858 Welcome to ISDNN0008589 3.3Analog versus ISDNISDN offers significantly higher bandwidth and speed than analog transmission because of itsend-to-end digital connectivity on all transmission circuits. Being digital allows ISDN lines toprovide better quality signaling than analog POTS lines, and ISDN out-of band data channelsignaling offers faster call set up and tear down.While an analog line carries only a single transmission at a time, an ISDN line can carry one ormore voice, data, fax, and video transmissions simultaneously.An analog modem operating at 14.4 K takes about 4.5 minutes to transfer a 1MB data file and a28.8K modem takes about half that time. Using one channel of an ISDN line, the transfer time isreduced to only 1 minute and if two ISDN channels are used, transfer time is just 30 seconds.When transmitting data, the connect time for an average ISDN call is about three seconds per call,compared to about 21 seconds for the average analog modem call.Types of ISDN serviceTwo types of ISDN services (lines) are available: Basic Rate Interface (BRI) and Primary RateInterface (PRI). Each line is made up of separate channels known as B and D channels whichtransmit information simultaneously.• BRI is known as 2B+D because it consists of two B-channels and one D-channel.• PRI is known as 23B+D(in North America) or as 30B+D (in Europe). In North America,23B+D consists of 23 B-channels and one D-channel (T1 carrier). In Europe, 30B+D consistsof 30 B-channels and one D-channel (E1 carrier).B channels: B channels are the bearer channel and are used to carry voice or data information andhave speeds of 64 kbps. Since each ISDN link (BRI or PRI) has more than one B-channel, a usercan perform more than one transmission at the same time, using a single ISDN link.D channels: The standard signaling protocol is transmitted over a dedicated data channel calledthe D-channel. The D-channel carries call setup and feature activation information to thedestination and has speeds of 16 kbps (BRI) and 64 kbps PRI. Data information consists of controland signal information and for BRI only, packet-switched data such as credit card verification.
