AC207-DS04-405-R datasheet(18/60 Pages) BOARDCOM

18 / 60 page

AC207

Preliminary Data Sheet

07/08/02

B roa dcom

Page 8

Addressing Algorithm, Routing, Learning and Aging

Document

AC207-DS04-405-R

Bit 30: Entry valid / empty indication, 1: valid entry, 0: empty entry.

Bit 29-24: Aging timer.

Bit 23-16: Port number

ADDRESS RECOGNITION

The exclusive or addressing algorithm is used for address lookup table addressing. Refer to Figure 2.

Figure 2: Exclusive or Hashing Algorithm

The final address of address lookup table is the hashed address[9:0].

ROUTING DECISION

If a record is empty, the packet is broadcast and treated as an unknown frame. Otherwise, the record is read, and compared

with the current DA. If two addresses are the same, the port number is decided, and the packet is forwarded to the assigned

port. If address collision occurred, different MAC address, the incoming packet is considered an unknown packet.

LEARNING PROCESS

The address learning process is composed of the SA packets and the addressing algorithm described above. The bridge

checks each incoming packets integrity and buffers availability. If a packet is error-free and the buffer is available, the SA/

port number pair of the packet is written into the address lookup table. Figure 3 describes the general operations of address

learning and recognition.

Figure 3: Address Learning and Recognition

MAC#6

MAC#4

MAC#2

xor

Hashed address[15:0]

MAC#5

MAC#3

MAC#1

xor

Xor Hashing Function

DA or SA

[9:0]

Address

Entry Point

AAA-1

AAA

AAA+1

Address Lookup Table

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