brian@ucsd.EDU (Brian Kantor) (12/20/88)
Network Working Group Gigabit Working Group Request for Comments: 1077 B. Leiner, Editor November 1988 Critical Issues in High Bandwidth Networking Status of this Memo This memo presents the results of a working group on High Bandwidth Networking. This RFC is for your information and you are encouraged to comment on the issues presented. Distribution of this memo is unlimited. ABSTRACT At the request of Maj. Mark Pullen and Maj. Brian Boesch of DARPA, an ad-hoc working group was assembled to develop a set of recommendations on the research required to achieve a ubiquitous high-bandwidth network as discussed in the FCCSET recommendations for Phase III. This report outlines a set of research topics aimed at providing the technology base for an interconnected set of networks that can provide highbandwidth capabilities. The suggested research focus draws upon ongoing research and augments it with basic and applied components. The major activities are the development and demonstration of a gigabit backbone network, the development and demonstration of an interconnected set of networks with gigabit throughput and appropriate management techniques, and the development and demonstration of the required overall architecture that allows users to gain access to such high bandwidth. Gigabit Working Group [Page 1] RFC 1077 November 1988 1. Introduction and Summary 1.1. Background The computer communications world is evolving toward both high- bandwidth capability and high-bandwidth requirements. The recent workshop conducted under the auspices of the FCCSET Committee on High Performance Computing [1] identified a number of areas where extremely high-bandwidth networking is required to support the scientific research community. These areas range from remote graphical visualization of supercomputer results through the movement of high rate sensor data from space to the ground-based scientific investigator. Similar requirements exist for other applications, such as military command and control (C2) where there is a need to quickly access and act on data obtained from real-time sensors. The workshop identified requirements for switched high-bandwidth service in excess of 300 Mbit/s to a single user, and the need to support service in the range of a Mbit/s on a low-duty-cycle basis to millions of researchers. When added to the needs of the military and commercial users, the aggregate requirement for communications service adds up to many billions of bits per second. The results of this workshop were incorporated into a report by the FCCSET [2]. Fortunately, technology is also moving rapidly. Even today, the installed base of fiber optics communications allows us to consider aggregate bandwidths in the range of Gbit/s and beyond to limited geographical regions. Estimates arrived at in the workshop lead one to believe that there will be available raw bandwidth approaching terabits per second. The critical question to be addressed is how this raw bandwidth can be used to satisfy the requirements identified in the workshop: 1) provide bandwidth on the order of several Gbit/s to individual users, and 2) provide modest bandwidth on the order of several Mbit/s to a large number of users in a cost-effective manner through the aggregation of their traffic. Through its research funding, the Defense Advanced Research Projects Agency (DARPA) has played a central role in the development of packet-oriented communications, which has been of tremendous benefit to the U.S. military in terms of survivability and interoperability. DARPA-funded research has resulted in the ARPANET, the first packet- switched network; the SATNET, MATNET and Wideband Network, which demonstrated the efficient utilization of shared-access satellite channels for communications between geographically diverse sites; Gigabit Working Group [Page 2] RFC 1077 November 1988 packet radio networks for mobile tactical environments; the Internet and TCP/IP protocols for interconnection and interoperability between heterogeneous networks and computer systems; the development of electronic mail; and many advances in the areas of network security, privacy, authentication and access control for distributed computing environments. Recognizing DARPA's past accomplishments and its desire to continue to take a leading role in addressing these issues, this document provides a recommendation for research topics in gigabit networking. It is meant to be an organized compendium of the critical research issues to be addressed in developing the technology base needed for such a high bandwidth ubiquitous network. 1.2. Ongoing Activities The OSTP report referred to above recommended a three-phase approach to achieving the required high-bandwidth networking for the scientific and research community. Some of this work is now well underway. An ad-hoc committee, the Federal Research Internet Coordinating Committee (FRICC) is coordinating the interconnection of the current wide area networking systems in the government; notably those of DARPA, Department of Energy (DoE), National Science Foundation (NSF), National Aeronautics and Space Administration (NASA), and the Department of Health and Human Services (HHS). In accordance with Phases I and II of the OSTP report, this activity will provide for an interconnected set of networks to support research and other scholarly pursuits, and provide a basis for future networking for this community. The networking is being upgraded through shared increased bandwidth (current plans are to share a 45 Mbit/s backbone) and coordinated interconnection with the rest of the world. In particular, the FRICC is working with the European networking community under the auspices of another ad-hoc group, the Coordinating Committee for Intercontinental Research Networks (CCIRN), to establish effective US-Europe networking. However, as the OSTP recommendations note, the required bandwidth for the future is well beyond currently planned public, private, and government networks. Achieving the required gigabit networking capabilities will require a strong research activity. There is considerable ongoing research in relevant areas that can be drawn upon; particularly in the areas of high-bandwidth communication links, high-speed computer switching, and high-bandwidth local area networks. Appendix A provides some pointers to current research efforts. Gigabit Working Group [Page 3] RFC 1077 November 1988 1.3. Document Overview This report outlines a set of research topics aimed at providing the technology base for an interconnected set of networks that can provide the required high-bandwidth capabilities discussed above. The suggested research focus draws upon ongoing research and augments it with basic and applied components. The major activities are the development and demonstration of a Gigabit Backbone network (GB) [3], the development and demonstration of an interconnected set of networks with gigabit throughput and appropriate management techniques, and the development and demonstration of the required overall architecture that allows users to gain access to such high bandwidth. Section 2 discusses functional and performance goals along with the anticipated benefits to the ultimate users of such a system. Section 3 provides the discussion of the critical research issues needed to achieve these goals. It is organized into the major areas of technology that need to be addressed: general architectural issues, high-bandwidth switching, high-bandwidth host interfaces, network management algorithms, and network services. The discussion in some cases contains examples of ongoing relevant research or potential approaches. These examples are intended to clarify the issues and not to propose that particular approach. A discussion of the relationship of the suggested research to other ongoing activities and optimal methods for pursuing this research is provided in Section 4. 2. Functional and Performance Goals In this section, we provide an assessment of the types of services a GN (four or five orders of magnitude faster than the current networks) should provide to its users. In instances where we felt there would be a significant impact on performance, we have provided an estimate of the amount of bandwidth needed and delay allowable to provide these services. 2.1. Networking Application Support It is envisioned that the GN will be capable of supporting all of the following types of networking applications. Gigabit Working Group [Page 4] RFC 1077 November 1988 Currently Provided Packet Services It is important that the network provide the users with the equivalent of services that are already available in packet- switched networks, such as interactive data exchange, mail service, file transfer, on-line access to remote computing resources, etc., and allow them to expand to other more advanced services to meet their needs as they become available. Multi-Media Mail This capability will allow users to take advantage of different media types (e.g., graphics, images, voice, and video as well as text and computer data) in the transfer of messages, thereby increasing the effectiveness of message exchange. Multi-Media Conferencing Such conferencing requires the exchange of large amounts of information in short periods of time. Hence the requirement for high bandwidth at low delay. We estimate that the bandwidth would range from 1.5 to 100 Mbit/s, with an end-to-end delay of no more than a few hundred msec. Computer-Generated Real-time Graphics Visualizing computer results in the modern world of supercomputers requires large amounts of real time graphics. This in turn will require about 1.5 Mbit/s of bandwidth and no more than several hundred msec. delay. High-Speed Transaction Processing One of the most important reasons for having an ultra-high-speed network is to take advantage of supercomputing capability. There are several scenarios in which this capability could be utilized. For example, there could be instances where a non-supercomputer may require a supercomputer to perform some processing and provide some intermediate results that will be used to perform still further processing, or the exchange may be between several supercomputers operating in tandem and periodically exchanging results, such as in a battle management, war gaming, or process control applications. In such cases, extremely short response times are necessary to accomplish as many as hundreds of interactions in real time. This requires very high bandwidth, on the order of 100 Mbit/s, and minimum delay, on the order of hundreds of msec. Gigabit Working Group [Page 5] RFC 1077 November 1988 Wide-Area Distributed Data/Knowledge Base Management Systems Computer-stored data, information, and knowledge is distributed around the country for a variety of reasons. The ability to perform complex queries, updates, and report generation as though many large databases are one system would be extremely powerful, yet requires low-delay, high-bandwidth communication for interactive use. The Corporation for National Research Initiatives (NRI) has promoted the notion of a National Knowledge base with these characteristics. In particular, an attractive approach is to cache views at the user sites, or close by to allow efficient repeated queries and multi-relation processing for relations on different nodes. However, with caching, a processing activity may incur a miss in the midst of a query or update, causing it to be delayed by the time required to retrieve the missing relation or portion of relation. To minimize the overhead for cache directories, both at the server and client sites, the unit of caching should be large---say a megabyte or more. In addition, to maintain consistency at the caching client sites, server sites need to multicast invalidations and/or updates. Communication requirements are further increased by replication of the data. The critical parameter is latency for cache misses and consistency operations. Taking the distance between sites to be on average 1/4 the diameter of the country, a one Gbit/s data rate is required to reduce the transmission time to be roughly the same as the propagation delay, namely around 8 milliseconds for this size of unit. Note that this application is supporting far more sophisticated queries and updates than normally associated with transaction processing, thus requiring larger amount of data to be transferred. 2.2. Types of Traffic and Communications Modes Different types of traffic may impose different constraints in terms of throughput, delay, delay dispersion, reliability and sequenced delivery. Table 1 summarizes some of the main characteristics of several different types of traffic. Gigabit Working Group [Page 6] RFC 1077 November 1988 Table 1: Communication Traffic Requirements +------------------------+-------------+-------------+-------------+ | | | | Error-free | | Traffic | Delay | Throughput | Sequenced | | Type | Requirement | Requirement | Delivery | +------------------------+-------------+-------------+-------------+ | Interactive Simulation | Low |Moderate-High| No | +------------------------+-------------+-------------+-------------+ | Network Monitoring | Moderate | Low | No | +------------------------+-------------+-------------+-------------+ | Virtual Terminal | Low | Low | Yes | +------------------------+-------------+-------------+-------------+ | Bulk Transfer | High | High | Yes | +------------------------+-------------+-------------+-------------+ | Message | Moderate | Moderate | Yes | +------------------------+-------------+-------------+-------------+ | Voice |Low, constant| Moderate | No | +------------------------+-------------+-------------+-------------+ | Video |Low, constant| High | No | +------------------------+-------------+-------------+-------------+ | Facsimile | Moderate | High | No | +------------------------+-------------+-------------+-------------+ | Image Transfer | Variable | High | No | +------------------------+-------------+-------------+-------------+ | Distributed Computing | Low | Variable | Yes | +------------------------+-------------+-------------+-------------+ | Network Control | Moderate | Low | Yes | +------------------------+-------------+-------------+-------------+ The topology among users can be of three types: point-to-point (one- to-one connectivity), multicast (one sender and multiple receivers), and conferencing (multiple senders and multiple receivers). There are three types of transfers that can take place among users. They are connection-oriented network service, connectionless network service, and stream or synchronous traffic. Connection and connectionless services are asynchronous. A connection-oriented service assumes and provides for relationships among the multiple packets sent over the connection (e.g., to a common destination) while connectionless service assumes each packet is a complete and separate entity unto itself. For stream or synchronous service a reservation scheme is used to set up and guarantee a constant and steady amount of bandwidth between any two subscribers. Gigabit Working Group [Page 7] RFC 1077 November 1988 2.3. Network Backbone The GB needs to be of high bandwidth to support a large population of users, and additionally to provide high-speed connectivity among certain subscribers who may need such capability (e.g., between two supercomputers). These users may access the GN from local area networks (LANs) directly connected to the backbone or via high-speed intermediate regional networks. The backbone must also minimize end-to-end delay to support highly interactive high-speed (supercomputer) activities. It is important that the LANs that will be connected to the GN be permitted data rates independent of the data rates of the GB. LAN speeds should be allowed to change without affecting the GB, and the GB speeds should be allowed to change without affecting the LANs. In this way, development of the technology for LANs and the GB can proceed independently. Access rate requirements to the GB and the GN will vary depending on user requirements and local environments. The users may require access rates ranging from multi-kbit/s in the case of terminals or personal computers connected by modems up to multi-Mbit/s and beyond for powerful workstations up to the Gbit/s range for high-speed computing and data resources. 2.4. Directory Services Directory services similar to those found in CCITT X.500/ISO DIS 9594 need to be provided. These include mapping user names to electronic mail addresses, distribution lists, support for authorization checking, access control, and public key encryption schemes, multimedia mail capabilities, and the ability to keep track of mobile users (those who move from place to place and host computer to host computer). The directory services may also list facilities available to users via the network. Some examples are databases, supercomputing or other special-purpose applications, and on-line help or telephone hotlines. The services provided by X.500 may require some extension for GN. For example, there is no provision for multilevel security, and the approach taken to authentication must be studied to ensure that it meets the requirements of GN and its user community. Gigabit Working Group [Page 8] RFC 1077 November 1988 2.5. Network Management and Routing The objective of network management is to ensure that the network functions smoothly and efficiently, and consists of the following: accounting, security, performance monitoring, fault isolation and configuration control. Accounting ensures that users are properly billed for the services that the network provides. Accounting enforces a tariff; a tariff expresses a usage policy. The network need only keep track of those items addressed by the tariff, such as allocated bandwidth, number of packets sent, number of ports used, etc. Another type of accounting may need to be supported by the network to support resource sharing, namely accounting analogous to telephone "900" numbers. This accounting performed by the network on behalf of resource providers and consumers is a pragmatic solution to the problem of getting the users and consumers into a financial relationship with each other which has stymied previous attempts to achieve widespread use of specialized resources. Performance monitoring is needed so that the managers can tell how the network is performing and take the necessary actions to keep its performance at a level that will provide users with satisfactory service. Fault isolation using technical control mechanisms is needed for network maintenance. Configuration management allows the network to function efficiently. Several new types of routing will be required by GN. In addition to true type-of-service, needed to support diverse distributed applications, real-time applications, interactive applications, and bulk data transfer, there will be need for traffic controls to enforce various routing policies. For example, policy may dictate that traffic from certain users, applications, or hosts may not be permitted to traverse certain segments of the network. Alternatively, traffic controls may be used to promote fairness; that is, to make sure that busy link or network segment isn't dominated by a particular source or destination. The ability of applications to reserve network bandwidth in advance of its use, and the use of strategies such as soft connections, will also require development of new routing algorithms. 2.6. Network Security Requirements Security is a critical factor within the GN and one of those features that are difficult to provide. It is envisioned that both Gigabit Working Group [Page 9] RFC 1077 November 1988 unclassified and classified traffic will utilize the GN, so protection mechanisms must be an integral part of the network access strategy. Features such as authentication, integrity, confidentiality, access control, and nonrepudiation are essential to provide trusted and secure communication services for network users. A subscriber must have assurance that the person or system he is exchanging information with is indeed who he says he is. Authentication provides this assurance by verifying that the claimed source of a query request, control command, response, etc., is the actual source. Integrity assures that the subscriber's information (such as requests, commands, data, responses, etc.) is not changed, intentionally or unintentionally, while in transit or by replays of earlier traffic. Unauthorized users (e.g., intruders or network viruses) would be denied use of GN assets through access control mechanisms which verify that the authenticated source is authorized to receive the requested information or to initiate the specified command. In addition, nonrepudiation services can be offered to assure a third party that the transmitted information has not been altered. And finally, confidentiality will ensure that the contents of a message are not divulged to unauthorized individuals. Subscribers can decide, based upon their own security needs and particular activities, which of these services are necessary at a given time. 3. Critical Research Issues In the section above, we discussed the goals of a research program in gigabit networking; namely to provide the technology base for a network that will allow gigabit service to be provided in an effective way. In this section, we discuss those issues which we feel are critical to address in a research program to achieve such goals. 3.1. General Architectural Issues In the last generation of networks, it was assumed that bandwidth was the scarce resource and the design of the switch was dictated by the need to manage and allocate the bandwidth effectively. The most basic change in the next generation network is that the speeds of the trunks are rising faster than the speeds of the switching elements. This change in the balance of speeds has manifested itself in several ways. In most current designs for local area networks, where Gigabit Working Group [Page 10] RFC 1077 November 1988 bandwidth is not expensive, the design decision was to trade off effective use of the bandwidth for a simplified switching technique. In particular, networks such as Ethernet use broadcast as the normal distribution method, which essentially eliminates the need for a switching element. As we look at still higher speed networks, and in particular networks in which the bandwidth is still the expensive component, we must design new options for switching which will permit effective use of bandwidth without the switch itself becoming the bottleneck. The central thrust of new research must thus be to explore new network architectures that are consistent with these very different speed assumptions. The development of computer communications has been tremendously distorted by the characteristics of wide-area networking: normally high cost, low speed, high error rate, large delay. The time is ripe for a revolution in thinking, technology, and approaches, analogous to the revolution caused by VCR technology over 8 and 16 mm. film technology. Fiber optics is clearly the enabling technology for high-speed transmission, in fact, so much so that there is an expectation that the switching elements will now hold down the data rates. Both conventional circuit switching and packet switching have significant problems at higher data rates. For instance, circuit switching requires increasing delays for FTDM synchronization to handle skew. In the case of packet switching, traditional approaches require too much processing per packet to handle the tremendous data flow. The problem for both switching regimes is the "intelligence" in the switches, which in turn requires electronics technology. Besides intelligence, another problem for wide-area networks is storage, both because it ties us to electronics (for the foreseeable future) and because it produces instabilities in a large-scale system. (See, for instance, the work by Van Jacobson on self- organizing phenomena for self-destruction in the Internet.) Techniques are required to eliminate dependence on storage, such as cut-through routing. Overall, high-speed WANs are the greatest agents of change, the greatest catalyst both commercially and militarily, and the area ripe for revolution. Judging by the attributes of current high-speed network research prototypes, WANs of the future will be photonic, multi-gigabit networks with enormous throughput, low delay, and low error rate. Gigabit Working Group [Page 11] RFC 1077 November 1988 A zero-based budgeting approach is required to develop the new high- speed internetwork architecture. That is, the time is ripe to significantly rethink the Internet, building on experience with this system. Issues of concern are manageability, understanding evolvability and support for the new communication requirements, including remote procedure call, real-time, security and fault- tolerance. The GN must be able to deal with two sources of high-bandwidth requirements. There will be some end devices (computers) connected more or less directly to the GN because of their individual requirements for high bandwidth (e.g., supercomputers needing to drive remote high-bandwidth graphics devices). In addition, the aggregate traffic due to large numbers of moderate rate users (estimates are roughly up to a million potential users needing up to 1 Mbit/s at any given time) results in a high-bandwidth requirement in total on the GN. The statistics of such traffic are different and there are different possible technical approaches for dealing with them. Thus, an architectural approach for dealing with both must be developed. Overall, the next-generation architecture has to be, first and foremost, a management architecture. The directions in link speeds, processor speeds and memory solve the performance problems for many communication situations so well that manageability becomes the predominant concern. (In fact, fast communication makes large systems more prone to performance, reliability, and security problems.) In many ways, the management system of the internetwork is the ultimate distributed system. The solution to this tough problem may well require the best talents from the communications, operating systems and distributed systems communities, perhaps even drawing on database and parallelism research. 3.1.1. High-Speed Internet using High-Speed Networks The GN will need to take advantage of a multitude of different and heterogeneous networks, all of high speed. In addition to networks based on the technology of the GB, there will be high-speed LANs. A key issue in the development of the GN will be the development of a strategy for interconnecting such networks to provide gigabit service on an end to end basis. This will involve techniques for switching, interfacing, and management (as discussed in the sections below) coupled with an architecture that allows the GN to take full advantage of the performance of the various high-speed networks. Gigabit Working Group [Page 12] RFC 1077 November 1988 3.1.2. Network Organization The GN will need an architecture that supports the need to manage the system as well as obtain high performance. We note that almost all human-engineered systems are hierarchically structured from the standpoint of control, monitoring, and information flow. A hierarchical design may be the key to manageability in the next- generation architecture. One approach is to use a general three-level structure, corresponding to interadministrational, intraadministrational, and cluster networks. The first level interconnects communication facilities of truly separate administrations where there is significant separation of security, accounting, and goals. The second level interconnects subadministrations which exist for management convenience in large organizations. For example, a research group within a university may function as a subadministration. The cluster level consists of networks configured to provides maximal performance among hosts which are in frequent communication, such as a set of diskless workstations and their common file server. These hosts are typically, but not necessarily, geographically collocated. For example, two remote networks may be tightly coupled by a fiber optic link that bridges between the two physical networks, making them function as one. Research along these lines should study the interorganizational characteristics of communications, such as those being investigated by the IAB Task Force on Autonomous Networks. Based on current results, we expect that such work would clearly demonstrate that considerable communication takes place between particular subadministrations in different administrations; communication patterns are not strictly hierarchical. For example, there might be intense direct communication between the experimental physics departments of two independent universities, or between the computer support group of one company and the operating system development group of another. In addition, (sub)administrations may well also require divisions into public information and private information. 3.1.3. Fault-Tolerant System Although the GN will be developed as part of an experimental research program, it will also serve as part of the infrastructure for researchers who are experimenting with applications which will use such a network. The GN must have reasonably high availability to support these research activities. In addition to facilitate the transfer of this technology to future operational military and Gigabit Working Group [Page 13] RFC 1077 November 1988 commercial users, it will need to be designed to become highly reliable. This can be accomplished through diversity of transmission paths, the development of fault-tolerant switches, use of a distributed control structure with self-correcting algorithms, and the protection of network control traffic. The architecture of a GN should support and allow for all of these things. 3.1.4. Functional Division of Control Between Network Elements Current protocol architectures use the layered model of functional decomposition first developed in the early work on ARPANET protocols. The concept of layering has been a powerful concept which has allowed dramatic variation in network technologies without requiring the complete reimplementation of applications. The concept of layering has had a first-order impact on the development of international standards for data communication---witness the ISO "Reference Model for Open Systems Interconnection." Unfortunately, however, the powerful concept of layering has been paired, both in the DoD Internet work and the ISO work, with an extremely weak concept of the interface between layers. The interface designs are all organized around the idea of commands and responses plus an error indicator. For example, the TCP service interface provides the user with commands to set up or close a TCP connection and commands to send and receive datagrams. The user may well "know" whether they are using a file transfer service or a character-at-a- time virtual terminal, but can't tell the TCP. The underlying network may "know" that failures have reduced the path to the user's destination to a single 9.6 kbit/s link, but it also can't tell the TCP implementation. All of the information that an analyst would consider crucial in diagnosing system performance is carefully hidden from adjacent layers. One "solution" often discussed (but rarely implemented) is to condense all of this information into a few bits of "Type of Service" or "Quality of Service" request flowing in one direction only---from application to network. It seems likely that this approach cannot succeed, both because it applies too much compression to the knowledge available and because it does not provide two-way flow. We believe it to be likely that the next-generation network will require a much richer interface between every pair of adjacent layers if adequate performance is to be achieved. Research is needed into the conceptual mechanisms, both indicators and controls, that can be implemented at these interfaces and that, when used, will result in Gigabit Working Group [Page 14] RFC 1077 November 1988 better performance. If real differences in performance can be observed, then the implementors of every layer will have a strong incentive to make use of the mechanisms. We can observe the first glimmers of this sort of coordination between layers in current work. For example, in the ISO work there are 5 classes of transport protocol which are supposed to provide a range of possible matches between application needs and network capabilities. Unfortunately, it is the case today that the class of transport protocol is chosen statically, by the implementer, rather than dynamically. The DARPA Wideband net offers a choice of stream or datagram service, but typically a given host uses all one or all the other---again, a static rather than a dynamic choice. The research that we believe is needed, therefore, is not how to provide alternatives, but how to provide them and choose among them on a dynamic, real-time basis. 3.1.5. Different Switch Technologies One approach to high-performance networking is to design a technology that is expected to work as a stand-alone demonstration, without addressing the need for interconnection to other networks. Such an experiment may be very valuable for rapid exploration of the design space. However, our experience with the Internet project suggests that a primary research goal should be the development of a network architecture that permits the interconnection of a number of different switching technologies. The Internet project was successful to a large extent because it could incorporate a number of new and preexisting network technologies: various local area networks, store and forward switching networks, broadcast satellite nets, packet radio networks, and so on. In this way, it decoupled the use of the protocols from a particular technology base. In fact, the technology base evolved rapidly, but the Internet protocols themselves provided a stability that led to their success. The next-generation architecture must similarly deal with a diverse and evolving technology base. We see "fast-packet" switching now being developed (for example in B-ISDN); we see photonic switching and wavelength division multiplexing as more advanced technologies. We must divorce our architecture from dependence on any one of these. At the host interface, we must divorce the multiplexing of the medium from the form of data that the host sees. Today the packet is used both as multiplexing and interface element. In the future, the host Gigabit Working Group [Page 15] RFC 1077 November 1988 may see the network as a message-passing system, or as memory. At the same time, the network may use classic packets, wavelength division, or space division switching. A number of basic functions must be rethought to provide an architecture that is not dependent on the underlying switching model. For example, our transport protocols assume that data will be lost in units of a packet. If part of a packet is lost, we discard the whole thing. And if several packets are systematically lost in sequence, we may not recover effectively. There must be a host-level unit of error recovery that is independent of the network. This sort of abstraction must be applied to all the aspects of service specification: error recovery, flow control, addressing, and so on. 3.1.6. Network Operations, Monitoring, and Control There is a hierarchy of progressively more effective and sophisticated techniques for network management that applies regardless of network bandwidth and application considerations: 1. Reactive problem management 2. Reactive resource management 3. Proactive problem management 4. Proactive resource management. Today's network management strategies are primarily reactive rather than proactive: Problem management is initiated in response to user complaints about service outages; resource allocation decisions are made when users complain about deterioration of quality of service. Today's network management systems are stuck at step 1 or perhaps step 2 of the hierarchy. Future network management systems will provide proactive problem management---problem diagnosis and restoral of service before users become aware that there was a problem; and proactive resource management---dynamic allocation of network bandwidth and switching resources to ensure that an acceptable level of service is continuously maintained. The GN management system should be expected to provide proactive problem and resource management capabilities. It will have to do so while contending with three important changes in the managed network environment: Gigabit Working Group [Page 16] RFC 1077 November 1988 1. More complicated devices under management 2. More diverse types of devices 3. More variety of application protocols. Performance under these conditions will require that we seriously re-think how a network management system handles the expected high volumes of raw management-related data. It will become especially important for the system to provide thresholding, filtering, and alerting mechanisms that can save the human operator from drowning in data, while still permitting access to details when diagnostic or fault isolation modes are invoked. The presence of expert assistant capabilities for early fault detection, diagnosis, and problem resolution will be mandatory. These capabilities are highly desirable today, but they will be essential to contend with the complexity and diversity of devices and applications in the Gigabit Network. In addition to its role in dealing with complexity, automation provides the only hope of controlling and reducing the high costs of daily management and operation of a GN. Proactive resource management in GNs must be better understood and practiced, initially as an effort requiring human intervention and direction. Once this is achieved, it too must become automated to a high degree in the GN. 3.1.7. Naming and Addressing Strategies Current networks, both voice (telephone) and data, use addressing structures which closely tie the address to the physical location on the network. That is, the address identifies a physical access point, rather than the higher-level entity (computer, process, human) attached to that access point. In future networks, this physical aspect of addressing must be removed. Consider, for example, finding the desired party in the telephone network of today. For a person not at his listed number, finding the number of the correct telephone may require preliminary calls, in which advice is given to the person placing the call. This works well when a human is placing the call, since humans are well equipped to cope with arbitrary conversations. But if a computer is placing the call, the process of obtaining the correct address will have to be incorporated in the architecture as a core service of the network. Gigabit Working Group [Page 17] RFC 1077 November 1988 Since it is reasonable to expect mobile hosts, hosts that are connected to multiple networks, and replicated hosts, the issue of mapping to the physical address must be properly resolved. To permit the network to maintain the dynamic mapping to current physical address, it is necessary that high-level entities have a name (or logical address) that identifies them independently of location. The name is maintained by the network, and mapped to the current physical location as a core network service. For example, mobile hosts, hosts that are connected to multiple networks, and replicated hosts would have static names whose mapping to physical addresses (many-to-one, in some cases) would change with time. Hosts are not the only entities whose physical location varies. Users' electronic mail addresses change. Within distributed systems, processes and files migrate from host to host. In a computing environment where robustness and survivability are important, entire applications may move about, or they may be redundant. The needed function must be considered in the context of the mobility and address resolution rates if all addresses in a global data network were of this sort. The distributed network directory discussed elsewhere in this report should be designed to provide the necessary flexibility, and responsiveness. The nature and administration of names must also be considered. Names that are arbitrary or unwieldy would be barely better than the addresses used now. The name space should be designed so that it can easily be partitioned among the agencies that will assign names. The structure of names should facilitate, rather than hinder, the mapping function. For example, it would be hard to optimize the mapping function if names were flat and unstructured. 3.2. High-Speed Switching The term "high-speed switching" refers to changing the switching at a high rate, rather than switching high-speed links, because the latter is not difficult at low speeds. (Consider, for example, manual switching of fiber connections). The switching regime chosen for the network determines various aspects of its performance, its charging policies, and even its effective capabilities. As an example of the latter, it is difficult to expect a circuit-switched network to provide strong multicast support. A major area of debate lies in the choice between packet switching and circuit switching. This is a key research issue for the GN, Gigabit Working Group [Page 18] RFC 1077 November 1988 considering also the possibility of there being combinations of the two approaches that are feasible. 3.2.1. Unit of Management vs. Multiplexing With very high data rates, either the unit of management and switching must be larger or the speed of the processor elements for management and switching must be faster. For example, at a gigabit, a 576 byte packet takes roughly 5 microseconds to be received so a packet switch must act extremely fast to avoid being the dominant delay in packet times. Moreover, the storage time for the packet in a conventional store and forward implementation also becomes a significant component of the delay. Thus, for packet switching to remain attractive in this environment, it appears necessary to increase the size of packets (or switch on packet groups), do so- called virtual cut-through and use high-speed routing techniques, such as high-speed route caches and source routing. Alternatively, for circuit switching to be attractive, it must provide very fast circuit setup and tear-down to support the bursty nature of most computer communication. This problem is rendered difficult (and perhaps impossible for certain traffic loads) because the delay across the country is so large relative to the data rate. That is, even with techniques such as so-called fast select, bandwidth is reserved by the circuit along the path for almost twice the propagation time before being used. With gigabit circuit switching, because it is not feasible to physically switch channels, the low-level switching is likely doing FTDM on micro-packets, as is currently done in telephony. Performing FTDM at gigabit data rates is a challenging research problem if the skew introduced by wide-area communication is to be handled with reasonable overhead for spacing of this micro-packets. Given the lead and resources of the telephone companies, this area of investigation should, if pursued, be pursued cooperatively. 3.2.2. Bandwidth Reservation Algorithms Some applications, such as real-time video, require sustained high data rate streams over a significant period of time, such as minutes if not hours. Intuitively, it is appealing for such applications to pre-allocate the bandwidth they require to minimize the switching load on the network and guarantee that the required bandwidth is available. Research is required to determine the merits of bandwidth Gigabit Working Group [Page 19] RFC 1077 November 1988 reservation, particular in conjunction with the different switching technologies. There is some concern to raise that bandwidth reservation may require excessive intelligence in the network, reducing the performance and reliability of the network. In addition, bandwidth reservation opens a new option for denial of service by an intruder or malicious user. Thus, investigations in this area need to proceed in concert with work on switching technologies and capabilities and security and reliability requirements. 3.2.3. Multicast Capabilities It is now widely accepted that multicast should be provided as a user-level service, as described in RFC 1054 for IP, for example. However, further research is required to determine the best way to support this facility at the network layer and lower. It is fairly clear that the GN will be built from point-to-point fiber links that do not provide multicast/broadcast for free. At the most conservative extreme, one could provide no support and require that each host or gateway simulate multicast by sending multiple, individually addressed packets. However, there are significant advantages to providing very low level multicast support (besides the obvious performance advantages). For example, multicast routing in a flooding form provides the most fault-tolerant, lowest-delay form of delivery which, if reserved for very high priority messages, provides a good emergency facility for high-stress network applications. Multicast may also be useful as an approach to defeat traffic analysis. Another key issue arises with the distinction between so-called open group multicast and closed group multicast. In the former, any host can multicast to the group, whereas in the latter, only members of the group can multicast to it. The latter is easier to support and adequate for conferencing, for example. However, for more client- server structured applications, such as using file/database server, computation servers, etc. as groups, open multicast is required. Research is needed to address both forms of multicast. In addition, security issues arise in controlling the membership of multicast groups. This issue should be addressed in concert with work on secure forms of routing in general. Gigabit Working Group [Page 20] RFC 1077 November 1988 3.2.4. Gateway Technologies With the wide-area interconnection of local networks by the GN, gateways are expected to become a significant performance bottleneck unless significant advances are made in gateway performance. In addition, many network management concerns suggest putting more functionality (such as access control) in the gateways, further increasing their load and the need for greater capacity. This would then raise the issue of the trade-off between general-purpose hardware and special-purpose hardware. On the general-purpose side, it may be feasible to use a general- purpose multiprocessor based on high-end microprocessors (perhaps as exotic as the GaAs MIPS) in conjunction with a high-speed block transfer bus, as proposed as part of the FutureBus standard (which is extendible to higher speeds than currently commercially planned) and intelligent high-speed network adaptors. This would also allow the direct use of hardware, operating systems, and software tools developed as part of other DARPA programs, such as Strategic Computing. It also appears to make this gateway software more portable to commercial machines as they become available in this performance range. The specialized hardware approach is based on the assumption that general-purpose hardware, particularly the interconnection bus, cannot be fast enough to support the level of performance required. The expected emphasis is on various interconnection network techniques. These approaches appear to require greater expense, less commercial availability and more specialized software. They need to be critically evaluated with respect to the general-purpose gateway hardware approach, especially if the latter is using multiple buses for fault-tolerance as well as capacity extension (in the absence of failure). The same general-purpose vs. special-purpose contention is an issue with operating system software. Conventionally, gateways run specialized run-time executives that are designed specifically for the gateway and gateway functions. However, the growing sophistication of the gateway makes this approach less feasible. It appears important to investigate the feasibility of using a standard operating system foundation on the gateways that is known to provide the required security and reliability properties (as well as real- time performance properties). Gigabit Working Group [Page 21] RFC 1077 November 1988 3.2.5. VLSI and Optronics Implementations It appears fairly clear that gigabit communication will use fiber optics for at least the near future. Without major advances in optronics to allow effectively for optical computers, communication must cross the optical-electronic boundary two or more times. There are significant cost, performance, reliability, and security benefits for minimizing the number of such crossings. (As an example of a security benefit, optics is not prone to electronic surveillance or jamming while electronics clearly is, so replacing an optic- electronic-optic node with a pure optic node eliminates that vulnerability point.) The benefits of improved technology in optronics is so great that its application here is purely another motivation for an already active research area (that deserves strong continued support). Therefore, we focus here in the issue of matching current (and near-term expected) optronics capabilities with network requirements. The first and perhaps greatest area of opportunity is to achieve totally (or largely) photonic switches in the network switching nodes. That is, most packets would be switched without crossing the optics-electronics boundary at all. For this to be feasible, the switch must use very simple switching logic, require very little storage and operate on packets of a significant size. The source- routed packet switches with loopback on blockage of Blazenet illustrate the type of techniques that appear required to achieve this goal. Research is required to investigate the feasibility of optronic implementation of switches. It appears highly likely that networks will at some point in the future be totally photonically switched, having the impact on networking comparable to the effect of integrated circuits on processors and memories. A next level of focus is to achieve optical switching in the common case in gateways. One model is a multiprocessor with an optical interconnect. Packets associated with established paths through the gateway are optically switched and processed through the interconnect. Other packets are routed to the multiprocessor, crossing into the electronics domain. Research is required to marry the networking requirements and technology with optronics technology, pushing the state of the art in both areas in the process. Given the long-term presence of the optic-electronic boundary, improvements in technology in this area are also important. However, it appears that there is already enormous commercial research Gigabit Working Group [Page 22] RFC 1077 November 1988 activity in this area, particularly within the telephone companies. This is another area in which collaborative investigation appears far better than an new independent research effort. VLSI technology is an established technology with active research support. The GN effort does not appear to require major new initiatives in the VLSI area, yet one should be open to significant novel opportunities not identified here. 3.2.6. High-Speed Transfer Protocols To achieve the desired speeds, it will be necessary to rethink the form of protocols. 1. The simple idea of a stateless gateway must be replaced by a more complex model in which the gateway understands the desired function of the end point and applies suitable optimizations to the flow. 2. If multiplexing is done in the time domain, the elements of multiplexing are probably so small that no significant processing can be performed on each individually. They must be processed as an aggregate. This implies that the unit of multiplexing is not the same as the unit of processing. 3. The interfaces between the structural layers of the communication system must change from a simple command/response style to a richer system which includes indications and controls. 4. An approach must be developed that couples the memory management in the host and the structure of the transmitted data, to allow efficient transfers into host memory. The result of rethinking these problems will be a new style of communications and protocols, in which there is a much higher degree of shared responsibility among the components (hosts, switches, gateways). This may have little resemblance to previous work either in the DARPA or commercial communities. 3.3. High-Speed Host Interfaces As networks get faster, the most significant bottleneck will turn out to be the packet processing overhead in the host. While this does Gigabit Working Group [Page 23]