HP 200 Series Services And Applications page 93

Figure 30 shows conversion to the Ethernet version 2 frame format. (This is
often called the PC/RT format, or 80D5 format.) The conversion is similar to
that of figure 29.
Bridge Technology Conversion
From the perspective of the nodes on the Ethernet, the bridge technology
conversion is an algorithm that makes it appear that all nodes on the token-
ring SRB side are running on the same Ethernet LAN. From the perspective
of the nodes on the token ring, this algorithm also performs the opposite
function, of making the Ethernet nodes appear to be performing source
routing.
To understand how the TRNSB converts between the bridging technologies,
begin by examining the conversion from SRB to TB. There are two basic
types of SRB frames:
Explorer frames
Specifically routed frames
When the router receives an explorer frame from an SRB circuit group, the
TRNSB code accesses the address table used for transparent bridging to see
if the node is known to be on one of the transparent bridging circuit groups.
If it is found, the frame is converted to Ethernet/802.3 format and forwarded
to that circuit group. If the destination is not known, then the TRNSB
converts the frame and floods it to all transparent circuit groups configured
for TRNSB. If the destination address in the frame indicates a functional
address or the broadcast address, the frame is always flooded. In all of these
cases, the source of the frame is learned in the address table. In addition to
learning the association of a station address with a circuit group, the Routing
Information Field (RIF) for that station is stored. (It will be used when
converting in the other direction.)
When the router receives a specifically routed frame, it converts the frame
only if the next hop in the Routing Information Field (RIF) indicates that a
transparent circuit group is the next hop in the source routing path.
When converting from TB circuit groups to SRB circuit groups, the TRNSB
converts to a specifically routed frame if the destination station address is
found in the address table. The RIF that was stored (as described above) is
inserted into the frame, and the frame is routed through a source-routed
network.
Bridging Service
Source-Routing Bridging
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