KSZ8893-MQL Micrel Semiconductor, Inc., KSZ8893-MQL Datasheet - Page 28

• Manufacturer Part Number: KSZ8893-MQL
• Description: Integrated 3-Port 10/100 Managed Switch with PHYs
• Manufacturer: Micrel Semiconductor, Inc.

Functional Overview: MAC and Switch
Address Lookup
The internal lookup table stores MAC addresses and their associated information. It contains a 1K unicast
address table plus switching information.
The KSZ8893MQL is guaranteed to learn 1K addresses and distinguishes itself from hash-based lookup tables,
which depending on the operating environment and probabilities, may not guarantee the absolute number of
addresses it can learn.
Learning
The internal lookup engine updates its table with a new entry if the following conditions are met:
1. The received packet's Source Address (SA) does not exist in the lookup table.
2. The received packet is good; the packet has no receiving errors, and is of legal length.
The lookup engine inserts the qualified SA into the table, along with the port number and time stamp. If the table
is full, the last entry of the table is deleted to make room for the new entry.
Migration
The internal lookup engine also monitors whether a station has moved. If a station has moved, it will update the
table accordingly. Migration happens when the following conditions are met:
1. The received packet's SA is in the table but the associated source port information is different.
2. The received packet is good; the packet has no receiving errors, and is of legal length.
The lookup engine will update the existing record in the table with the new source port information.
Aging
The lookup engine updates the time stamp information of a record whenever the corresponding SA appears. The
time stamp is used in the aging process. If a record is not updated for a period of time, the lookup engine removes
the record from the table. The lookup engine constantly performs the aging process and will continuously remove
aging records. The aging period is about 200 seconds. This feature can be enabled or disabled through register 3
(0x03) bit [2].
Forwarding
The KSZ8893MQL forwards packets using the algorithm that is depicted in the following flowcharts. Figure 4
shows stage one of the forwarding algorithm where the search engine looks up the VLAN ID, static table, and
dynamic table for the destination address, and comes up with “port to forward 1” (PTF1). PTF1 is then further
modified by spanning tree, IGMP snooping, port mirroring, and port VLAN processes to come up with “port to
forward 2” (PTF2), as shown in Figure 5. The packet is sent to PTF2.
Micrel
November 2005
28
KSZ8893MQL/MQLI
M9999-111705