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Network Working Group                                       C. PartridgeRequest for Comments: 1152                  BBN Systems and Technologies                                                              April 1990Workshop ReportInternet Research Steering Group Workshop onVery-High-Speed NetworksStatus 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 cleverPartridge                                                       [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 1990Session 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 toPartridge                                                       [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 1990Session 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 routingPartridge                                                       [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 atPartridge                                                       [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 suggestedPartridge                                                       [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:      -  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.      -  Compression - Some forms of compression/expansion may belong         on the network interface; most will be application-specific.      -  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.      -  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?      -  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.      -  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.      -  Blocking/Segmentation - The consensus is that B/S shouldPartridge                                                      [Page 10]

RFC 1152                  IRSG Workshop Report                April 1990         occur wherever the transport layer is processed.      -  Routing - This is related to communications with other         controllers.  A routing-capable interface can reduce the bus         requirements by a factor of two.      -  Intelligent participation in the host structure as a gateway,         router, or bridge.      -  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 aPartridge                                                      [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, orPartridge                                                      [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 congestionPartridge                                                      [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 memoryPartridge                                                      [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 topicPartridge                                                      [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 1990Session 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 1990Session 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/netPartridge                                                      [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 wasPartridge                                                      [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 attendeesPartridge                                                      [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:    -    How to avoid a one round-trip set up delay, for less than one         round-trip time's worth of data?    -    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.    -    Should we use window flow-control or rate-based flow control         when delays were long?    -    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 lookedsimilar to those of today, the subtle differences caused by operating anetwork at gigabit speeds led them to believe the actual approaches tosolving these problems would have to be very different from those ofPartridge                                                      [Page 22]

RFC 1152                  IRSG Workshop Report                April 1990today.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.COMPartridge                                                      [Page 23]