rfc898.txt
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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
Hinden, Postel, Muuss, & Reynolds [Page 9]
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)
Hinden, Postel, Muuss, & Reynolds [Page 10]
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
Hinden, Postel, Muuss, & Reynolds [Page 11]
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
Hinden, Postel, Muuss, & Reynolds [Page 12]
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.
Hinden, Postel, Muuss, & Reynolds [Page 13]
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
Hinden, Postel, Muuss, & Reynolds [Page 14]
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.
Hinden, Postel, Muuss, & Reynolds [Page 15]
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
Hinden, Postel, Muuss, & Reynolds [Page 16]
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