PM3350-SW datasheet(110/224 Pages) PMC

110 / 224 page

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

108

descriptor flags to determine whether the source and destination MAC address

lookups have been successful. If valid 16-bit encoded source and/or destination

hash bucket indices are present, the firmware will convert these to the actual 24-

bit memory addresses of the corresponding hash buckets. The source address

checking and learning process is then carried out.

If the source address lookup has failed, the frame contains a new, un-learned

MAC address; the firmware will then execute the address learning function, as

described in a succeeding section. If the source address lookup has succeeded

but the hash bucket is inconsistent with the expected address table entry (e.g., it

is a forwarding tag rather than a hash bucket, or the hash bucket indicates an

improper source physical port), then the firmware will declare a topology change

and invoke the spanning tree functions. If the source address lookup has

returned a valid hash bucket, the firmware will write a 32-bit timestamp

(obtained from the CLOCK register within the Switch Processor) into the hash

bucket for aging purposes, and then proceed to the next step.

13. The firmware now verifies that the destination address lookup was successful; if

not, the firmware invokes the frame flooding function to broadcast the frame to

all ports that are on the spanning tree. If the destination address lookup

succeeded, but locates a forwarding tag, this indicates that the firmware must

transfer the frame to a remote device; this is described in the next section.

Finally, the physical ports referenced by the source and destination hash

buckets are compared to determine whether the frame should be filtered (i.e.,

the source and destination ports are the same). The frame is forwarded to a

single local port only if the destination address lookup succeeded and returned

a valid hash bucket referencing a different physical port present on this ELAN

8x10. Note that the Flags field in the destination hash bucket is also checked to

verify whether the frame requires special handling.

14. The frame type is classified according to the Type subfield in the Flags field of

the destination hash bucket, i.e., whether the frame is to be treated as a unicast

or broadcast/multicast. If the frame is to be a broadcast/multicast, the

MulticastMask field in the hash bucket is consulted to determine the ports and

devices to which the frame should be sent.

15. The frame has been successfully processed and classified; the source MAC

address statistics (i.e., the per-host statistics in the source hash bucket) as well

as the source per-port statistics are updated appropriately at this time.

16. The firmware now queues the frame for transmission or transfer (or both, in the

case of broadcasts). It is assumed here that the frame is intended to be

transmitted out one or more local MAC channels. In this case, the firmware

identifies the physical port(s) on which the frame must be transmitted, locates

the local port descriptor(s), and obtains the transmit queue head and tail

pointers from these local port descriptor(s). The firmware then enters the frame

PM3350-SW Datasheet(PDF) 110 Page - PMC-Sierra, Inc

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