Classifications

• • 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
  • H04L47/18—End to end
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F15/00—Digital computers in general; Data processing equipment in general
  • G06F15/16—Combinations of two or more digital computers each having at least an arithmetic unit, a program unit and a register, e.g. for a simultaneous processing of several programs
  • G06F15/163—Interprocessor communication
  • G06F15/173—Interprocessor communication using an interconnection network, e.g. matrix, shuffle, pyramid, star, snowflake
  • G06F15/17356—Indirect interconnection networks
  • G06F15/17368—Indirect interconnection networks non hierarchical topologies
  • G06F15/17375—One dimensional, e.g. linear array, ring
• • 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]
  • H04L12/46—Interconnection of networks
  • H04L12/4604—LAN interconnection over a backbone network, e.g. Internet, Frame Relay
  • H04L12/4608—LAN interconnection over ATM networks
• • 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
• • 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
  • H04L12/5602—Bandwidth control in ATM Networks, e.g. leaky bucket
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L41/00—Arrangements for maintenance, administration or management of data switching networks, e.g. of packet switching networks
  • H04L41/08—Configuration management of networks or network elements
  • H04L41/0896—Bandwidth or capacity management, i.e. automatically increasing or decreasing capacities
• • 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
• • 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
  • H04L47/26—Flow control; Congestion control using explicit feedback to the source, e.g. choke packets
• • 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
  • H04L47/26—Flow control; Congestion control using explicit feedback to the source, e.g. choke packets
  • H04L47/266—Stopping or restarting the source, e.g. X-on or X-off
• • 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
  • H04L47/29—Flow control; Congestion control using a combination of thresholds
• • 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
  • H04L47/30—Flow control; Congestion control in combination with information about buffer occupancy at either end or at transit nodes
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/50—Queue scheduling
  • H04L47/62—Queue scheduling characterised by scheduling criteria
  • H04L47/621—Individual queue per connection or flow, e.g. per VC
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/10—Packet switching elements characterised by the switching fabric construction
  • H04L49/104—Asynchronous transfer mode [ATM] switching fabrics
  • H04L49/105—ATM switching elements
  • H04L49/106—ATM switching elements using space switching, e.g. crossbar or matrix
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/10—Packet switching elements characterised by the switching fabric construction
  • H04L49/104—Asynchronous transfer mode [ATM] switching fabrics
  • H04L49/105—ATM switching elements
  • H04L49/107—ATM switching elements using shared medium
• • H—ELECTRICITY
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  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/15—Interconnection of switching modules
  • H04L49/1515—Non-blocking multistage, e.g. Clos
  • H04L49/153—ATM switching fabrics having parallel switch planes
• • H—ELECTRICITY
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  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/15—Interconnection of switching modules
  • H04L49/1553—Interconnection of ATM switching modules, e.g. ATM switching fabrics
• • H—ELECTRICITY
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  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/15—Interconnection of switching modules
  • H04L49/1553—Interconnection of ATM switching modules, e.g. ATM switching fabrics
  • H04L49/1576—Crossbar or matrix
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/20—Support for services
  • H04L49/201—Multicast operation; Broadcast operation
  • H04L49/203—ATM switching fabrics with multicast or broadcast capabilities
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/25—Routing or path finding in a switch fabric
  • H04L49/253—Routing or path finding in a switch fabric using establishment or release of connections between ports
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/25—Routing or path finding in a switch fabric
  • H04L49/253—Routing or path finding in a switch fabric using establishment or release of connections between ports
  • H04L49/255—Control mechanisms for ATM switching fabrics
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/25—Routing or path finding in a switch fabric
  • H04L49/256—Routing or path finding in ATM switching fabrics
• • 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
• • 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
  • H04L49/309—Header conversion, routing tables or routing tags
• • H—ELECTRICITY
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  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/45—Arrangements for providing or supporting expansion
  • H04L49/455—Provisions for supporting expansion in ATM switches
• • H—ELECTRICITY
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  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/55—Prevention, detection or correction of errors
  • H04L49/552—Prevention, detection or correction of errors by ensuring the integrity of packets received through redundant connections
• • H—ELECTRICITY
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  • H04L49/00—Packet switching elements
  • H04L49/55—Prevention, detection or correction of errors
  • H04L49/555—Error detection
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L69/00—Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass
  • H04L69/30—Definitions, standards or architectural aspects of layered protocol stacks
  • H04L69/32—Architecture of open systems interconnection [OSI] 7-layer type protocol stacks, e.g. the interfaces between the data link level and the physical level
  • H04L69/322—Intralayer communication protocols among peer entities or protocol data unit [PDU] definitions
  • H04L69/324—Intralayer communication protocols among peer entities or protocol data unit [PDU] definitions in the data link layer [OSI layer 2], e.g. HDLC
• • 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
  • H04J—MULTIPLEX COMMUNICATION
  • H04J3/00—Time-division multiplex systems
  • H04J3/02—Details
  • H04J3/06—Synchronising arrangements
  • H04J3/0635—Clock or time synchronisation in a network
  • H04J3/0682—Clock or time synchronisation in a network by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J3/00—Time-division multiplex systems
  • H04J3/02—Details
  • H04J3/06—Synchronising arrangements
  • H04J3/0635—Clock or time synchronisation in a network
  • H04J3/0685—Clock or time synchronisation in a node; Intranode synchronisation
• • 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
  • H04L2012/5614—User Network Interface
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  • H04L12/56—Packet switching systems
  • H04L12/5601—Transfer mode dependent, e.g. ATM
  • H04L2012/5614—User Network Interface
  • H04L2012/5616—Terminal equipment, e.g. codecs, synch.
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  • H04L12/5601—Transfer mode dependent, e.g. ATM
  • H04L2012/5625—Operations, administration and maintenance [OAM]
  • H04L2012/5627—Fault tolerance and recovery
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  • H04L2012/5628—Testing
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  • H04L2012/5629—Admission control
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  • H04L2012/5635—Backpressure, e.g. for ABR
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  • H04L2012/564—Connection-oriented
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  • H04L2012/5647—Cell loss
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• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L7/00—Arrangements for synchronising receiver with transmitter
  • H04L7/04—Speed or phase control by synchronisation signals
  • H04L7/041—Speed or phase control by synchronisation signals using special codes as synchronising signal
  • H04L7/046—Speed or phase control by synchronisation signals using special codes as synchronising signal using a dotting sequence

Definitions

• the present invention is generally related to telecommunications networks, and more particularly to reduction of cell loss in network switches.
• ATM networks such as asynchronous transfer mode (“ATM”) networks are used for transfer of audio, video and other data.
• ATM networks deliver data by routing data units such as ATM cells from source to destination through switches.
• Switches include input/output ("I/O") ports through which ATM cells are received and transmitted. The appropriate output port for transmission of the cell is determined based on the cell header.
• a problem associated with ATM networks is loss of cells.
• Cells are buffered within each switch before being routed and transmitted from the switch. More particularly, switches typically have buffers at either the inputs or outputs of the switch for temporarily storing cells prior to transmission. As network traffic increases, there is an increasing possibility that buffer space may be inadequate and data lost. If the buffer size is insufficient, cells are lost. Cell loss causes undesirable interruptions in audio and video data transmissions, and may cause more serious damage to other types of data transmissions. Avoidance of cell loss is therefore desirable.
• SUMMARY OF THE INVENTION A method and apparatus are disclosed for eliminating cell loss within a network switch through the use of flow control.
• the switch includes at least one input port, at least one output port, and input and output buffers associated with the respective input and output ports.
• each queue includes multiple buffers, and each switch includes multiple input queues and multiple output queues. Upon entering the switch, each cell is loaded into a particular input queue for eventual transmission to a particular output queue. Individual queues are then assigned to traffic type groups in order to provide traffic type flow control if shared resources are being utilized. In an alternate implementation, each queue could be dedicated to a particular traffic type (sometimes referred to as a service class) such as the variable bit rate (“VBR”) service class and the available bit rate (“ABR”) service class.
• VBR variable bit rate
• ABR available bit rate
• Flow control can then be implemented on a per traffic type basis. Further, flow control can be implemented on traffic sub-types and queues where each queue may be assigned to a particular connection, thereby providing flow control on a per connection as well as traffic subtype basis. Table 1 below shows possible flow control configurations. TABLE 1
• Each connection is assigned bandwidth types based on the traffic type associated with the connection.
• bandwidth There are two types of bandwidth to grant within the switch: allocated and dynamic.
• Allocated bandwidth is bandwidth which is "reserved" for use by the connection to which the bandwidth is allocated.
• a connection with allocated bandwidth is guaranteed access to the full amount of bandwidth allocated to that connection.
• traffic types that need deterministic control of delay are assigned allocated bandwidth.
• Dynamic bandwidth is bandwidth which i ⁇ "shared" by any of various competing connections. Because dynamic bandwidth is a shared resource, there is generally no guarantee that any particular connection will have access to a particular amount of bandwidth. For this reason dynamic bandwidth is typically assigned to connections with larger delay bounds. Other connections may be assigned a combination of dynamic and allocated bandwidth.
• a digital feedback message with first and second bits is provided to facilitate flow control.
• the feedback message may also include a REJECT message.
• REJECT When REJECT is received by the requesting input queue, the cell is not transferred. However, further requests to transfer may be sent by the input queue.
• the feedback message may also include a NO-OP/XOFF message.
• An XOFF message can be received while transmitting via allocated bandwidth or dynamic bandwidth.
• an XOFF (allocated) message may be received with regard to allocated bandwidth and an XOFF (dynamic) message may be received with regard to dynamic bandwidth.
• An optional tagging technique may be employed to distinguish between requests for dynamic and allocated bandwidth.
• the XOFF (dynamic) message temporarily halts transmission of requests to transfer via dynamic bandwidth.
• Each input queue receiving XOFF (dynamic) from a particular output queue temporarily ceases submitting requests to transmit to that particular output queue via dynamic bandwidth until a specified event occurs.
• the specified event could be passage of a predetermined amount of time or receipt of an XON signal which enables further requests to transfer to be sent.
• the input queues could also be enabled with an XON signal on a regular basis, i.e., without regard to when each particular input queue was placed in the XOFF (dynamic) state. Such a regular basis could be, for example, every 100 msec. When the second bit of the two bit message equals 0, such indicates an NO-OP (no operation) signal. Each input queue receiving a NO-OP signal is not disabled.
• the XOFF (allocated) feedback message temporarily halts transmission of requests to transfer via allocated bandwidth.
• Each input queue receiving XOFF (allocated) from a particular output queue temporarily ceases submitting requests to transmit to that particular output queue via allocated bandwidth until a specified event occurs.
• the specified event is typically receipt of an XON signal which enables further requests to transfer to be sent.
• the input queues could also be enabled with an XON signal on a regular basis, i.e., without regard to when each particular input queue was placed in the XOFF (allocated) state. Such a regular basis could be, for example, every 100 msec. When the second bit of the two bit message equals 0, such indicates an NO-OP signal.
• Each input queue receiving a NO-OP (no operation) signal is not disabled.
• an XON signal is used to enable input queues which have been placed in either XOFF state.
• Each input queue receiving XON from a particular output queue is enabled to submit requests to transmit to that output queue.
• the XON resets both the XOFF (dynamic) and XOFF (allocated) states.
• the XON signal can be used in conjunction with enabling on a regular basis to both reduce unnecessary switch traffic and prevent flow blockage due to errors.
• Receipt of NO-OP and either ACCEPT or REJECT operates as described above. Receipt of either XOFF (dynamic) and ACCEPT or XOFF (allocated) and ACCEPT indicates that further requests to transfer via the designated bandwidth type should cease following transfer of one cell. Receipt of XOFF (dynamic) and REJECT or XOFF (allocated) and REJECT indicates that further requests to transfer via the designated bandwidth type should cease immediately and no cells may be transmitted. Thus, the XOFF commands effect future requests while the REJECT command provides for denial of the current request.
• NO-OP/XOFF (dynamic) message is employed to reduce unnecessary feedback signaling within the switch.
• Switch bandwidth is inefficiently used when REJECT is repeatedly asserted when a cell can not be transmitted through the switch.
• XOFF (dynamic) is thus used to modify To Switch Port Processor ("TSPP") behavior to reduce the number of requests made to a full From Switch Port Processor (“FSPP”) queue.
• TSPP To Switch Port Processor
• FSPP Full From Switch Port Processor
• Flow control with the feedback messages described above provides reliable point-to-multipoint transmission within the switch, i.e., transmission from a single input queue to multiple output queues.
• the feedback messages from the multiple output queues to the single input queue are logically OR , d such that a single XOFF (dynamic) or REJECT message from any one of the plurality of output queues prevents transmission.
• point-to- multipoint cells are transmitted at the rate of the slowest destination queue.
• Flow control with the two bit feedback messages described above also provides reliable multipoint-to-point transmission within the switch, i.e., transmission from multiple input queues to a single output queue.
• Each output queue has a threshold, and sends the XON message when the output queue drains to that threshold.
• the XON threshold of the output queue is dynamically set to reserve sufficient space for each input queue to transmit to the output queue. For example, if there are eight input queues then the threshold is set to eight so that the output queue will free sufficient space to receive all of the cells contemporaneously in serial fashion.
• Fig. 1 is a switch interconnect block diagram
• Fig. 2 is a block diagram illustrating point-to-point operation, switch flow control and link flow control
• Fig. 3 is a block diagram illustrating point-to- multipoint operation
• Fig. 4 is a block diagram illustrating multipoint-to- point operation.
• the switch includes an NxN switch fabric 10, a bandwidth arbiter 12, a plurality of To Switch Port Processor subsystems ("TSPP") 14, a plurality of To Switch Port Processor ASICs 15, a plurality of From Switch Port Processor subsystems ("FSPP") 16, a plurality of From Switch Port Processor ASICs 17 and a plurality of multipoint topology controllers 18.
• the NxN switch fabric such as an ECL cross point switch fabric, is used for cell data transport, and yields N times 670 Mbps throughput.
• the bandwidth arbiter controls switch fabric interconnection, dynamically schedules unassigned bandwidth and resolves multipoint-to-point bandwidth contention.
• Each TSPP schedules transmission of cells to the switch fabric from multiple connections. Not shown are the physical line interfaces between the input link and the TSPP subsystem.
• the FSPP receives cells from the switch fabric and organizes those cells onto output links. Not shown are the physical line interfaces between the output link and the FSPP subsystem.
• the switch includes a plurality of input ports 20, a plurality of output ports 22, and input buffers 26 and output buffers 28 associated with the input ports and output ports, respectively.
• a cell 24 enters the switch through an input port and is buffered in the input buffers. The cell is then transmitted from the input buffers to output buffers in an output port. From the output port the cell is transmitted outside of the switch, for example, to another switch 29.
• a feedback message 30 is provided to the input ports to prevent transmission of cells from the input ports to the output buffers.
• the feedback message 30 prevents cell loss within the switch. If the number of cells 24 transmitted to the output buffers is greater than the number of available output buffers 28 then cells are lost. However, in response to a transfer request, when the output buffers 28 become filled to the threshold level the feedback message is transmitted to the input ports 20 to prevent transmission of cells from the input buffers.
• the threshold level is set to a value which prevents transmission of more cells than can be handled by the available output buffers. Hence, cell loss between the input buffers and the output buffers is prevented by the flow control feedback message.
• the buffers 26, 28 are organized into queues 32, 34 respectively and flow control is implemented on a per queue basis.
• Each queue includes multiple buffers, and each input port and output port includes multiple input queues 32 and multiple output queues 34.
• each cell 24 Upon entering the switch, each cell 24 is loaded into a particular input queue 32 for eventual transmission to a particular output queue 34.
• the queues are also assigned to traffic type groups in order to provide traffic type flow control if shared resources are being utilized. By assigning a unique queue per connection, flow control can then be implemented on a per connection basis.
• nested queues of queues may be employed to provide per traffic type, per connection flow control.
• a scheduling list is effectively a queue of queues where the queues have cells to be transmitted for that connection, and there is a scheduling list for each connection at the TSPP and the TSPP supports multiple connections.
• a scheduling list may be considered an input queue, and the terms are hereafter used synonymously.
• Each connection is assigned bandwidth types based on the traffic type associated with the connection.
• bandwidth There are two types of bandwidth to grant within the switch: allocated and dynamic.
• Allocated bandwidth is bandwidth which is "reserved" for use by the connection to which the bandwidth is allocated.
• a connection with allocated bandwidth is guaranteed access to the full amount of bandwidth allocated to that connection.
• traffic types that need deterministic control of delay are assigned allocated bandwidth.
• Dynamic bandwidth is bandwidth which is "shared" by any of various competing connections. Because dynamic bandwidth is a shared resource, there is generally no guarantee that any particular connection will have access to a particular amount of bandwidth. For this reason dynamic bandwidth is typically assigned to connections with larger delay bounds. Other connections may be assigned a combination of dynamic and allocated bandwidth.
• each transfer request is tagged. More particularly, transfer requests of a connection utilizing dynamic bandwidth are tagged with a bit in a first state and transfer requests of a connection utilizing allocated bandwidth are tagged with the bit in a second state. If the connection is above the allocated cell rate then the transfer request is tagged as dynamic. If the connection is operating at or below the allocated cell rate then the transfer request is tagged as allocated.
• the feedback message 30 is provided in response to a request message 36.
• the request message including the allocated/dynamic tag Prior to transmitting a cell from an input port 20 to an output port 22 the request message including the allocated/dynamic tag is sent from the input port to the output port to determine whether sufficient buffers 28 are available in the output port.
• the feedback message 30 provides an indication of buffer status at the output port, and transmission proceeds accordingly.
• the request message 36 always precedes cell transfer within the switch so that cells are only transferred under selected conditions.
• the feedback message 30 from the output port to the input port includes several sub-type messages.
• the feedback message includes an ACCEPT message which may be sent in response to the request message.
• ACCEPT is received by the requesting input queue, the cell is transferred to the output queue.
• the feedback message 30 may also include an XOFF (dynamic) message which temporarily halts transmission of request messages 36 via dynamic bandwidth.
• XOFF dynamic
• Each input queue 32 receiving XOFF (dynamic) from a particular output queue 34 temporarily ceases transmission of request messages for dynamic bandwidth to that particular output queue until a specified event occurs.
• the specified event could be passage of a predetermined interval of time or receipt of another signal.
• the feedback message may also include an XOFF (dynamic) message which temporarily halts transmission of request messages 36 via dynamic bandwidth.
• Each input queue 32 receiving XOFF (dynamic) from a particular output queue 34 temporarily ceases transmission of request messages for dynamic bandwidth to that particular output queue until a specified event occurs.
• the specified event could be passage of
• Each input queue receiving XOFF (allocated) from a particular output queue temporarily ceases submitting requests to transmit to that particular output queue via allocated bandwidth until a specified event occurs.
• the specified event is typically receipt of an XON signal which enables further requests to transfer to be sent.
• the input queues could also be enabled with an XON signal on a regular basis, i.e., without regard to when each particular input queue was placed in the XOFF (allocated) state. Such a regular basis could be, for example, every 100 msec. In practice the request tagging technique allows use of a single XOFF message to designate either XOFF (dynamic) or XOFF (allocated) .
• the request tagging technique tags requests for bandwidth with a tag bit based upon whether the request is for dynamic or allocated bandwidth.
• the tag bit thus distinguishes allocated and dynamic requests and feedback, i.e., the XOFF transmitted in response to a request for dynamic bandwidth is XOFF (dynamic) .
• various responses to each request message may be received by the requesting input queue. Such responses are interpreted as follows. Receipt of NO-OP and either ACCEPT or REJECT operates as described above. Receipt of XOFF (dynamic) and ACCEPT indicates that further requests to transfer should cease following transfer of one cell. Receipt of XOFF (dynamic) and REJECT indicates that further requests to transfer should cease immediately and no cells may be transmitted.
• the XOFF (dynamic) command effects future requests while the REJECT command provides for denial of the current request.
• the feedback message 30 may also include an XON message which enables further transmission of request messages.
• the XON message occurs asynchronously to the request to transfer messages, and is not provided in response thereto.
• the XON message is effective to remove both XOFF conditions.
• Each input queue receiving XON from a particular output queue is enabled to submit requests to transmit to that output queue.
• timeout type functions which will allow continued operation despite the removal or failure of internal elements such as ports.
• an input queue 32 which has ceased transmission of request messages to a particular output queue 34 following receipt of an XOFF (dynamic or allocated) message may transmit a further request message to that output queue if an XON message is not received from that output queue within a predetermined interval of time.
• input queues may periodically transmit request messages regardless of XOFF (dynamic or allocated) state.
• each input port includes a TSPP 14, and each output port includes an FSPP 16.
• the TSPPs and FSPPs each include cell buffer RAM which is organized into queues 32, 34, respectively. All cells in a connection 40 pass through a single queue at each port, one at the TSPP and one at the FSPP, for the life of the connection. The queues thus preserve cell ordering. This strategy also allows quality of service (“QoS”) guarantees on a per connection basis.
• QoS quality of service
• the request message 36 is a probe which is sent to the FSPP 16 from the TSPP 14 to determine whether sufficient buffers 34 are available for cell transmission.
• a TSPP cannot transmit a cell to an FSPP unless there is buffer space available for that cell.
• the probe communicates destination multiqueue numbers which indicate the FSPP queue or queues to which the cell is to be transmitted. For example, a destination multiqueue number could identify output queue 34a as the destination queue.
• the FSPP responds to the probe with either or both of the "REJECT" and "XOFF (dynamic or allocated)" messages, as will be described below.
• the Probe Crossbar 42 is an NxN crosspoint switch fabric which is used to transmit an FSPP multiqueue Number to each FSPP.
• the multiqueue number identifies a plurality of destination queues for the cell for use in point-to-multipoint connections.
• the FSPP uses the multiqueue number to direct the probe 36 to the appropriate output queue or queues 34 and thereby determine if there are enough output buffers available in the destination queues for receipt of the cell or cells.
• the XOFF Crossbar 44 is an NxN serial crosspoint switch fabric which is used to communicate "Don't Send" type messages from the FSPP 16 to the TSPP 14.
• Each TSPP includes multiple scheduling lists 48 which have queues of cells to be transmitted for each connection.
• the first bit of the feedback message 30, namely XOFF is asserted to halt transmission of request message probes 36 from a particular TSPP's scheduling list, and is thus a state control bit which puts the receiving TSPP's scheduling list in an XOFF state, meaning that this TSPP's scheduling list 48 will not use dynamic bandwidth.
• This TSPP's Scheduling List then remains in the XOFF state until receiving an XON message.
• the second bit namely REJECT
• REJECT REJECT
• the TSPP responds to an asserted REJECT feedback message by not dequeueing the cell 24 through the data crossbar 47.
• An idle cell denoted by a complemented CRC is transmitted instead.
• the TSPP responds to an asserted XOFF (dynamic) feedback message by modifying the TSPP's scheduling list XOFF state bits.
• the XOFF state bits prevent the TSPP from attempting to send a request message from that queue on that Scheduling List until notified by the FSPPs that cell buffers are available.
• the XON Crossbar 46 is an NxN serial contention-based switch which is used to communicate "Enable Send" type messages. More particularly, the XON Crossbar is employed to communicate the XON message from the FSPP to the TSPP. When the number of buffered cells in the FSPP queue drops below an XON threshold, the XON message is sent from the FSPP to the TSPP. The XON message enables the TSPP Scheduling List to resume sending request messages.
• Fig. 3 illustrates point-to-multipoint switch flow control, i.e., transmission from a single input queue 32 to multiple output queues 34.
• the XOFF crossbar performs a logical OR function. More particularly, the XOFF crossbar performs a logical OR of the feedback messages 30 asserted by the FSPPs to provided a single feedback message.
• the single resultant feedback message will be interpreted as asserting REJECT and/or XOFF respectively.
• This technique limits the TSPP to transmission at the rate of the slowest destination queue. However, the technique also provides desirable contemporaneous serial transmission of cells.
• a TSPP may receive multiple XON messages. Such is true because multiple XOFFs could be set by the FSPPs, i.e., more than one FSPP can assert XOFF on a transfer request. In such a case, XON messages received when the TSPP scheduling list XOFF state is clear are ignored. For example, when multiple XON messages are sent, the TSPP ignores the XONs received after the first received XON message. In the case of multipoint-to-point transmission the XON message is sent simultaneously to all TSPPs with scheduling lists transferring to an FSPP queue.
• Fig. 4 illustrates multipoint-to-point switch flow control, i.e., transmission from multiple input queues 32 to a single output queue 34.
• Each output queue has a threshold, and the XON message is sent when the output queue drains below that threshold.
• the XON threshold of the output queue is dynamically set to reserve enough buffers for each input queue to transmit to the output queue. For example, if eight queues are transmitting, the threshold is set to eight so that the output queue will free sufficient buffers to receive all eight of the cells contemporaneously in serial fashion, and thereby insuring that each queue has an opportunity to transmit. Referring now to Figs.
• the XON crossbar 46 is used to broadcast to all TSPPs in the switch, regardless of whether or not any of the TSPPs were transmitting to the asserting FSPP queue.
• the multipoint topology controller 18 transmits a reverse broadcast channel number on behalf of the FSPP.
• the receiving multipoint topology controller then performs a reverse broadcast channel to scheduling list number lookup to determine which scheduling list 48 to enable. Any TSPPs without queues transmitting to that particular FSPP queue are unaffected by the broadcast XON message since the reverse broadcast channel number look-up entry will be marked invalid.
• an additional flow control enhancement provides for the queues to be organized on an hierarchical basis with multiple individual flows 52 at each hierarchical level and the feedback message 30 from the output queues to the input queues is made on the basis of the combined flow at each of the hierarchical levels.
• Still another enhancement provides for the queues to be organized on an hierarchical basis with multiple individual flows at each of the hierarchical levels and the feedback message from the output queues to the input queues is made on the basis of each of the individual flows.
• the Probe & XOFF communication paths operate in a pipeline fashion.
• the TSPP 14 selects an input queue 34, and information associated with that queue is used to determine output ports for transmission, i.e., a destination output queue.
• the bandwidth arbitrator reduces this information to a TSPP to FSPP connectivity map which is employed to control the Probe, XOFF, and data cross-points in sequence.
• the FSPP multiqueue number is transmitted to the FSPP using the Probe crossbar 42.
• the FSPP tests for buffer availability, and asserts REJECT and/or XOFF on the XOFF crossbar 44 if sufficient buffers are not available.
• the TSPP transmits an idle cell if REJECT was asserted. If XOFF was asserted, the TSPP puts the Scheduling List into the XOFF state. If sufficient buffers are available, the TSPP transmits the cell to the FSPP output queue through the data crossbar 47.
• Table 3 summarizes the policies used by the FSPP to assert REJECT and XOFF in response to requests tagged as utilizing dynamic bandwidth.
• the policies are based upon two relationships: the traffic type cell count in relation to the cell count limit and the queue's dynamic buffer count in relation to the buffer count limit.
• the traffic type cell count is a count of all cells shared by connections within a traffic type, e.g., "VBR.”
• VBR traffic type
• both REJECT and XOFF dynamic are asserted.
• the traffic type cell count is greater than or equal to the limit and the queue's dynamic buffer count is not greater than or equal to buffer limit XOFF is not asserted but REJECT is asserted.
• REJECT is asserted.
• the traffic type cell count is greater than or equal to the limit and the queue's dynamic buffer count greater than or equal to the limit both REJECT and XOFF are asserted.
• Table 4 summarizes the policies used by the FSPP to assert REJECT and XOFF in response to requests tagged to use allocated bandwidth.
• the policies are based upon three relationships: the queue's allocated buffer-state count in relation to the buffer-state count limit, the traffic type cell count in relation to the cell count limit, and the queue's allocated buffer count in relation to the buffer count limit.
• Link flow control uses a buffer-state counter to indicate cells in flight.
• the allocated buffer-state counter is used to track cells in flight for the allocated component of a connection using link flow control.
• Neither XOFF nor REJECT are asserted if the queue's allocated buffer- state count is greater than or equal to the count limit, the traffic type cell count is greater than or equal to the cell count limit, and the queue's allocated buffer count is greater than or equal to the count limit. Both XOFF and REJECT are asserted if the queue's allocated buffer count is greater than or equal to the buffer count limit. If the queue's allocated buffer count is not greater than or equal to the count limit, but either the queue's allocated buffer- state count is greater than or equal to the count limit or the traffic type cell count is greater than or equal to the cell count limit then REJECT is asserted and XOFF is not asserted. In all cases, if an FSPP queue has already sent an XOFF, that queue will reassert XOFF on the next probe.

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• 1996
  • 1996-07-18 JP JP9506879A patent/JPH11510009A/ja active Pending
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  • 1996-07-18 EP EP96927240A patent/EP0839421A4/en not_active Withdrawn
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