From: dean@pico.OZ (Dean Economou)
Newsgroups: comp.dcom.cell-relay
Subject: Re: Issues, mostly unresolved
Date: 30 Jul 92 06:10:23 GMT
Organization: Comp Sci, Uni. Western Australia.
X-Newsreader: Tin 1.1 PL4

nikolaid@cc.gatech.edu (Ioanis Nikolaidis) writes:
: Related to article <1992Jul17.152436.4409@iscnvx.lmsc.lockheed.com> 
: from young@bantha.decnet.lockheed.com:
: >3) 10 Mbps cell relay will not support HDTV?
: >
: >  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": 
: 
: Video coding is performed in a "layered" fashion. 
: The sender of a video connection encodes the 
: signal with a layered approach. Each layer "adds up" some more
: detail on the visual result of the previous layers.  
: If all layers are decoded and presented at the video
: terminal, then the images are presented 
: with the best fidelity. 
: 
: However, the terminal equipment may be capable of receiving 
: only some of these layers (and not necessarily all). The number 
: of layers received by a terminal is related of course to the 
: quality of the equipment. A terminal is free to decode only part 
: of the transmitted layers to obtain just enough information to 
: reconstruct the image at its own level of image fidelity.
: This alone "solves" the diversity problem of video terminals. 
: 
: The same approach can be used to cope with limited bandwidth 
: BUT we need an active network entity that selectively discards
: the cells related to the "redundant" layers and in a way "filters
: out" the portion of the bandwidth that is used for improvement 
: of the image. Hence, the connection can be squeezed in a slower 
: link but with a penalty on image quality. 
: 
: 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.) 
: 
: Has there been any followup to the idea? 
: OR is my copy of the standard terribly outdated? 
:  
: Final note: The direction towards a "layered" approach 
: does not encourage diversity of video coding
: algorithms. In fact, all applicable coding methods must be 
: in reference (at least) to the overall layered structure -- i.e. if we 
: decide that layer 1 is luminosity and layer 2 is hue (a B+W receiver only 
: uses layer 1) then a coding algorithm that "mixes" 
: luminosity and hue information is not appropriate. 
: 
: --- 
: Yannis Nikolaidis
: (nikolaid@cc.gatech.edu)

Perhaps we could contemplate sending the various layers on different
VCIs?  That would make the selection somewhat easier as the VCIs
carrying the higher resolution could be rejected at VCI set up time by
the terminal.

Dean
(use dean@qpsx.oz.au, NOT reply)