Need help to understand the basic SDH???

[balendran bala]

Hello sonet-sdh Gurus

I need bit of your time to understand the basic sdh!!!

I was reading the SDH Telecommunications standard from Tektronix and
it states that the STM-1(155Mbits/s) is the basic transmission format
for the SDH. The same document also talks about STM-0 (51 Mbits/s),
which is mapped with STS-1 (sonet) signal.

So my questions are:

1) What is the purpose of having STM-0 defined?
2) How does the STM-0 frame looks like?
3) Can we multiplex 3xSTM-0 into a STM-1 frame like 3xSTS-1 frames are
multiplexed into a STS-3 frame?

Thank you!
Balendran

[Vladislav Muravin]

Hi, there.

I am a new one in the field, yet a young engineer, but I will try to help.

Here we go.

First two of your questions are answered in the following way:

STM-0 is defined only for the analogy with STS-1. SDH defines STM-1 as the
lowest

Bit-rate (155 Mbit/s).

Now, the STM-0 looks like STS-1 frame.

> 3) Can we multiplex 3xSTM-0 into a STM-1 frame like 3xSTS-1 frames are

> multiplexed into a STS-3 frame?

Now, this question, I presume, will be answered IN DETAIL if you take a look

at the G.707 standard (ITU-T).

If you take a look at the multiplexing hierarchy, you will see, that STM-0
does not appear there.

Moreover, there're two basic modes of SDH multiplexing:

The first one is fully compatible with SONET from the STS-n frame structure
point of view.

(I am talking about STM-1/3xAU-3 <==> STS-3/3xSTS1)

The second one is not present within the SONET

(I am talking here about STM-1/AU-4/VC-4)

OK, now, AU-4 is something like STS-3c, but can carry payload which cannot
be carried within SONET.

I am talking about VC-4 that carries either 84 Tus (61 E1s/84 T1s) or 3
containers of DS-3/PPP/etc.

Now each AU-4/VC-4 that contains non-channelized payload (not Tus) has 3
sets of

H1/H2/H3 payload pointers (yep, besides one set at the STS-3c level), which

point to 9x85 container, which itself consists of POH and 9x84 structure

which might carry PPP/HDLC/DS-3/etc.

This is kind of information that you should check within the G.707 for more
details.

"balendran bala" <ba...@innocor.com> wrote in message
news:fdcfdc67.02021...@posting.google.com...

[onlie...@gmail.com]

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[Huub van Helvoort]

Hello Balendran,

You wrote:

> I need bit of your time to understand the basic sdh!!!

OK, I will try to help.

> I was reading the SDH Telecommunications standard from Tektronix and
> it states that the STM-1(155Mbits/s) is the basic transmission format
> for the SDH. The same document also talks about STM-0 (51 Mbits/s),
> which is mapped with STS-1 (sonet) signal.

An STM-0 can also transport a VC-3 (actually the same as an STS-1).

> So my questions are:
>
> 1) What is the purpose of having STM-0 defined?

STM-0 is mainly deployed in Japan.
The reason is that Japan has its own version of SDH, and in the
access part of the netowrk they already had PDH DS3, and wanted
replace this with SDH signal. So for this purpose STM-0 was introduced.

It is docuemnted in ITU-T G.707 free to download at:
http://www.itu.int/rec/T-REC-G.707-200701-I

> 2) How does the STM-0 frame looks like?

The same as other STM-N frames, with 3 columns X 9 rows overhead and
87 columns X 9 rows payload area, see G.707 figure 6-6.

> 3) Can we multiplex 3xSTM-0 into a STM-1 frame like 3xSTS-1 frames
> are multiplexed into a STS-3 frame?

No, that is not possible, the same as an STM-1 frame cannot be
multiplexed in an STM-4.
However it is possible to multiplex the VC-3 in the STM-0 into
a VC-4 in an STM-1 (or STM-4, STM-16, etc). See figure G.707 6-1.

> Thank you!

You're welcome.

Regards, Huub. (editor G.707)

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