rfc898.txt

RFC 相关的技术文档

RFC 898                                                       April 1984
Gateway SIG Meeting Notes


         IP Processing-

            o   Consistency checks
            o   Redirects does not forward misrouted packets
            o   Fragmentation - ICMP dest unreach If DF Set
            o   Access list for who can pass through

         No GGP, no EGP, Uses known gateways

         Ordinary devices and PDP-10 and PDP-20

   The Wisconsin BITNET/CSNET Gateway -- UWisc - Solomon

      Postel:  This was a discussion of a mail relay between the
      Internet and BITNET to be installed at Wisconsin.

      Muuss:

      WISC-IBM (192.5.2.24) will connect to BITNET

      Mail gateway, BITNET uses RFC 822 headers!

   LAN to X.25 Gateway -- Computer Gateways Inc. - Buhr

      Postel:  This was a description of a protocol translation device
      between an X.25 world and the DATAPOINT ARCNET world.

      Muuss:

      ARCNET to X.25 Bridge
      
      ARCNET - from Datapoint,
        Baseband coax, 2.5 mbps
        Token passing
        Reserve/send/wait/ack protocol
        RIM chip implements this

      "The OSI models seem less clear than the Internet models, perhaps
      because they are less well developed."

      Wraps the subnetwork in an enhanced subnetwork layer.

      Every pair of subnetworks must be connected in this design - hence
      a bridge not a gateway.

      Bridge is a network layer RELAY.

      ARCNET address is sent as X.25 data


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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


   ISI-UCI Gateway -- UCI - Rose

      Postel:  This was a description of the UCI dumb gateway. This one
      is made up of two hosts (VAX 750s) 50 miles apart.  The VAXs are
      connected via a 9.6 Kbs leased line.  One is interfaced to the
      ISI-NET (an Ethernet) and the other to UCIICS net (also an
      Ethernet).  The VAXs run Berkeley Unix 4.1.  These VAXs run as
      regular hosts too.

      Muuss:

      MTU is 512. Effective bandwidth of approximately 6000 baud over
      9600 baud line.

   FACC Gateway -- FACC - Holkenbrink

      Postel:  A description of a gateway designed by Ford.  The gateway
      is based on a MC68000 multiprocessor and a VME bus.  An
      interesting question that came up during this presentation  was
      "What is the least information a host (or gateway) must have when
      it comes up, and how can it acquire the rest of what it needs to
      go into full operation from the environment?"

      Muuss:

      Inter-segment Processor. M68000 CPU with various co-processors.
      68000 IOPS, 1822, IOP Ethernet IOP. 1 cpu does IP, routing.
      Multi-cpu version of MOS

   Lincoln IP/ST Gateway -- LL - Forgie/Kantrowitz

      Postel:  This was a discussion of the design of the Lincoln
      gateways used primarily in the WBCNET for speech transmission
      research.  This gateway uses special I/O interfaces to promote a
      high packet processing rate.  The gateway implements both the
      regular IP, and the ST protocol which permits resource
      reservations to minimize the variation in transmission delay.
      These gateways can, of course, act as regular internet gateways,
      and have achieved very good performance in terms of datagrams per
      second.

      Muuss:

      Packet voice experiments, wideband SATNET. Concentrate traffic
      from local nets to trunk net. Needed enough performance to load
      WBSATNET. 11/44 and ACC IF11 (Z-80). T1 trunk protocol converter.
      (voice T1 <--> datagram)
      


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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      IP problems -
        o   Congestion
        o   High packet header overhead
        o   No support for conference call

      ST -
        o   Virtual circuit
        o   Know capacity in advance, schedule channel
        o   Abbreviated header

      11/44 - 900 to 1000 pkts/sec.
      
      Port processor:
        Sync low speed:     600K bits/sec.
        Packet processing:  500 pkts/sec. average
          20-talker LPC voice loop, 28 data
            bytes/pkt, 50% duty cycle
        Data handling
          4 pcm voice stream loop  64K bps
          184 data bytes/pkt, 100% duty cycle

      Dispatcher Requirements
        o  Timely do ST
        o  Utilize rest of circuit for IP
        o  Performance measurement

      Reservations on the SATNET: Each host makes a reservation for
      Nbytes of M messages every INTERVAL. Reservations are absolute.

      ST and IP for each distant run = MPP multipurpose packets.

      12,000 lines of C code in 11/44 portion.

   Minimal Stub Gateways -- MITRE - Nabielsky

      Postel:  This was a more abstract discussion of how stub gateways
      could interact and acquire information about the topology of the
      Internet.

      Muuss:

      Ethernet stub to Internet
      Inexpensive, single-band  ISBC  186/51 Intel @ $3000
      High performance.  EGP?

      128K bytes/board

      The Internet forest


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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      Alternative to ARP using Multicast

   SPF routing -- BBN - Seamonson

      Postel:  This was a fine presentation of the principles of the
      "Shortest Path First" (SPF) routing procedures with some remarks
      on how it is tailored to the Internet gateway situation.  One
      point that was impressed on me was that when using SPF in a set of
      gateways (say, the core autonomous system) the procedure will do
      routing to an "exit" gateway.  Somehow I had not thought about it
      in those terms before, but (obviously) just as there is a source
      and a destination IMP in the ARPANET there will be an entrance and
      an exit gateway in an SPF autonomous system.

      Muuss:

      Features -
        Metric, update procedures, path calculation, forwarding

      Current GGP problems -
        o   Counting to infinity
        o   Not enough topology information in each Gw
        o   Updates potentially very large

      SPF in ARPANET
        o   Single path (not optimal) - no split of flow
        o   Delay based, to minimize delay
        o   Global knowledge of connection topology and delays

      Metric used -
        o   Delay, delay of each packet averaged
              (queueing plus transmission plus propagation)
              arrival-to-arrival time.
        o   Average delay on each trunk computed every 9.6 seconds.
            Report large changes in delay, fast

      Update procedure -
        o   Updates report delay to each neighbor
        o   Update triggered by topology change, significant delay
            change, or 1 time/minute.
            Decay of threshold to direct to send update
        o   Sequence numbers
        o   Flooding on all trunks sent out on all lines
        o   Receipt of echo is acknowledgement
        o   Retransmission
        o   Aging of information
        o   Updates are 2*n*l packet growth.  n = number imps,
            l = number lines


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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


          - When lines goes up, rather than dumping routing
            table,just waits one minute until all updates have
            been heard.

      Path calculation
         o   Dijkstras Algorithm

                                  20
                         A _______________ F
                        / \  \
                     3 /   \10\15
                      /     \  \
                    B/___5___\D \E
                     \      /  /
                      \    /  /
                     1 \  /  /5
                        \/  /
                         C /

      1.         A       B(A, 3), D(A, 10), E(A, 15). F(A, 20)

      2.         A       C(B, 4), D(B, 8), E(A, 15), F(A, 20)
                 |
                 B

      4.         A          E(C, 9),  F(A,20)
                 |
                 B
                / \
               C   D

      5.         A
                 |
                 B
                 |
                 C
                /
               E

      Then tree is inverted into a "go here to get to this destination."

      For Internet -

          Similar algorithm, needs special packet header to
          indicate "exit" gateway to get to destination network.

         Update procedure -
            Neighbor interface, neighbors, and delay to neighbor.


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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


            "Next door neighbors" for minimizing traffic.
            Ability to package multiple updates in one average
            explicit Acks.

         Path calculation -
           o   Possible to build different trees based on type of
               service.

         Forwarding -
           o   Exit Gw
           o   Consistent databases are important.

   Multiple Constraint Routing -- SRI - Shacham

      Postel:  This was a clear presentation of some of the consequences
      of the idea of type of service routing.  The level of complexity
      of the routing procedure is determined to depend on how many
      catagories of service there are and how many selections there are
      in each catagory.  A few examples were discussed including the
      current type of service parameters of IP.

      Muuss:

      Both current and proposed ARPANET algorithms provide "best" path
      under single constraint (number of hops, delay).
      Internet will have diverse characteristics, it would be nice to
      consider more than one constraint.

        o   Determine a set of measures.
        o   Represent each measure as a single number.
        o   Determine range of values.  (complexity 0(c**n) range of n)
        o   Define path measure as a function of measure of length.
             sum (delay, cost)
             min/capacity, length, security)

      If just one cost is used, then SPF (or whatever) can be used for
      each cost.  However, under multiple constraints there is a more
      difficult problem. e.g.:  minimum delay with packet size of at
      least 1000 bytes.

      RUMC has been shown to be in the NP complete family.

      RUMC needs bigger tables, more processing and routing overhead.
      Its not awful for 2-choice TOS, like in IP.

      Table size is random, we have to be prepared for the worst case.

      Possible strategies:  flood a "search packet," dropped when


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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      constraints are not met, see if it makes it though. Good only for
      virtual circuit. Weighted sum (VC only) works only with some
      probability.

      TOS is needed for Internet, but the algorithms are costly.
      Complexity for providing TOS IP style is not too high.

   FACC Multinet Gateway Routing -- FACC - Cook

      Postel:  This approach considered hop count to be an inadequate
      metric for routing decsions in a system of different types of
      networks (e.g., Ethernets, ARPANETs, 2.4Kb lines).  Delay was
      selected as the metric to use.  There are some interesting issues
      in the measurement of delay for some types of networks.  Also, the
      design considers the use of multiple paths when they are avaiable,
      and routing to provide connectivty between the parts of
      partitioned networks.

      Muuss:

      Routing with a single constraint.
      A network of gateways Access, Transport, or Dual networks.
      Some networks are used as backbones between gateways only.
      
      Routing updates
        Variable length
        Broadcast routing updates

      Unitary ends - A - Gw - B - Rest
         Routing for A is really just routing to B
         Neighbor Gws, nets
         Lots and lots of tables

   Metanet Gateway -- SRI - Denny

      Postel:  This is a project to invent several new addressing
      features for gateways.  In particular, there is a scheme to use an
      option much like the source route option to do multi-addressing of
      IP datagrams.  It seems as if the gateways that implement this
      option will have to know which other gateways do and don't
      implement it.  Also, there was discussion of a gateway to a
      network that is in radio silence, and how to keep TCP connections
      going with hosts that can't talk.  This project is also concerned
      about network reconstitution, security, survivability, congestion
      control, and supporting multimedia data (voice, bitmaps, etc.) in
      applications.  A gateway is being developed in ADA for a MC68000
      machine (SUN), and the initial version of the gateway is to be up
      in May 84.


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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      Muuss:

      Navy internet
        Multimedia mail and conf.
         Radio silence (EMCON)
         Security and Survivability.

      EMCON - Causes special problems for EGP and IGP one way nonTCP
      mail delivery.  No Acks. Uses name screen to redirect mail to
      special one-way mail catcher, who then forwards using ordinary
      methods.

      Security and survivability
      Access control - "capability" - 32/64 bit key which changes
      frequently (every hour or so)
      
      Reconstitution - Partitioning, coalescing, mobile host
      Test and monitoring - HMP

      Gateway target - 68000 in ADA.  Telesoft compiler

   Address Mapping and Translation -- UCL - Crowcroft

      Postel:  This was a discussion of some of the issues in
      interconnecting networks of different types including the Internet
      and networks in England such as the Universe network.  The
      Universe network is made up of Cambridge Rings at several sites
      linked via a satellite channel.

      Muuss:

      ARPA - SATNET - NULLNET - UCLNET UNIVERSE Satellite, 3 UCL rings

      SAM -
        o   IP switch to several 1822 hosts
        o   IP/universe mapper, overlays UCLNET on universe
        o   Mask and match
              128. 11. code. host

      Three types:

         1.  Direct:  code --> subnet
              2.  Redirect: 2nd lookup (for multihoming)
              3.  Logical: Logical address into a table of universe
         names.
                           Name lookups give addresses and routes.

      IP tunnels through X.25


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