PM3350-SW datasheet(90/224 Pages) PMC

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ELAN 8X10

PM3350 ELAN 8 X10

DATA SHEET

PMC-970109

ISSUE 3

8 PORT ETHERNET SWITCH

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND PMC-SIERRA, INC. CUSTOMERS ONLY

Frame Transfer Queue

A set of eight frame transfer queues are used to exchange forwarded packets and

messages with up to seven external ELAN 8x10 devices that are part of the same

switch. On a given ELAN 8x10 device, each frame transfer queue is dedicated to

transferring data to a single external device (another ELAN 8x10, or any other device

implementing the same transfer protocol).

The frame transfer queues are maintained by means of the FirstDD and LastDD

pointers in the expansion port descriptors corresponding to the external devices. Each

queue consists of a linked list of data descriptors, with each data descriptor pointing in

the usual manner to the start and end of a list of packet buffers to be transferred from

the local ELAN 8x10 to the remote device.

When an Ethernet frame or a message is to be forwarded to a remote device, the

Switch Processor in the ELAN 8x10 will, as already described, initialize the blank data

descriptor at the tail of the corresponding frame transfer queue to point to the packet

buffers containing the Ethernet frame or message, and allocate a new blank descriptor

to form the new tail of the transfer queue. It will then notify the remote device that data

are available to be read from the frame transfer queue. The remote device is

responsible for reading the contents of the data descriptor and all of the associated

packet buffers from the local ELAN 8x10 memory space over the PCI bus. When the

read is complete, the remote device must signal the local ELAN 8x10 that the data have

been transferred and the queued packet and data descriptor can be freed.

None of the frame transfer queue data structures are cached by the Switch Processor;

thus they may be read at will over the PCI bus interface without difficulty.

Address Hash Table

The ELAN 8x10 stores all learned or pre-configured Ethernet addresses using a

hash

table approach. Each entry in the address hash table is associated with a particular 48-

bit IEEE MAC address. The table contains all of the information required to accept,

process and switch packets to known (i.e., previously learned or set up) addresses. (In

consonance with standard bridging practice, packets destined for unknown (not

previously seen or set up) destinations must be flooded to all ports, or those determined

using the standard IEEE 802.1d spanning tree.) The hash table also serves to hold per-

host statistics information.

Note that when multiple ELAN 8x10 devices are present in a system the hash table

becomes a distributed data structure, with a separate table being maintained by each

device and kept consistent by exchanging information among the different ELAN 8x10

devices according to a predefined protocol.

PM3350-SW Datasheet(PDF) 90 Page - PMC-Sierra, Inc

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