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      ATM Forum Document Number: ATM Forum/96-1760

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      Title: Real-Time ABR: Proposal for a New Work Item

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      Abstract:

      Real-time   ABR  service  class,  which  is  useful  for  many  video
      applications, is proposed.

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      Source:

      Raj Jain, Shivkumar Kalyanaraman, Rohit Goyal, Sonia Fahmy
      The Ohio State University (and NASA)
      Department of CIS
      Columbus, OH 43210
      Phone: 614-292-3989, Fax: 614-292-2911, Email: Jain@cse.wustl.edu

      Seong-Cheol Kim
      Samsung Electronics Co. Ltd.
      Chung-Ang Newspaper Bldg.
      8-2, Karak-Dong, Songpa-Ku
      Seoul, Korea 138-160
      Email: kimsc@metro.telecom.samsung.co.kr

      Deepak Kataria, T. V. Lakshman, Albert Wong
      Lucent Technologies
      200 Laurel Avenue
      Middletown, NJ 07748
      Email: Kataria@lucent.com, lakshman@research.bell-labs.com,
      albertwong@lucent.com

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      Date: December 1996

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      Distribution: ATM Forum Technical Working Group Members (TM, TEST)

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      Notice: This contribution has been prepared to assist the ATM  Forum.
      It  is  offered  to  the Forum as a basis for discussion and is not a
      binding  proposal  on  the  part   of   any   of   the   contributing
      organizations.   The  statements  are  subject  to change in form and
      content after further study.  Specifically, the contributors  reserve
      the right to add to, amend or modify the statements contained herein.

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      Motion: Include the following item in the  living  list  for  the  TM
      group.

      Title: Real-time ABR

      Problem Statement:

      Currently  video is supported by the CBR, rt-VBR, and nrt-VBR service
      classes in  TM4.0.  This  requires  the  sources  to  estimate  their
      sustained cell rate (SCR) and/or peak cell rate (PCR) before making a
      connection.  If  the  requested  capacity  is  not   available,   the
      connection is refused.

      There  are a number of applications, particularly, in the defense and
      military environments, where a user will prefer a lower quality video
      to  no  video  at  all. In other words, "available quaility" video is
      preferable to a "given quality" video. The codecs, today, are capable
      of  dynamically adjusting the compression parameters to make the best
      use of available  rates.  Similar  applications  occur  in  real-time
      manufacturing environments.

      rt-ABR  is  the  service designed for such applications. (Current ABR
      can be renamed as nrt-ABR.)  We  can  use  the  inherent  negotiation
      capability  of  ABR  (provided  continuously via RM cells without the
      need for signaling over short intervals) for the switches to indicate
      the available rate.

      ABR  as currently defined allocates available cell rate to contending
      flows. Such flows are allocated a rate on a best effort basis and  do
      not  have  any  delay  guarantees.  However, it is possible to design
      switch algorithms such that once a flow is given an  ACR,  its  delay
      can  also  be  guaranteed  on  a  best effort basis.  In general, any
      algorithm with a  fast  transient  response  and  queue  control  can
      guarantee the delay through the switch.

      Weighted  max-min  fairness  criterion  can  be  used to provide rate
      allocation to flows in proportion  to  their  weights.   Higher  rate
      sources,  whose quality is more likely to be affected, can be treated
      preferentially (instead of all sources  experiencing  the  same  rate
      reduction).

      If the sources are willing to adapt only minimally, we can operate in
      a VBR-like  mode,  by  setting  their  MCR  values  to  an  effective
      bandwidth  calculated  using  buffering at the sources and acceptable
      loss at that buffer.

      We can use the minimum cell rate (MCR) guarantee  of  ABR  to  ensure
      that  a  transported  video  stream gets a minimum acceptable service
      quality.  Each source at call set up time may decide for itself  what
      this  minimum  acceptable  level  is.  This  use of minimum cell rate
      distinguishes this approach (rt-ABR)  from  completely  rate-adaptive
      video such as those used in Internet video tools.

      We,  therefore, propose that TM group should explore this new service
      for the next generation of traffic management specifications.

      Solution Requirements: Must provide loose  end-to-end  delay  bounds.
      Other parameters TBD.

      Last Update: December 1996

      Status: Under study.

      Date of Introduction: December 1996