HP 600 Series, Services And Applications

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Source-Routing Bridging
The term source routing was coined by IBM to describe a method of
bridging frames across token ring networks. Source-routing bridges differ
from transparent bridges in two critical ways:
Source-routing bridges tolerate a multiplicity of paths between any
two nodes in the extended network; transparent bridges, in contrast,
require a loop-free topology.
Source-routing bridges require hosts to supply the information
needed to deliver a frame to its intended recipient. Within a source-
routing extended network, bridges need not maintain address tables.
Rather they make the decision to forward or to drop a frame solely
on the basis of data contained within the frame itself. To implement
such a scheme, each source node determines the route to a destina-
tion node through a process called route discovery.
The route discovery process is enabled by four types of routing directives,
listed below. Each type is known by several names, some of which are listed
here.
All routes explorer (ARE),
All paths explorer (APE),
All routes broadcast (ARB),
All paths broadcast:
Generates multiple frames that traverse all paths between source
and destination stations. Such frames are called all routes explorer
(ARE) or all paths explorer (APE) frames, or one of the other names
listed above. Upon receiving an ARE frame, each bridge within the
extended network appends a routing designator. A routing designa-
tor is an information triplet which takes the following form:
[LAN ID i] [Bridge ID] [LAN ID j]
where:
LAN ID i is a unique number that identifies the LAN (or ring)
upon which the ARE frame arrived.
Bridge ID is a number that identifies the intervening bridge.
LAN ID j is a unique number that identifies the LAN (or ring)
upon which the ARE frame is relayed by the bridge.
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Bridging Service
Source-Routing Bridging
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