Re: Linking LAN's via Public X.25

David Roode (
Sat, 4 Jun 88 22:25:19 PDT

There's no question that X.25 packet switching is a service built on
top of point-to-point data circuit (leased line) capability. The
tariffs in the U.S treat this as a 'value added' service and prohibit
the basic operating companies from competing in the national market.
The Public Data Networks offering packet services have to pay the same
leased line rates as an end-user, both for backbone circuits and for
ties between their switch locations and customer premises.
At the same time, the charges for leased line service are obviously
much cheaper in the U.S. than they are elsewhere. (It calls for a
judgement, but it seems likely that much in excess of costs is
recovered in the charges for leased line service in Europe.)

As a result, it may be illogical to 'blame' the U.S. Public Data Nets
for their charges. European PTT's may subsidize their X.25 offerings.
U.S. PDN's see reduced usage volume due to reasonable competition from
leased lines. The main service a PDN provides is the sharing of data
circuits. So, in the U.S. a smaller fraction of uses see an economic
incentive to share costs by making use of a PDN. (It takes a smaller
volume of usage to cost justify switching to a leased line in the
U.S.) The operating efficiency of the U.S. PDN's may be the same or
even higher than the European PTT's in providing PDN service.

It appears the hierarchy in terms of increasing cost for a 2400 baud
data flow is something like:

        leased lines at U.S. typical rates
        Public Data nets at European rates
        Public Data nets at U.S. rates
        leased lines at European rates

For 300 baud data flow, it is something like:

        Public Data nets at European rates
        Public Data nets at U.S. rates
        leased lines at U.S. typical rates
        leased lines at European rates

For 9600 baud data flow, sequence might be:

        leased lines/ U.S. rates leased lines/ U.S. rates
        Public Data nets/ U.S. rates Public Data nets/ U.S. rates
        Public Data nets/ Europe rates leased lines/Europe rates
        leased lines/Europe rates Public Data nets/ Europe rates

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