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V.90/56kbps Modem Status for ACB
V.90/56kbps modem test status
With the intention of extending ACB (CERN's Automatic Call Back
service for access to CERN from home), to include modems
running at up to 56kbps (approximately twice the maximum speed of
the existing ACB modems), we recently tested a V.90 product on
evaluation loan. The tests were unfortunately only partially
successful. They identified a serious inter-operability problem
between CERN and France Telecom equipment, such that V.90 callback
is not possible to normal (analogue) French numbers at this
time. Solutions are under discussion, but are likely to require
major changes. In the meantime, evaluation of alternative products
will continue and we hope to resume tests towards the end of this
year, with the view to opening a V.90 modem callback service early
in the year 2000.
Is ISDN a better choice than V.90 modems for ACB?
Yes. ISDN gives both higher throughput (up to 128kbps) and better
response time (approximately 10 ms) than V.90 modems. Being
digital, ISDN throughput rates are guaranteed and not dependent on
the telephone line quality, which can significantly reduce the
actual throughput achieved by analogue modems. The only drawback of
ISDN is the cost of the physical ISDN installation in your
home (contact your local Telecom provider for an estimate) and
the additional rental fee (ISDN gives you 2 phone lines so
rental is charged accordingly). More information on the
ACB ISDN service is available via the ACB Home Page
The planned V.90 ACB modem service will be aimed at people
requiring higher speed than the existing ACB modem service, but not
willing to install ISDN in their home.
What is V.90?
V.90 is an international standard which allows modems to run at up
to 56kbps in one direction and up to 33.6kbps in the other. It is
slightly different technology to lower speed modems since it
requires that one end of the connection is digital (ISDN). Only the
digital end of the connection is able to transmit data at the
higher rate and the maximum achieved rate depends on the quality of the
telephone lines. In practice the maximum tends to be around 40
kbps. The latency, which affects interactive response time, tends
to remain around 100ms for most modems. It does not generally
improve with V.90 modems.
What is ISDN?
Basic rate ISDN (Integrated Services Digital Network)
is an international standard for 2 digital (B) channels at 64kbps,
with a separate 16kbps (D) control channel. This gives a guaranteed
(i.e not dependent on telephone line quality) rate of either 64 or
128 kbps in both directions between CERN and your home. The latency
is around 10ms, giving better interactive response than modems. It
allows 2 simultaneous calls (data and/or voice). It requires an
ISDN installation in your home. The rental is approximately twice
the rental of a single telephone line.
What is ACB?
ACB (Automatic Call Back) provides modem and
ISDN access to systems on the CERN network and general
Internet access beyond CERN. It is used by people needing to
work from home. Registration for the service requires
CERN budget code approval. More information about ACB,
including the registration form, is available via the ACB Home
Page, at URL:
For matters related to this article please contact the author.
Last Updated on Fri Sep 24 18:02:40 GMT+03:30 1999.
Copyright © CERN 1999 -- European Laboratory for Particle Physics