Cisco S4C5

ISDN

ISDN

• Designed to solve low bandwidth problems in small offices

• Also designed for dial-in users with traditional telephone dial-in services

• Designed to use existing telephone wiring

• WAN length brought up for duration of call

• Sane process as when you call a friend

Benefits

• Carries many types of network traffic (data, voice, video)

• Sets up calls faster than basic telephone service• Faster data transfer rate than modems

– Uses D channel (out of band) signaling– B channel 64 Kbps up to 128 when both B channels are

used

• Uses UNI (user-network interface)• International compatibility

– Standards for end-to-end digital connectivity

ISDN Components

• TE1 connects to network termination of type 1 or 2 –device compatible with ISDN

• TE2 device that is not compatible– requires terminal adapter

• TA Converts standard electrical signals to ISDN form

• NT1 Connects four-wire ISDN subscriber wiring to conventional two-wire local loop

• NT2 performs layer 2 and layer 3 protocol services

ISDN Reference Points

• R connections between non ISDN and a TA

• S connections to customer switching device

• T outbound connection from NT2 to ISDN or NT1

• U connections NT1 and ISDN owned by telephone company – only in NA

Switch Types

• North America– AT&T 5ESS

Nortel DMA-100

Japan

NTT

UK

Net3 Net5

ISDN Protocols

• E recommend telephone network standards; e.g. E.164 international addressing

• I concepts, terminology and methods; e.g. I.100 concepts and structure

• Q switching and signaling; signaling means process of call setup

Layers

• Physical– ISDN BRI and PRI

• Data Link– LAPD; LAPB

• Network Layer– Q.930 – user to user, circuit switched, and

packet switched connections

Physical Layer

• 48 bits or 24 bits plus 24 bits– Framing – synchronization– Load Balancing– Echo of previous D channel bits– Activation bit– Spare bit– B1 channel bits– B2 channel bits– D channel bits

• 8000 frames per second; effective rate is 144 Kbps

Data Link Layer

• Flag, address, control, data, FCS, flag

• Address – SAPI C/R EA TEI EA

• LAPD – similar to HDLC– Used to ensure control and signaling

information flows and is received properly– Flag and control fields identical to HDLC– The address field can be expanded to 2 bytes

Network Layer

• ITU-T.1.450

• ITU-TQ.931– Support user to user, circuit switched and

packet switched connections– Specifies call establishment, termination,

information, and miscellaneous messages

ISDN and OSI Reference Model

• Two most common encapsulations– PPP and HDLC– ISDN defaults to HDLC– PPP is more robust – authentication and negotiation of

compatible link and protocol configuration

• ISDN allows only one encapsulation type– Most use PPP – peer to peer– Can be used by IP and IPX to establish network

connectivity– PPP specified by RFC 1661 – open standard– PPP uses LCP to establish link

PPP Security

• PAP Password Authentication Protocol• CHAP Challenge Handshake

Authentication Protocol– If syn used on one end, asyn used on other– LCP established Point to point– PPP provides primary security – RFC 1334– CHAP is bidirectional– PAP is unidirectional

ISDN Uses

• Remote access– Lowest speed link in enterprise

• Remote nodes– Remote user appears to be network node– Components are ISDN router and remote client sw

• Small office/home office – ISDN router with multiple users - dialup– Fees depend on geographic area, service availability,

and billing method– May be distance limitations

ISDN Services

• BRI– 2 B and 1 D channel, 144 kbps total bandwidth– B channels provide service; D channel used for

signaling

• PRI– 23 B 8-bit channels and 1 8-bit D channel – 1.544 Mbps– In Europe, 30 8-bit channels and 1 D

How It Works

• Routers provide routing by using DDR (dial on demand) routing to provide transparent connectivity

• DDR controls B channels based on load thresholds

• Multilink PPP is used to provide bandwidth aggregation

Configuration Tasks

• Global– Select switch type, specify traffic to trigger DDR call

• Set destination details

• Interface Configuration– Select interface specs, configure ISDN addressing

• Specify BRI and number for BRI port

• Configure with ID supplies by service provider

• Can configure waiting time for carrier to respond

• Involves ISDN, switch type, and ISDN SPIDs

BRI Configuration

• INTERFACE BRI 0– Number describes port, connector, or interface

card number– Displayed with SHOW INTERFACES

command

Switch Types

• Need to define ISDN Switch type before using BRI

• Use global configuration mode– ISDN Switch-type name-of-switch-type

SPIDS

• ISDN spid1 spid-number [idn] seta a B channel service profile identifier– SPIDs allow multiple ISDN devices to share

local loop– Typically used for dialup connectivity

Typical Commands

• Isdn switch-type• Dialer-list 1 protocol ip permit• Interface bri 0• Dialer-group 1• Dialer wait-for-carrier-time• Ip• Bane• Connection number • Show ISDN status

DDR Operations

• Ping/Telnet• Show dialer – diagnostics• Show ISDN Active – monitor call in progress• Show ISDN status – shows statistics of all line

connections• Debug isdn q921• Debug dialer• Clear interface