AC208-DS01-R datasheet(18/58 Pages) BOARDCOM

18 / 58 page

AC208

Preliminary Data Sheet

07/08/02

B roa dcom

Page 10 Addressing Algorithm, Routing, Learning, and Aging

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AC208-DS04-405-R

ADDRESS RECOGNITION

The exclusive or addressing algorithm is used for address lookup table addressing (see the following figure).

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. The following figure describes the general operations

of address learning and recognition.

Figure 3: Address Learning and Recognition

AGING TIME

The switch automatically examines the status of address lookup table. The round robin speed and checking timer are

dependent on the aging time. The switch aging time is set at 300s. When the aging timer is started after power on, the switch

guaranties that free spaces can be released from occupied address entries.

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

Tbl

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