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rfc:rfc1152

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

Partridge [Page 1] 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

Partridge [Page 3] 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.

Partridge [Page 4] 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
 providing a multicast capability is critical.
 Finally, Greg Watson (HP) presented an overview of ongoing work at
 the Hewlett-Packard Bristol lab.  Their belief is that, while
 applications for high-speed networks employing supercomputers are the
 the technology drivers, the economic drivers will be applications
 requiring moderate bandwidth (say 10 Mbps) that are used by everyone
 on the network.
 They are investigating how multimedia workstations can assist
 distributed research teams - small teams of people who are
 geographically dispersed and who need to work closely on some area of
 research.  Each workstation provides multiple video channels,
 together with some distributed applications running on personal
 computers.  The bandwidth requirements per workstation are about 40
 Mbps, assuming a certain degree of compression of the video channels.
 Currently the video is distributed as an analog signal over CATV
 equipment.  Ideally it would all be carried over a single, unified
 wide-area network operating in the one-to-several Gbps range.

Partridge [Page 5] RFC 1152 IRSG Workshop Report April 1990

 They have constructed a gigabit network prototype and are currently
 experimenting with uncompressed video carried over the same network
 as normal data traffic.

Session 3: Lightwave Technology and its Implications (Ira Richer, Chair)

 Bob Kennedy (MIT) opened the session with a talk on network design in
 an era of excess bandwidth.  Kennedy's research is focused on multi-
 purpose networks in which bandwidth is not a scarce commodity,
 networks with bandwidths of tens of terahertz.  Kennedy points out
 that a key challenge in such networks is that electronics cannot keep
 up with fiber speeds.  He proposes that we consider all-optical
 networks (in which all signals are optical) with optoelectronic nodes
 or gateways capable of recognizing and capturing only traffic
 destined for them, using time, frequency, or code divisions of the
 huge bandwidth.  The routing algorithms in such networks would be
 extremely simple to avoid having to convert fiber-optics into slower
 electronic pathways to do switching.
 Rich Gitlin (AT&T Bell Labs) gave a talk on issues and opportunities
 in broadband telecommunications networks, with emphasis on the role
 of fiber optic and photonic technology.  A three-level architecture
 for a broadband telecommunications network was presented.  The
 network is B-ISDN/ATM 150 (Mbps) based and consists of: customer
 premises equipment (PBXs, LANs, multimedia terminals) that access the
 network via a router/gateway, a Network Node (which is a high
 performance ATM packet switch) that serves both as a LAN-to-LAN
 interconnect and as a packet concentrator for traffic destined for
 CPE attached to other Network Nodes, and a backbone layer that
 interconnects the NODES via a Digital Cross-Connect System that
 provide reconfigurable SONET circuits between the NODES (the use of
 circuits minizes delay and avoids the need for implementation of
 peak-transmission-rate packet switching).  Within this framework, the
 most likely places for near-term application of photonics, apart from
 pure transport (ie, 150 Mbps channels in a 2.4 Gbps SONET system),
 are in the Cross-Connect (a Wavelength Division Multiplexed based
 structure was described) and in next-generation LANs that provide
 Gigabit per second throughputs by use of multiple fibers, concurrent
 transmission, and new access mechanisms (such as store and forward).
 A planned interlocation Bell Labs multimedia gigabit/sec research
 network, LuckyNet, was described that attempts to extend many of the
 above concepts to achieve its principal goals: provision of a gigabit
 per second capability to a heterogeneous user community, the
 stimulation of applications that require Gpbs throughput (initial
 applications are video conferencing and LAN interconnect), and, to
 the extent possible, be based on standards so that interconnection
 with other Gigabit testbeds is possible.

Partridge [Page 6] RFC 1152 IRSG Workshop Report April 1990

Session 4: High Speed Networks and the Phone System

         (David Tennenhouse, Chair)
 David Tennenhouse (MIT) reported on the ATM workshop he hosted the
 two days previous to this workshop.  His report will appear as part
 of the proceedings of his workshop.
 Wally St. John (LANL) followed with a presentation on the Los Alamos
 gigabit testbed.  This testbed is based on the High Performance
 Parallel Interface (HPPI) and on crossbar switch technology.  LANL
 has designed its own 16x16 crossbar switch and has also evaluated the
 Network Systems 8x8 crossbar switch. Future plans for the network
 include expansion to the CASA gigabit testbed.  The remote sites (San
 Diego Supercomputer Center, Caltech, and JPL) are configured
 similarly to the LANL testbed.  The long-haul interface is from HPPI
 to/from SONET (using ATM if in time).
 Wally also discussed some of the problems related to building a
 HPPI-SONET gateway:
    a)  Flow control.  The HPPI, by itself, is only readily extensible
        to 64 km because of the READY-type flow control used in the
        physical layer.  The gateway will need to incorporate larger
        buffers and independent flow control.
    b)  Error-rate expectations.  SONET is only specified to have a
        1E-10 BER on a per hop basis.  This is inadequate for long
        links.  Those in the know say that SONET will be much better
        but the designer is faced with the poor BER in the SONET spec.
    c)  Frame mapping.  There are several interesting issues to be
        considered in finding a good mapping from the HPPI packet
        to the SONET frame.  Some are what SONET STS levels will be
        available in what time frame, the availability of concatenated
        service, and the error rate issue.
 Dan Helman (UCSC) talked about work he has been doing with Darrell
 Long to examine the interconnection of Internet networks via an ATM
 B-ISDN network.  Since network interfaces and packet processing are
 the expensive parts of high-speed networks, they believe it doesn't
 make sense to use the ATM backbone only for transmission; it should
 be used for switching as well.  Therefore gateways (either shared by
 a subnet or integrated with fast hosts) are needed to encapsulate or
 convert conventional protocols to ATM format.  Gateways will be
 responsible for caching connections to recently accessed
 destinations.  Since many short-lived low-bandwidth connections as
 foreseen (e.g., for mail and ftp), routing in the ATM network (to set
 up connections) should not be complicated - a form of static routing

Partridge [Page 7] RFC 1152 IRSG Workshop Report April 1990

 should be adequate.  Connection performance can be monitored by the
 gateways.  Connections are reestablished if unacceptable.  All
 decision making can be done by gateways and route servers at low
 packet rates, rather than the high aggregate rate of the ATM network.
 One complicated issue to be addressed is how to transparently
 introduce an ATM backbone alongside the existing Internet.

Session 5: Distributed Systems (David Farber, Chair)

 Craig Partridge (BBN Systems and Technologies) started this session
 by arguing that classic RPC does not scale well to gigabit-speed
 networks.  The gist of his argument was that machines are getting
 faster and faster, while the round-trip delay of networks is staying
 relatively constant because we cannot send faster than the speed of
 light.  As a result, the effective cost of doing a simple RPC,
 measured in instruction cycles spent waiting at the sending machine,
 will become extremely high (millions of instruction cycles spent
 waiting for the reply to an RPC).  Furthermore, the methods currently
 used to improve RPC performance, such as futures and parallel RPC, do
 not adequately solve this problem.  Future requests will have to be
 made much much earlier if they are to complete by the time they are
 needed.  Parallel RPC allows multiple threads, but doesn't solve the
 fact that each individual sequence of RPCs still takes a very long
 time.
 Craig went on to suggest that there are at least two possible ways
 out of the problem.  One approach is to try to do a lot of caching
 (to waste bandwidth to keep the CPU fed).  A limitation of this
 approach is that at some point the cache becomes so big that you have
 to keep in consistent with other systems' caches, and you suddenly
 find yourself doing synchronization RPCs to avoid doing normal RPCs
 (oops!).  A more promising approach is to try to consolidate RPCs
 being sent to the same machine into larger operations which can be
 sent as a single transaction, run on the remote machine, and the
 result returned.  (Craig noted that he is pursuing this approach in
 his doctoral dissertation at Harvard).
 Ken Schroder (BBN Systems and Technologies) gave a talk on the
 challenges of combining gigabit networks with wide-area heterogeneous
 distributed operating systems.  Ken feels the key goals of wide area
 distributed systems will be to support large volume data transfers
 between users of conferencing and similar applications, and to
 deliver information to a large number of end users sharing services
 such as satellite image databases.  These distributed systems will be
 motivated by the natural distribution of users, of information and of
 expensive special purpose computer resources.
 Ken pointed to three of the key problems that must be addressed at

Partridge [Page 8] RFC 1152 IRSG Workshop Report April 1990

 the system level in these environments: how to provide high
 utilization; how to manage consistency and synchronization in the
 presence of concurrency and non-determinism; and how to construct
 scalable system and application services.  Utilization is key only to
 high performance applications, where current systems would be limited
 by the cost of factors such as repeatedly copying messages,
 converting data representations and switching between application and
 operating system.  Concurrency can be used improve performance, but
 is also likely to occur in many programs inadvertently because of
 distribution.  Techniques are required both to exploit concurrency
 when it is needed, and to limit it when non-determinism can lead to
 incorrect results.  Extensive research on ensuring consistency and
 resolving resource conflicts has been done in the database area,
 however distributed scheduling and the need for high availability
 despite partial system failures introduce special problems that
 require additional research.  Service scalability will be required to
 support customer needs as the size of the user community grow.  It
 will require attention both ensuring that components do not break
 when they are subdivided across additional processors to support a
 larger user population, and to ensure that performance does to each
 user can be affordably maintained as new users are added.
 In a bold presentation, Dave Cheriton (Stanford) made a sweeping
 argument that we are making a false dichotomy between distributed
 operating systems and networks.  In a gigabit world, he argued, the
 major resource in the system is the network, and in a normal
 operating system we would expect such a critical resource to be
 managed by the operating system.  Or, put another way, the gigabit
 network distributed operating system should manage the network.
 Cheriton went on to say that if a gigabit distributed operating
 system is managing the network, then it is perfectly reasonable to
 make the network very dumb (but fast) and put the system intelligence
 in the operating systems on the hosts that form the distributed
 system.
 In another talk on interprocess communication, Jonathan Smith (UPenn)
 again raised the problem of network delay limiting RPC performance.
 In contrast to Partridge's earlier talk, Smith argued that the
 appropriate approach is anticipation or caching.  He justified his
 argument with a simple cost example.  If a system is doing a page
 fetch between two systems which have a five millisecond round-trip
 network delay between them, the cost of fetching n pages is:
                       5 msec + (n-1) * 32 usec
 Thus the cost of fetching an additional page is only 32 usec, but
 underfetching and having to make another request to get a page you
 missed costs 5000 usec.  Based on these arguments, Smith suggested

Partridge [Page 9] RFC 1152 IRSG Workshop Report April 1990

 that we re-examine work in virtual memory to see if there are
 comfortable ways to support distributed virtual memory with
 anticipation.
 In the third talk on RPC in the session, Tommy Joseph (Olivetti), for
 reasons similar to those of Partridge and Smith, argued that we have
 to get rid of RPC and give programmers alternative programming
 paradigms.  He sketched out ideas for asynchronous paradigms using
 causal consistency, in which systems ensure that operations happen in
 the proper order, without synchronizing through a single system.

Session 6: Hosts and Host Interfaces (Gary Delp, Chair)

 Gary Delp (IBM Research) discussed several issues involved in the
 increase in speed of network attachment to hosts of increasing
 performance.  These issues included:
  1. Media Access - There are aspects of media access that are

best handled by dedicated silicon, but there are also aspects

       that are best left to a general-purpose processor.
  1. Compression - Some forms of compression/expansion may belong

on the network interface; most will be application-specific.

  1. Forward Error Correction - The predicted major packet loss

mode is packet drops due to internal network congestion, rather

       than bit errors, so forward error correction internal to a
       packet may not be useful.  On the other hand, the latency cost
       of not being able to recover from bit errors is very high.
       Some proposals were discussed which suggest that FEC among
       packet groups, with dedicated hardware support, is the way
       to go.
  1. Encryption/Decryption - This is a computationally intensive

task. Most agree that if it is done with all traffic, some

       form of hardware support is helpful.  Where does it fit in the
       protocol stack?
  1. Application Memory Mapping - How much of the host memory

structure should be exposed to the network interface?

       Virtual memory and paging complicate this issue considerably.
  1. Communication with Other Channel Controllers - Opinions were

expressed that ranged from absolutely passive network

       interfaces to interfaces that run major portions of the
       operating system and bus arbitration codes.
  1. Blocking/Segmentation - The consensus is that B/S should

Partridge [Page 10] RFC 1152 IRSG Workshop Report April 1990

       occur wherever the transport layer is processed.
  1. Routing - This is related to communications with other

controllers. A routing-capable interface can reduce the bus

       requirements by a factor of two.
  1. Intelligent participation in the host structure as a gateway,

router, or bridge.

  1. Presentation Layer issues - All of the other overheads can be

completely overshadowed by this issue if it is not solved well

       and integrated into the overall host architecture.  This points
       out the need for some standardization of representation (IEEE
       floating point, etc.)
 Eric Cooper (CMU) summarized some initial experience with Nectar, a
 high-speed fiber-optic LAN that has been built at Carnegie Mellon.
 Nectar consists of an arbitrary mesh of crossbar switches connected
 by means of 100 Mbps fiber-optic links.  Hosts are connected to
 crossbar switches via communication processor boards called CABs.
 The CAB presents a memory-mapped interface to user processes and
 off-loads all protocol processing from the host.
 Preliminary performance figures show that latency is currently
 limited by the number of VME operations required by the host-to-CAB
 shared memory interface in the course of sending and receiving a
 message.  The bottleneck in throughput is the speed of the VME
 interface: although processes running on the CABs can communicate
 over Nectar at 70 Mbps, processes on the hosts are limited to
 approximately 25 Mbps.
 Jeff Mogul (DEC Western Research Lab) made these observations:
 Although off-board protocol processors have been a popular means to
 connect a CPU to a network, they will be less useful in the future.
 In the hypothetical workstation of the late 1990s, with a 1000-MIPS
 CPU and a Gbps LAN, an off-board protocol processor will be of no
 use.  The bottleneck will not be the computation required to
 implement the protocol, but the cost of moving the packet data into
 the CPU's cache and the cost of notifying the user process that the
 data is available.  It will take far longer (hundreds of instruction
 cycles) to perform just the first cache miss (required to get the
 packet into the cache) than to perform all of the instructions
 necessary to implement IP and TCP (perhaps a hundred instructions).
 A high-speed network interface for a reasonably-priced system must be
 designed with this cost structure in mind; it should also eliminate
 as many CPU interrupts as possible, since interrupts are also very
 expensive.  It makes more sense to let a user process busy-wait on a

Partridge [Page 11] RFC 1152 IRSG Workshop Report April 1990

 network-interface flag register than to suspend it and then take an
 interrupt; the normal CPU scheduling mechanism is more efficient than
 interrupts if the network interactions are rapid.
 David Greaves (Olivetti Research Ltd.) briefly described the need for
 a total functionality interface architecture that would allow the
 complete elimination of communication interrupts.  He described the
 Cambridge high-speed ring as an ATM cell-like interconnect that
 currently runs at 500-1000 MBaud, and claims that ATM at that speed
 is a done deal.   Dave Tennenhouse also commented that ATM at high
 speeds with parallel processors is not the difficult thing that
 several others have been claiming.
 Bob Beach (Ultra Technologies) started his talk with the observation
 that networking could be really fast if only we could just get rid of
 the hosts.   He then supported his argument with illustrations of
 80-MByte/second transfers to frame buffers from Crays that drop to
 half that speed when the transfer is host-to-host.  Using null
 network layers and proprietary MAC layers, the Ultra Net system can
 communicate application-to-application with ISO TP4 as the transport
 layer at impressive rates of speed.  The key to high-speed host
 interconnects has been found to be both large packets and large (on
 the order of one megabyte) channel transfer requests.  Direct DMA
 interfaces exhibit much smaller transfer latencies.
 Derek McAuley (University Cambridge Computer Laboratory) described
 work of the Fairisle project which is producing an ATM network based
 on fast packet switches.  A RISC processor (12 MIPS) is used in the
 host interface to do segmentation/reassembly/demultiplexing.  Line
 rates of up to 150 Mbps are possible even with this modest processor.
 Derek has promised that performance and requirement results from this
 system will be published in the spring.
 Bryan Lyles (XEROX PARC) volunteered to give an abbreviated talk in
 exchange for discussion rights.  He reported that Xerox PARC is
 interested in ATM technology and wants to install an ATM LAN at the
 earliest possible opportunity.  Uses will include such applications
 as video where guaranteed quality of service (QOS) is required.  ATM
 technology and the desire for guaranteed QOS places a number of new
 constraints on the host interface.  In particular, they believe that
 they will be forced towards rate-based congestion control.  Because
 of implementation issues and burst control in the ATM switches, the
 senders will be forced to do rate based control on a cell-by-cell
 basis.
 Don Tolmie (Los Alamos National Laboratory) described the High-
 Performance Parallel Interface (HPPI) of ANSI task group X3T9.3.  The
 HPPI is a standardized basic building block for implementing, or

Partridge [Page 12] RFC 1152 IRSG Workshop Report April 1990

 connecting to, networks at the Gbps speeds, be they ring, hub,
 cross-bar, or long-haul based.  The HPPI physical layer operates at
 800 or 1600 Mbps over 25-meter twisted-pair copper cables in a
 point-to-point configuration.  The HPPI physical layer has almost
 completed the standards process, and a companion HPPI data framing
 standard is under way, and a Fiber Channel standard at comparable
 speeds is also being developed.  Major companies have completed, or
 are working on, HPPI interfaces for supercomputers, high-end
 workstations, fiber-optic extenders, and networking components.
 The discussion at the end of the session covered a range of topics.
 The appropriateness of outboard protocol processing was questioned.
 Several people agreed that outboarding on a Cray (or similar
 cost/performance) machines makes economic sense.  Van Jacobson
 contended that for workstations, a simple memory-mapped network
 interface that provides packets visible to the host processor may
 well be the ideal solution.
 Bryan Lyles reiterated several of his earlier points, asserting that
 when we talk about host interfaces and how to build them we should
 remember that we are really talking about process-to-process
 communication, not CPU-to-CPU communication.  Not all processes run
 on the central CPU, e.g., graphics processors and multimedia.
 Outboard protocol processing may be a much better choice for these
 architectures.
 This is especially true when we consider that memory/bus bandwidth is
 often a bottleneck.  When our systems run out of bandwidth, we are
 forced towards a NUMA model and multiple buses to localize memory
 traffic.
 Because of QOS issues, the receiver must be able to tell the sender
 how fast it can send.  Throwing away cells (packets) will not work
 because unwanted packets will still clog the receiver's switch
 interface, host interface, and requires processing to throw away.

Session 7: Congestion Control (Scott Shenker, Chair)

 The congestion control session had six talks.  The first two talks
 were rather general, discussing new approaches and old myths.  The
 other four talks discussed specific results on various aspects of
 packet (or cell) dropping: how to avoid drops, how to mitigate their
 impact on certain applications, a calculation of the end-to-end
 throughput in the presence of drops, and how rate-based flow control
 can reduce buffer usage.  Thumbnail sketches of the talks follow.
 In the first of the general talks, Scott Shenker (XEROX PARC)
 discussed how ideas from economics can be applied to congestion

Partridge [Page 13] RFC 1152 IRSG Workshop Report April 1990

 control.  Using economics, one can articulate questions about the
 goals of congestion control, the minimal feedback necessary to
 achieve those goals, and the incentive structure of congestion
 control.  Raj Jain (DEC) then discussed eight myths related to
 congestion control in high-speed networks.  Among other points, Raj
 argued that (1) congestion problems will not become less important
 when memory, processors, and links become very fast and cheap, (2)
 window flow control is required along with rate flow control, and (3)
 source-based controls are required along with router-based control.
 In the first of the more specific talks, Isidro Castineyra (BBN
 Communications Corporation) presented a back-of-the-envelope
 calculation on the effect of cell drops on end-to-end throughput.
 While at extremely low drop rates the retransmission strategies of
 go-back-n and selective retransmission produced similar end-to-end
 throughput, at higher drop rates selective retransmission achieved
 much higher throughput.  Next, Tony DeSimone (AT&T) told us why
 high-speed networks are not just fast low-speed networks.   If the
 buffer/window ratio is fixed, the drop rate decreases as the network
 speed increases.  Also, data was presented which showed that adaptive
 rate control can greatly decrease buffer utilization.  Jamal
 Golestani (Bellcore) then presented his work on stop-and-go queueing.
 This is a simple stalling algorithm implemented at the switches which
 guarantees no dropped packets and greatly reduces delay jitter.  The
 algorithm requires prior bandwidth reservation and some flow control
 on sources, and is compatible with basic FIFO queues.  In the last
 talk, Victor Frost (University of Kansas) discussed the impact of
 different dropping policies on the perceived quality of a voice
 connection.  When the source marks the drop priority of cells and the
 switch drops low priority cells first, the perceived quality of the
 connection is much higher than when cells are dropped randomly.

Session 8: Switch Architectures (Dave Sincoskie, Chair)

 Dave Mills (University of Delaware) presented work on a project now
 under way at the University of Delaware to study architectures and
 protocols for a high-speed network and packet switch capable of
 operation to the gigabit regime over distances spanning the country.
 It is intended for applications involving very large, very fast, very
 bursty traffic typical of supercomputing, remote sensing, and
 visualizing applications.  The network is assumed to be composed of
 fiber trunks, while the switch architecture is based on a VLSI
 baseband crossbar design which can be configured for speeds from 25
 Mbps to 1 Gbps.
 Mills' approach involves an externally switched architecture in which
 the timing and routing of flows between crossbar switches are
 determined by sequencing tables and counters in high-speed memory

Partridge [Page 14] RFC 1152 IRSG Workshop Report April 1990

 local to each crossbar.  The switch program is driven by a
 reservation-TDMA protocol and distributed scheduling algorithm
 running in a co-located, general-purpose processor.  The end-to-end
 customers are free to use any protocol or data format consistent with
 the timing of the network.  His primary interest in the initial
 phases of the project is the study of appropriate reservation and
 scheduling algorithms.  He expect these algorithms to have much in
 common with the PODA algorithm used in the SATNET and WIDEBAND
 satellite systems and to the algorithms being considered for the
 Multiple Satellite System (MSS).
 John Robinson (JR, BBN Systems and Technologies) gave a talk called
 Beyond the Butterfly, which described work on a design for an ATM
 cell switch, known as MONET.  The talk described strategies for
 buffering at the input and output interfaces to a switch fabric
 (crossbar or butterfly).  The main idea was that cells should be
 introduced to the switch fabric in random sequence and to random
 fabric entry ports to avoid persistent traffic patterns having high
 cell loss in the switch fabric, where losses arise due to contention
 at output ports or within the switch fabric (in the case of a
 butterfly).  Next, the relationship of this work to an earlier design
 for a large-scale parallel processor, the Monarch, was described.  In
 closing, JR offered the claim that this class of switch is realizable
 in current technology (barely) for operation over SONET OC-48 2.4
 Gbps links.
 Dave Sincoskie (Bellcore) reported on two topics: recent switch
 construction at Bellcore, and high-speed processing of ATM cells
 carrying VC or DG information.  Recent switch design has resulted in
 a switch architecture named SUNSHINE, a Batcher-banyan switch which
 uses recirculation and multiple output banyans to resolve contention
 and increase throughput.  A paper on this switch will be published at
 ISS '90, and is available upon request from the author.  One of the
 interesting traffic results from simulations of SUNSHINE shows that
 per-port output queues of up to 1,000 cells (packets) may be
 necessary for bursty traffic patterns.  Also, Bill Marcus (at
 Bellcore) has recently produced Batcher-banyan (32x32) chips which
 test up to 170Mb/sec per port.
 The second point in this talk was that there is little difference in
 the switching processing of Virtual Circuit (VC) and Datagram (DG)
 traffic that which has been previously broken into ATM cells at the
 network edge.  The switch needs to do a header translation operation
 followed by some queueing (not necessarily FIFO).  The header
 translation of the VC and DG cells differs mainly in the memory
 organization of the address translation tables (dense vs. sparse).
 The discussion after the presentations seemed to wander off the topic

Partridge [Page 15] RFC 1152 IRSG Workshop Report April 1990

 of switching, back to some of the source-routing vs. network routing
 issues discussed earlier in the day.

Session 9: Open Mike Night (Craig Partridge, Chair)

 As an experiment, the workshop held an open mike session during the
 evening of the second day.  Participants were invited to speak for up
 to five minutes on any subject of their choice.  Minutes of this
 session are sketchy because the chair found himself pre-occupied by
 keeping speakers roughly within their time limits.
 Charlie Catlett (NSCA) showed a film of the thunderstorm simulations
 he discussed earlier.
 Dave Cheriton (Stanford) made a controversial suggestion that perhaps
 one could manage congestion in the network simply by using a steep
 price curve, in which sending large amounts of data cost
 exponentially more than sending small amounts of data (thus leading
 people only to ask for large bandwidth when they needed it, and
 having them pay so much, that we can afford to give it to them).
 Guru Parulkar (Washington University, St. Louis) argued that the
 recent discussion on appropriateness of existing protocol and need
 for new protocols (protocol architecture) for gigabit networking
 lacks the right focus.  The emphasis of the discussion should be on
 what is the right functionality for gigabit speeds, which is simpler
 per packet processing, combination of rate and window based flow
 control, smart retransmission strategy, appropriate partitioning of
 work among host cpu+os, off board cpu, and custom hardware, and
 others.  It is not surprising that the existing protocols can be
 modified to include this functionality.  By the same token, it is not
 surprising that new protocols can be designed which take advantage of
 lessons of existing protocols and also include other features
 necessary for gigabit speeds.
 Raj Jain (DEC) suggested we look at new ways to measure protocol
 performance, suggesting our current metrics are insufficiently
 informative.
 Dan Helman (UCSC) asked the group to consider, more carefully, who
 exactly the users of the network will be.  Large consumers? or many
 small consumers?

Partridge [Page 16] RFC 1152 IRSG Workshop Report April 1990

Session 10: Miscellaneous Topics (Bob Braden, Chair)

 As its title implies, this session covered a variety of different
 topics relating to high-speed networking.
 Jim Kurose (University of Massachussetts) described his studies of
 scheduling and discard policies for real-time (constrained delay)
 traffic.  He showed that by enforcing local deadlines at switches
 along the path, it is possible to significantly reduce overall loss
 for such traffic.  Since his results depend upon the traffic model
 assumptions, he ended with a plea for work on traffic models, stating
 that Poisson models can sometimes lead to results that are wrong by
 many orders of magnitude.
 Nachum Shacham (SRI International) discussed the importance of error
 correction schemes that can recover lost cells, and as an example
 presented a simple scheme based upon longitudinal parity.  He also
 showed a variant, diagonal parity, which allows a single missing cell
 to be recreated and its position in the stream determined.
 Two talks concerned high-speed LANs.  Biswanath Muhkerjee (UC Davis)
 surveyed the various proposals for fair scheduling on unidirectional
 bus networks, especially those that are distance insensitive, i.e.,
 that can achieve 100% channel utilization independent of the bus
 length and data rate.  He described in particular his own scheme,
 which he calls p-i persistant.
 Howard Salwen (Proteon), speaking in place of Mehdi Massehi of IBM
 Zurich who was unable to attend, also discussed high-speed LAN
 technologies.  At 100 Mbps, a token ring has a clear advantage, but
 at 1 Gbps, the speed of light kills 802.6, for example.  He briefly
 described Massehi's reservation-based scheme, CRMA (Cyclic-
 Reservation Multiple-Access).
 Finally, Yechiam Yemeni (YY, Columbia University) discussed his work
 on a protocol silicon compiler.  In order to exploit the potential
 parallelism, he is planning to use one processor per connection.
 The session closed with a spirited discussion of about the relative
 merits of building an experimental network versus simulating it.
 Proponents of simulation pointed out the high cost of building a
 prototype and limitation on the solution space imposed by a
 particular hardware realization.  Proponents of building suggested
 that artificial traffic can never explore the state space of a
 network as well as real traffic can, and that an experimental
 prototype is important for validating simulations.

Partridge [Page 17] RFC 1152 IRSG Workshop Report April 1990

Session 11: Protocol Architectures (Vint Cerf, Chair)

 Nick Maxemchuk (AT&T Bell Labs) summarized the distinctions between
 circuit switching, virtual circuits, and datagrams.  Circuits are
 good for (nearly) constant rate sources.  Circuit switching dedicates
 resources for the entire period of service.  You have to set up the
 resource allocation before using it.  In a 1.7 Gbps network, a 3000-
 mile diameter consumes 10**7 bytes during the circuit set-up round-
 trip time, and potentially the same for circuit teardown.  Some
 service requirements (file transfer, facsimile transmission) are far
 smaller than the wasted 2*10**7 bytes these circuit management delays
 impose.  (Of course, these costs are not as dramatic if the allocated
 bandwidth is less than the maximum possible.)
 Virtual circuits allow shared use of bandwidth (multiplexing) when
 the primary source of traffic is idle (as in Voice Time Assigned
 Speech Interpolation).  The user notifies the network of planned
 usage.
 Datagrams (DG) are appropriate when there is no prior knowledge of
 use statistics or usage is far less than the capacity wasted during
 circuit or virtual circuit set-up.  One can adaptively route traffic
 among equivalent resources.
 In gigabit ATMs, the high service speed and decreased cell size
 increases the relative burstiness of service requests.  All of these
 characteristics combine to make DG service very attractive.
 Maxemchuk then described a deflection routing notion in which traffic
 would be broken into units of fixed length and allowed into the
 network when capacity was available and routed out by any available
 channel, with preference being given to the channel on the better
 path.  This idea is similar to the hot potato routing of Paul Baran's
 1964 packet switching design.  With buffering (one buffer), Maxemchuk
 achieved a theoretical 90% utilization.  Large reassembly buffers
 provide for better throughput.
 Maxemchuk did not have an answer to the question: how do you make
 sure empty "slots" are available where needed? This is rather like
 the problem encountered by D. Davies at the UK National Physical
 Laboratory in his isarythmic network design in which a finite number
 of crates are available for data transport throughout the network.
 Guru Parulkar (Washington University, St. Louis) presented a broad
 view of an Internet architecture in which some portion of the system
 would operate at gigabit speeds.  In his model, internet, transport,
 and application protocols would operate end to end.  The internet
 functions would be reflected in gateways and in the host/net

Partridge [Page 18] RFC 1152 IRSG Workshop Report April 1990

 interface, as they are in the current Internet.  However, the
 internet would support a new type of service called a congram which
 aims at combining strengths of both soft connection and datagram.
 In this architecture, a variable grade of service would be provided.
 Users could request congrams (UCON) or the system could set them up
 internally (Picons) to avoid end-to-end setup latency.  The various
 grades of service could be requested, conceptually, by asserting
 various required (desired) levels of error control, throughput,
 delay, interarrival jitter, and so on.  Gateways based on ATM
 switches, for example, would use packet processors at entry/exit to
 do internet specific per packet processing, which may include
 fragmentation and reassembly of packets (into and out of ATM cells).
 At the transport level, Parulkar argued for protocols which can
 provide application-oriented flow and error control with simple per
 packet processing.  He also mentioned the notion of a generalized RPC
 (GRPC) in which code, data, and execution might be variously local or
 remote from the procedure initiator.  GRPC can be implemented using
 network level virtual storage mechanisms.
 The basic premise of Raj Yavatkar's presentation (University of
 Kentucky) was that processes requiring communication service would
 specify their needs in terms of peak and average data rate as well as
 defining burst parameters (frequency and size).  Bandwidth for a
 given flow would be allocated at the effective data rate that is
 computed on the basis of flow parameters.  The effective data rate
 lies somewhere between the peak and average data rate based on the
 burst parameters.  Statistical multiplexing would take up the gap
 between peak and effective rate when a sudden burst of traffic
 arrives.  Bounds on packet loss rate can be computed for a given set
 of flow parameters and corresponding effective data rate.
 This presentation led to a discussion about deliberate disciplining
 of inter-process communication demands to match the requested flow
 (service) profile.  This point was made in response to the
 observation that we often have little information about program
 behavior and might have trouble estimating the network service
 requirements of any particular program.

Architectural Discussion

 An attempt was made to conduct a high-level discussion on various
 architectural questions.  The discussion yielded a variety of
 opinions:
    1.  The Internet would continue to exist in a form similar
        to its current incarnation, and gateways would be required,

Partridge [Page 19] RFC 1152 IRSG Workshop Report April 1990

        at least to interface the existing facilities to the high
        speed packet switching environment.
    2.  Strong interest was expressed by some participants in access
        to raw (naked ATM) services.  This would permit users
        to construct their own gigabit nets, at the IP level, at any
        rate.  The extreme view of this was taken by David Cheriton
        who would prefer to have control over routing decisions and
        other behavior of the ATM network.
    3.  The speed of light problem (latency, round-trip delay)
        is not going to go away and will have serious impact on
        control of the system.  The optimistic view was taken,
        for example, by Craig Partridge and Van Jacobson, who felt
        that many of the existing network and communications
        management mechanisms used in the present Internet protocols
        would suffice, if suitably implemented, at higher speeds.
        A less rosy view was taken by David Clark who observed
        (as did others) that many transactions would be serviced in
        much less than one round-trip time, so that any end-to-end
        controls would be largely useless.
    4.  For applications requiring fixed, periodic service,
        reservation of resource seemed reasonably attractive to many
        participants, as long as the service period dominated the
        set-up time (round-trip delay) by an appreciable
        margin.
    5.  There was much discussion throughout the workshop of
        congestion control and flow control.  Although these
        problems were not new, they took on somewhat newer
        character in the presence of much higher round-trip delays
        (measured in bits outstanding).  One view is that end-to-end
        flow control is needed, in any case, to moderate sources
        sending to limited bandwidth receivers.  End-to-end flow
        control may not, however, be sufficient to protect the
        interior of the network from congestion problems, so
        additional, intra-network means are needed to cope with
        congestion hot spots.   Eventually such conditions
        have to be reflected to the periphery of the network to
        moderate traffic sources.
    6.  There was disagreement on the build or simulate
         question.  One view was in favor of building network
        components so as to collect and understand live application
        data.  Another view held that without some careful
        simulation, one might have little idea what to build
        (for example, Sincoskie's large buffer pool requirement was

Partridge [Page 20] RFC 1152 IRSG Workshop Report April 1990

        not apparent until the system was simulated).

Comments from Workshop Evaluation Forms

 At the end of the IRSG workshop, we asked attendees to fill out an
 evaluation form.  Of the fifty-one attendees, twenty-nine (56%)
 turned in a form.
 The evaluation form asked attendees to answer two questions:
    #1.  Do you feel that having attended this workshop will help you
         in your work on high speed networks during the next year?
    #2.  What new ideas, questions, or issues, did you feel were
         brought up in the workshop?
 In this section we discuss the answers we got to both questions.

Question #1

 There was a satisfying unanimity of opinion on question #1.  Twenty-
 four attendees answered yes, often strongly (e.g., Absolutely and
 very much so).  Of the remaining five respondents, three said they
 expected it to have some effect on their research and only two said
 the workshop would have little or no effect.
 Some forms had some additional notes about why the workshop helped
 them.  Several people mentioned that there was considerable benefit
 to simply meeting and talking with people they hadn't met before.  A
 few other people noted that the workshop had broadened their
 perspective, or improved their understanding of certain issues.  A
 couple of people noted that they'd heard ideas they thought they
 could use immediately in their research.

Question #2

 Almost everyone listed ideas they'd seen presented at the conference
 which were new to them.
 It is clear that which new ideas were important was a matter of
 perspective - the workshop membership was chosen to represent a broad
 spectrum of specialties, and people in different specialities were
 intrigued by different ideas.  However, there were some general
 themes raised in many questionnaires:
    (1)  Limitations of our traffic models.  This particular subject
         was mentioned, in some form, on many forms.  The attendees

Partridge [Page 21] RFC 1152 IRSG Workshop Report April 1990

         generally felt we didn't understand how network traffic would
         behave on a gigabit network, and were concerned that people
         might design (or worse, standardize) network protocols for
         high speed networks that would prove inadequate when used
         with real traffic.  Questions were raised about closed-loop
         vs. open-loop traffic models and the effects of varying types
         of service.  This concern led several people to encourage the
         construction of a high-speed testbed, so we can actually see
         some real traffic.
    (2)  Congestion control.  Despite the limitations of our traffic
         models, respondents felt that congestion control at both
         switching elements and network wide was going to be even more
         important than today, due to the wider mix of traffic that
         will appear on gigabit networks.  Most forms mentioned at
         least one of the congestion control talks as a containing a
         new idea.  The talks by Victor Frost, Jamal Golestani and
         Scott Shenker received the most praise.  Some attendees were
         also interested in methods for keeping the lower-layer
         switching fabric from getting congested and mentioned the
         talks by Robinson and Maxemchuk as of interest.
    (3)  Effects of fixed delay.  While the reviews were by no means
         unanimous, many people had come to the conclusion that the
         most serious problem in gigabit networking was not bandwidth,
         but delay.  The workshop looked at this issue in several
         guises, and most people listed at least one aspect of fixed
         delay as a challenging new problem.  Questions that people
         mentioned include:
  1. How to avoid a one round-trip set up delay, for less than one

round-trip time's worth of data?

  1. How to recover from error without retransmission (and thus

additional network delays)? Several people were intrigued by

       Nachum Shacham's work on error detection and recovery.
  1. Should we use window flow-control or rate-based flow control

when delays were long?

  1. Can we modify the idea of remote procedure calls to deal with

the fact that delays are relatively long?

A couple of attendees noted that while some of these problems looked similar to those of today, the subtle differences caused by operating a network at gigabit speeds led them to believe the actual approaches to solving these problems would have to be very different from those of

Partridge [Page 22] RFC 1152 IRSG Workshop Report April 1990

today.

Security Considerations

 Security issues are not discussed in this memo.

Author's Address

 Craig Partridge
 Bolt Beranek and Newman Inc.
 50 Moulton Street
 Cambridge, MA 02138
 Phone: (617) 873-2459
 EMail: craig@BBN.COM

Partridge [Page 23]

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