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From: hagouel@ittvax.UUCP (Jack Hagouel)
Newsgroups: net.mail
Subject: Line costs used in pathalias
Message-ID: <1605@ittvax.UUCP>
Date: Fri, 18-Jan-85 11:12:06 EST
Article-I.D.: ittvax.1605
Posted: Fri Jan 18 11:12:06 1985
Date-Received: Mon, 21-Jan-85 03:03:19 EST
Distribution: net
Organization: ITT-ATC, Stratford Ct.
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Given the interest in the meaning of the DAILY, HOURLY, ... designations
I thought that this excerpt of a message I sent to Mark Horton may be
of interest to this newsgroup. I believe that a more rigorous
approach to defining the line costs used by pathalias is possible
if the optimization objectives are more clearly defined. The
syntax of expressing these costs is not addressed here, although
it is also important.

----- start of excerpt -----

The cost values allocated to connections appear to be arbitrary.
If there was a formula that was used to compute them I would
be interested to learn it. The rest of this letter deals with
thoughts and sketchy suggestions on computing the cost. I think
that a good definition of cost will be appreciated by both
the users and the providers of Usenet service.

Current cost trend appears to be that frequent connections have lower
cost (but not proportionally so). Telephone charges may also
be relevant. I couldn't guess any more factors.

The issue to be resolved is how to achieve least cost routing
(using the pathalias program). The problem arises in that the
user perceives a different cost (delay) from the cost of the
service provider (mostly dollars and fairness). To top it
all, the "network manager" is concerned with efficient 
utilization of the resources, i.e. throughput.

With the advent of domains the problem becomes more manageable.
At least for some domains (like ATT) the domain manager and the
service providers are the same; possibly even many of the users 
(internal traffic).

Since the whole concept of Usenet is based on voluntary,
non-abused, contribution of resources for the collective good,
fairness appears to be the driving force. For Usenet to become
useable low delay could work wonders. Throughput may have to
be left in the background.

Currently pathalias is not very dynamic (path computations occur 
infrequently). In the future that may change, I hope. It is
desirable to preserve the same cost definition in both cases.

Focus on fairness: I think that the best way to define it is that
a site will not be asked to handle more mail than it commited
to when it joined the network. 

Question: do sites declare their capacity constraints? If not
maybe some semi-formal definition is necessary (beyond the
frequency of calls). I've often seen new sites mentioning
a vague "as long as we do not get a lot of transient traffic".

Based on these capacity constraints pathalias should be able
to do some load splitting, i.e. the optimal path is not always
used since that would overutilize the "good" connections and
ignore the "bad" ones.

The following algorithm could be used: each node is initially
allocated bandwidth through other nodes in the network. The
amount allocated would depend on the topological distance of
the two nodes and the total bandwidth available. Each node
may allocate its own bandwidth. The allocation would
last for a predetermined amount of time (say a month).

Pathalias will execute based on these values. The source of
traffic will monitor its bandwidth consumption. When it
exceeds a limit on a node then it generates a new path
based on the remaining allocation. Intermediate nodes may
monitor for adherence to their limits and inhibit excess traffic.

Allocations that are underutilized may be either redistributed
or negotiated periodically. Bids for additional bandwidth
may be automatically processed at allocation time.

This becomes an organic algorithm where node bandwidth becomes
a commodity and it is fairly allocated to demand. The penalty
is increased bookeeping and control traffic. The advantage is
that nodes can budget their Usenet contribution in some
predictable and consistent fashion.

Jack Hagouel
...!ittvax!hagouel
(203) 929-7341 x244