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- Newsgroups: comp.dcom.cell-relay
- Path: sparky!uunet!mcsun!sun4nl!research.ptt.nl!walvdrk
- From: walvdrk@research.ptt.nl (KEES VAN DER WAL)
- Subject: Re: Issues, mostly unresolved
- Message-ID: <1992Jul27.213924.1@research.ptt.nl>
- Followup-To: comp.dcom.cell-relay
- Sender: usenet@spider.research.ptt.nl (USEnet News)
- Nntp-Posting-Host: dnlts0
- Organization: PTT Research, The Netherlands
- References: <1992Jul17.152436.4409@iscnvx.lmsc.lockheed.com> <1992Jul21.201052.22822@cc.gatech.edu>
- Date: Mon, 27 Jul 1992 20:39:24 GMT
- Lines: 81
-
- 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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