MVTX2803 查看數據表（PDF） - Zarlink Semiconductor Inc

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MVTX2803

Unmanaged 8-Port 1000 Mbps Ethernet Switch

Zarlink Semiconductor Inc 

MVTX2803

Data Sheet

5.0 Search Engine

5.1 Search Engine Overview

The MVTX2803AG search engine is optimized for high throughput searching, with enhanced features to

support:

• Up to 64K MAC addresses

• 4 groups of port trunking

• Traffic classification into 8 transmission priorities, and 2 drop precedence levels

5.2 Basic Flow

Shortly after a frame enters the MVTX2803AG and is written to the Frame Data Buffer (FDB), the frame engine

generates a Switch Request, which is sent to the search engine. The switch request consists of the first 64

bytes of the frame, which contain all the necessary information for the search engine to perform its task. When

the search engine is done, it writes to the Switch Response Queue, and the frame engine uses the information

provided in that queue for scheduling and forwarding.

In performing its task, the search engine extracts and compresses the useful information from the 64-byte

switch request. Among the information extracted are the source and destination MAC addresses, the

transmission and discard priorities and whether the frame is unicast or multicast. Requests are sent to the

external SRAM Switch Database to locate the associated entries in the external MCT table.

When all the information has been collected from external SRAM, the search engine has to compare the MAC

address on the current entry with the MAC address for which it is searching. If it is not a match, the process is

repeated on the internal MCT Table. All MCT entries, other than the first of each linked list, are maintained

internal to the chip. If the desired MAC address is still not found, then the result is either learning (source MAC

address unknown) or flooding (destination MAC address unknown).

If the destination MAC address belongs to a port trunk, then the trunk number is retrieved instead of the port

number. But on which port of the trunk will the frame be transmitted? This is easily computed using a hash of

the source and destination MAC addresses.

When all the information is compiled, the switch response is generated, as stated earlier.

5.3 Search, Learning, and Aging

5.3.1 MAC Search

The search block performs source MAC address and destination MAC address searching. As indicated earlier,

if a match is not found, then the next entry in the linked list must be examined, and so on until a match is found

or the end of the list is reached.

In port based VLAN mode, a bitmap is used to determine whether the frame should be forwarded to the

outgoing port. The bitmap is not dynamic. Ports cannot enter and exit groups dynamically.

The MAC search block is also responsible for updating the source MAC address timestamp, used for aging.

5.3.2 Learning

The learning module learns new MAC addresses and performs port change operations on the MCT database.

The goal of learning is to update this database as the networking environment changes over time. Learning and

port change will be performed based on memory slot availability only.

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