User`s guide

Configuring
3-49
Example #4: Maximum Transmit Unit
The maximum frame size on FDDI is 4500 bytes, maximum on
Ethernet is 1518 bytes and the maximum on Token Ring is 17800
bytes. As you can see when transmitting a TR frame over Ethernet
or FDDI via a bridge, there could be a frame size conflict. The
mechanism for Token Ring end stations to be notified of the
maximum frame size a bridge will forward is in the Routing
Control field. In this field the bridge can select one of seven frame
sizes (516, 1470, 2052, 4472, 8144, 11407, 17800 according to the TI
TMS380 guide) to notify the end station that this is the maximum
frame size this bridge will forward.
For the ATX, this field is selectable via SNMP and defaults to 81144
for 16MB rings and 4472 for 4Mb rings. The scenarios below
ATX LAN SWITCH
WITH SRTB
ENABLED
ATX LAN SWITCH
WITH SRTB
ENABLED
STATION A
TR
TR
SOURCE ROUTE
BRIDGE
SOURCE ROUTE
BRIDGE
TR
FDDI
UNSUPPORTED CONFIGURATION