Classifications

• • 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
  • H04Q—SELECTING
  • H04Q11/00—Selecting arrangements for multiplex systems
  • H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing
• • 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
  • H04L2012/5619—Network Node Interface, e.g. tandem connections, transit switching
  • H04L2012/562—Routing
• • 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
  • H04L2012/5638—Services, e.g. multimedia, GOS, QOS
  • H04L2012/5645—Connectionless
• • 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
  • H04L2012/5685—Addressing issues

Definitions

• This invention relates to a method of transmitting an asynchronous transfer mode (ATM) cell over an ATM network between an ATM input interface and an ATM output interface.
• ATM asynchronous transfer mode
• VPI virtual path identifier
• VCI virtual channel identifier
• the routing table and the updating values for the VPI and/or VCI fields are set up partly by network management and partly by signalling during call set up. Consequently, a conventional ATM network provides a connection-oriented service. In a connection-oriented service, the call is set up by signalling at the commencement of the call and cleared down at the end of the call. Alternatively, the routing table and the updating values may be set up to provide a permanent connection.
• a switched ATM network for example data from a computer provided with an ATM card
• a conventional switched ATM network is not optimal for intermittent transmission of data.
• ATM asynchronous transfer mode
• the present invention provides the advantage that the routing tables do not need to be set up by signalling for each transmission of ATM cells between a particular access node and a particular destination node. Consequently, where cells are transmitted in bursts, there is no overhead cost of setting up a call for each burst of cells.
• a method of operating an ATM network so as to transmit cells between a source node and a destination node over the network selectively in either a connectionless manner or a connection-oriented manner, said source node and destination node each having a network address, each ATM cell comprising a header and a user section, said network comprising a network of interconnected nodes at least some of which are switching nodes; in the event of transmitting an ATM cell over the network in a connectionless manner between an ATM input interface and an ATM output interface, said method comprising the steps of at the ATM input interface, setting a field in the header of the ATM cell to a value which indicates connectionless transmission and inserting a destination address and a source address into the header, the source address being the network address of the source node and the destination address being the network address of the destination node; and at each switching node between the ATM input interface and the ATM output interface, establishing the cell is to be forwarded in a connectionless manner by reading said field in the header, reading the destination address
• ATM asynchronous transfer mode
• FIG. 1 is a block diagram of a conventional asynchronous transfer mode (ATM) network
• Figure 2 shows the structure of a basic ATM cell
• Figure 3 shows the header fields used in a basic ATM cell during transmission between a user and an ATM network interface
• Figure 4 shows the fields used in the header of a basic ATM cell during transmission between nodes within an ATM network
• FIG. 5 is a block diagram of an ATM network embodying this invention
• Figure 6 is a flow chart of the operations performed on an ATM cell at the input interface to the network of Figure 5;
• FIG. 7 is a flow chart showing the operations performed on an ATM cell in a switching node of the network of Figure 5,
• FIG 8 is a flow chart of the series of operations which are used to form an ATM cell in an Internet Protocol (IP) gateway to the network of Figure 5; and
• IP Internet Protocol
• Figure 9 shows the header fields which are used in an ATM cell in the network of Figure 5 when it is providing a connectionless service.
• the ATM network comprises a network of partially interconnected switching nodes in the form of ATM switches 10 to 1 8.
• switches 10, 1 1 , 1 2, 1 3, 1 5, 1 6, 1 7 and 1 8 also function as access switches.
• FIG. 1 shows switch 1 7 connected by one access line to a computer 22 and by another access line to a multiplexer 24
• the computer 22 is provided with an ATM card which enables it to transmit and receive data in the form of ATM cells
• the multiplexer 24 can receive video, data and speech signals and convert these in a multiplexed manner into ATM cells Likewise, it can receive ATM cells from the switch 1 7 and convert these to video, data and voice signals
• the multiplexer 24 will be located at the premises of a user of the ATM network
• VPI virtual path identifier
• VCI virtual channel identifier
• the values of one or both of the VPI and VCI fields are updated in accordance with data contained in a routing table
• the VPI field provides a coarse level of routing whereas the VCI field provides a fine level of routing
• the routing tables are set up partly by network management and partly during call set up Mainly, but not entirely, virtual path routing tables are set up by network management and virtual channel routing tables are set up by signalling during call set up
• a basic ATM cell comprises a five-octet header
• the cell header 40 is used to route the cell between switches across the network and the user payload section 42 contains the user's data and it is carried transparently across the network and delivered unchanged at the far end
• Figures 3 and 4 there are shown the fields in the header of a basic conventional ATM cell
• Figure 3 shows the fields which are used in transmitting an ATM cell across a user-network interface
• Figure 4 shows the fields which are used in transmitting the cell across a network node interface within an ATM network
• the key for the fields is set out in Table 1 below.
• GFC generic flow control
• the virtual path identifier (VPI) field provides the coarse level routing for
• VPI changes each time the cell is switched at a switch which provides virtual path switching.
• the VPI field has only eight bits. This increases to 1 2 bits between nodes of the network as there is no need for generic flow control bits as a cell is transmitted through a network.
• the virtual channel identifier (VCI) field provides fine level routing for ATM cells.
• the VCI value in the header changes each time a cell is switched by a switch which provides virtual channel routing.
• the VCI field is 16 bits long
• the payload type (PT) field is used to indicate the general type of data in the cell. Typical uses of this field are to identify operation, administration and maintenance cells, congestion conditions and resource management or the last cell of a multi-cell message. This field is three bits long. There is always a slight risk of cells being lost in an ATM network.
• the cell loss priority (CLP) field is one bit long. When this bit is set, it tells the network that this cell is less important and should be discarded in favour of another cell when a loss must take place.
• the head error check (HEC) field provide a check sum over the ceil header. It can detect bit errors in the cell header and can sometimes be used to correct them. This field is eight bits long
• a conventional switched ATM network such as the network shown in Figure 1 , is unsuitable for transmitting data which is transmitted intermittently or in bursts If a conventional switched ATM network is used to transmit this type of data, the routing tables are set up during call set up before it is required to transmit data and the connection is maintained for as long as data transmission is required.
• connection-oriented service This type of service is generally unsuited to transmitting data in bursts. Transmission of data in bursts is generally more suited to what is known as a connectionless service.
• connectionless service In a connectionless service, there is no call set up procedure and routing tables are set up by routing protocol or network management processes and not during call set up.
• the header includes a field for indicating the type of service required It is envisaged that each possible type of service may have a corresponding value in this field Examples of type of service are low delay, a request for a switch to reserve buffer space for a return call, and multi-casting in which a call is routed to more than one destination.
• IP Internet protocol
• the ATM network is capable of transmitting ATM cells in either a connection-oriented manner or a connectionless manner It is also capable of providing various types of service such as the services mentioned above and also additional processing.
• the general layout of the network of Figure 5 is similar to that shown in Figure 1 .
• the network of Figure 5 comprises a network of partially interconnected switching nodes in the form of ATM switches 1 10 to 1 1 8
• the switches 1 10, 1 1 1 , 1 1 3, 1 1 5, 1 17 and 1 1 8 are access switches which can receive data from other networks or directly from user equipment on input/output lines 1 20.
• switch 1 1 7 is shown connected to a computer 1 22, generally similar to the computer 22 of Figure 1 , and also to a multiplexer 1 24, which is generally similar to the multiplexer 24 of Figure 1 .
• the switch 1 1 6 is connected by an input/output line to an IP gateway 1 31 and the switch 1 1 2 in connected by a line 1 32 to an IP gateway 133.
• Each of the IP gateways 1 31 and 1 33 can receive data from, and transmit data to, an IP network on input/output lines 134
• IP gateways 1 31 or 1 33 In operation, when one of the IP gateways 1 31 or 1 33 is acting as an input access node for data received from an IP network, it decomposes the IP packets into ATM cells. When one of these gateways is acting as an output access node, it re-assembles the ATM cells into IP packets.
• the source address (SA) field indicates the network address of the source node.
• the source node will normally be at the input interface to the ATM network shown in Figure 5
• the source node could be switch 1 1 3 or the computer 1 22 or the multiplexer 1 24 or the IP gateway 1 31 .
• the option field may be set to a value which indicates that a particular service is required or that additional processing is required.
• services which may be supported are a request for a switch to reserve buffer space for a return call, a request for low delay or multicasting.
• Each possible type of service is assigned a unique value in the option field.
• a requirement to perform additional processing is also assigned a unique value in the option field.
• additional processing are an intelligent network operation, a network management operation or a routing operation.
• the cell When a cell which requires additional processing is received at a switch, the cell is passed to a higher layer in the switch and its payioad section is examined to determine what additional processing is required. For example, if an intelligent network operation is required, the switch may access a remote database to determine a new destination address from the destination address in the cell. The destination address is then changed accordingly.
• some of the bits of the payload section of a cell may specify that a network management operation is required.
• the switch performs the required operation.
• the destination address (DA) field is used to indicate the network address of the destination node.
• the destination address will normally be at the output interface.
• the destination address is the network address for the multicasting service
• the source address, destination address and option field ordering and structure are network domain specific where a domain is a collection of nodes sharing the same formats for these fields.
• This invention is not restricted to ATM networks using the conventional cell header and payload structure and sizes shown in Figures 3 and 4 Where, as in the present example these conventional cell header and payload structures are used, 28 bits in total are allocated to the SA, DA and OF fields. The reason for this is that this is the number of bits used by the conventional GFC, VPI and VCI fields. The bits then allocated to the SA, DA and OF fields can be arbitrarily chosen, but they must be specific within a specific domain.
• the SA and DA fields are each 1 2 bits long and the OF field is 4 bits long Consequently, the network domain shown in Figure 5 can support 4096 source addresses, 4096 destination addresses and 16 options.
• Source and destination addresses outside the network may additionally be specified in the payload section of the first cell of each transmission.
• the payload type (PT) field is identical to this field used in the header of a conventional ATM cell except that a predefined value, which in the present example is " 1 1 1 ", is used to indicate that the service is connectionless.
• the CLP and HEC fields are identical to these fields in the header of a conventional ATM ceil.
• a user of the network shown in Figure 5 wishes to transmit ATM cells over the network using a connectionless service, it indicates to one of the access switches, for example switch 1 1 7, that a connectionless service is required and it provides the destination address If a particular service or additional processing is required, it also indicates this.
• the access switch then performs the operations shown in Figure 6 on each ATM cell which it receives from the user. These operations will now be described Alternatively, if the input interface is at a node outside the network, the operations are performed at that node.
• the PT field is set to a value " 1 1 1 " to indicate a connectionless service
• the destination address is inserted and in a step 202 the source address is inserted
• the PT field is set to the appropriate value.
• FIG. 7 shows the operations which are performed at each switch between the input interface and the output interface on each ATM cell. These operations will now be described.
• a step 220 the cell enters the switch.
• the switch reads the PT field to determine whether a connectionless service is required. If a connectionless service is not required, it performs the operations which are performed by a conventional ATM switch.
• a step 222 it reads the VPI and/or VCI fields.
• Some ATM switches are only virtual path switches, some are only virtual channels switches and some are both virtual path and virtual channel switches. Thus, the fields which are read and used will depend upon the type of switch.
• the routing table together with the values of the VPI and/or VCI fields are used to select an output port.
• the VPI and/or VCI fields are updated in accordance with the data in the routing table.
• a step 225 the cell leaves the switch on a selected output port.
• step 221 If it is found in step 221 that a connectionless service is required, the following operations are performed.
• a step 230 it reads the source and destination addresses (SA and DA fields) in the header.
• a step 231 it reads the OF field to determine the service type.
• a step 232 it performs such operations as may be specified in the option field, for example reserving buffer space or performing additional processing.
• a step 233 it selects the outgoing port by using the value of the destination addresses or the values of both the source and destination addresses and also the routing table. Therefore, the route which is followed by a connectionless ATM cell as it is transmitted over the network could depend upon the source address as well as the destination address.
• FIG. 8 there is shown the series of operations which are performed on IP packets received at one of the IP gateways 1 31 and 1 33 to form each ATM cell.
• an ATM cell is formed by decomposition of IP packets.
• the source and destination addresses, the required type of service and any request for additional processing are read.
• a step 251 the PT field is set to indicate that a connectionless service is required.
• steps 252 and 253 the destination address and source address are inserted into the header.
• the option field is set to indicate the required type of service or that additional processing is required
• the network shown in Figure 5 could be a public wide area network
• WAN wide area network
• LAN local area network
• the network addresses of the source and destination nodes are established by network management. These addresses are permanent in the sense that they are established for an indefinite period
• the routing tables used in the switching nodes for cells being transmitted in accordance with the connectionless service are established by network management and not by signalling. Consequently, even on the first occasion that a source node transmits ATM cells through the network to a particular destination node, the cells are transmitted without performing a signalling operation.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Data Exchanges In Wide-Area Networks (AREA)

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• 1997
  • 1997-03-21 CN CN97193411A patent/CN1132489C/zh not_active Expired - Fee Related
  • 1997-03-21 NZ NZ331325A patent/NZ331325A/xx unknown
  • 1997-03-21 EP EP97908406A patent/EP0890290A1/de not_active Withdrawn
  • 1997-03-21 WO PCT/GB1997/000801 patent/WO1997036453A1/en not_active Application Discontinuation
  • 1997-03-21 JP JP09534126A patent/JP2000510665A/ja not_active Ceased
  • 1997-03-21 KR KR1019980707053A patent/KR19990087607A/ko not_active Application Discontinuation
  • 1997-03-21 AU AU20379/97A patent/AU725361B2/en not_active Ceased
• 1998
  • 1998-09-25 NO NO984468A patent/NO984468D0/no unknown

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