adm6993 Infineon Technologies Corporation, adm6993 Datasheet - Page 25

• Manufacturer Part Number: adm6993
• Description: Adm6993/x Hdlc To Fast Ethernet Converter
• Manufacturer: Infineon Technologies Corporation

The ADM6993/X 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.
3.3.2
The ADM6993/X 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 ADM6993/X 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 ADM6993/X 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 ADM6993/X.
3.3.3
The ADM6993/X 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 ADM6993/X will check
2. If the DA is an UNICAST address and the address was not found, the ADM6993/X treats it as a multicast
3. If the DA is a Multicast address, the packet is forwarded across the bridge.
4. If the DA is PAUSE Command (01-80-C2-00-00-01), then this packet will be dropped by ADM6993/X.
5. ADM6993/X will forward by defaulted or filtering out the packet with DA of (01-80-C2-00-00-00), discarding the
3.3.4
Address aging is supported for topology changes such as an address moving from one port to the other. When
this happens, the ADM6993/X internally has a 300 seconds timer will aged out (remove) the address from the
address table. Aging function can be enabled/disabled by user. Normally, disabling aging function is for security
purpose.
3.3.5
The ADM6993/X incorporates transmitted queues and the receiving buffer area for the three ETHERNET ports.
The receiving buffers as well as the transmitted queues are located within the ADM6993/X along with the switch
fabric. The buffers are divided into 192 blocks of 256 bytes each. The queues of each port are managed according
to each port's read/write pointer.
3.3.6
The ADM6993/X implements the truncated exponential back off algorithm compliant to the IEEE802.3 CSMA/CD
standard. ADM6993/X will restart the back off algorithm by choosing 0-9 collision counts. The ADM6993/X resets
the collision counter after 16 consecutive retransmit trials.
Data Sheet
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.
packet and forwards across the bridge.
ADM6993/X can issue and learn PAUSE command.
packet with DA of (01-80-C2-00-00-01), filtering out the packet with DA of (01-80-C2-00-00-02 ~ 01-80-C2-00-
00-0F), and forwarding the packet with DA of (01-80-C2-00-00-10 ~ 01-80-C2-00-00-FF) decided by EEPROM
Reg.7
H
.
Address Learning
Address Recognition and Packet Forwarding
Address Aging
Buffers and Queues
Back off Algorithm
25
Function Description
Rev 1.11, 2005-11-28
ADM6993/X