Network Computingwww.networkcomputing.com

To view the Report card on
V.90 Internal/External Modems
V.90 PC Card Modems
If you're an early technology adopter, you're probably already on your way to 56-Kbps technology. On the other hand, if you are purchasing or recommending modems for your organization, it may pay to hold off on a V.90 modem rollout until the first quarter of 1999. Historically, the marketers of new technologies outpace the engineers. And in this case, V.90 interoperability remains an issue. It took three to four months before stable V.34 modems were available. Similarly, we don't expect to see reliable V.90 modems until the end of 1998.

General Observations We tested a host of V.90 internal, external and PC Card modems in one of our Real-World Labs® at Syracuse University. While every one of them successfully negotiated some V.90 connections, none made V.90 connections every time. We ran the V.90 modems against a set of common PSTN (public switched telephone network) conditions using equipment from TAS (Telecom Analysis Systems). For more details on our testing, see "How We Tested V.90 Modems," on page 114.

We didn't expect perfection with this round of products, but we did expect these modems to at least attempt a V.90 connection and fall back to V.34 if it failed. Problems in negotiating V.90 connections arose when Lucent-based DSPs dealt with our Ascend Communications Ascend MAX, which uses a Rockwell-based DSP.

V.90 connection rates to our 3Com Corp. I-Modem-based server, which was connected to our network simulation equipment using an ISDN BRI, were higher than those to our Ascend MAX. BRI is a clean digital link offering a full 64-Kbps channel with no digital to analog (D to A) conversion or RBS (robbed bit signaling) to impair the line. Of the modems we tested, only one Rockwell-based modem, from Best Data Products, successfully fell back to V.34 mode. Otherwise, Rockwell-based designs either connected at V.90 or failed entirely. Also of note, the PC Card modems we tested negotiated more often at V.90 with the I-Modem than did their internal or external counterparts.

V.90 connections to our Ascend MAX were not completed at quite as high a rate as those to our 3Com I-Modem, but the fallback to V.34 was good. We found this to be most significant when using PC Card modems. When you're on the road, the path from your laptop to the remote-access server may undergo multiple digital-to-analog conversions, which explains the importance of high V.34 fallback rates.