rfc1152.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                       C. Partridge
Request for Comments: 1152                  BBN Systems and Technologies
                                                              April 1990


                            Workshop Report
              Internet Research Steering Group Workshop on
                        Very-High-Speed Networks

Status of this Memo

   This memo is a report on a workshop sponsored by the Internet
   Research Steering Group.  This memo is for information only.  This
   RFC does not specify an Internet standard.  Distribution of this memo
   is unlimited.

Introduction

   The goal of the workshop was to gather together a small number of
   leading researchers on high-speed networks in an environment
   conducive to lively thinking.  The hope is that by having such a
   workshop the IRSG has helped to stimulate new or improved research in
   the area of high-speed networks.

   Attendance at the workshop was limited to fifty people, and attendees
   had to apply to get in.  Applications were reviewed by a program
   committee, which accepted about half of them.  A few key individuals
   were invited directly by the program committee, without application.
   The workshop was organized by Dave Clark and Craig Partridge.

   This workshop report is derived from session writeups by each of the
   session chairman, which were then reviewed by the workshop
   participants.

Session 1: Protocol Implementation (David D. Clark, Chair)

   This session was concerned with what changes might be required in
   protocols in order to achieve very high-speed operation.

   The session was introduced by David Clark (MIT LCS), who claimed that
   existing protocols would be sufficient to go at a gigabit per second,
   if that were the only goal.  In fact, proposals for high-speed
   networks usually include other requirements as well, such as going
   long distances, supporting many users, supporting new services such
   as reserved bandwidth, and so on.  Only by examining the detailed
   requirements can one understand and compare various proposals for
   protocols.  A variety of techniques have been proposed to permit
   protocols to operate at high speeds, ranging from clever



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RFC 1152                  IRSG Workshop Report                April 1990


   implementation to complete relayering of function.  Clark asserted
   that currently even the basic problem to be solved is not clear, let
   alone the proper approach to the solution.

   Mats Bjorkman (Uppsala University) described a project that involved
   the use of an outboard protocol processor to support high-speed
   operation.  He asserted that his approach would permit accelerated
   processing of steady-state sequences of packets.  Van Jacobson (LBL)
   reported results that suggest that existing protocols can operate at
   high speeds without the need for outboard processors.  He also argued
   that resource reservation can be integrated into a connectionless
   protocol such as IP without losing the essence of the connectionless
   architecture.  This is in contrast to a more commonly held belief
   that full connection setup will be necessary in order to support
   resource reservation.  Jacobson said that he has an experimental IP
   gateway that supports resource reservation for specific packet
   sequences today.

   Dave Borman (Cray Research) described high-speed execution of TCP on
   a Cray, where the overhead is most probably the system and I/O
   architecture rather than the protocol.  He believes that protocols
   such as TCP would be suitable for high-speed operation if the windows
   and sequence spaces were large enough. He reported that the current
   speed of a TCP transfer between the processors of a Cray Y-MP was
   over 500 Mbps.  Jon Crowcroft (University College London) described
   the current network projects at UCL.  He offered a speculation that
   congestion could be managed in very high-speed networks by returning
   to the sender any packets for which transmission capacity was not
   available.

   Dave Feldmeier (Bellcore) reported on the Bellcore participation in
   the Aurora project, a joint experiment of Bellcore, IBM, MIT, and
   UPenn, which has the goal of installing and evaluating two sorts of
   switches at gigabit speeds between those four sites.  Bellcore is
   interested in switch and protocol design, and Feldmeier and his group
   are designing and implementing a 1 Gbps transport protocol and
   network interface.  The protocol processor will have special support
   for such things as forward error correction to deal with ATM cell
   loss in VLSI; a new FEC code and chip design have been developed to
   run at 1 Gbps.

   Because of the large number of speakers, there was no general
   discussion after this session.








Partridge                                                       [Page 2]

RFC 1152                  IRSG Workshop Report                April 1990


Session 2: High-Speed Applications (Keith Lantz, Chair)

   This session focused on applications and the requirements they impose
   on the underlying networks.  Keith Lantz (Olivetti Research
   California) opened by introducing the concept of the portable office
   - a world where a user is able to take her work with her wherever she
   goes.  In such an office a worker can access the same services and
   the same people regardless of whether she is in the same building
   with those services and people, at home, or at a distant site (such
   as a hotel) - or whether she is equipped with a highly portable,
   multi-media workstation, which she can literally carry with her
   wherever she goes.  Thus, portable should be interpreted as referring
   to portability of access to services rather than to portability of
   hardware.  Although not coordinated in advance, each of the
   presentations in this session can be viewed as a perspective on the
   portable office.

   The bulk of Lantz's talk focused on desktop teleconferencing - the
   integration of traditional audio/video teleconferencing technologies
   with workstation-based network computing so as to enable
   geographically distributed individuals to collaborate, in real time,
   using multiple media (in particular, text, graphics, facsimile,
   audio, and video) and all available computer-based tools, from their
   respective locales (i.e., office, home, or hotel).  Such a facility
   places severe requirements on the underlying network.  Specifically,
   it requires support for several data streams with widely varying
   bandwidths (from a few Kbps to 1 Gbps) but generally low delay, some
   with minimal jitter (i.e., isochronous), and all synchronized with
   each other (i.e., multi-channel or media synchronization).  It
   appears that high-speed network researchers are paying insufficient
   attention to the last point, in particular.  For example, the bulk of
   the research on ATM has assumed that channels have independent
   connection request and burst statistics; this is clearly not the case
   in the context of desktop teleconferencing.

   Lantz also stressed the need for adaptive protocols, to accommodate
   situations where the capacity of the network is exceeded, or where it
   is necessary to interoperate with low-speed networks, or where human
   factors suggest that the quality of service should change (e.g.,
   increasing or decreasing the resolution of a video image).  Employing
   adaptive protocols suggests, first, that the interface to the network
   protocols must be hardware-independent and based only on quality of
   service.  Second, a variety of code conversion services should be
   available, for example, to convert from one audio encoding scheme to
   another.  Promising examples of adaptive protocols in the video
   domain include variable-rate constant-quality coding, layered or
   embedded coding, progressive transmission, and (most recently, at
   UC-Berkeley) the extension of the concepts of structured graphics to



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RFC 1152                  IRSG Workshop Report                April 1990


   video, such that the component elements of the video image are kept
   logically separate throughout the production-to-presentation cycle.

   Charlie Catlett (National Center for Supercomputing Applications)
   continued by analyzing a specific scientific application, simulation
   of a thunderstorm, with respect to its network requirements.  The
   application was analyzed from the standpoint of identifying data flow
   and the interrelationships between the computational algorithms, the
   supercomputer CPU throughput, the nature and size of the data set,
   and the available network services (throughput, delay, etc).

   Simulation and the visualization of results typically involves
   several steps:

      1.  Simulation

      2.  Tessellation (transform simulation data into three-dimensional
          geometric volume descriptions, or polygons)

      3.  Rendering (transform polygons into raster image)

   For the thunderstorm simulation, the simulation and tessellation are
   currently done using a Cray supercomputer and the resulting polygons
   are sent to a Silicon Graphics workstation to be rendered and
   displayed.  The simulation creates data at a rate of between 32 and
   128 Mbps (depending on the number of Cray-2 processors working on the
   simulation) and the tessellation output data rate is in typically in
   the range of 10 to 100 Mbps, varying with the complexity of the
   visualization techniques.  The SGI workstation can display 100,000
   polygons/sec which for this example translates to up to 10
   frames/sec.  Analysis tools such as tracer particles and two-
   dimensional slices are used interactively at the workstation with
   pre-calculated polygon sets.

   In the next two to three years, supercomputer speeds of 10-30 GFLOPS
   and workstation speeds of up to 1 GFLOPS and 1 million
   polygons/second display are projected to be available.  Increased
   supercomputer power will yield a simulation data creation rate of up
   to several Gbps for this application.  The increased workstation
   power will allow both tessellation and rendering to be done at the
   workstation.  The use of shared window systems will allow multiple
   researchers on the network to collaborate on a simulation, with the
   possibility of each scientist using his or her own visualization
   techniques with the tessellation process running on his or her
   workstation.  Further developments, such as network virtual memory,
   will allow the tessellation processes on the workstations to access
   variables directly in supercomputer memory.




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RFC 1152                  IRSG Workshop Report                April 1990


   Terry Crowley (BBN Systems and Technologies) continued the theme of
   collaboration, in the context of real-time video and audio, shared
   multimedia workspaces, multimedia and video mail, distributed file
   systems, scientific visualization, network access to video and image
   information, transaction processing systems, and transferring data
   and computational results between workstations and supercomputers.
   In general, such applications could help groups collaborate by
   directly providing communication channels (real-time video, shared
   multimedia workspaces), by improving and expanding on the kinds of
   information that can be shared (multimedia and video mail,
   supercomputer data and results), and by reducing replication and the
   complexity of sharing (distributed file systems, network access to
   video and image information).

   Actual usage patterns for these applications are hard to predict in
   advance.  For example, real-time video might be used for group
   conferencing, for video phone calls, for walking down the hall, or
   for providing a long-term shared viewport between remote locations in
   order to help establish community ties.  Two characteristics of
   network traffic that we can expect are the need to provide multiple
   data streams to the end user and the need to synchronize these
   streams.  These data streams will include real-time video, access to
   stored video, shared multimedia workspaces, and access to other
   multimedia data.  A presentation involving multiple data streams must
   be synchronized in order to maintain cross-references between them
   (e.g., pointing actions within the shared multimedia workspace that
   are combined with a voice request to delete this and save that).
   While much traffic will be point-to-point, a significant amount of
   traffic will involve conferences between multiple sites.  A protocol