rfc1077.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.


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