cisco s4c5 isdn. designed to solve low bandwidth problems in small offices also designed for dial-in...
TRANSCRIPT
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
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