Virtual concatenation
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The SDH granularity problem
The virtual containers of the SDH have fixed sizes. These virtual containers are
important for the transport of Ethernet frames over the SDH network:
• VC-12: 2 Mbit/s
• VC-3: 50 Mbit/s
• VC-4: 150 Mbit/s
It is difficult to fit the Ethernet traffic into one of these virtual containers. For many
applications the containers, or contiguously concatenated virtual containers, such as
VC-4-4C (600 Mbit/s) for example, are either too small or too big. This is known as
the granularity problem.
Virtual concatenation is a mechanism by which a number of independent VCs can be
used to carry a single payload. This way, the granularity problem is solved.
The following table shows the possible payload sizes, and the virtual containers that
are used for the transport.
Payload Virtual containers Concatenation
2 Mbit/s 1 × VC-12 VC-12
4 Mbit/s 2 × VC-12 VC-12-2v
6 Mbit/s 3 × VC-12 VC-12-3v
8 Mbit/s 4 × VC-12 VC-12-4v
10 Mbit/s 5 × VC-12 VC-12-5v
50 Mbit/s 1 × VC-3 VC-3
100 Mbit/s 2 × VC-3 VC-3-2v
150 Mbit/s 1 × VC-4 VC-4
300 Mbit/s 2 × VC-4 VC-4-2v
450 Mbit/s 3 × VC-4 VC-4-3v
600 Mbit/s 4 × VC-4 VC-4-4v
750 Mbit/s 5 × VC-4 VC-4-5v
900 Mbit/s 6 × VC-4 VC-4-6v
1 Gbit/s 7 × VC-4 VC-4-7v
Virtual concatenation
Virtual concatenation can be used for the transport of payloads that do not fit
efficiently into the standard set of virtual containers (VCs).
Virtual concatenation splits the contiguous bandwidth into individual VCs, transports
these VCs separately over the SDH network, and recombines them to a contiguous
signal at the path termination. An important aspect of virtual concatenation is that it
Traffic provisioning
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8-40
Alcatel-Lucent - Proprietary
See notice on first page
365-312-807R7.2
Issue 4, May 2007
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