Source Route Bridging (Provided Only Between Front Panel Rings); Sr-Tb Bridging (Front Panel Token Ring To Fnb) - Cabletron Systems SmartSwitch 9000 User Manual

Source Route Bridging
Source Route Bridging operates by transmitting frames over a designated route.
Unlike Transparent Bridging, all devices in a Source Route Bridged (SRB) network
"know" the locations of other stations within the network. Using a portion of the
MAC frame header known as the RIF (Routing Information Field), the source
device determines the route for the frames it sends.
In order for source routing to work, the source station must determine the proper
route to reach the desired destination. To accomplish this:
1. The source station sends out frames called All Route Explorer (ARE) or Single
Route Explorer (SRE) frames onto the network. All Source Route Bridges
recognize these frames and forward them to their outbound ports.
2. The receiving bridges append their own route information to the Route
Information Field (RIF) in the MAC frame header and transmit the frame
again.
3. Eventually, the original source device receives all of the ARE replies from the
other end stations on the network.
4. From this information, the source device can determine a desired route for
each frame it transmits.
SR-TB Bridging
Source Routing (SR) packets from the front panel Token Ring must be converted
to Transparent Bridging (TB) type packets before it is sent over the FNB. The RIF
is stripped off the packet and placed in a RIF cache.
The SR-TB bridge is a learning type bridge. It learns what nodes are present by
listening to incoming packets and saving their MAC addresses to a database
table. If the packet is source routed, it also updates the RIF cache.
If the destination is unknown or is a broadcast address, the bridge sends either a
STE or a ARE packet for the Token Ring interface, or a TP packet for the FDDI
interface, to carry the data to the end station. This is user configurable.
(Provided Only Between Front Panel Rings)
(Front Panel Token Ring to FNB)
Operation
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