Nortel BCM50 2.0 Installation Manual

Also see for BCM50 2.0: User guide System overview guide User guide Configuration guide User guide

Contents

Nortel BCM50 2.0 Installation Manual Manual pdf 30 page image

30 Chapter 5 ISDN overviewNN40020-309NN40020-309An analog modem operating at 14.4K 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 kb/s. 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 kb/s (BRI) and 64 kb/s PRI. Data information consists of controland signal information and for BRI only, packet-switched data such as credit card verification.ISDN layersISDN layers refer to the standards established to guide the manufacturers of ISDN equipment andare based on the OSI (Open Systems Interconnection) model. The layers include both physicalconnections, such as wiring, and logical connections, which are programmed in computersoftware.When equipment is designed to the ISDN standard for one of the layers, it works with equipmentfor the layers above and below it. There are three layers at work in ISDN for BCM50. To supportISDN service, all three layers must be working properly.• Layer 1: A physical connection that supports fundamental signaling passed between the ISDNnetwork (your service provider) and the BCM50 system. When the LED on a BRI S/T MediaBay Module configured as BRI is lit, your layer 1 is functioning.• Layer 2: A logical connection between the central office or the far end and the BCM50 system.Without Layer 2, call processing is not possible.