number of ADPCM channels in E1 ???

Started by sahar August 25, 2005
Hi fellows
im newcomer . could anyone reply to my Question please ....

How many ADPCM channels are transmitted in E1 (2mb) stream if the bitrate
is 40kbps , 32kbps , 24kbps, 16kbps 
Is their any standard frame structure for it as their is for PCM .

Kindly help me out
With regards
Sahar


		
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"sahar" <sahar_jamshaid@yahoo.com> wrote in message 
news:qvadneUGJr4RZJDeRVn-1A@giganews.com...
> Hi fellows > im newcomer . could anyone reply to my Question please .... > > How many ADPCM channels are transmitted in E1 (2mb) stream if the bitrate > is 40kbps , 32kbps , 24kbps, 16kbps > Is their any standard frame structure for it as their is for PCM . > > Kindly help me out > With regards > Sahar >
Hello Sahar, In telephony, An E1 is 2.048MB/S where you have 32 - 64kB/S streams. Two of the streams are usually reserved for signaling for the other 30 streams. In voice storage and retrieval systems we used to convert the audio to 32 kBPS ADPCM for storage on the hard drive. On playback we would convert it back to standard 64 KBPS PCM for outputting to the PSN. I'm not sure what the standard(s) is/are for transport and muxing of compressed speech. Clay
Like Clay I don't think ADPCM over E1 is standard compliant. The most common 
configuration I've seen is just to use 32Kbps ADPCM to trasmint 62 channels 
over E1 (30x2 voice + 2 signaling). I don't know of any system using ADPCM 
with other bitrates with E1. Even in the case of 32Kbps, this configuration 
is noramlly used in a point to point network with such conversion circuits 
on both sites so the E1 bit streams is not going to pass through a 
switch/mixer/whatever...

"sahar" <sahar_jamshaid@yahoo.com> wrote in message 
news:qvadneUGJr4RZJDeRVn-1A@giganews.com...
> Hi fellows > im newcomer . could anyone reply to my Question please .... > > How many ADPCM channels are transmitted in E1 (2mb) stream if the bitrate > is 40kbps , 32kbps , 24kbps, 16kbps > Is their any standard frame structure for it as their is for PCM . > > Kindly help me out > With regards > Sahar > > > > This message was sent using the Comp.DSP web interface on > www.DSPRelated.com
Hi Sahar,

If you have both ends of the circuti and your system(s) supports ADPCM it
is most likely 32Kbps ADPCM.  Using 32Kbps ADPCM also allows easy A-law to
mu-law conversion since most codec's allow conversion to 32Kbps ADPCM,
though in-band signalling issues can occur.

There is no such thing as 40Kbps ADPCM.  32Kbps is 4 bit ADPCM, 24Kbps is
3 Bit ADPCM and 16Kbps is 2 bit ADPCM.  I have used all three and the
16Kbps is likely to not be acceptable if you have alot of women on the
phone.  Their voice spectrum is not powerful enought to sample well with
at 16Kbps.

E1 (2.048) circuits actually have 32 64Kbps channels (in a channelized
operating mode) of which 2 are normally taken for signalling channels,
though BT used to offer 31 + 1 between the US and UK, but that was 7-8
years ago.

You will have to check with the circuit provider(s) that service your
locations to be sure.

Padapa






		
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padapa wrote:

>Hi Sahar, > >If you have both ends of the circuti and your system(s) supports ADPCM it >is most likely 32Kbps ADPCM. Using 32Kbps ADPCM also allows easy A-law to >mu-law conversion since most codec's allow conversion to 32Kbps ADPCM, >though in-band signalling issues can occur. > >There is no such thing as 40Kbps ADPCM. >
G.726 says you are wrong. Of course, G.726 is not the only form of ADPCM, and a wide variety of rates are used by other specs. However, from the original poster's list of rates, I guess they are referring to G.726.
>32Kbps is 4 bit ADPCM, 24Kbps is >3 Bit ADPCM and 16Kbps is 2 bit ADPCM. I have used all three and the >16Kbps is likely to not be acceptable if you have alot of women on the >phone. Their voice spectrum is not powerful enought to sample well with >at 16Kbps. > >
Certainly true if using G.726. I think its 16kbps mode is useless. In fact, I have never seen any significant deployment of G.726 rates other than the original 32kbps (which was not originally called G.726, anyway). The simple OKI 24kbps ADPCM format is heavily used for voicemail and IVRs, simply because Dialogic chose to use it. There are other ADPCM schemes which do better at 16kbps. However, 16kbps is the sort of bit rate that really needs handling by more sophisticated forms of compression.
>E1 (2.048) circuits actually have 32 64Kbps channels (in a channelized >operating mode) of which 2 are normally taken for signalling channels, >though BT used to offer 31 + 1 between the US and UK, but that was 7-8 >years ago. > >You will have to check with the circuit provider(s) that service your >locations to be sure. > >
Which completely fails to answer the original question. I have seen different ways of sending G.726 ADPCM streams, but I don't think any of them appear in an ITU spec. The common method with 32kbps ADPCM is to use the low and high nibbles of each octet in each of the 30 or 31 64kbps channels of an E1 to carry one 32kbps stream. I assume something similar was done with T1s, but robbed bit issues might have complicated that. Regards, Steve