adm6999ux Infineon Technologies Corporation, adm6999ux Datasheet - Page 23

• Manufacturer Part Number: adm6999ux
• Description: Adm6999u 9 Port 10/100 Mb/s Single Chip Ethernet Switch Controller
• Manufacturer: Infineon Technologies Corporation

3.3
ADM6999U/UX builds in 768K bits memory inside. Memory buffer is divided as two blocks. One is MAC
addressing table and another one is data buffer.
MAC address Learning Table size is 2048 entries with each entry occupying eight bytes length. These eight bytes
data include 6 bytes source address, VLAN information, Port information and Aging counter.
Data buffer is divided into 512 bytes/block. ADM6999U/UX buffer management is per port fixed block number and
all port share one global buffer. This architecture can get better memory utilization and network balance on
different speed and duplex test conditions.
Received packet will separate as several 512 bytes/block and chain together. If packet size more than 512 bytes
then ADM6999U/UX will chain two or more blocks to store receiving packet.
3.4
The ADM6999U/UX uses a “store & forward” switching approach for the following reason:
Store & forward switches allow switching between different speed media (e.g. 10BaseX and 100BaseX). Such
switches require the large elastic buffer especially bridging between a server on a 100Mbps network and clients
on a 10Mbps segment.
Store & forward switches improve overall network performance by acting as a “network cache”
Store & forward switches prevent the forwarding of corrupted packets by the frame check sequence (FCS) before
forwarding to the destination port.
3.4.1
The ADM6999U/UX receives incoming packets from one of its ports, searches in the Address Table for the
Destination MAC Address and then forwards the packet to the other port within the same VLAN group, if
appropriate. If the destination address is not found in the address table, the ADM6999U/UX treats the packet as
a broadcast packet and forwards the packet to the other ports which in the same VLAN group.
The ADM6999U/UX automatically learns the port number of attached network devices by examining the Source
MAC Address of all incoming packets at wire speed. If the Source Address is not found in the Address Table, the
device adds it to the table.
3.4.1.1
The ADM6999U/UX uses a hash algorithm to learn the MAC address and can learn up to 2K MAC addresses.
Address is stored in the Address Table. The ADM6999U/UX searches for the Source Address (SA) of an incoming
packet in the Address Table and acts as below:
If the SA was not found in the Address Table (a new address), the ADM6999U/UX waits until the end of the packet
(non-error packet) and updates the Address Table. If the SA was found in the Address Table, then aging value of
each corresponding entry will be reset to 0.
When the DA is PAUSE command, then the learning process will be disabled automatically by ADM6999U/UX.
3.4.1.2
The ADM6999U/UX forwards the incoming packets between bridged ports according to the Destination Address
(DA) as below. All the packet forwarding will check VLAN first. A forwarding port must be within the same VLAN
as the source port.
1. If the DA is an UNICAST address and the address was found in the Address Table, the ADM6999U/UX will
Data Sheet
check the port number and acts as follows:
a) If the port number is equal to the port on which the packet was received, the packet is discarded.
b) If the port number is different, the packet is forwarded across the bridge.
Memory Block Description
Switch Functional Description
Basic Operation
Address Learning
Address Recognition and Packet Forwarding
23
Rev. 1.42, 2005-11-25
ADM6999U/UX
Data Sheet
Descriptions