Information Technology Reference
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A P P E N D I X
A
Multiprotocol BGP Extensions for
CLNS Support
The use of BGP has expanded beyond the IP environment. BGP's ability to manage large
amounts of routing information efficiently can be capitalized on elsewhere. A primary
example of where BGP can be leveraged is in the Data Communications Network (DCN)
environment. The DCN is a management network for Synchronous Optical Network
(SONET) and Synchronous Digital Hierarchy (SDH) network elements (NEs). The Con-
nectionless Network Service (CLNS) is used to manage the NEs, with File Transfer Access
Method (FTAM) and Common Management Interface Protocol (CMIP).
This appendix covers the general design for DCN management networks and how BGP can
best be used. The details of the CLNS protocol and the IS-IS routing protocol are outside
the scope of this topic, so only very brief coverage is provided. This appendix is primarily
intended for engineers who are familiar with DCNs and who are looking at BGP as a
scalability mechanism.
DCN Scalability
The primary scalability challenge that IP networks face is the amount of prefix information
that must be advertised. This is also the case in the DCN environment; however, the number
of nodes in the network has created additional constraints.
The DCN environment network is composed of SONET or SDH network elements (NEs),
typically add/drop multiplexers (ADMs). The number of NEs in a single SONET/SDH ring
averages around 10 but can range from 3 to 40. A typical DCN can have well over a thou-
sand rings, resulting in tens of thousands of NEs. This would not pose a problem, except
that each NE acts like an intermediate system (IS) and not an end system (ES).
SONET rings have a control channel, called the Data Communications Channel (DCC),
which is used to send control messaging between network elements. This control channel
has a bandwidth of 192 kbps. Bellcore specifies the architecture for the SONET DCC to
run an HDLC-based protocol that provides the equivalent of a point-to-point connection
between each adjacent network element, forming a ring architecture. (ITU-T does likewise
for SDH.)
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