Many portions of the ARPAnet are very congested during
the busy part of the day. Additional links are planned
to alleviate this congestion, but the implementation
will take a few months.
These problems and the future direction of the Internet are
determined by the Internet Architect (Dave Clark of MIT)
being advised by the Internet Activities Board (IAB). This
board is composed of chairmen of a number of committees with
responsibility for various specialized areas of the Internet.
The committees composing the IAB and their chairmen are:
Committee Chair
Autonomous Networks Deborah Estrin
End-to-End Services Bob Braden
Internet Architecture Dave Mills
Internet Engineering Phil Gross
EGP2 Mike Petry
Name Domain Planning Doug Kingston
Gateway Monitoring Craig Partridge
Internic Jake Feinler
Performance & Congestion ControlRobert Stine
NSF Routing Chuck Hedrick
Misc. MilSup Issues Mike St. Johns
Privacy Steve Kent
IRINET Requirements Vint Cerf
Robustness & Survivability Jim Mathis
Scientific Requirements Barry Leiner
Note that under Internet Engineering, there are a set of
task forces and chairs to look at short term concerns. The
chairs of these task forces are not part of the IAB.
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Routing
Routing is the algorithm by which a network directs a packet
from its source to its destination. To appreciate the problem,
watch a small child trying to find a table in a restaurant.
From the adult point of view the structure of the dining room
is seen and an optimal route easily chosen. The child, however,
is presented with a set of paths between tables where a good path,
let alone the optimal one to the goal is not discernible.***
A little more background might be appropriate. IP gateways
(more correctly routers) are boxes which have connections to
multiple networks and pass traffic between these nets. They
decide how the packet is to be sent based on the information
in the IP header of the packet and the state of the network.
Each interface on a router has an unique address appropriate
to the network to which it is connected. The information in
the IP header which is used is primarily the destination address.
Other information (e.g. type of service) is largely ignored at this
time. The state of the network is determined by the routers passing
information among themselves. The distribution of the database
(what each node knows), the form of the updates, and metrics used
to measure the value of a connection, are the parameters
which determine the characteristics of a routing protocol.
Under some algorithms each node in the network has complete
knowledge of the state of the network (the adult algorithm).
This implies the nodes must have larger amounts of local
storage and enough CPU to search the large tables in a short
enough time (remember this must be done for each packet).
Also, routing updates usually contain only changes to the
existing information (or you spend a large amount of the
network capacity passing around megabyte routing updates).
This type of algorithm has several problems. Since the only
way the routing information can be passed around is across
the network and the propagation time is non-trivial, the
view of the network at each node is a correct historical
view of the network at varying times in the past. (The
adult algorithm, but rather than looking directly at the
dining area, looking at a photograph of the dining room.
One is likely to pick the optimal route and find a bus-cart
has moved in to block the path after the photo was taken).
These inconsistencies can cause circular routes (called
routing loops) where once a packet enters it is routed in a
closed path until its time to live (TTL) field expires and
it is discarded.
Other algorithms may know about only a subset of the network.
To prevent loops in these protocols, they are usually used in
a hierarchical network. They know completely about their
own area, but to leave that area they go to one particular
place (the default gateway). Typically these are used in
smaller networks (campus, regional...).
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Routing protocols in current use: