International Business Machines Corporation

Bernard Brezzo

Alain R Blanc

Alain Saurel

Daniel Wind

Rene Gallezot

Pierre Debord

Jean L Calvignac

Michel Poret

Sylvie Gohl

Albert X Widmer

Francois Le Maut

Jean-Claude Abbiate

Patrick J Jeanniot

Bernard J Naudin

Pierre Austruy

Jean-Pierre Lips

Thierry Roman

Jean-Claude Robbe

Richard Dambricourt

Richard H Waller

Andre Masclet

Jean-Pierre Sanche

Francois Le Mauf

Franco Le Maut

A queue scheduling mechanism in a data packet transmission system, the data packet transmission system including a transmission device for transmitting data packets, a reception device for receiving the data packets, a set of queue devices respectively associated with a set of priorities each defined by a priority rank for storing each data packet transmitted by the transmission device into the queue device corresponding to its priority rank, and a queue scheduler for reading, at each packet cycle, a packet in one of the queue devices determined by a normal priority preemption algorithm. The queue scheduling mechanism includes a credit device that provides at each packet cycle a value N defining the priority rank to be considered by the queue scheduler whereby a data packet is read by the queue scheduler from the queue device corresponding to the priority N instead of the queue device determined by the normal priority preemption algorithm.

Queue scheduling mechanism in a data packet transmission system

A data switch is provided which routes fixed-size data packets from input ports to output ports, using shared memory which holds a copy of each packet in buffers. Output ports have a queue which contains pointers to buffers holding packets bound for that port. The number of shared memory buffers holding packets is compared to the number of buffer pointers in the output queues. In this way, a Multicast Index (MCI), a metric of the level of multicast traffic, is derived. The switch includes a Switch Core Adaptation Layer (SCAL) which has a multicast input queue. Because traffic is handled based on priority class P, a multicast threshold MCT(P), associated with the multicast input queue, is established per priority. While receiving traffic, the MCI is updated and, for each priority class in each SCAL, the MCI is compared to the MCT(P) to determine whether corresponding multicast traffic must be held.

System and method for controlling the multicast traffic of a data packet switch

The invention permits an effective traffic flow control, down to all sub-ports, of a switch made of a N-port core switch fabric. Sub-ports concentrate traffic from lower speed lines to a switch fabric native port. In each sub-port adapter, when congestion is detected in the OUT leg, it is reported through the corresponding IN leg. Congestion is piggybacked over the incoming traffic entering the input port of the N-port core switching fabric and is broadcast so that all sub-ports become aware of the detected congestion in any of the sub-ports. Each sub-port adapter performs a checking of the congestion status of all the other sub-ports and acts to stop forwarding received traffic destined for congested sub-ports and holds further received traffic until the sub-ports are reported to be no longer congested. The full intrinsic performance of a N-port switch fabric is realized by concentrating, through port and sub-port adapters, the traffic of more than N independent lines.

System and method for enabling a full flow control down to the sub-ports of a switch fabric

A service message system for a switching architecture including at least one Switch Fabric ( ) comprising a switch core ( ) located in a centralized building and a set of Switch Core Access Layer (SCAL) elements distributed in different physical areas for the attachment to the different Port adapters ( ). Each SCAL elements particularly includes a SCAL receive element ( - ) and a SCAL Xmit element ( - ) for the respective access to one input port and one output port via serial links. The service message is based on the use of a Cell qualifier field at the beginning of each cell, which comprises a first and a second field. The first field is the Filtering Control field which permits an easy decoding of a service message cell, when applicable. The second field is used for determining which particular type of service message is conveyed via the cell. Following the Cell qualifier is the Switch Routing Header (SRH) which permits the characterization of the destination of the cell and is used for controlling the routing process. Preferably, the service message is used in a fault tolerance configuration where two different Switch Fabrics act as a standby to each other and shares a part of the traffic. Each one is configured as a default routing path for some ports adapters and a backup path for the others. In that particular configuration, the service message system of the invention uses the first field of the Cell qualifier to transport a Direct filtering command causing the Switch fabric to route the cell when the SRH is representative of its default output port destination. Conversely, the first field may transport a Reverse filtering command in the first field that causes the Switch fabric to reverse the default routing process. The first field is also used for characterizing a service message cell which the second field indicates the accurate type. Particularly, two types are used for the production of the filling cells when no data cell is to be transmitted at a particular location of the switching architecture.

Service message system for a switching architecture

A flow control process for a switching system having at least one switch core connected through serial communication links to remote and distributed Protocol Adapters or Protocol Engines through Switch Core Access Layer (SCAL) elements. For each input port i, the SCAL element contains a receive Protocol Interface corresponding to the adapter assigned to the input port i and a first serializer for providing attachment to the switch core by means of a first serial communication link. When the cells are received in the switch core, they are deserialized by means of a first deserializer. At each output port, the cells are serialized again by means of a second serializer and then transmitted via a second serial communication link, to the appropriate SCAL. The SCAL contains a second deserializer and a transmit Protocol Interface circuit for permitting attachment of the Protocol Adapter. The flow control process permits two flow control signals, a flow control receive (FCR) from the core to the SCAL, and a flow control transmit (FCX) from the SCAL back to the core. For transmission of the FCR signal in response to the detection of local saturation in the switch core, the process causes transfer of an internal FCR signal to the serializer located within the saturated core. The FCR is introduced in the normal data flow to be conveyed through the second serial link to the remote SCAL corresponding to the saturated input port of the core. An internal control signal can be transmitted to the Protocol Interface that is originating too many cells which results in the overloaded input port of the core. For the transmission of the FCX signal in response to the detection of a saturated Protocol Interface element at one output port, the process generates an internal control signal to the serializer located in the SCAL element. The serializer can introduce a FCX signal in the normal data flow which is conveyed to the core and then decoded by the deserializer in the core. Thus, the core can be informed of the saturation condition that has occurred in the considered output port. Particular adaptations are provided in which the switching system is arranged in a set of individual switching structures mounted in a port expansion mode.

Flow control process for a switching system and system for performing the same

A switching system having at least two switch fabrics. Each fabric has a switch core and a set of SCAL (Switch Core Access Layer) receive and transmit elements. The switch cores are preferably located in the same physical area but the SCALs may be distributed in different physical areas. Port Adapters distributed at different physical areas are connected to the switch fabrics via a particular SCAL element so that each switch core can receive cells from any port adapter and conversely any port adapter may receive data from either switch core. Control logic assigns a particular switch core to one port adapter for normal operations while reserving the other switch core for use when the first core is out of service. Each switch core has a mask mechanism which uses the value in a mask register to alter a bitmap value which controls the routing process. The mask registers in the two switch cores are loaded with complementary values.

Switch system comprising two switch fabrics

A switching system receives a data cell from a set of n input ports for routing to one or more output ports in accordance with the contents of a bitmap value retrieved from the cell upon its receipt. The system has a module comprising a shared buffer for storing the cells which are to be routed and a mask mechanism with a mask register for altering the value of the bitmap before it is used for controlling the routing process. As a result of operation of the mask mechanism, a cell is either transported to an output port or discarded. Two switching systems are combined in first and second switch fabrics, each having a switch core and a set of switch core access layer (SCAL) elements. Each SCAL element respectively comprises a SCAL Receive element and a SCAL Xmit element for permitting access to input and output ports of one of the switching systems.

Switching system including a mask mechanism for altering the internal routing process

A flow control process for a switching architecture having a central switch core with associated distributed Switch Core Access Layers communicating with the core by means of serial data communication links. The serial links carry data flows that are coded in accordance with the 8B/10B coding, where two among the three comma characters are used for creating an additional specialized flow control channel. When the cells are idle or empty, the nature of the comma character that appears at the beginning of the cell provides the appropriate flow control bit information. For instance, should the K.28.5 character be detected, the receiving entity (either the switching structure or a distributed SCAL element) decodes the character as positive flow control information, corresponding to a request to reduce the incoming data flow. Also, should the K.28.1 character be decoded, then the receiving entity decodes this as information according to which no reduction in the data flow is requested. When the incoming flow provides data cells, the invention uses a predetermined bit within the data cell, generally that immediately following the beginning of the cell, in order to carry the flow control information.

Flow control process for a switching architecture using an out-of-band flow control channel and apparatus for performing the same

A method and apparatus for managing contention in a self-routing switching architecture based on a set of n&times;n individual switching structures that are connected in a port expansion mode by means of fan-out and fan-in circuits providing access of the Switch Core Access Layer (SCAL) to the different input and output ports of the switching core. The fan-in circuits use an arbitration mechanism for providing a token to the switch that is allowed to deliver the next cell and the arbiter operates from a detection of a special comma character in accordance with the 8B/10B coding scheme which is introduced in the data flow between the individual switching structures and the fan-in circuits. This provides a compensation for the difference in transfer delays of the cells even when high switching speed and long length of the physical media are involved.

Method and apparatus for managing contention in a self-routing switching architecture in a port expansion mode

A switching system comprising a switching structure for routing cells from a set of M input ports towards a set of M output ports. The system includes a set of distributed individual Switch Core Access layer elements which communicate with one input and output port of the switching structure by means of a set of serial communication links. Each SCAL element provides attachment to at least one Protocol Adapter and comprises a set of circuits. The receive part of each circuit, which includes at least one first FIFO storage for storing the cells being received, receives the data cells from the attached Protocol Adapter and introduces at least one extra byte to every cell. Each transmit part of the destination circuit, which includes at least one second FIFO storage having a greater capacity than the first FIFO storage, receives all the cells that are generated at the corresponding output port and uses the at least one extra byte for cell buffering. Additionally, each distrubuted SCAL element comprises control means for performing Time Division Multiplexing access of the FIFOs.

Switching system comprising distributed elements allowing attachment to

This invention relates to a protocol implemented in a communication system for exchanging data and control messages between adapters to which are attached different users, and a shared memory subsystem comprising a depository storage, a manager of storage and a microprocessor. Such protocol enables the adapters to be the initiators of the transmission and reception of data by using the control lines that connect the manager of storage to all adapters in the same way as the data bus and the address bus. Moreover, the adapters slice the messages into data bursts to which are associated control words specifying the sizes, the owner and the position of the burst in the message. Consequently, those data bursts may be interleaved when transiting on the data bus without the intervention of the microprocessor for the routing, and they will be stored in or read from the depository storage according to the identification of the user in the control word. Therefore, only the shared memory needs to have a high capacity of storage, whereas the manager of storage and the adapters can operate with a reduced capacity of storage, and the time to send or to access a data burst is much more improved.

Method for exchanging messages between a shared memory and communication

A line scanning device which operates under the control of a microprocessor connected to a control memory in which a memory location area is assigned to each line is provided for a line adapter in a communication controller for receiving or sending message bits in series from or to terminals connected to the lines using any protocols. It comprises a first store which includes a first and a second memories, an area being assigned to each line in each of the memories which can be read and written in the same time and a second store which includes a single memory in which a storage location area is assigned to each line. These stores are addressed by a control and address unit which includes first and second address counters under the control of an elementary time counter, the first counter outputting the address information relating to the first store during time t provided for scanning a line, and the second counter outputting the address information relative to the second store during time nt, n being at least equal to 4, and control circuitry receiving said address information and the elementary time information for providing at the outputs of the control and address unit, memory address and read/write control information at times selected during the scanning period and sequentially, the addresses of the present lines which are scanned.

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Nice, France

Bernard Brezzo