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Videoconferencing: it's more affordable when you use ISDN.

A number of factors are responsible for increased interest in videoteleconferencing. Chief among them is the need for companies to cut back on travel-related expenses in tight economic times.

Until recently the cost of bandwidth for videoconferencing was as unappealing as travel costs. If T1 bandwidth was not available on the private network, applications had to be discontinued to free up the necessary bandwidth.

An alternative is additional bandwidth for scheduled usage, such as AT&T's Accunet Reserved Digital Service (ARDS). A coast-to-coast videoconference using ARDS at 384 kb/s costs $225 per hour, over and above fixed monthly access costs. This is a bit more than most companies want to pay.

Now an economical alternative is the H0 channel of ISDN, which operates at 384 kb/s. The cost for a one-hour video-conference on an H0 channel is one-third the cost of the same service using AT&T's ARDS at 384 kb/s--cost-to-coast for only $75 per hour.

Both ISDN and ARDS require a T1 digital access line from the customer's site to the nearest AT&T serving office. Both provide the 384 kb/s bandwidth used by today's video codecs, a data rate that provides good video quality.

Videoconferencing users must be concerned about geographic availability. Tariffs for both services became effective last year, and as of this spring, ISDN H0 service is available from 139 AT&T points of presence (POPs) and 384 kb/s ARDS from 133 AT&T POPs.

Similarities end there. With ISDN H0 service, calls for videoconferencing can be placed at the convenience of users. The service can be in operation for as long or short a time as necessary. Call set-up time is only a few seconds, like an ordinary telephone call.

After the initial 30 seconds, billing is in six-second increments. When the conference is over, users simply hang up.

An ARDS call must be reserved at least 24 hours in advance, except in emergencies (when an emergency set-up charge is tacked on). ARDS billing is in 30-minute increments, so a 35-minute session costs the same as a session that lasts an hour.

Also, a hefty penalty is incurred if the reserved service is canceled within 24 hours of its scheduled start-up time, or if the connection is discontinued before its reserved time is up.

As far as customer premises equipment, usually the videoconferencing equipments is remote from the multiplexer location. If the distance is more than 60 feet, assuming a V.35 interface, a pair of 384 kb/s line drivers will be necessary. This requirement can be met with digital service units (DSUs) designed to provide fractional T1 service.

Videoconference equipment is interconnected via a 384 kb/s channel of the ISDN-equipped T1 multiplexer. One DSU can be collocated with the mux. The mux's videoconference channel is cabled to a 384 kb/s V.35 channel port of the DSU. External timing is selected for the port.

The companion DSU, with slave timing selected, is located in the meeting room with the video equipment. The two DSUs can be up to 6000 feet apart when two 22-gauge twisted pairs are used. The video equipment is plugged into the DSU's 384 kb/s V.35 channel port.

The question is, does all of this actually work in a real-time business environment?

Well, NCR put this arrangement to the test in a General Data Comm joint trial. Successful videoconferencing sessions were run between NCR locations over the ISDN H0 service using GDC DSUs and a Megamux T1 multiplexer. Videoconferencing equipment was Compression Labs'.

The trial concluded in February, but equipment was left in place to showcase other potential applications for the ISDN H0 channel. In addition to videoconferences, the H0 channel was used by NCR for LAN-to-LAN connections.

ISDN and videoconferencing are a superb match of equipment and service that can translate into tangible benefits for cost-conscious businesses.
COPYRIGHT 1991 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:ISDN User Strategies
Author:O'Neil, J.M.
Publication:Communications News
Date:Jul 1, 1991
Words:647
Previous Article:More users are putting ISDN to work and fitting it into their planning.
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