

Network Working Group                                    R. Hinden (BBN)
Request for Comments: 898                                J. Postel (ISI)
                                                          M. Muuss (BRL)
                                                       J. Reynolds (ISI)
                                                              April 1984

              GATEWAY SPECIAL INTEREST GROUP MEETING NOTES

STATUS OF THIS MEMO

   This memo is a report on a meeting.  No conclusions, decisions, or
   policy statements are documented in this note.

INTRODUCTION

   This memo is a report on the Gateway Special Interest Group Meeting
   that was held at ISI in Marina del Rey, California on 28 and 29
   February 1984.  Robert Hinden of BBNCC chaired, and Jon Postel of ISI
   hosted the conference.  Approximately 35 gateway designers and
   implementors attended.  These notes are based on the recollections of
   Jon Postel and Mike Muuss.  Under each topic area are Jon Postel's
   brief notes, and additional details from Mike Muuss.

   The rest of this memo has three sections: the agenda, notes on the
   talks, and the attendees list.

MEETING AGENDA

   Tuesday, February 28

      9:00  Opening Remarks -- BBN - Hinden
      9:15  Opening Remarks -- ISI - Postel
      9:30  The MIT C Gateway -- MIT - Martin
      10:00 The Butterfly Gateway -- BBN - Hinden
      10:30 Break
      11:00 The EGP C Gateway -- ISI - Kirton
      11:20 The BRL Gateway -- BRL - Natalie
      11:40 The CMU Gateway -- CMU - Accetta
      12:00 Lunch
      1:30  The Wisconsin BITNET/CSNET Gateway -- UWisc - Solomon
      2:00  LAN to X.25 Gateway -- Computer Gateways Inc. - Buhr
      2:20  ISI-UCI Gateway -- UCI - Rose
      2:40  FACC Gateway -- FACC - Holkenbrink
      3:00  Break
      3:30  Lincoln IP/ST Gateway -- LL - Forgie/Kantrowitz
      3:50  Minimal Stub Gateways -- MITRE - Nabielsky
      4:10  Discussion







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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


   Wednesday, February 29

      9:00  Opening Remarks -- BBN - Hinden
      9:10  SPF routing -- BBN - Seamonson
      9:35  Multiple Constraint Routing -- SRI - Shacham
      10:00 FACC Multinet Gateway Routing -- FACC - Cook
      10:30 Break
      11:00 Metanet Gateway -- SRI - Denny
      11:20 Address Mapping and Translation -- UCL - Crowcroft
      11:40 Design of the FACC Multinet Gateway -- FACC - Cook
      12:00 Lunch
      1:30  SAC Gateway -- SRI - Su/Lewis
      2:00  EGP -- Linkabit - Mills
      2:30  Congestion Control -- FACC - Nagle
      3:00  Break
      3:30  A Gateway Congestion Control Policy--NW Systems - Niznik
      4:00  Discussion

NOTES ON THE MEETING

   The MIT C Gateway -- MIT - Martin

      Postel:  A description of the gateway implemented at MIT.  The
      gateway was first developed by Noel Chiappa.  It is written in C.
      The MIT environment has 32 internal networks which are treated as
      subnets of the MITNET on the Internet.  The MIT gateways then do
      subnet routing in their interior protocol.  The subnet routing
      scheme is similar to GGP.  Liza has added an EGP implementation to
      this gateway.

      Muuss:

      Campus network/project Athena
      Dynamic routing
      Congestion control - grad student
                      +---------------+---+
       Class A net  : | 18|subnet|res|host|
                      +---------------+---+

      "Bridges" forward between subnets.

      Campus Network and Project Athena 65 VAX 750s, 200 IBM PCs.

      Hosts: Now = 400, 1986 = 3,000, 1990 = 10,000

      Subnets: Now = 42, 1985 = 60, 1990 = 200, (4 subnets/building)

      Protocols: Internet, DECnet, Chaosnet


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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      FiberOptic spine between campus buildings.

      MIT gateways:

         11/03s and 11/23s
         68000 on Abus
         6800 on Multibus (Bridge communications)

         MIT C gateway -
         Runs under MOS, bridge OS, homegrown OS. Multiple protocols,
         multiple interfaces.

         11/03 - 100 packets/sec.
         11/23 - 180 packets/sec.

         GGP - Gw/Gw
         EGP - Exterior Gw
         IGP - Interior Gw

         EGP:  Autonomous systems

         EGP:
           Neighbor acquisition
           Hello/I heard you
           Net reachability poll
           Net reachability message

      MIT IGP:

         IP header on EGP protocol
         Dest: net number, subnet number, 0, 0377 (broadcast address)

      IGP header:

         Autonomous system number
         Sequence number
         Tasks:
             Propagate exterior and subnet routing.

      Packets
         Ext route request, and update Routing server
             Default gateway
             Exceptional gateways
             Nets reached

      MIT - Gw broadcasts initial routings when it comes up, and again
      on each change, net is flooded on each change several times. Each
      bridge can ask for help.


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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      Future:  Wideband net gateway from BBN will also sit on net  18,
      and an MIT routing server to acquire routing information. Trick -
      BBN-Gw will be on an Ethernet, and a modified ARP will be used by
      the bridges to "fool" the BBN gateway into acquiring the routes.

      Subnet Routing - inspired by PUP and CHAOS
         Neighbor Bridge
           Net I/F
           Bridge address
           Latest seq number
           Aging value
         Route to subnet
           Distance

         Packets
           Request
           I'm up

             Route update
               Distance vector (256 bytes)
                       0 - Direct
                       1 -127 - hop count
                       128-255 - "Interface used for next hop" to subnet
                                 and hop count
                       255 - Unreachable

      Problem -
         Many neighbors --> too much time and traffic needed for
      processing.
      
         3 level addressing and routing strategy
         Ext Gw:
           Routing server
           Default Gw
         Subnet routing
           Small but rich subnet routing updates.

   The Butterfly Gateway -- BBN - Hinden

      Postel:  A description of the butterfly hardware and a discussion
      of the plans for the new gateway software to be implemented on it.
      The butterfly machine is a multiprocessor (MC68000's)
      interconnected with a funny switch.  The new software will
      incorporate the so called "Shortest Path First" or SPF routing
      algorithm.





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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      Muuss:

      Replacement for existing 30 PDP-11 "core" gateways.
      Problems to be solved.

         o  Replace GGP
              - Routing updates filling up
              - Neighbor probes (N**2)
              - Few buffers

         o  Present GGP updates only hold 70 net numbers, repacking
            data will increase that to approximately 100 nets, but
            this is just short term.

      Features of Butterfly -
         o  1000's of nets
         o  Partitioned nets
         o  Type of service routing, access control
         o  Flow control
         o  Large and small gateway configurations

      New functions -
         o  Routing
         o  Neighbor discovery
         o  Reduce neighbor pinging
         o  Access/departure model
         o  Connect gateways with point-to-point lines

      Routing -
         o  SPF - shortest path first
         o  Gateway based routing (opposed to network routing)
         o  Routing updates
              Gw ID
              <nets directly connected>
              <neighbor, distance>
         o  Updates flooded to other gateways

      Next-door - Neighbors
         o  Neighbor gateways closest to gateway
         o  Ping next-door-neighbors only
         o  For up/down acquisition, partition into rings.  Reduces
            pinging.
      
      Access/departure model
      
          First Gw (entrance) picks exit gateway




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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


          First Gw adds Gw - Gw header
      
      Butterfly gateway

          Processor nodes and switch nodes
         
          4-legged switch nodes, decision is simply UP or DOWN.  2
         inputs
          and 2 outputs.

          Processor:  MC 68000
          Memory management Unit
          Processor node controller - 2901 bit slice
          PVC is the memory controller.

         Butterfly -
          32 M bps/path
          Bandwith:   approximately N - speed
          Size:       approximately N/2   log  N 2

         Butterfly will support multibus interface; 1822, HDLC,
         Ethernet, Ring

      Terminal and load device will be a personal computer

      Small Gw for ARPA is approximately $20K

      New Gw processor structure

      Buffer Management
        o   Scatter/gather buffers minimum size and extensions
        o   Buffer pool on processors with I/O
        o   Primary and secondary collections per device
             ==>  guaranteed minimum service per device
                  (implemented w/counts)

   The EGP C Gateway -- ISI - Kirton

      Postel:  A user process was installed in Berkeley 4.2 Unix to do
      EGP protocol functions leaving the normal router kernel function
      in charge of forwarding datagrams.  The EGP user process may do
      system calls to update the kernel routing data.  Based on the work
      of Liza Martin.







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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      Muuss:

      EGP under 4.2

      Elimination of nonrouting gateways

      Design -
          Forwarding done in kernel
          Kernel does not send redirects
          EGP user process for route updates
          Written in C
          EGP based on Liza Martin's code

      Routing Tables
        o   Kernel
        o   EGP Process

      EGP Process Table -
        o   External updates
        o   Internal information

      Facilities -

         Configuration file-
             o   Trusted neighbors
             o   Internal non - routing gateways

         Acquisition -
           o   Predetermined number of core gateways are EGP'd to
           o   Only accept from trusted neighbors
           o   Cannot acquire neighbors indirectly, for now

         Unix Interfaces -
           Reuse IP socket (problem with protocol number)
           Listening to ICMP for redirects
           System calls for -
             o   Route updates
             o   I/F config reading
             o   I/F status check

         Performance -
             o   60 ms/packet pair (CPU time)
             o   Typically 1% of CPU for 1 minute polling

         Protocol function going
         Routing updates being implemented

         Should be all going in April.


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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


   The BRL Gateway -- BRL - Natalie

      Postel:  This was a description of the BRL dumb gateway.  More
      interesting was the description of the BRL complex and the
      inteconnections between machines.  The gateway is written in C
      (and derived from the MIT C-Gateway) and based on a simple
      multiprocess operating system called LOS.

      Muuss:

      BRL history
      
      LOS design
        Message passing
        Memory Management
        No copying of data, buffer size

   The CMU Gateway -- CMU - Accetta

      Postel:  This was a description of the CMU dumb gateway.

      Muuss:

      History -
        o   "Logical-Host" multiplexor (March 81)
        o   Gateway (Oct 82) remote debugger and monitor
        o   Router (Oct 83)
              - Modular device and protocol support
              - Stub IP dynamic routing
              - Local inter-network cable routing.
        o   Written in "C"

      Uses low memory for buffers (maximum 32K)!
        (autoboot of 3M bps Ethernet)
      Auto-configuration of devices
      Individual stack contents
      Round-robin scheduler
      Dynamic memory allocation

      Device driver
        Network interfaces
        Auxiliary support devices

      Does IP, ICMP, UDP

         Splicing through of PUP and CHAOS on chaos net, uses ARP.

         Configuration testing protocol (as in Ethernet Spec).


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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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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      BBN Van gateway PSS - IPSS -Telenet - for hosts that can't use
      SATNET.

      SAM does access control and multihoming.  Clever Multihoming gives
      host a second address and sends an ICMP/Redirect to force TCP
      connection to go through a different route, but  wind up at same
      place!!!

      Wrote EGP in ADA.  It didn't help at all.

   Design of the FACC Multinet Gateway -- FACC - Cook

      Postel:  This is a distributed multiprocessor machine using a
      special bus network for the interprocessor communication.  The
      softaware is written in C.  The gateways is in an early test
      phase.

      Muuss:

      RADC program

      Started with AUTODIN II, switched to DDN.
      Small to large switching devices.
      DoD uses of PDNs, and partitioned network problems.
      
      Distributed processing architecture -
        Parallel contention, 90M bps bus, 22 wires. Each node has cpu,
        memory, optimal comm line. Wire - OR presentation of address,
        contention happens each time bus becomes free, all requestors
        put out type of msg, pri, and address.   Reads back wire - OR of
        result, and highest gwy wins, sorted by (pri, type, higher
      addr).
        Bus was originally designed for our FAA fail-soft application
        Z-800l w/MMU. Not binary addressing, but unitary (base1)
      One element resolved per bus transaction.
      Boards may be plugged in while running.
      Inherent parallelism in layered protocols.

      Interface connector clues board to modem levels and date rate.  Up
      to 100K bps now, soon up to T1 rate.

      Multiprocessor approach allows routing calculation to take place
      out-of-band from the measurement of delay and traffic, and allows
      use of more compute power for routing.

      Mostly written in C, with some assembler.  Multiprocessor
      operating system, designed from scratch.



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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


   SAC Gateway -- SRI - Su/Lewis

      Postel:  This was a presentation of the design for the gateways to
      be used in the advanced SAC demo experiments on network
      partitioning and reconstitution, and communication between
      intermingiling mobile networks.  Much of these demonstrations will
      be done with packet radio units and networks.  Some of the ideas
      are to use a gateway-centered type of addressing and double
      encapsulation (i.e., an extra IP header) to route datagrams.

      Muuss:

      Network dynamics due to component mobility or failure.
      Mobile host, reconstitution, partitioning.
        H/W:  11/23
        S/W:  Some "C" gateway
        OS:   VMOS (SRI)

      Gateway-centered addressing, rather than network.
        Gw host instead of net.host.
      Double encapsulation:  additional IP header.
        TCP uses addr as an ID, IP uses it as an ADDRESS (-> route)
        Need to separate these dual uses of this address field.
      Incremental Routing (next-hop indication)

   EGP -- Linkabit - Mills

      Postel:  A presentation of the EGP design.  EGP has three major
      aspects, neighbor acquisition, neighbor reachability, and network
      reachability.  The autonomous system concept was discussed.

      Muuss:

      Background, Implementation, Experience, Disparaging Remarks

      Design goals -
        o   Established demarcations
        o   Decouple implementations
        o   Confine routing loops
        o   Exchange reachability information
        o   Provide flow control for connectivity information
        o   Medium-term lifetime

      Non goals                       Not trying to do these!
        o   Flexibility of topology
        o   Rapid response             Very slow update




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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


        o   Adaptive routing
        o   Common routing metric      No agreement at all
        o   Load sharing or splitting

      "Good news travels fast and bad news travels forever."
      Not for routing, but only provides reachability
      
      RFC827 initial mode, RFC888 stub protocol

      Neighbor acquisition protocol
         o   2-way shake
         o   Flow - rates
         o   Explicit acquisition/cause

      Neighbor reachability protocol
         o   Periodic polling
         o   Parasitic information
         o   Reachability algorithm Network reachability
             protocol
         o   Periodic pulling
         o   Remote information
         o   Direct and indirect neighbors
         o   Indirect internal and indirect external
             neighbors
         o   Distance information

      EGP neighbors do not need to peer with more than one
      CORE gateway, but you may peer with anybody you wish.

      Shortcomings -
         o   Slow reaction due polling
         o   Tree-structured routing constraint
           - Rigid topology
           - Administrative resistance to odering
           - Lack of adaptive connectivity
         o   Neighbor acquisition incomplete.

      Loops between autonomous systems will last a long
      time, and are a real no-no.

      System models -
         o   "Appropriate first hop" criterion
           - Not useful for implementation
           - Requires global information
           - Inadequate for verification
         o   Graph models
           - N-graph shows net connectivity
           - T-graph shows system connectivity


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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


           - T-acycloc criterion insures loop-free
         o   Derived features
           - Induces spanning tree

      N-graph

                                        G1
                                  A_______________B
                                 / \            /\
                            G2  /   \  G3   G4 /  \ G5
                               /     \        /    \
                              C------D        E-----F G6

         AS1 = G2, G3, G6                   A         B
         AS2 = G1
         AS3 = G4, G5                 AS1 ----- AS2 ----- AS3

                                               T-graph

      Test:  to ensure that there are no cycles

      Spanning subtree

      Specification effort - Status report State machine designed

      Remaining issues -
        o   Remove extra hop in core system
        o   Expand tables
        o   Test backdoor "GGP"
        o   Resolve specification issues
        o   Resolve full gateway configuration
              - Back door connectivity guidance
              - can only advertise 1 path at a time.
              - APF rule guidancee
              - Self organization issues
        o   Implement and distribute for operational systems.

   Congestion Control -- FACC - Nagle

      Postel:  This was a discussion of the situation leading to the
      ideas presented in RFC 896, and how the policies described there
      improved overall performance.








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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      Muuss:

      First principle of congestion control:

         DON'T DROP PACKETS (unless absolutely necessary)

      Second principle:

         Hosts must behave themselves (or else)

         Enemies list -

            1.  TOPS-20 TCP from DEC
            2.  VAX/UNIX 4.2 from Berkeley

      Third principle:

         Memory won't help (beyond a certain point).

         The small packet problem: Big packets are good, small are bad
         (big = 576).

      Suggested fix: Rule: When the user writes to TCP, initiate a send
      only if there are NO outstanding packets on the connection. [good
      for TELNET, at least] (or if you fill a segment). No change when
      Acks come back. Assumption is that there is a pipe-like buffer
      between the user and the TCP.

      The source quench problem Rule: When a TCP gets an ICMP Source
      Quench, it must reduce the number of outstanding datagrams on
      relevant TCP connections.

      Rule: When a gateway nears overload, before starting to drop
      packets, send a Source Quench.

      Node capacity: Each node ought to have one buffer for each TCP
      connection, plus some for overload.

      Both fixes really need to be done together, although the first one
      is often helpful by itself. Side effect: FTPs start off "slowly,"
      until the first Ack comes back Dave Mills thinks this will
      increase the mean delay for medium-size interactions. This
      probably will not work so well for SATNET.

      Problems about propagation time of links biasing the validity of
      this result!!




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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


   A Gateway Congestion Control Policy--NW Systems - Niznik

      Postel:  This talk was (for Postel) hard to follow.  There were a
      number of references to well known results in queuing theory etc,
      but I could not follow how they were being used.

      Muuss:

      Replacements for IMP SPF
      Topological observations
      Nodal congestion control policy
        GMD - control application [from German network]
        RPN - relational Petri net
        DCT - dynamic congestion table
      NCCP performance evaluation
      Planned GCCP:  Gateway congestion control policy

      Lots of diagrams and figures.

      Better throughput than SPF, but somewhat higher delay.

      Cubic structure of table.

   DISCUSSION (Postel's personal comments)

      There was very little organized discussion during the meeting and
      not really very much question and answer interaction during the
      presentation.  There was a lot of discussion during the breaks,
      and at lunch time, and at the end of each day.

      Some things that occured to me during the meeting that may have
      been triggered by something someone said (or maybe by the view out
      the window):

         Don't design a protocol where you expect to get a lot of
         messages from a lot of sources at the same time.  For example,
         don't ask all the hosts on an Ethernet to send you an ack to a
         broadcast packet.

         Has anyone worked out in detail the routing traffic costs for
         the GGP vs the SPF procedures for the actual case of the
         Internet?

         How will the fact that thinking of the routing in the core
         autonomous system is cast in terms of an entry and an exit
         gateway effect other things?  Will there be special




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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


         arrangements between the entry and exit gateway?  Will an
         autonomous system become a circuit switch connecting pairs of
         entry/exit gateways?

         Is TOS routing worth the cost?

         Should we allow (as a new type of ICMP message) redirects to
         Gateways?

         Does making memory larger ever hurt?  If a gateway's memory is
         full of inappropriately retransmitted TCP segments would it be
         better if there were less memory?

         Is there something reasonable to do with source quench at the
         TCP?  Re: RFC-896.

         If there are links (or networks) of vastly differing delay and
         thruput characteristics what impact would an IP level load
         splitting (say by gateways) have on TCP connections (some of
         the segments of the connection go one path and others go a
         different path)?

         Are any problems avoided (either way) by using double IP
         headers vs a "source route like" IP option to separate the IP
         level addressing and routing function from the TCP level
         end-point naming function of the IP addresses.

         What bad things could happen from the proposed IP
         multidestination routing option?





















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RFC 898                                                       April 1984
Gateway SIG Meeting Notes


MEETING ATTENDEES

   Mike Accetta - CMU
   R. Buhr - Canada
   J. Noel Chiappa - MIT
   Paul Cook - Ford
   Jon Crowcroft - UCL
   Barbara Denny - SRI
   Jim Forgie  - LL
   Steve Groff - BBN
   Phill Gross - Linkabit
   Kjell Hermansen - NTA
   Robert Hinden - BBN
   Patrick Holkenbrink - FACC
   Ruth Hough - AIRINC
   Willie Kantrowitz - LL
   Paul Kirton -ISI
   Mark Lewis -SRI
   Liza Martin - MIT
   Doug Miller - MITRE
   Dave Mills - Linkabit
   Mike Muuss - BRL
   Jose Nabielsky - MITRE
   Ron Natalie - BRL
   John Nagle  - Ford
   Carol Niznick  NW Systems
   Jon Postel - ISI
   Joyce Reynolds  -ISI
   Marshall Rose - UCI
   Joe Sciortino - AIRINC
   Linda Seamonson - BBN
   Nachum Shacham - SRI
   Alan Sheltzer - UCLA
   Marvin Solomon  - WISC
   Zaw-Sing Su - SRI
   Mitch Tasman - BBN














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