AC207-DS04-405-R datasheet(19/60 Pages) BOARDCOM

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Preliminary Data Sheet

AC207

07/08/02

B roa dcom

Document

AC207-DS04-405-R

Addressing Algorithm, Routing, Learning and Aging

Page 9

AGING TIME

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

dependent on the aging time. The bridge aging time is set at 300 seconds. When the aging timer is started after power-on,

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

FORWARDING SCHEME

The store-and-forward algorithm is used. The incoming packet has to be completely stored in the buffer and verified error-

free before forwarding operations take place.

BUFFER MANAGEMENT AND QUEUES

The bridge buffering management continues to store received packets into memory. The buffer size for 100M port is 16K

bytes, and 8K bytes for 10M port.

Figure 4: Basic Memory Management Concept

The bridge uses the six pointers to control per port buffer status. Start Address point is the beginning of memory address for

each port and the End Address point is the last address of memory for each port. The Read/Write and shadow Read/Write

pointers are dynamically changed depending on the current outgoing and incoming packets in the storage. If the Write

pointer reaches the Read pointer and the size between write and read pointers is smaller than 2K bytes, buffer is full. On the

other hand, when read/write pointers are equal, the buffer is empty.

Table 3: Embedded Memory Structure

0x0000

2k x 32 for address lookup table

0x07FF

0x0800

4k x 32 for 100M Bridge Port

0x17FF

0x1800

2k x 32 for 10M Bridge Port

0x1FFF

Write Point

End Address

Start Address

Read Point

Free buffer

Per Port Buffer Management

AC207-DS04-405-R Datasheet(PDF) 19 Page - Broadcom Corporation.