WO1991015909A1 - Procede et agencement de commande d'admission d'appel dans un systeme de communication de paquets - Google Patents

Procede et agencement de commande d'admission d'appel dans un systeme de communication de paquets Download PDF

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Publication number
WO1991015909A1
WO1991015909A1 PCT/GB1991/000571 GB9100571W WO9115909A1 WO 1991015909 A1 WO1991015909 A1 WO 1991015909A1 GB 9100571 W GB9100571 W GB 9100571W WO 9115909 A1 WO9115909 A1 WO 9115909A1
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Prior art keywords
node
nodes
link
packets
access
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PCT/GB1991/000571
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English (en)
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John Leonard Adams
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British Telecommunications Public Limited Company
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Priority to JP91507001A priority Critical patent/JPH05508272A/ja
Publication of WO1991015909A1 publication Critical patent/WO1991015909A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L47/00—Traffic control in data switching networks
    • H04L47/10—Flow control; Congestion control
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L47/00—Traffic control in data switching networks
    • H04L47/10—Flow control; Congestion control
    • H04L47/11—Identifying congestion

Definitions

  • the present invention relates to a communication system suitable for use, for example, in a metropolitan area network (MAN). It is particularly, but not exclusively, concerned with a network using a Distributed Queue Dual Bus (DQDB).
  • DQDB Distributed Queue Dual Bus
  • DQDB DQDB
  • Known systems such as DQDB provide for the communication of packets of fixed lengths between nodes connected to a link, in this case a bus.
  • the packets are assembled from multiple data streams received from one or more terminals connected to the node.
  • Such systems generally include some mechanism for controlling the access of the nodes to the bus.
  • the DQDB system for example, uses two buses whose signals run in opposite directions carrying user data and network signalling information in a series of fixed length packets inserted into slot positions on each bus.
  • a queuing discipline is used, whereby the packet at the head of the queue of data in each of a number of nodes forms, together with the corresponding packets at the heads of the queues in the other nodes, a distributed logical first come first serve queue.
  • simulation results show that the technique is slow to converge to the desired access rate and it is difficult to fine-tune the allocations to each node.
  • a communication system including a link and a number of nodes connected to the link, each node including means to communicate packets with other nodes via the link, in which at least one node includes means to measure the availability of the link capacity for the transmission of packets by the said node, comparison means to compare the measured availability with a threshold for that node and reduction means for generating a signal for reducing the utilisation availability by other nodes when the availability at the at least one node is below the threshold as determined by the comparison means.
  • the present invention provides a communication system with nodes capable individually of monitoring the capacity of a link such as a bus. It is therefore particularly suitable for use with critical services requiring a minimum packet transfer rate.
  • the said means to measure include an access rate monitor responsive to the rate at which the respective node outputs packets onto the link, and the reduction means comprises means to output a restriction request signal to enforce restriction of the output of other nodes when the rate falls below the threshold for that node.
  • the said node is connected to a terminal adapter and the threshold is determined in accordance with the minimum packet transfer rate required by the terminal adapter.
  • a terminal adapter packetises the terminal data stream into fixed length packets and depacketises information received from the network, converting it to a form suitable for sending to the terminals.
  • the minimum transfer rate is ensured by monitoring the access rate of the node and, when it approaches a minimum value, transmitting a control signal which causes other similarly modified nodes on the network to restrict or "throttle" their own data access rates. This results in there being more free slots on the link so that, in accordance with whatever priority or contention mechanism is adopted by the system, the node making the request is able to increase its link access rate.
  • the system of the present invention effectively provides a higher level access control protocol for the modified nodes, the higher level protocol operating in conjunction with the basic level protocol for the system thereby ensuring complete compatibility with the basic level protocol and any unmodified nodes using that protocol.
  • the provision of full backwards compatibility with existing systems is a major advantage, and in this respect ' the present invention contrasts with previously proposed systems, such as the Orwell system described in the applicant' s earlier application number EP-A-0, 168, 265.
  • This is a system which while it is able to provide a guaranteed minimum bandwidth for terminals attached to the nodes, requires a dedicated control protocol. Nodes within this system have their own internal mechanism for setting their own access requirements and use available empty slots to seek additional slot allocations.
  • a further advantage of the present invention is that it allows efficient use of the available bandwidth on the link by services of different bit rates, including services of variable bit rates such as a variable bit rate video service. Again this contrasts with previously proposed systems such as DQDB with isochronous slots.
  • isochronous slots that is the provision of slots of fixed, equal duration for use by different nodes, is poorly adapted to coping with a variable bit rate and in particular provides reduced efficiency through partial filling or large delays with low bit rate services such as voice telephony.
  • the said node includes means to receive and process a restriction request signal from another node
  • the terminal adapter includes means responsive to a control - A -
  • the terminal adapter includes a data buffer, when the terminal adapter is in the second mode, the data buffer being enabled to output data only in response to an output request signal from the node or after the lapsing of a predetermined delay from the initiation of the second mode.
  • the terminal adapter includes a register arranged to store a value d, where d is the number of packets to be transmitted to the node in response to each output request from the node, the value for d and the predetermined time being chosen to provide the required minimum packet transfer rate for the terminal.
  • the communication system includes nodes of first and second types, at least two of the said first type nodes including the means to measure availability, and at least one node of said second type without the capability of responding directly to the signal generated by the reduction means from another node, the or each second node being arranged to concede access to the link to first type nodes transmitting higher priority level packets.
  • Such second (or unmodified) type nodes are found on existing DQDB protocols and hence can be ac ⁇ o odated in the present system configuration.
  • the communication system includes at least two sub-networks connected to a central switch for the system via respective head-end nodes, the head-end nodes being unmodified nodes and each sub-network being connected to its respective head-end node by a bridge node.
  • a bridge node monitors its link access rate and responds to restriction request signals.
  • a mixed network including unmodified head-end nodes it interfaces its respective sub-network to the system in such a way that the system as a whole remains responsive to restriction requests from individual nodes.
  • a method of controlling a communication system including a number of nodes which can communcate via a communication link utilising packets, said method including measuring on at least one node the availability of link capacity for the transmission of packets by the said node, comparing the measured availability with a threshold for that node and generating a signal for reducing the utilisation availability by other nodes when the availability at the at least one node is below the threshold as determined by the comparison step.
  • a node for connection to a link in a data communication system including an output buffer arranged to hold packets for transmission onto the link, and an access rate monitor including means to determine from the packet through-put of the output buffer a parameter indicative of the link access rate available to the node.
  • the access rate monitor includes timer means arranged to measure the cumulative delay of the data packets in the output buffer waiting for access to the link, counter means arranged to count the number of packets output from the buffer onto the link, and processor means responsive to the timer means and the counter means and arranged to determine the said parameter from the number of packets output while the cumulative delay measured by the timer means is less than a predetermined value.
  • This second aspect of the present invention provides a node which has the advantage that it is able to measure the link access rate using a method which increases in speed of response as the available link capacity decreases.
  • a method of operating a node in a communication system including a link and a number of nodes connected to the link, including the steps of measuring the availability on the link of capacity for the transmission of packets by the node, comparing the measured availability with a threshold for the node and reducing the utilisation by other nodes if the availability is below the threshold.
  • Figure 1 is a block diagram of a DQDB data communications system
  • Figure 2 is a block diagram of a modified DQDB node
  • Figure 3 is a block diagram of a terminal adapter for use in the system of Figure 1;
  • Figure 4 is a block diagram of a node adapter
  • Figure 5 is a block diagram of a modified node combined with a terminal adapter
  • Figure 6 is a block diagram of a system including sub-networks connected via bridge nodes.
  • Figure 7 shows an alternative embodiment
  • a DQDB data communications system includes a dual bus 1 and modified nodes 2 and unmodified nodes 3 connected to the bus 1.
  • the unmodified nodes 3 communicate data with the bus in accordance with the DQDB protocol described in the proposed standard "Distributed Queue Dual Bus (DQDB) Metropolitan Area Network (MAN)", IEEE 802.6.
  • DQDB distributed Queue Dual Bus
  • MAN Metropolitan Area Network
  • Each modified node 2 is connected to a terminal adapter 4 which is in turn connected to a terminal 5 for a service such as voice telephony requiring a guaranteed minimum data rate.
  • a service such as voice telephony requiring a guaranteed minimum data rate.
  • data is communicated between the adapter 4 and the node 2 in the form of ATM (asynchronous transfer mode) packets.
  • the existing standard for the ATM frame format includes four previously unassigned bits. It has been proposed that these bits hould be used to provide Generic Flow Control (GFC), whereby a node is able to transmit control signals to, e. g. , a terminal adapter, to modify the output from the adapter.
  • GFC Generic Flow Control
  • the GFC bits are used to throttle the output from a given terminal adapter as described in further detail below.
  • the modified node may in some circumstances be formed by the addition of a node adapter to an existing unmodified node. Also, as described below with respect to Figure 6, a combined modified node and terminal adapter may be used.
  • the different nodes 2, 3 contend for the bus using a contention system which, in the present example using the DQDB protocol, takes the form of a distributed first come first service queue with a place in the distributed queue assigned to each foremost packet in the internal queues of the different nodes.
  • the modified DQDB nodes 2 are arranged to monitor the bus access rate achieved in accordance with this contention system.
  • the modified node 2 monitors the rate of available empty slots passing the node.
  • An available empty slot is one which the node can use to transmit data. Not all empty slots are available because of the internal DQDB protocol.
  • the modified node 2 compares this available empty slot rate against the minimum requirement ' d' .
  • this approaches a certain level, e. g. available empty slot rate is less than 1.25d the modified node 2 broadcasts to all other modified nodes 2 to commence throttle.
  • the terminal adapters 4 perceive an interface state equivalent to ' unrestricted access' . Now the state of the interface is changed into ' throttled access' controlled by a reset rate.
  • the modified node 2 does not directly monitor empty slots on the DQDB bus 1. Instead it uses the departure rate of full packets onto the bus 1 to determine the available empty slot rate. This relies on the fact that when the queue of packets waiting for bus access is non-zero, the departure rate is a direct indication of the available empty slot rate.
  • two FIFOs 6 are provided within the node, one for each bus direction.
  • the FIFOs 6 hold packets waiting for access to the bus.
  • the timers 7 are connected to a clock 8 provided within the node and so keep a cumulative total of the time spent by the packets in the FIFOs 6 waiting for access to the bus.
  • a counter 9 which is incremented each time a packet departs from the FIFO onto the bus 1.
  • the timer 7 When the total time recorded by the timer 7 reaches a predetermined value, which in the present example is 125 microseconds, then it transmits an interrupt to the control processor 10. In response to this interrupt the processor 10 reads the value of the counter 9 into a register R and both the timer and counter are reset.
  • the processor also includes a d register which holds the value d for the corresponding terminal.
  • R is compared with a parameter proportional to d, which is in turn dependent on the minimum packet transfer rate needed by the terminal. If, for example, R is less than 1.25d (rounded up to the nearest integer) it implies that the terminal cannot gain access to more than 1.25d empty slots per 125 microseconds. If d slots per 125 microseconds is the minimum data rate then 1.25d represents the threshold value at which the bus access rate is considered to be too low. Accordingly the control processor generates a restriction request signal which is broadcast to the other nodes to cause them to restrict or ' throttle' the rate at which they are putting data onto the bus.
  • the control processor uses a packetiser 11 to output a restrict request signal in the form of an appropriately headed ATM packet which is then output onto the bus via an ATM processor 12 and one of the FIFOs 6.
  • a packetiser 11 to output a restrict request signal in the form of an appropriately headed ATM packet which is then output onto the bus via an ATM processor 12 and one of the FIFOs 6.
  • the other modified node 2 switches into a mode in which the terminal, instead of having unrestricted access to the node, transfers data only in response to a request generated by the node.
  • the terminal adapter 4 includes its own processor 13 which receives incoming GFC bits, and in response generates an appropriate input for the upstream access control logic 14.
  • a timer 15 provides a further input.
  • the upstream access control logic 14 controls the flow of data through buffers 16, 17.
  • the packet containing the restriction request signal received by the terminal adapter also carries a value indicating a reset rate in the range for the present example, from 32 per 2 milliseconds (two resets per 125 microseconds) down to 16 per 2 milliseconds (the minimum guaranteed).
  • the reset rate is transmitted to a remote terminal adapter using a 4-bit field setting in the header of an ATM slot.
  • the 4-bit setting i. e. GFC field setting
  • Any such setting is written into the header of the next slot (full or empty) travelling downstream towards the terminal adapter 4. For intermediate values of R, a corresponding proportional value for the reset rate is calculated.
  • the modified nodes 2 are arranged to take the most stringent of the two rate restrictions as the current setting. Throttled access continues until a time out occurs on each modified node 2 indicating that no throttled access message has been received for 3 milliseconds. This timeout is sufficiently long so that a corrupted revised reset message will not cause exit to unrestricted access provided the next revised reset message is received. Once the 3 millisecond timeout has occurred no further resets are transmitted to the terminal adapter 4 until a new message is received from one of the modified nodes or a value of R ⁇ 1.25d is detected.
  • the terminal adapter 4 may be arranged to operate at two different reset rates in which case the restriction request control packet carries two corresponding values for required reset rates applying to different service classes. They are distinguished by an additional class of service field.
  • the different resets can have different minimum rates e. g. a rate of 16 per 2 milliseconds (equivalent to 1 per 125 microseconds) can be maintained for one group of services, while another reset with a minimum of 1 per 6 milliseconds could be maintained for low bit-rate services which provides a more severe throttle for the latter group (note that constant bit-rate services such as 64 kbit/s voice are not throttled since their minimum allocations are set at 64 kbit/s).
  • the processor receives the incoming advised reset rate and calculates two or more rates at which it will provide GFC settings towards the downstream terminal adapter.
  • two types of reset can be provided to the terminal adapter to indicate the bus direction which has restricted access.
  • the node processor sends either one type of reset if only one bus has restricted access, or two types if both buses simultaneously have restricted access.
  • This modification can be exploited by terminal adapters which employ two internal buffers which are multiplexed together to provide the output to the node as described in more detail below.
  • the terminal adapter terminates the GFC protocol in the downstream direction (i.e. network to terminal). It maintains a ' d' counter whose value is negotiated at call set-up time. Call control will ensure that no call is accepted if the sum of all ' d' s exceeds a predefined level of the bus capacity (say 90%). This implies that when throttled to maximum the terminals will each receive their guaranteed share.
  • Call control responds to a call request message with information which enables the packetiser in the terminal adapter to associate a correctly labelled header with the pa ⁇ ketised information of the new call.
  • This response also provides the terminal adapter with the go-ahead to change the allocation d, either via an explicit field within the message from call control or else through information stored in the terminal adapter based on the known type of terminals connected to it.
  • the packet header information from call control will include information to indicate which of the two buffers should be used.
  • the terminal adapter will signal to the processor in the modified node any change in its d-allocation as agreed with call control.
  • the modified node maintains a record of the current d-value of any terminal adapter connected to it so that it can load the appropriate value of 1.25d in its register.
  • the terminal adapters will pass packets upstream in an unrestricted way.
  • the terminals On receipt of an ' immediate return to floor' setting of the GFC the terminals will halt transmission awaiting the first reset (another setting of the GFC). On receipt of the first reset the terminal adapters will transmit ' d' packets and halt again awaiting a further reset.
  • the change from unrestricted access to restricted access depends on the bus direction setting associated with the ' immediate return to floor' message and the associated resets. Separate controls are maintained in the terminal adapter dealing with each direction.
  • a timer Upon receipt of each reset a timer is started (see Figure 3). If no further reset is achieved after 125 microseconds the timer will generate an ' auto-reset' which provides the node with a further allocation. If after a further 125 microseconds still no reset has been received via the GFC field, the terminal adapter will revert to unrestricted access.
  • Equipment to provide guaranteed bandwidth control may be remotely connected to some types of DQDB nodes which satisfy the following conditions: -the DQDB node has an ATM terminal interface, i. e. information is conveyed from the terminal to the node already packetised in fixed length ATM packets, -the DQDB node operates some of the GFC bits on that interface to throttle terminals under conditions of overload on either of the buses. This could be via the simple use of the ' immediate return to floor' setting which stops/reduces the transmission of packets for a known period.
  • a node adapter may be connected to the DQDB node on a terminal interface.
  • the node adapter can signal to other node adapter or modified nodes when they should enter restricted access.
  • entry into restricted access is not specific to a particular bus direction as it can be with the modified node as this information is not necessarily available from the GFC settings from the DQDB node.
  • the need for an auto-reset and associated timer is removed since reset-controlled access from the output FIFOs is handled directly by the node processor.
  • an output enable signal and packet sent indication are connected to the node processor for each bus direction.
  • the node processor permits only d packets to be sent within a period equivalent to the reset interval (i. e. the time between successive resets) when the state of restricted access has been entered. There is no requirement to set or use any GFC bits since no remote resets are required.
  • the control processor 10' directly controls the output from the node by the transmission of enable signals to the output buffer 6' .
  • a further aspect to be considered is how modified DQDB nodes can be added to a public MAN arrangement such as that shown in Figure 6.
  • the distinguishing features of this arrangement are: -each customer has a DQDB bus connection to a central switch 18 known as the MAN switching system. This interface is known as the Subscriber Network Interface or ' SNI' . The customer can connect one or several DQDB nodes on his premises to the same SNI.
  • a head-end DQDB node 19 At the network-end of each SNI, where it terminates on the central switch, is a head-end DQDB node 19. -in any arrangement where several customers are connected to the same MAN, the head-end node 19 would not normally be owned by a customer wishing to upgrade his network for multi-services. These nodes would therefore remain unmodified whenever such a customer adds modified nodes to his SNI.
  • the unmodified head-end node 19 at the central switch does not compete with any modified node in the customer' s premises. This can easily be seen by considering the load on each bus direction of the SNI in turn. In the network-to-customer direction only the head-end node loads the bus. In the customer-to-network direction only the modified bridge node loads the bus. Hence there is no competition for bandwidth on the SNI.
  • the bridge node 20 becomes the head-end node, but it is of the modified variety. Hence throttle controls can be applied to this head end and therefore it can operate successfully with other modified nodes added to this subnetwork.
  • the functions of the bridge node 20 are:
  • the bridge node may throttle all modified nodes (including itself) if the high priority load from customer to network approaches the capacity of the SNI. To do this the bridge node must monitor the high priority load using a separate counter and timer for this purpose. The timer would be set to interrupt the node processor after, say 6 milliseconds, and is clocked whether the FIFO is full or empty (unlike the timer used for bandwidth into the FIFO. After 6 milliseconds the counter is compared against a d value used for the SNI (e. g. d could be set to 80% of the total SNI packets within a 6 millisecond interval rounded down to the nearest integer).
  • a d value used for the SNI e. g. d could be set to 80% of the total SNI packets within a 6 millisecond interval rounded down to the nearest integer.
  • the bridge node may throttle all other bridge nodes if the measured network-to-customer load attempting to access the customer-owned DQDB bus exceeded say 80% of its capacity. This requires in the bridge node a separate timer and counter to measure the load say every 6 milliseconds with operations as described above for entry and exit from the restricted access condition.
  • the multiplexers in addition to handling the queues at any one node and determining their d values for the various priority queues, will additionally include the mechanism for sensing the bandwidth availability on the bus at any time and to request reduction of utilization of other nodes if availability is unduly limited.
  • Figure 1 arrangement described above could include Orwell type multiplexers forming each node and all/some of these nodes being configured to include the ability to measure and request reduced utilization from other similar nodes.
  • FIG. 7 includes a number of nodes 100.
  • three nodes 100 are within the Customer premises network connected by means of dual bus 103 at the Broadband ISDN user network interface (BISDN-UNI) to the public BISDN network with a further node 100 being shown within BISDN switch 101.
  • BISDN-UNI Broadband ISDN user network interface
  • Each node 100 independently monitors the utilisation level of the bus (in each direction) and when this approaches a critical level it will set the generic flow control (GFC) field of the BISDN packet headers (known as ATM cells) so as to restrict the access rate of all nodes.
  • GFC generic flow control
  • a key feature of the GFC mechanism for restricted access is that it provides a certain minimum guaranteed bandwidth available to each node. This relies on the inclusion of a counter in each node, whose value is the number of packets which the node can send between successive GFC signals known as ' resets' . Clearly the value in the counter can differ on each node, according to the needs of the service. Furthermore the protocol ensures that the reset rate is never less than one per 125 microsecs, which therefore represents the minimum guaranteed bandwidth for the node.
  • each node estimates how much bus bandwidth is currently available to it as follows. For each bus direction, whenever a packet is waiting for bus access timing pulses are fed to a timer T. No timing pulses are counted when there is no packet waiting. For each bus direction a counter C is enabled to count the number of cells departing onto the bus. When T equals 125 microsecs C is read into a register R and the timers and counters are reset.
  • the value in register R is an estimate of the bus bandwidth available to the node (expresesed as the number of cells that can be output in 125 microsecs).
  • Nodes are configured to be a particular ' access state' dependent on bandwidth utilisation conditions as now described.
  • M 1.25d, ie 25% above minimum
  • This state applies to a particular bus and all nodes are limited to an access rate of d packets per ' reset' signal.
  • the node which originated the restricted access signal becomes the ' master node' determining the reset rate.
  • Each reset signal is placed on the opposite bus by the master node and is then re-issued by the head end node on the correct bus.
  • the reset rate may vary from N per millisec (eg 16 resets per millisec) down to 8 per millisec (the minimum guaranteed).
  • the master node sets GFC field to return all nodes to ' unrestricted access' . Once again the signal is passed down the opposite bus and is reflected at the head end.
  • a node may issue a ' restricted access' signal even when it is already in the restricted access state. This is when it wishes to take over as master because it observes that its measured value R has fallen below M. It issues a ' restricted access' signal and this causes the current master to relinquish control as explained further below. The new master is immediately free to use its own slower reset rate to provide more bandwidth for it to use.
  • While current master (of particular bus direction) a node reads the opposite bus and overwrites any reset signal from other nodes if the GFC setting indicates that such reset signals are to be reflected at the head end.
  • the master node Following the issue of a ' restricted access' signal the master node immediately issues a ' reset' signal and simultaneously resets its own counter. For each cell which it transmits on to the bus for which it is master it decrements the counter by 1. Then if either:
  • the master issues a further reset signal and immediately resets its counter. When these reset signals return via the head-end they are ignored by the master node (but not by other nodes).
  • each node resets its counter by one each time. When the counter reaches zero the node ceases transmission until either:
  • a timeout occurs indicating that 125 microsecs have elapsed since the last reset.
  • the node issues an ' auto-reset' and resets its own counter and sets its own state to ' auto-resetting' .
  • the reset timer continues to measure the time elapsed since the last auto-reset. If no further reset arrives whilst the node state is auto-resetting then the occurrences of a further time out of 125 microseconds since the last autoreset causes the node to enter the unrestricted access state.
  • Each GFC signal is transmitted via the head end where it is modified to show the particular bus direction to which it applies. Any signal is written into the header of a full or empty slot.
  • nodes can be allowed access to the bus in an unrestricted way. This is signified by a continuous series of ' null' GFC settings.
  • the reset and change access state signals (3 signals) are coded by overwriting the other 2 bits of any GFC field where the lower 2 bits are already set to read ' null' and the upper two bits are also set to ' null' .
  • the protocol can take account of operations on a service class basis as follows. Change access state signal and reset signals are supplemented with information about the service class in the upper two bits, ie.
  • the head end node operates more intelligently by trying to decide which service class to append to the signal (no service class information is appended to signals until they reach the head end). For example on entry from the unrestricted access state, the head end could append ' lowest class' only. It could then successively change the class parameter until the reset rate is at least greater than say 8M/d per millisec indicating that the master node is now above the threshold ' M' discussed above. If a second ' restricted access' signal is received while in the restricted access state it could immediately change the class parameter to restrict more classes.
  • the response of the head end node to more than one ' restricted access' signal can be exploited as follows.
  • the master node can shift the class parameter to the desired mode by sending a sequence of x ' restricted access' signals (x is not more than 4) prior to sending the first reset.
  • a copy of the current class mode is kept in each node. It would need to be kept in synchronisation with other nodes by an occasional broadcast signal from the head end.
  • the nodes are informed of the current class of service status at the head end wherever a restricted access signal or unrestricted access signal is dispatched from the head end. In this arrangement it would be of benefit if the bandwidth monitoring function is replicated in each node on the basis of one per service queue.
  • each node can independently monitor its available bus bandwidth and to do no more than this until the bandwidth drops below a measured level. Until such a level is reached there is no restriction on bus load which can be important on long busses, for example. When restriction is deemed necessary, each node is guaranteed at least a minimum bandwidth.

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Abstract

Système de communication de données comprenant un bus de données (1) et un certain nombre de n÷uds (2, 3) reliés au bus (1). Chacun des n÷uds (2, 3) est conçu pour communiquer des paquets de données de longueur fixe par l'intermédiaire du bus (1). Des niveaux de priorité différents sont affectés aux paquets de données et chacun des n÷uds (2, 3) est conçu pour laisser l'accès au bus (1) à un autre ÷ud transmettant un paquet de données à niveau prioritaire. Quelques-uns des n÷uds sont modifiés pour contrôler leur cadence respective d'accès au bus. Chacun des n÷uds modifiés (2) émet un signal de demande de restriction au bus (1) quand sa cadence d'accès tombe au-dessous d'un seuil respectif prédéterminé. Les autres n÷uds modifiés (2) réduisent leur cadence respective d'accès au bus en réponse au signal de demande de restriction, libérant ainsi un espace sur le bus (1) que le n÷ud (2) utilise.
PCT/GB1991/000571 1990-04-11 1991-04-10 Procede et agencement de commande d'admission d'appel dans un systeme de communication de paquets WO1991015909A1 (fr)

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JP91507001A JPH05508272A (ja) 1990-04-11 1991-04-10 パケット通信システムの呼出承認制御方法および装置

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GB909008230A GB9008230D0 (en) 1990-04-11 1990-04-11 Communication systems
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Cited By (1)

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Publication number Priority date Publication date Assignee Title
WO1999026379A2 (fr) * 1997-11-18 1999-05-27 Telefonaktiebolaget Lm Ericsson Reseau permettant de controler un moyen d'acces, tel qu'un protocole d'acces au support, d'une pluralite d'adaptateurs de terminal

Citations (2)

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WO1999026379A2 (fr) * 1997-11-18 1999-05-27 Telefonaktiebolaget Lm Ericsson Reseau permettant de controler un moyen d'acces, tel qu'un protocole d'acces au support, d'une pluralite d'adaptateurs de terminal
WO1999026379A3 (fr) * 1997-11-18 1999-09-02 Ericsson Telefon Ab L M Reseau permettant de controler un moyen d'acces, tel qu'un protocole d'acces au support, d'une pluralite d'adaptateurs de terminal
US6697874B1 (en) 1997-11-18 2004-02-24 Telefonaktiebolaget Lm Ericsson (Publ) Method for controlling the access, such as medis access protocol, of a plurality of terminal adapters

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JPH05508272A (ja) 1993-11-18
AU7659591A (en) 1991-10-30

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