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V.90/56kbps Modem Status for ACB

Denise Heagerty , IT/CS

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