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مشاهدة النسخة كاملة : Whats the difference between SONET and SDH?



A7med Baraka
04-15-2009, 08:51 PM
SONET and SDH are very close, but with just enough differences that
they don't really interoperate. Probably the major difference between them
is that SONET is based on the STS-1 at 51.84 Mb/s (for efficient carrying
of T3 signals), and SDH is based on the STM-1 at 155.52 Mb/s (for efficient
carrying of E4 signals). As such, the way payloads are mapped into these
respective building blocks differ (which makes sense, given how the European
and North American PDHs differ). Check the September 1993 issue of IEEE
Communications Magazine for an overview article on SONET/SDH.

The following table shows how the US STS and the European STM levels
compare:

US Europe Bit Rate (total)

STS-1 -- 51.84 Mb/s
STS-3 STM-1 155.52 Mb/s
STS-12 STM-4 622.08 Mb/s
STS-24 STM-8 1244.16 Mb/s
STS-48 STM-16 2488.32 Mb/s
STS-192 STM-64 9953.28 Mb/s

From a formatting perspective, however, OC-3/STS-3 != STM-1 even though
the rate is the same. SONET STS-3c (i.e., STS-3 concatenated) is the
same as SDH STM-1, followed by STS-9c = STM-3c, etc.

There are other minor differences in overhead bytes (different places,
slightly different functionality, etc), but these shouldn't provide
many problems. By the way, most physical interface chips that support SONET
also include a STM operation mode. Switch vendors which use these devices
could then potentially support STS-3 and STM-1 for example.