T71L6816A Taiwan Memory Technology, T71L6816A Datasheet - Page 8

• Manufacturer Part Number: T71L6816A
• Description: Sixteen-port 10/100 Switch
• Manufacturer: Taiwan Memory Technology

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3.7 Address
3.7.1 Address Learning
The T71L6816A has a on-chip address table with 2K entries to map the MAC address to
port -ID for the operation of packet forwarding engine. The T71L681 6A use either hash
algorithm or direct mapping to locate every entry and each entry contains the information
about incoming port number, partial MAC address and age timer.
The T71L6816A learns the MAC address of attached network devices by checking the so urce
MAC address(SA) of all incoming packets and acts as follows: If the SA is an unicast address
and can’t be found in address table, the T71L6816A will allocate an entry for this address
after this packet has been received with no error detected. If the SA was found in address
table, the T71L6806A will update the aging value of the corresponding entry to zero.
The T71L6816A will disable the learning process while the incoming packet is a PAUSE command
defined by IEEE 802.3x.
3.7.2 Address Aging
If the “ AgeEn” option configured in EEPROM is set, the T71L6816A will periodically check
every entry in address table and mark the entry as invalid if its aging timer is over
300 seconds. Once a entry is marked as invalid, this entry no longer be used for address
lookup until it is remarked as valid for new address.
3.8 Broadcast Storm Control
In general, the T71L6816A will forward the broadcast packets to other ports. It’s obviously
broadcast packets will use switch resources(bandwidth and available transmit queue) much
more than normal packets. In extreme case of unstable network with something wrong, it
may produce massive broadcast packets from one mal -functional device and results in the
crash of whole network, that is so-called broadcast storm.
If the “BRDCTRL” option configured in EEPROM is set, the T71L6816A provide a scheme to
prevent the broadcast storm by temporarily discarding the broadcast/multicast packets
if the number of those kind of packets exceeds the internal threshold.
Taiwan Memory Technology, Copy-Right reserved.
Change to products or specifications without notice.
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P. 8
Preliminary T71L6816A
Publication Date:Jun. 2001
Revision:0.A