PM9313 datasheet(35/343 Pages) PMC

35 / 343 page

PM9311/2/3/5 ETT1™ CHIP SET

PMC-2000164

ISSUE 3

ENHANCED TT1™ SWITCH FABRIC

Released

Data Sheet

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

PMC-Sierra, Inc.

1.3.1

Unicast Traffic (OC-192)

Every ETT1 port has a separate request counter and ingress queue for each (output port, priority)

combination to which it can send unicast cells. In a full configuration, an ETT1 port can send to 32 ETT1

ports (including itself), at four priorities, and so will have 128 unicast request counters and ingress queues.

All of these counters and queues are independent so that the switch does not suffer from head-of-line

blocking1.

Figure 9 illustrates the unicast ingress queueing model for one port.

Figure 9. The Unicast Ingress Queueing Model for One Port

The ingress queues are referred to as Virtual Output Queues (VOQs). This name indicates that each

queue holds cells going to just one output port.

Every ETT1 port also has the same number of unicast egress queues; one queue for every (input port,

priority) combination that can send cells to the port. Every port will have 128 unicast egress queues. It is

not acceptable to have a single egress queue per priority, as this can lead to gross unfairness between

ports. These egress unicast ports are called Virtual Input Queues (VIQs) as each queue only holds cells

that have come from a single input port. A useful model is to think of a VOQ as being directly connected

through the Crossbar to a single VIQ. The cell at the head of the VOQ is waiting to be scheduled in such a

way that it can move to the tail of the VIQ in the egress port.

The associated ingress EPP is informed whenever an egress queue is full. In this case, the ingress port

will not issue any new requests to the Scheduler until sufficient cell space becomes available at the egress

queue. The transfer of cells from ingress to egress queues is lossless from a queueing perspective.

The best effort unicast ingress and egress queues can store up to 64 cells.

1.3.2

Multicast Traffic (OC-192)

The ETT1 core also supports multicast cells. Multicast cells are cells that must be forwarded to one or

more egress ports. The LCS header will indicate that a cell is multicast, and it will also contain a multicast

group identifier. The ETT1 port uses this identifier to determine the list of ports to which the cell should go.

This list of ports is called the multicast fanout. Different multicast groups will probably have different

fanouts.

The Scheduler arbitrates among unicast and multicast cells. A multicast cell of a given priority will always

have priority over a unicast cell of the same priority, all else being equal. Physical cell replication takes

place within the Crossbar.

1. Head -of-line blocking is a phenomenon encountered by input queued switches in the case where a cell destined for one out-

put port is delayed because the cell at the head of the same FIFO queue is destined for some other output which is currently

congested.

PM9313 Datasheet(PDF) 35 Page - PMC-Sierra, Inc

PM9313 Datasheet(HTML) 35 Page - PMC-Sierra, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL