HP 200 Series Services And Applications page 88

Bridging Service
Source-Routing Bridging
Source-Routing/Transparent Bridging
The SRT bridging provides concurrent transparent and source-routing
services. Figure 24 shows a sample multi-ring, multi-Ethernet extended
network linked by four routers serving as SRT bridges. Router T provides
only transparent bridging services. The three other routers (all labeled S)
provide both source-routing and transparent bridging services, when they
have source routing enabled. However, HP routers do not support source-
routing transparent bridging to traverse both Ethernet and token ring LANs
using a single bridging technique. The two different methodologies are
provided concurrently.
The transparent bridge treats all frames as if they are transparent-bridging
frames. In order to effect route discovery, however, the SRT bridge needs to
separate frames which require source-routing service from those frames
which require transparent-bridging service.
Figure 24. Sample SRT Topology
In order to identify source-routing frames, the SRT bridge inspects the value
of the most significant bit of the frame's source address (referred to as the
routing information indicator or RII). An RII value of 1 specifies source
routing; an RII value of 0 specifies transparent bridging.
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Ethernet
Token
S
Ring
Token
Ring
S SRT Bridge
Transparent Bridge
T
Synchronous Lines
S
T
S
Ethernet
Token
Ring