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Method and apparatus for performing cut-through virtual circuit merging
| Details |
Inventors: Ganmukhi, Mahesh N.; Palnati, Prasasth R.;
Assignee: Ascend Communications, Inc. (Westford, MA)
Primary Examiner: Nguyen; Chau
Assistant Examiner: Kwoh; Jasper
Attorney, Agent or Firm: Weingarten, Schurgin, Gagnebin & Hayes LLP
A method and apparatus for performing virtual connection merging in an output port of a network switch are disclosed. In the event no completely assembled packets have been received and scheduled for transmission, a partially received packet is selected for cut-through transmission prior to receipt of all cells comprising the packet. Transmission of the selected packet is initiated and a timer is started. If the timer expires prior to the receipt of an end of packet indication for the packet for which transmission has commenced, and end of packet signal is generated and transmitted and the transmission of additional cells for the cut-through packet is aborted. In this manner, delays associated with packet reassembly may be avoided and buffer sizes of reassembly buffers may be reduced. |
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DETAILED DESCRIPTION OF THE INVENTION An improved method and apparatus for performing virtual circuit merging in a network switch is disclosed which minimizes inherent delays in store and forward virtual circuit merging techniques and additionally provides the ability to utilize smaller reassembly cell buffers.
Referring to FIG.
1 a network switch 10 in accordance with the present invention is depicted which incorporates the ability to perform cut-through virtual circuit merging.
The network switch includes a plurality of input or ingress ports 12, identified herein as 12a, 12b, .
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12n, for receiving packets from one or more ingress communication links 14 identified herein as 14a, 14b, .
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14n, and a plurality of output or egress ports 16, identified herein as 16a, 16b, .
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16n, for transmitting packets from each of the output ports to one or more egress communications links 18, identified herein as 18a, 18b, .
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18n, which are coupled to the respective output ports 16.
A packet comprises one or more cells, such as ATM cells.
The end of a packet is signaled by an end of packet (EOP) indicator.
A switch fabric 20 is operative to forward cells received a the input ports to one or more of the output ports 16 in accordance with forwarding techniques known in the art.
Upon reception at an input port, each cell is associated with a connection identifier (CID) which is employed within the network switch 10 to specify cell routing.
Typically, the CID is generated upon receipt of a cell in an ATM network switch by performing a table lookup on the VPI/VCI address or some portion thereof to locate the CID for the respective cell.
In the event that the cell is a multicast or broadcast cell intended for transmission out of more than one port, or plural links coupled to a single port (not shown), a multicast identifier (MID) is associated with the cell in the network switch upon reception to identify the cell as a multicast or broadcast cell.
For simplicity, MIDs are considered herein as one form of CID
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CPUs 
