Cell Relay Archive

[Robert Sarullo <rsarullo@crl.com>]

>Ken Head writes:

>MPEG2 hardware for ATM is under development by Divicom, AT&T and
>others and its very, very expensive.

General DataComm is also developing MPEG2.
>
>However motion JPEG seems to have caught on for video conferencing
>over ATM.  At the Interop Trade Show in Vegas last week 5 vendors
>were showing ATM JPEG video codecs:
>
>	-AT&T,  EMMI
>	-STS Tech., MMX
>	-Newbridge, JPEG video card for the 36150 ATM switch
>	-General Data Com, JPEG video card for ATM switch
>	-Fujitsu, JPEG card for ATM service mux.
>
>Both STS Tech and Newbridge uses a LSI chip set (I believe
>AT&T uses the same chip set as well).  These codecs offer
>full NTSC resolution and frame rate and the quality is quite
>good.  Both of these codecs uses AAL1 (like, both vendors hardware
>predates the finalized standards). 

General DataComm's product uses Motion JPEG over AAL1  or AAL5.

>However the quality is not quite
>broadcast, if you have a trained eye you can see the compression
>artifacts (edges are not quite as sharp). If anyone is familiar with
>the current digital satilite services using MPEG then the quality
>is similar.  At the higest quality settings these codecs run at 25 to 
>35 Mbps depending on video content (yes VBR on AAL1!).

Key point that's missing here is:  if you are going to use VBR over AAL5, then the ATM 
switch must be able to provide for traffic management and policing.  Of these vendors 
mentioned, General DataComm's APEX switch is the only platform which can do it.  
So, unless the switch can provide for traffic management, you are forced to use AAL1. 
 This is why you have said "(yes VBR on AAL1!)" because you must not have stopped 
by the General DataComm booth!
>
>Another interesting way to do video over ATM is to use DS-3 
>circuit emulation and then utilize broadcast quality codecs
>for DS-3.  This is currentlt in use on NCIH for some
>distance learning applications.  DS-3 cir. emu. certainly
>uses AAL1 based on the lastest standards.
>
>Ken Head
>kjh0@gte.com
>

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Name: Robert Sarullo
E-mail: rsarullo@mail.crl.com (Robert Sarullo)

Disclaimer:  this message represents my personal opinion only
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