CHAPTER

Digital Lines and the Integrated Service Digital Network (ISDN)

Chapter ObjectivesDefine ISDN, its standards and the type of services offeredDescribe the two main types of services, namely BRI and PRI Give examples of ISDN linksSimple SOHO line, ISDN remote bridges etcBriefly outline a few other features of ISDN

Chapter ModulesAn overview of ISDNBasic Rate Interchange (BRI)Primary Rate Interchange (PRI)A practical SOHO ISDN lineISDN applicationsOther features of ISDN

MODULE

An Overview of ISDN

ISDN DefinedKnown as the Integrated Services Digital Network Data, audio, image and video transmissionIt is a switched digital telecommunication line that can be delivered over regular copper wiresPossible to provide end-to-end digital communications

ISDN Application ExamplesOn/off ramp to the information super-highway to communicate at speeds of 128 Kbps for a single ISDN lineMultiple ISDN lines can be combined together to achieve higher communication speedsHome useOn/Off ramp to the InternetBusiness worldProvide remote access to LANs.

ISDN StandardThere is a national ISDN standard known as the NI standardIt is being implemented in phasesCurrent implementation is termed as NI-1 to indicate that it is in phase 1 of the implementation process

ISDN ConnectionsCan be obtained from a local telephone company in the same way an analog connection is obtainedPhone companies offer different types of ISDN connections

ISDN Basic CharacteristicsSignalingDataDataDataD Channel16-64 KbpsB Channels64 Kbps

Inverse Multiplexing of B ChannelsB (64 Kbps)B (64 Kbps)128 Kbps128 KbpsInverse Multiplexers

Bonding of B Channels or BOD (Bandwidth on Demand)B (64 Kbps)B (64 Kbps)64- 128 Kbps64- 128 KbpsInverse Multiplexers with Dynamic BondingChannel Bonded on Demand

ISDN Service ConnectionsThere are two different types of ISDN services that are widely availableOne is known as the Basic Rate Interface or BRI Used for home or SOHO connectionThe other is known as the Primary Rate Interface or the Used in large businesses

World-wide CoverageU.K.India GermanyFranceAustraliaJapanCanadaetc.

In SummaryISDN is a switched digital networkCan be used for establishing a point-to-point digital connectionBRI and PRINumber of B Channels vary in each caseB channels can be combined together to achieve a higher communication speed

END OF MODULE

MODULEBasic Rate Interface (BRI)

BRI Characteristics2 B Channels1 D Channel

A Simple BRI Connection to a MicrocomputerNT 1ISDN Terminal AdapterPhoneComputerISDN BRI Line2B +DNetwork Terminator

Channels in BRI ServiceB channels are known as bearer channelsCarry informationD channel is known as the Delta channelUsed for signaling purposes2B + D channel service

The B Channel64k bps per channelThe two B channels can be inverse multiplexed or boded together Achieve a maximum aggregate communication speed of 128 Kbps

The D Channel16 KbpsEntire bandwidth is not used for signaling purposeExcess of 9.6 Kbps is available for packet switched data transmission applicationsExcess bandwidth usageClimate control, security alarm system etc.

In SummaryBRI is the basic ISDN serviceComposed of 2 B channels and a D channelB Channels are circuit switchedD Channel is packet switchedExcess capacity can be utilized for packet switched applications

END OF MODULE

MODULEPrimary Rate Interface (PRI)

PRI ServiceMore sophisticated service compared to BRIPRI service offers 23 B channels and 1 D channel

Properties of B Channels in PRIEach B channel operates at a speed of 64K bps The B channels are used for carrying dataB channels can be combined together to increase the aggregate communication speed

Properties of D Channel in PRIEach D channel operates at a speed of 64 KbpsConsiderably faster than the D channel in BRI23 B channels share a D channel for signaling purpose

PRI Channel DeliveryPRI channels are delivered over a T1 lineT1 speed1.544M bpsAggregate speed of PRI from all 23 B channels and the single D Channel is computed as follows:23 * 64 + 64 + xx = 1.544 Mbps

Sample Services (PacBell)Centrex ISDNFor businesses that already have the Pac Bells centrex phone systemSDS-ISDNBRI service offered for small businessesChargesPer channelPer minute

Sample Services (ISDN)Home ISDNOffers a BRI connection2B + D Charges are cheaper especially during off-peak hourPer channelPer minuteSDS-56Single channel switched 56 Kbps digital service

Sample Cost ComparisonServiceMonth Inst.Usage

Cen-ISDN31.65220.75Bus. MeasuredSDS-ISDN26.04190.75Bus. MeasuredHome24.50159.758-5 Bus. MeasuredISDNFlat OtherwisePRI220.00750Bus. MeasuredSDS- 5645.00500Bus Measured* Rebates may apply to Installation

END OF MODULE

MODULESample ISDN Applications

Use of ISDN AdaptersComputerComputerComputerISDN AdapterISDN AdapterAnalog ModemNT1NT1Pub. SwitchedNetwork

Remote ISDN Access to a LAN ComputerISDN AdapterNT1ISDN RouterNT1PSNEthernetBRIBRIRemoteISDNBridge128K bps28.8K bps to 56K bps

Remote Access Over PRIComputerISDN AdapterNT1ISDN RouterDSU/CSUPSNEthernetBRIPRI

Important Features of the PRI ConnectionCommunication links can be established between:remote computers and this LANthis LAN and remote locationsthis LAN and other remote LANs Link is established using a powerful routerA separate DSU/CSU unit is used as opposed to the NT1 network terminator used in the case of BRI

Commercial Examples of ISDN EquipmentISDN adapter3Com Impact IQISDN routers Ascend and Cisco are sample manufacturersAscend Pipeline 50 and Ascend Pipeline 100 are examples of such routersFor the latest information on ISDN equipment access the manufacturers web sites

ISDN Use in Video ConferencingDynamic bandwidth allocationCircuit switchedSymmetric bandwidth

END OF MODULE

END OF MODULE

END OF CHAPTER