contiguous concatenation and virtual concatenation
ramu
Why concatenations is required in SONET?Can you please tell me the
differences between contiguous concatenation and virtual concatenation?
How exactly they are done with an example?
Thanks,
Pieter Hulshoff
Contiguous concatenation is performed using concatenated AU pointers,
and concatenated payloads. All VCs in the concatenated group will be
transported through the same path in the network, and considered
concatenated by each node it passes. Either all or none of the payload
reaches its destination, and there is no delay between the VCs in the
concatenated group.
Virtual concatenation is performed using concatenation information in
the POH, but each VC has its own pointer and POH information.
Intermediate nodes are usually not aware that a VC is part of a group.
The VCs in the group can travel different paths through the network, so
delay will probably exist between the VCs when they arrive at their
destination, which must be undone by a store mechanism (store early VCs
until all VCs of that 'timestamp' (multiframe) have arrived).
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Kind regards,
Pieter Hulshoff
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Huub van Helvoort
You wrote:
> Why concatenations is required in SONET?
Concatenation is a methodology to provide a bandwidth larger
than the bandwidth provided by the original transport entity.
In SONET this is the STS-1 SPE providing 50 Mbit/s and in
SDH the VC-4 providing 150 Mbit/s.
E.g. to transport a VC-4 in a SONET network three STS-1 have to
be concatenated to provide the required bandwidth: STS-1-3c or
in short an STS-3c SPE has to be created.
With an increasing demand for larger bandwidth, especially in
LAN, MAN, WAN, SAN, higher concatenation rates were required.
> Can you please tell me the differences between contiguous
> concatenation and virtual concatenation?
In contiguous concatenation the payload of a multiple of
STS-1 (or VC-4) is "glued" together. Only on set of Path
Overhead is used, and only one pointer is used for this
container STS-Nc or VC-4-Xc with N=3X=4,16,64,256.
In Virtual concatenation the bandwidth is divided in X
pieces, that are transported using X STS-1 SPE or X VC-4
and glued together at the receive end, with X=1,2,3,...256
As you see virtual concatenation provides more flexibility
to math the bandwidth that needs to be transported.
> How exactly they are done with an example?
Providing an example here will be very difficult because
it is very hard to draw figures.
Either look at ITU-T recommendation G.707 or get a copy
of my book (see my webpage) that ives a very detailed
explanation of concatenation including the enhanced
virtual concatenation: LCAS.
Cheers, Huub.
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