Texas Instruments THUNDERSWITCH II TNETX4090 - Manual (Page 50)

TNETX4090
ThunderSWITCH II

9-PORT 100-/1000-MBIT/S ETHERNET

SWITCH
SPWS044E – DECEMBER 1997 – REVISED AUGUST 1999
50
POST OFFICE BOX 655303
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DALLAS, TEXAS 75265
aging algorithms
time-threshold aging
When learning addresses, the IALE adds the address to the table and tags it with a time stamp. If another frame
is received with this address, the time stamp is refreshed. If the aging counter expires before another frame is
received from this source address, the address is deleted from the table. If the table is full, the oldest address
is deleted to make room for a new address, even if the age for this address has not expired.
table-full aging
In table-full aging, the oldest address (or one of the oldest addresses if there is more than one) automatically
is deleted from the IALE records only if the table is full, and a new address must be added to the table. In this
mode, the age stamp for the addresses is not refreshed.
frame-routing determination
When a frame is received, its 48-bit destination and source addresses are extracted and the VLAN index is
determined as described in
VLAN Support. The destination address and VLAN index are then looked up in the
IALE records to determine if they exist. If a match is found, the information associated with the record is passed
on to the frame-routing algorithm. Figure 11 provides a flow diagram of the routing algorithm. For details of the
register information referred to in Figure 11, see the
TNETX4090 Programmer’s Reference Guide, literature
number SPAU003.
The source address and VLAN index combination also are looked up in the IALE records to determine if they
exist. If a match is found, additional information is provided to the routing process (for details see the
TNETX4090 Programmer’s Reference Guide, literature number SPAU003).