From: walvdrk@research.ptt.nl (KEES VAN DER WAL)
Subject: Re: Issues, mostly unresolved
Followup-To: comp.dcom.cell-relay
Organization: PTT Research, The Netherlands
Date: Mon, 27 Jul 1992 20:39:24 GMT

In article <1992Jul21.201052.22822@cc.gatech.edu>, nikolaid@cc.gatech.edu
(Ioanis Nikolaidis) writes: 

>>  True, but it supports compressed video quite nicely, and uncompressed
>>low resolution video, as well has high quality sound, voice mail, and
>>works great for image distribution and distributed data bases.  It allows
>>for deskttop controlled conferencing.  These things are important, probably 
>>more important than HDTV in the private network business.  

> In the document COM XVIII-R 34-E of CCITT Study Group XVIII - 
> (Report R 34) of June 1990, on page 46, a specification of the 
> service integration for video is given. 
> They recognize the enormous differences of the 
> video terminal equipment capabilities and link speeds and 
> propose the following "solution": 
>
> [text about layered coding deleted]
>
> The subject was left for "further study" in report 34. 
> 
> My question is the following: 
> 
> If an approach is implemented as described above, what is the 
> network component that will discard the "upper" "enhancement" 
> layers of the video connection to reduce the required bandwidth 
> (to be conveyed on a (say) 10Mbps link)? 
> Will this component work on the ATM layer or on the AAL? 
> (If you reply "the ATM layer" you must show me a place in 
> the header where the video layer "level" is placed. If you 
> reply "the AAL" the question is if we will need reassembly 
> of video packets.) 

On of the "attractive" things is that the base layer needs low-loss 
transportation but is more or less constant in cellrate. The enhancement 
layer(s) is varying in cellrate but can tolerate quite high cell losses.
The first one is ideal for peak-rate allocation, the latter ne is ideal to be 
multiplexed togehter with other connections with similar properties.

The question "how to transport the different layers" in an ATM network has been 
brought up in ETSI (the European Telecommunications Standardisation Institute; 
similar to ANSI I guess) by BT.

There is no final anwer to that but several possibilities could be compared.
To name a few:

1) the use of the CLP-bit to distinguish base- from enhancement layer. 

2) different VCs of VPs preferably routed along the same links and switch
routes to prevent too much difference in delay. 

Option 1) would restrict the user to only a single enhancement layer and
wouldn't work if the network operator is opting for the "tagging option" when
doing UPC (but who's going to tag anyway?). There's also no possibility to 
select in the ATM network whether only the base layer or both base- and
enhancement layer should be switched. On the ATM layer it's just a sinngle 
connection.

Option 2) would allow more than a single enhancement layer. The user may select 
as many enehancement layers as he'd like and the ATM network just adds another 
VC to the call to support it.


There exists an ETSI document describing these possibilities (mainly from the
network point of view) and making reference to the appropriate CCITT documents.
The document was prepared before the CCITT June meeting so the latest changes
have not (yet) been included. It's going to be used in a joint meeting between
ETSI-NA5-TCR (dealing with Traffic Control and Resource Management) and
ETSI-NA5-VCM (Video Coding Matters) in September'92. 

I don't think there's any problem in distributing the document outside ETSI.
Just let me know if you're interested in a copy (LaTeX format - ZIPped and 
UUencoded or plain).


Regards, <kees>

Kees  van der Wal		       e-mail: J.C.vanderWal@research.ptt.nl
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