum cell rate for the virtual circuit.
The description of the invention and the following description for carrying out the best mode of the invention should not restrict the scope of the claimed invention.
Both provide examples and explanations to enable others to practice the invention.
_7_ WO 98!31156 PCT/US98l00781 The accompanying drawings, which form part of the description for carrying out the best mode of the invention, show several embodiments of the invention, and together with the description, explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure la is a block diagram of an asynchronous transfer mode (ATM) communications network.
Figure 1 b is a block diagram of an end-to-end path of a virtual circuit that passes through N switching systems in an asynchronous transfer mode (ATM) communications network.
Figure 2 is a block diagram of a switching system in accordance with an embodiment of the invention.
Figure 3 is a block diagram of an output port in a switching system in accordance with an embodiment of the invention.
Figure 4 is a flow chart of the steps a switching system performs to process a resource management cell in accordance with an embodiment of the invention.
Figure 5 is a flow chart of the steps a switching system performs to process a resource management cell in accordance with an embodiment of the invention.
Figure 6 is a flow chart of the steps a switching system performs to determine bandwidth parameters for an output port and a virtual circuit in accordance with an embodiment of the invention.
Figure 7 is a flow chart of the steps a switching system performs to determine a new explicit rate for a virtual circuit in accordance with an embodiment of the invention.
Figure 8 is a flow chart of the steps a switching system performs to determine the total expected rate for active Available Bit Rate virtual circuits that are bottlenecked elsewhere in accordance with an embodiment of the invention.
Figure 9 is a flow chart of the steps a switching system performs to determine a the total expected rate for recently active Available Bit Rate virtual circuits that are bottlenecked elsewhere in accordance with an embodiment of the invention.
Figure 10 is a flow chart of the steps a switching system performs to determine _g_ ~r the total number of active Available Bit Rate virtual circuits that are bottlenecked at an output port of the switching system in accordance with an embodiment of the invention.
Figure 11 is a flow chart of the steps a switching system performs to determine the total number of recently active Available Bit Rate virtual circuits that are bottlenecked at an output port of the switching system in accordance with an embodiment of the invention.
Figure 12 is a flow chart of the steps a switching system performs to determine the total bandwidth available to active Available Bit Rate virtual circuits that are bottlenecked at an output port of the switching system in accordance with an embodiment of the invention.
Figure 13 is a flow chart of the steps a switching system performs to make available a new total bandwidth to active Available Bit Rate virtual circuits that are bottlenecked at an output port of the switching system in accordance with an embodiment of the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.
Wherever possible) the same reference numbers will be used throughout the drawings to refer to the same or like parts.
Figure 1 a illustrates a block diagram of an asynchronous transfer mode (ATM) communications network in accordance with an embodiment of the invention.
Virtual source (VS) 100 interfaces with ATM network 160 via transmission link 120.
Virtual destination (VD) 110 interfaces with ATM network 160 via transmission link 125. In establishing a connection between VS 100 and VD 110, ATM network 160 sets up a virtual circuit (VC) (not shown) between VS 100 and VD 110. During the set-up phase of the connection, VS 100 negotiates with ATM network 160 for an Available Bit Rate-Explicit Rate {ABR-ER) service.
After completion of the set-up phase of the connection, VS 100 generates Forward resource management {RM) cell 130 and transmits it on transmission link 120. Forward RM cell 130 passes through ATM network 160 and transmission link 125, and arnves at VD 110. VD 1 IO processes Forward RM cell 130, and generates Backward RM cell 140 in response to Forward RM cell 130. VD 110 then transmits Backward RM cell I40 on transmission link I25. Backward RM cell 140 passes through ATM network 160 and transmission /ink 120, and arrives at VS I00.
VS I00 generates data cell 150 and transmits it on transmission link 120. Data cell 150 passes through ATM network 160 and transmission link 125, and arrives at VD 110. Similarly, VD 110 generates data cell 150 and transmits it on transmission link I25. Data cell 150 passes through ATM network I60 and transmission link I20, IO and arrives at VS 100.
Figure Ib illustrates a block diagram of the end-to-end path of VC in ATM
network 160 in accordance with an embodiment of the invention. The path of the VC
established between VS 100 and VD 110 passes through N switching systems 105, through I05,~. Accordingly, when VS 100 transmits Forward RM cell 130 on transmission link 120, Forward RM cell passes through N switching systems 105, through 105,. Each switching system 105, through 105N connects to its adjacent switching system via a corresponding transmission link. For example, switching system 105, connects to switching system I05z via transmission link 121.
Switching System Figure 2 illustrates a block diagram of a switching system, for example switching system 1052, in accordance with an embodiment of the invention. As shown, switching system 1052 comprises M input ports 240, through 240,. Each input port interfaces with an input line, which can carry K virtual circuits.
For example, input port 240M interfaces with input line 121 M, which can carry K
virtual circuits (not shown). Input ports 240, through 240,, preferably interface with a cross-point switch fabric 250 via input links 220, through 220M respectively.
Alternatively, switch fabric 250 may be a Batcher-Banyan switch network, Sunshine switch, or any other switch fabric capable of switching ATM cells.
Switch fabric 250 interfaces with N output ports 260, through 260, via output links 230, through 230, respectively. For example, output port 260; interfaces with __. ~. ... _.. ..m ....
w, r switch fabric 250 via output Iink 230,. Each output port interfaces with an output line, which can carry K virtual circuits. For example, output port 260N
interfaces with output line 122N, which can carry K virtual circuits (not shown).
Output Ports Figure 3 illustrates a preferred embodiment for each output port 260, through 260N in accordance with an embodiment of the invention. As shown, each output port, for example output port 260N, preferably has access to central processing unit 310 (CPU), memory unit 360, controller 390, secondary storage 380, and high speed buses 370, 371, and 372. CPU 310 interfaces with controller 390 via high speed bus 372. Controller 390 interfaces with memory unit 360 and secondary storage 380 via high speed buses 370 and 371 respectively.
Memory unit 360 preferably includes VC Handler 320, Port Handler 330, Bandwidth Allocation Update 340, and Buffer 350. VC Handler 320, Port_Handler 330, Bandwidth Allocation Update 340, and Buffer 350 each preferably include a set of instructions in the form of software, which CPU 310 executes. VC_Handler receives and processes RM cells for VCs in output port 260N. Specifically, Port Handler 330 deterniines a new ER and Exp Rate for a VC, and recomputes the global bandwidth parameters for the VCs in output port 260;x, when a VC
receives an RM cell. At fixed time intervals, Bandwidth Allocation Update 340_ recomputes the total bandwidth that output port 260y can make available to active VCs that are bottlenecked at output port 260N. Buffer 350 stores cells (i.e, data cells and RM
cells) that arrive at output port 260N in queues (not shown), which are in memory unit 360. Alternatively, each VC Handler 320, Port Handler 330, Bandwidth Allocation Update 340, and Buffers 350 may be implemented in hardware using hardware technology known to one of ordinary skill in the art.
Secondary storage 380 includes disk drive unit 382 and tape cartridge 381.
Stored in disk drive unit 382 are software and data for switching system 105,.
For example, disk drive unit 382 contains software for VC Handler 320, Port_Handler 330, Bandwidth Allocation Update 340, and Buffer 350. Secondary storage 380 can copy software and data for switching system 105, from tape cartridge 381 into disk drive unit 382. Controller 390 can then upload the software and data from disk drive unit 382 into memory unit 360. Similarly, controller 390 can download software and data from memory unit 360 into disk drive unit 382. Secondary storage 380 can then copy the downloaded software and data from disk drive unit 382 into tape cartridge 381.
VC Handler A VC Handler processes and stores data specific to each VC in an output port.
Specifically, a VC Handler preferably stores for each VC a MCR, the time that an RM cell last arrived for the VC, an Exp Rate, and a Bottlenecked Elsewhere indicator. VC,Handler sets Bottlenecked Elsewhere indicator to a logical value of l, when at the time VC Handler receives an RM cell for a VC, the VC is bottlenecked elsewhere. If the VC is instead bottlenecked at an output port of the switching system, then VC Handler sets Bottlenecked Elsewhere indicator to a logical value of 0.
Figure 4 illustrates a flow chart of the steps a VC Handler, for example VC Handler 320, preferably performs to process an- RM cell, for example RM
cell 130, for a VC. VC Handler 320 receives RM cell 130 VC from switch fabric 250 (step 400). VC Handler 320 then generates an RM Cell Request (step 405). An RM-Cell Request includes a MCR, Bottlenecked_Elsewhere indicator, current Exp'Rate for VC, CCR, and a current ER for VC.
VC Handler 320 then sends the RM Cell Request to Port Handler 330 (step 410). Port Handler 330 computes a new ER, Exp Rate, and Bottlenecked Elsewhere indicator, and incorporates them in RM Cell Request.
VC Handler 320 waits until it receives the RM_Cell Request back from Port Handler 330 (step 415). If VC Handler 320 does not receive the RM_Cell Request back from Port_Handler 330 (step 415), then VC Handler continues to wait until it receives the RM Cell Request from Port-Handler 330 (step 420). If VC Handler 320 receives the RM Cell Request back from Port Handier 330, then VC Handler 320 resumes the processing of the- RM-Cell Request (step 425).
~Y ...
VC Handler 320 stores the new ER, Exp Rate, and the Bottlenecked Elsewhere indicator in memory unit 360 (step 430}. Alternatively, VC Handler 320 may store each of these values in a register. Finally, VC_Handler 320 replaces the current ER in RM cell 130 with the new ER in RM_Ceil Request (step 435). VC Handler 320 then sends RM cell 130 to Buffer 350 in output port 260N (step 440).
Port Handler A Port_Handler determines a new ER and Exp Rate for a VC, and recomputes the global bandwidth parameters for VCs in an output port. Specifically, a Port Handler preferably stores the time of the most recent bandwidth allocation update, the time of the second most recent bandwidth allocation update, the total bandwidth available to all VCs (i.e., CBR, VBR, ABR, and UBR VCs) in the output port, the total bandwidth available to all ABR VCs (i.e., active and inactive ABR
VCs), the total Exp Rate for active ABR VCs bottlenecked elsewhere, total Exp Rate for recently active ABR VCs bottlenecked elsewhere, the total bandwidth available to ABR VCs bottlenecked at the output port, the total number of active ABR VCs bottlenecked at the output port, and the total number of recently active ABR
VCs bottlenecked at the output port. When the Port_Handler receives an RM_Cell Request from a VC Handler, the Port Handler- _ recomputes the above mentioned global bandwidth parameters.
Figure 5 illustrates a flow chart of the steps a Port_Handler, for example Port_Handler 330, preferably performs to process an RM-Cell Request.
Pol-t_Handler 330 receives RM-Cell Request from VC Handler 320 (step 500).
Port Handler 330, as explained below,- recomputes global bandwidth parameters for output port 260N, and new ER and Exp'Rate for VC (step 505). Port_Handler 330 stores the new global bandwidth parameters for output port 260, in memory unit (step 510). Port Handler 330 sets the global bandwidth parameters for VC in the RM Cell Request (step 515). Port Handler 330 then returns the updated RM_Cell Request to VC Handler 320 (step 520).
Figure 6 illustrates a flow chart of the steps a Port Handler, for example Port-Handler 330, preferably performs to determine new global bandwidth parameters for an output port, for example output port 260N, and a VC. Port Handler 330 determines whether the last RM cell for VC arrived at output port 260N within the two most recent bandwidth allocation updates in output port 260N (step 600).
If Port Handler 330 determines that the last RM cell for VC arrived at output port 260N before the two most recent bandwidth allocation updates in output port 260N
(step 610), Port Handler 330 resets the current Exp Rate for VC to zero (step 615), and determines that VC is bottlenecked elsewhere and sets the Bottlenecked Elsewhere indicator in the RM Cell Request equal to a logical 1 (step 620). Port-Handler then determines whether VC is bottlenecked elsewhere (step 625).
If Port_Handler 330 determines that the last RM cell for VC arrived at output port 260, within the two most recent bandwidth allocation updates in output port 260, (step 605), then Port-Handler 330 determines whether VC is bottlenecked elsewhere (step 625).
If Port Handler 330 determines that VC is bottlenecked elsewhere (step 640), then Port Handler 330 determines an upper threshold, namely "Cutoff," for the amount of bandwidth that output port 260N can make available to VC. Port Handler 330 preferably determines the Cutoff for VC by dividing the total bandwidth available to active ABR VCs bottlenecked at output port 260; plus the current Exp Rate for VC by the total number of active ABR VCs bottlenecked at output port 260, plus one (step 645). Step 645 may alternatively be expressed as follows:
Cutoff = (Total Bandwidth Available to Active ABR VCs at Output Port 260N + Current Exp Rate for VC) / (Total Number of Active ABR VCs Bottlenecked at Output Port 260N + 1 ) If Port Handler 330 determines that VC is bottlenecked at output port 260N
(step 630), Port Handler 330 sets the Cutoff for VC equal to the total bandwidth available to active ABR VCs bottlenecked at output port 260, divided by the total number of active ABR VCs bottlenecked at output port 260; (step 650).
Port Handler 330 then, as explained below, determines a new ER for VC (step ~, ~
655), a new ExpTRate for VC (step 660), a new total Exp Rate for recently active ABR VCs bottlenecked elsewhere (step 665), a new total Exp Rate for active A.BR
VCs bottlenecked elsewhere (step 670), a new total number of recently active ABR
VCs bottlenecked at output port 260N (step 675), a new total bandwidth that output port 260N can make available to active ABR VCs bottlenecked at output port (step 680), and a new total number of active ABR VCs bottlenecked at output port 260N (step 685).
Figure 7 illustrates a flow chart of the steps a Port_Handler, for example Port Handler 330, preferably performs to determine a new ER for a VC.
Port_Handler 330 determines whether the Cutoff for VC is less than or equal to MCR
for VC (step 700). If Port-Handler 330 deterTnines that Cutoff for VC is greater than MCR (step 710), Port_Handler 330 sets the new ER equal to the minimum of the current ER and MCR (step 715). Port Handler 330 then determines that VC is bottlenecked elsewhere, and sets the Bottlenecked Elsewhere indicator in the 1 S RM_Cell Request to a logical 1 (step 755).
If Port Handler 330 determines that Cutoff for VC is less than or equal to MCR for VC (step 705), Port Handler 330 determines a most likely new Exp Rate for VC (step 720). Port Handler 330 selects the maximum of CCR and MCR for VC, and sets the most likely new Exp Rate to the minimum of that maximum value and the current ER for VC.
Port-Handler 330 determines whether the Cutoff for VC is greater than the most likely new Exp Rate for VC (step 725). If Port Handler 330 determines that the Cutoff is not greater than the most likely new Exp Rate (step 735), then Port_Handler 330 sets the new ER for VC to the minimum of current ER and the Cutoff (step 740).
Port Handier 330 then determines that VC is bottlenecked elsewhere and sets the Bottlenecked Elsewhere indicator in the RM Cell Request to a logical 1 (step 755).
If Port Handler 330 determines that the Cutoff for VC is greater than the most likely new Exp Rate (step 730), Port_Handler 330 sets the new ER equal to the Cutoff (step 745). Port_Handler 330 then determines that VC is bottlenecked at output port 260,x, and sets the Bottlenecked Elsewhere indicator in the RM_Cell Request to a logical 0 (step 750).
Figure 8 illustrates a flow chart of the steps a Port Handler, for example Port Handler 330, preferably performs to determine a new total Exp Rate for active ABR VCs that are bottlenecked elsewhere. Port-Handler 330 determines whether a VC is currently bottlenecked elsewhere (step 800). If Port-Handler 330 determines that VC is bottlenecked at output port 260, (step 810), then Port Handler 330 determines whether, when last time output port 260N received an RM cell for VC, VC
was bottlenecked elsewhere (step 815). If Port-Handler 33 determines that last time VC was bottlenecked at output port 260, (step 820), then Port Handler 330 determines that the total Exp Rate for active ABR VCs that are bottlenecked elsewhere remains unchanged (step 82S).
If Port Handler 330 determines that, when last time output port 260, received an RM cell for VC, VC was bottlenecked elsewhere (step 830), then Port Handler 330 decreases the total Exp Rate for active A.BR VCs that are bottlenecked elsewhere by the current Exp Rate for VC (step 835).
1 S If Port-Handler 330 determines that VC is currently bottlenecked elsewhere (step 80S), then Port Handler 330 determines whether, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 840). If Port Handler 330 determines that last time VC was bottlenecked at output port 260, (step 84S), Por-t_Handler 330 increases the total Exp Rate for active ABR VCs that are bottlenecked elsewhere by the new Exp Rate for VC (step 8S0).
If Port-Handler 330 determines that last time VC was bottlenecked elsewhere (step 85S), the Port Handler 330 decreases the total Exp Rate for active- ABR
VCs by the current Exp Rate for VC and increases the total Exp Rate for active- ABR
VCs by the new Exp Rate for VC (step 860).
2S Figure 9 illustrates a flow chart of the steps a Port Handler, for example Port Handler 320, preferably performs to determine a new total Exp Rate for recently active. ABR VCs that are bottlenecked elsewhere. Port Handler 330 determines whether the last RM cell for a V C arrived at output port 260; after the most recent bandwidth allocation update in output port 260N (step 900).
If Port Handler 330 determines that the last RM cell for VC arrived at output port 260N before the most recent bandwidth allocation update in output port 260N (step *~
905), then Port_Handler 330 determines whether VC is currently bottlenecked elsewhere (step 920). If Port_Handler determines that VC is currently bottlenecked elsewhere (step 920), the Port-Handler 330 increases the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere by the new Exp Rate for VC
(step 980).
If Port Handler 330 determines that VC is currently bottlenecked at output port 260N (step 915), then Port Handler 330 determines that the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere remains unchanged (step 925).
If Port Handler 330 determines that last- RM cell for VC arrived after the most recent bandwidth allocation update in output port 260v (step 930), then Port_Handler 330 determines whether VC is currently bottlenecked elsewhere (step 935). If Port_Handler 330 determines that VC is bottlenecked at output port 260N (step 940), then Port Handler 330 determines whether, when last time output port 260N
received an RM cell for VC, VC was bottlenecked elsewhere (step 950). If Port_Handler determines that last time VC was bottlenecked at output port 260N (step 955), then Port Handler 330 determines that the total Exp Rate for recently active ABR
VCs that are bottlenecked elsewhere remains unchanged (step 925).
If Port_Handler 330 determines that VC is bottlenecked at output port 260N
(step 940) and determines that, when last time output port 260N received an RM
cell for VC, VC was bottlenecked elsewhere (step 960), then Port-Handler 330 decreases the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere by the current Exp Rate for VC (step 965).
If Port Handler 330 determines that last RM cell for VC arrived after the most recent bandwidth allocation update in output port 260N (step 930) and determines that VC is currently bottlenecked elsewhere (step 945), then Port_Handler 330 determines whether, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 970). If Port_Handler determines that last time VC was bottlenecked at output port 260, (step 975), then Port_Handler 330 increases the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere by the new Exp Rate for VC (step 980).
If Port-Handler 330 determines that last RM cell for VC arnved after the most recent bandwidth allocation update in output port 260N (step 930), determines that VC
is currently bottlenecked elsewhere (step 945), and determines that, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 985), then Port_Handler 330 decreases the total Exp Rate for recently active ABR
VCs that are bottlenecked elsewhere by the current Exp Rate for VC and increases the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere by the new Exp Rate for VC (step 990).
Figure 10 illustrates a flow chart of the steps a Pol-t_Handler, for example Port Handler 330, preferably performs to determine the new total number of active ABR VCs that are bottlenecked at an output port, for example output port 260N.
Port Handler 330 determines whether a VC is currently bottlenecked elsewhere (step 1000). If Port-Handler 330 determines that VC is currently bottlenecked at output port 260, (step 1005), then Port Handler 330 determines whether, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 1015). If Port Handler 330 determines that last time VC was bottlenecked at output port 260N (step 1020), then Port Handler 330 determines that the total number of active ABR VCs that are bottlenecked at output port 260N remains unchanged (step I050).
If Port Handler 330 determines that VC is currently bottlenecked elsewhere (step 1010), then Port-Handler 330 determines whether, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 1030). If Port Handler 330 determines that last time VC was bottlenecked at output port 260h (step 1040), then Port Handler 330 decreases the total number of active- ABR
VCs that are bottlenecked elsewhere by one (step 1045).
If Port-Handler 330 determines that VC is currently bottlenecked elsewhere (step 1010) and determines that, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 1035), then Port Handler 330 determines that the total number of active ABR VCs that are bottlenecked at output port 260, remains unchanged (step 1050).
Figure 11 illustrates a flow chart of the steps a Port Handler, for example ., Port_Handler 330, preferably performs to determine the new total number of recently active A.BR VCs that are bottlenecked at an output port, for example output port 260N.
If Port Handler 330 determines that the last RM cell for a VC arrived before the most recent bandwidth allocation update (step 1105), then Port_Handler 330 determines whether VC is currently bottlenecked elsewhere (step 1115). If Port_Handler determines that VC is currently bottlenecked at output port 260, (step 1120), then Port Handler 330 determines that the total number of recently active- ABR VCs that are bottlenecked at output port 260N remains unchanged (step 1165).
If Port_Handler 330 determines that the last RM cell for VC arrived before the most recent bandwidth allocation update (step 1105) and determines that VC is currently bottlenecked elsewhere (step 1125), then Port Handler 330 increases the total number of recently active A.BR VCs that are bottlenecked at output port 260N by one (step I 130).
If Port-Handler 330 determines that last RM cell for VC arrived after the most recent bandwidth allocation update (step 1110), then Port_Handler 330 determines whether, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 1135). If Port Handler 330 determines that last time VC
was bottlenecked elsewhere (step I 140), then Port_Handler 330 determines whether VC is currently bottlenecked elsewhere (step 1115). If Port_Handler 330 determines that VC is currently bottlenecked at output port 260N (step 1120), then Port_Handler 330 determines that the total number of recently active ABR VCs that are bottlenecked at output port 260N remains unchanged (step 1165).
If Port Handler 330 determines that, when last time output port 260N received an RM cell for VC, VC was bottlenecked elsewhere (step 1140) and determines that VC is currently bottlenecked elsewhere (step 1125), then Port-Handler 330 increases the total number of recently active ABR VCs that are bottlenecked at output port 260.
by one (step 1130).
If Port Handler 330 determines that the last- RM cell for VC arrived after the most recent bandwidth allocation update (step 11 IO) and determines that VC
was bottlenecked at output port 260N (step 1145), then Port Handler 330 determines whether VC is currently bottlenecked elsewhere (step 1150). If Port Handler determines that VC is currently bottlenecked at output port 260N (step 1155), then Port Handler 330 determines that the total number of recently active ABR VCs that are bottlenecked at output port 260N remains unchanged (step 1165).
If Port Handler 330 determines that last RM cell for VC arrived after the most recent bandwidth allocation update (step 1110), determines that, when last time output port 260, received an RM cell for VC, VC was bottlenecked at output port 260N
(step 1145), and determines that VC is currently bottlenecked elsewhere (step 1160), then Port-Handler 330 decreases the total number of active ABR VCs that are bottlenecked at output port 260N by one (step 1170).
Figure 12 illustrates a flow chart of the steps a Port_Handler, for example Port Handler 330, preferably performs to determine the new total bandwidth that an output port, for example output port 260N, can make available to active ABR
VCs that are bottlenecked at output port 260N. Port_Handler 330 determines whether a VC
is currently bottlenecked elsewhere (step 1200). If Port_Handler 330 determines that VC is bottlenecked at output port 260, (step 1205), then Port Handler 330 determines whether, when last time output port 260, received an RM cell for VC, VC was bottlenecked elsewhere (step 1215). If Port Handler 330 determines that last time VC
was bottlenecked at output port 260, (step 1220), then Port Handler 330 determines that the total bandwidth that output port 260N can make available to active ABR VCs at output port 260, remains unchanged (step 1230).
If Port-Handler 330 determines that VC is bottlenecked at output port 260, (step 1205) and determines that, when Iast time output port 260y received an RM cell for VC, VC was bottlenecked elsewhere (step 1225), then Port Handler 330 increases the total bandwidth that output port 260N can make available to active ABR VCs that are bottlenecked at output port 260N by the current Exp Rate for VC (step I235).
If Port_Handler 330 determines that VC is bottlenecked elsewhere (step 1210), then Port Handler 330 determines whether, when last time output port 260N
received an RM cell for VC, VC was bottlenecked elsewhere (step 1240). If Port Handler determines that last time VC was bottlenecked at output port 260, (step 1245), then Port Handler 330 decreases the total bandwidth available to active ABR VCs that are bottlenecked at output port 260; by the new Exp Rate for VC (step 1255).
_, If Port Handler 330 determines that VC is bottlenecked elsewhere (step 1210) and determines that, when last time output port 260N received an RM cell for VC, VC
was bottlenecked elsewhere (step 1250), then Port Handler 330 increases the total bandwidth that output port 260N can make available to active ABR VCs that are bottlenecked at output port 260N by the current Exp Rate for VC and decreases the total bandwidth that output port 260N can make available to active ABR VCs that are bottlenecked at output port 260N by the new Exp Rate for VC (step 1260).
Bandwidth Allocation Update An output port, for example output port 260N, invokes, at preferably fixed time intervals, Bandwidth Allocation Update 340. Bandwidth Allocation Update 340 preferably stores the time interval between each invocation in a static memory. The manufacturer of a switching system may set a default for the fixed time interval, which a switching system administrator or network administrator may subsequently reconfigure.
The time interval between each invocation may preferably be twice the upper bound for the time interval between each RM cell generated by an active virtual source. The upper bound may preferably be in the range of 2'S milliseconds to milliseconds. Alternatively, the time interval between each invocation may be less than twice the upper bound for the time interval between each RM cell, in which case the time interval between each invocation must still be sufficiently large to allow for arrival of at least one RM cell between two consecutive invocations of Bandwidth Allocation Update 340.
Bandwidth Allocation Update 340 preferably has access to the global bandwidth parameters stored in memory unit 360 by Port_Handler 330.
Specifically, Bandwidth Allocation Update 340 has access to the time of the most recent bandwidth allocation update, the time of a second most recent bandwidth allocation update, the total bandwidth available to all ABR VCs (i.e., active and inactive ABR
VCs), the total Exp Rate for active ABR VCs bottlenecked elsewhere, the total Exp Rate for recently active ABR VCs bottlenecked elsewhere, the total bandwidth available to active ABR VCs bottlenecked at output port 260N, the total number of active ABR VCs bottlenecked at output port 260N, and the total number of recently active ABR VCs bottlenecked at the output port 260N.
Figure 13 illustrates a flow chart of the steps a Bandwidth Allocation Update, for example Bandwidth Allocation Update 340, preferably performs to make available a new total bandwidth to active ABR VCs that are bottlenecked at an output port, for example output port 260N. Bandwidth Allocation Update 340 sets the total Exp Rate for active ABR VCs that are bottlenecked elsewhere equal to the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere (step 1300).
Next, Bandwidth Allocation Update 340 sets the total number of active- - ABR
VCs that are bottlenecked at output port 260N equal to the total number of recently active ABR VCs that are bottlenecked at output port 260, (step 1305).
Bandwidth Allocation Update 340 then sets the total bandwidth that output port 260, can make available to active ABR VCs that are bottlenecked at output port 260N equal to the difference between the total bandwidth available to all ABR
VCs 1 S (i.e., active and inactive ABR VCs) and the total Exp Rate for recently active ABR
VCs that are bottlenecked elsewhere (step 1310).
Next, Bandwidth Allocation Update 340 resets the total Exp Rate for recently active ABR VCs that are bottlenecked elsewhere (step I315).
Bandwidth Allocation Update 340 then resets the total number of recently active ABR VCs that are bottlenecked at output port 260N (step 1320). Finally, Bandwidth Allocation Update 340 sets a timer for the next update to the total bandwidth that output port 260N can make available to active ABR VCs that are bottlenecked at output port 260N (step 1325).
To prevent reallocation of bandwidth from a VC when an RM cell for the VC
is lost, for example, due to network congestion for an extended period of time, an ATM network may assign a high priority to RM cells. Alternatively, by keeping the time interval between the updates to the global bandwidth parameters (i.e., invocation of Bandwidth Allocation Update) sufficiently large, if an RM cell is lost due to network congestion, the impact to allocation of an optimum bandwidth to the VC
would be minimal.
While it has been illustrated and described what are at present considered to be ,. f. ..
preferred embodiments and methods of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the invention.
In addition, many modifications may be made to adapt a particular element, technique or implementation to the teachings of the present invention without departing from the central scope of the invention. Therefore, it is intended that this invention not be limited to the particular embodiments and methods disclosed herein, but that the invention include all embodiments falling within the scope of the appended claims.
Claims (13)
1. A method for allocating bandwidth to virtual circuits in an asynchronous transfer mode (ATM) switching system, said method comprising the steps of:
a) at predetermined times, determining bandwidth allocated to inactive virtual circuits in said switching system; and b) making said bandwidth available to active virtual circuits in said switching system.
a) at predetermined times, determining bandwidth allocated to inactive virtual circuits in said switching system; and b) making said bandwidth available to active virtual circuits in said switching system.
2. The method according to claim 1 further comprising the step of making said bandwidth available to new virtual circuits in said switching system.
3. A system for allocating bandwidth to virtual circuits in an asynchronous transfer mode (ATM) switching system, comprising:
a) means for determining, at predetermined times, bandwidth allocated to inactive virtual circuits in said switching system; and b) means for making said bandwidth available to active virtual circuits in said switching system.
a) means for determining, at predetermined times, bandwidth allocated to inactive virtual circuits in said switching system; and b) means for making said bandwidth available to active virtual circuits in said switching system.
4. A computer-readable medium capable of configuring an asynchronous transfer mode (ATM) switching system to perform a method for allocating bandwidth to virtual circuits in said switching system, said method comprising the steps of:
a) at predetermined times, determining bandwidth allocated to inactive virtual circuits in said switching system; and b) making said bandwidth available to active virtual circuits in said switching system.
a) at predetermined times, determining bandwidth allocated to inactive virtual circuits in said switching system; and b) making said bandwidth available to active virtual circuits in said switching system.
5. A method for allocating bandwidth to virtual circuits in an asynchronous transfer mode (ATM) switching system, said method comprising the steps of:
a) determining a first total expected rate for recently active virtual circuits in said switching system that are bottlenecked elsewhere;
b) adjusting a second total expected rate for active virtual circuits that are bottlenecked elsewhere to said first total expected rate;
c) determining total bandwidth available in said switching system for active virtual circuits that are bottlenecked in said switching system;
and d) resetting said first total expected rate.
a) determining a first total expected rate for recently active virtual circuits in said switching system that are bottlenecked elsewhere;
b) adjusting a second total expected rate for active virtual circuits that are bottlenecked elsewhere to said first total expected rate;
c) determining total bandwidth available in said switching system for active virtual circuits that are bottlenecked in said switching system;
and d) resetting said first total expected rate.
6. The method according to claim 5 further comprising the steps of:
e) determining a first total number of recently active virtual circuits that are bottlenecked in said switching system;
f) adjusting a second total number of said active virtual circuits that are bottlenecked in said switching system to said first total number; and g) resetting said first total number.
e) determining a first total number of recently active virtual circuits that are bottlenecked in said switching system;
f) adjusting a second total number of said active virtual circuits that are bottlenecked in said switching system to said first total number; and g) resetting said first total number.
7. A system for allocating bandwidth to virtual circuits in an asynchronous transfer mode (ATM) switching system, comprising:
a) means for determining a first total expected rate for recently active virtual circuits in said switching system that are bottlenecked elsewhere;
b) means for adjusting a second total expected rate for active virtual circuits that are bottlenecked elsewhere to said first total expected rate;
c) means for determining total bandwidth available in said switching system for active virtual circuits that are bottlenecked in said switching system; and d) means for resetting said first total expected rate.
a) means for determining a first total expected rate for recently active virtual circuits in said switching system that are bottlenecked elsewhere;
b) means for adjusting a second total expected rate for active virtual circuits that are bottlenecked elsewhere to said first total expected rate;
c) means for determining total bandwidth available in said switching system for active virtual circuits that are bottlenecked in said switching system; and d) means for resetting said first total expected rate.
8. The system according to claim 7 further comprising:
e) means for determining a first total number of recently active virtual circuits that are bottlenecked in said switching system;
f) means for adjusting a second total number of said active virtual circuits that are bottlenecked in said switching system to said first total number; and g) means for resetting said first total number.
e) means for determining a first total number of recently active virtual circuits that are bottlenecked in said switching system;
f) means for adjusting a second total number of said active virtual circuits that are bottlenecked in said switching system to said first total number; and g) means for resetting said first total number.
9. A computer-readable medium capable of configuring an asynchronous transfer mode (ATM) switching system to perform a method for allocating bandwidth to virtual circuits in said switching system, said method comprising the steps of:
a) determining a first total expected rate for recently active virtual circuits in said switching system that are bottlenecked elsewhere;
b) adjusting a second total expected rate for active virtual circuits that are bottlenecked elsewhere to said first total expected rate;
c) determining total bandwidth available in said switching system for active virtual circuits that are bottlenecked in said switching system;
and d) resetting said first total expected rate.
a) determining a first total expected rate for recently active virtual circuits in said switching system that are bottlenecked elsewhere;
b) adjusting a second total expected rate for active virtual circuits that are bottlenecked elsewhere to said first total expected rate;
c) determining total bandwidth available in said switching system for active virtual circuits that are bottlenecked in said switching system;
and d) resetting said first total expected rate.
10. The computer-readable medium according to claim 9, wherein said method further comprises the steps of:
e) determining a first total number of recently active virtual circuits that are bottlenecked in said switching system;
f) adjusting a second total number of said active virtual circuits that are bottlenecked in said switching system to said first total number; and g) resetting said first total number.
e) determining a first total number of recently active virtual circuits that are bottlenecked in said switching system;
f) adjusting a second total number of said active virtual circuits that are bottlenecked in said switching system to said first total number; and g) resetting said first total number.
11. A method for allocating bandwidth to a virtual circuit in an asynchronous transfer mode (ATM) switching system, said method comprising the steps of:
a) receiving a resource management cell for said virtual circuit, wherein said resource management cell comprises an explicit rate and a minimum cell rate; and b) allocating said explicit rate to said virtual circuit when said explicit rate is less than said minimum cell rate.
a) receiving a resource management cell for said virtual circuit, wherein said resource management cell comprises an explicit rate and a minimum cell rate; and b) allocating said explicit rate to said virtual circuit when said explicit rate is less than said minimum cell rate.
12. A computer-readable medium capable of configuring an asynchronous transfer mode (ATM) switching system to perform a method for allocating bandwidth to a virtual circuit in said switching system, said method comprising the steps of:
a) receiving a resource management cell for said virtual circuit, wherein said resource management cell comprises an explicit rate and a minimum cell rate; and b) allocating said explicit rate to said virtual circuit when said explicit rate is less than said minimum cell rate.
a) receiving a resource management cell for said virtual circuit, wherein said resource management cell comprises an explicit rate and a minimum cell rate; and b) allocating said explicit rate to said virtual circuit when said explicit rate is less than said minimum cell rate.
13. A system for allocating bandwidth to a virtual circuit in an asynchronous transfer mode (ATM) switching system, comprising:
a) means for receiving a resource management cell for said virtual circuit, wherein said resource management cell comprises an explicit rate and a minimum cell rate; and b) means for allocating said explicit rate to said virtual circuit when said explicit rate is less than said minimum cell rate.
a) means for receiving a resource management cell for said virtual circuit, wherein said resource management cell comprises an explicit rate and a minimum cell rate; and b) means for allocating said explicit rate to said virtual circuit when said explicit rate is less than said minimum cell rate.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US3533497P | 1997-01-14 | 1997-01-14 | |
| US60/035,334 | 1997-01-14 | ||
| PCT/US1998/000781 WO1998031156A2 (en) | 1997-01-14 | 1998-01-14 | Method and system for dynamic allocation of bandwidth in asynchronous transfer mode (atm) switching systems |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2278317A1 true CA2278317A1 (en) | 1998-07-16 |
Family
ID=21882013
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002278317A Abandoned CA2278317A1 (en) | 1997-01-14 | 1998-01-14 | Method and system for dynamic allocation of bandwidth in asynchronous transfer mode (atm) switching systems |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0960513A2 (en) |
| JP (1) | JP2000508500A (en) |
| KR (1) | KR20000070154A (en) |
| AU (1) | AU5919398A (en) |
| CA (1) | CA2278317A1 (en) |
| WO (1) | WO1998031156A2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4294723B2 (en) | 2007-08-28 | 2009-07-15 | パナソニック株式会社 | Network control apparatus, method, and program |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2068847C (en) * | 1991-07-01 | 1998-12-29 | Ronald C. Roposh | Method for operating an asynchronous packet bus for transmission of asynchronous and isochronous information |
| CA2104753C (en) * | 1992-10-29 | 1999-02-16 | Kotikalapudi Sriram | Bandwidth allocation, transmission scheduling, and congestion avoidance in broadband atm networks |
| US5448567A (en) * | 1993-07-27 | 1995-09-05 | Nec Research Institute, Inc. | Control architecture for ATM networks |
| US5541912A (en) * | 1994-10-04 | 1996-07-30 | At&T Corp. | Dynamic queue length thresholds in a shared memory ATM switch |
| US5559798A (en) * | 1995-04-19 | 1996-09-24 | Lucent Technologies Inc. | Data segmentation within a renegotiated bit-rate service transmission system |
| GB2337895B (en) * | 1995-06-05 | 2000-01-19 | Fujitsu Ltd | Detecting congestion in ATM networks |
| KR0146764B1 (en) * | 1995-07-29 | 1998-08-17 | 양승택 | Equipment and method for control of abr service by managing buffer using multi stage critical value |
-
1998
- 1998-01-14 KR KR1019997006380A patent/KR20000070154A/en not_active Application Discontinuation
- 1998-01-14 AU AU59193/98A patent/AU5919398A/en not_active Abandoned
- 1998-01-14 CA CA002278317A patent/CA2278317A1/en not_active Abandoned
- 1998-01-14 EP EP98902565A patent/EP0960513A2/en not_active Withdrawn
- 1998-01-14 JP JP10531275A patent/JP2000508500A/en active Pending
- 1998-01-14 WO PCT/US1998/000781 patent/WO1998031156A2/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0960513A2 (en) | 1999-12-01 |
| JP2000508500A (en) | 2000-07-04 |
| KR20000070154A (en) | 2000-11-25 |
| AU5919398A (en) | 1998-08-03 |
| WO1998031156A2 (en) | 1998-07-16 |
| WO1998031156A3 (en) | 1998-11-12 |
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