CCNA4_M4_ISDN_and_DDR (1130795)
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CCNA – Semester4Module 4ISDNObjectives• ISDN standards used for addressing, concepts, andsignaling• ISDN physical and data link layers• Configure the router ISDN interface• Configure Dial-on-demand RoutingISDN ConceptsIntroducing ISDN•••ISDN can be used as a solution to the low bandwidth problems,carries a variety of user traffic signals, including data, voice, andvideo .Offers much faster call setup than modem connectionsISDN allows digital signals to be transmitted over existingtelephone wiring.ISDN Data• The bearer channel, or B channel, is defined asa clear digital path of 64 kbps.• It is said to be clear because it can be used totransmit any type of digitized data in full-duplexmode.• It uses either HDLC or PPP as the Layer 2protocol.ISDN signaling• ISDN uses out-of-band signaling, the delta (Dchannel), for call setup and signaling.• D channel carries signaling messages, such ascall setup and teardown, to control calls on Bchannels.• The delta channel, or D channel can either be 16kbps for the Basic Rate Interface (BRI) or 64kbps for the Primary Rate Interface (PRI).• Traffic over the D channel employs the LinkAccess Procedure on the D Channel (LAPD)protocol.
LAPD is a data link layer protocolbased on HDLC.ISDN standards• The ISDN standards are a set of protocols thatencompass digital telephony and datacommunications.• The ITU-T groups and organizes the ISDNprotocols according to the following generaltopic areas:– E Protocols– I Protocols– Q ProtocolsISDN standardsISDN D channel• The delta channel, or D channel can either be 16kbps for the Basic Rate Interface (BRI) or 64 kbpsfor the Primary Rate Interface (PRI).• The D channel is used to carry control informationfor the B channel.• D channel carries signaling messages, such as callsetup and teardown, to control calls on B channels.• Traffic over the D channel employs the Link AccessProcedure on the D Channel (LAPD) protocol.
LAPDis a data link layer protocol based on HDLC.ISDN access method• ISDN specifies two standard access methods:– Basic Rate Interface - BRI– Primary Rate Interface - PRI• A single BRI or PRI interface provides a multiplexedbundle of B and D channels.ISDN BRI• BRI uses two 64 kbps B channels plus one16kbps D channel.• Because it uses two B channels and one Dchannel, BRI is sometimes referred to as 2B+D.ISDN PRI• In North America and Japan, PRI offers twenty-three 64kbps B channels and one 64 kbps D channel. A PRIoffers the same service as a T1 or DS1 connection.• In Europe and much of the rest of the world, PRI offers30 B channels and one D channel in order to offer thesame level of service as an E1 circuit.• PRI uses a Data Service Unit/Channel Service Unit(DSU/CSU) for T1/E1 connections.ISDN 3-layers model• ISDN BRI and PRI physical layer specifications aredefined in ITU-T I.430 and I.431, respectively.• ISDN data link specification is based on LAPD and isformally specified in Q920, Q921, Q922, Q923.• ISDN network layer is defined in ITU-T Q.930, alsoknown as I.450 and ITU-T Q.931, also known as I.451.These standards specify user-to-user, circuit-switched,and packet-switched connections.ISDN physical layer: Frame formatISDN BRI bit rate• Note that ISDN BRI frames are sent at a rateof 8000=8K per second.• Bit rate: (2*8B+2D+6F)*8K = 192Kbps• Effective rate: (2*8B+2D)*8K = 144Kbps• Bearer (B) rate: (8B)*8K = 64Kbps• Delta (D) rate: (2D)*8K = 16KbpsISDN D channel: FramingISDN componentsISDN component: TE• Specialized ISDN terminals are referred toas Terminal Equipment type 1 (TE1).– Connect to the ISDN network through a four-wire,twisted-pair digital link.• Non-ISDN terminals such as DTE thatpredate the ISDN standards are referred toas Terminal Equipment type 2 (TE2).
It isconnected to the ISDN network through aTA.ISDN component: NT• Network Termination type 1 (NT1) or NetworkTermination type 2 (NT2) device.• These are NT devices that connect the four-wiresubscriber wiring to the conventional two-wire localloop.– In North America, the NT1 is a Customer Premises Equipment(CPE) device.– In most parts of the world, the NT1 is part of the network providedby the carrier.• The NT2 is a more complicated device, that performsL2 and L3 protocol services.• An NT1/2 is a single device that combines thefunctions of an NT1 and an NT2.ISDN reference points• ISDN standards define functional groups asdevices or pieces of hardware that enable theuser to access the services of the BRI or PRI.• Vendors can create hardware that supports oneor more functions.ISDN reference pointsCisco ISDN BRI interfaceISDN switch types• Routers must be configured to identify the typeof switch with which they will communicate.• As a consequence of various implementationsof Q.931, the D channel signaling protocol usedon ISDN switches varies from vendor to vendor.Service profile identifiers• SPID is a number provided by the ISDN carrierto identify the line configuration of the BRIservice.• SPIDs allow multiple ISDN devices, such asvoice and data equipment, to share the localloop.• SPIDs are required by DMS-100 and NationalISDN-1 switches.ISDN ConfigurationConfigure ISDN switch type•isdn switch-type switch-typecan be configured at the global or interface command mode tospecify the provider ISDN switch.•National ISDN-1 and DMS-100 ISDN switches require SPIDs to beconfigured, but the AT&T 5ESS switch does not.Sample configurationConfiguring ISDN PRI• ISDN PRI is delivered over a leased T1 or E1 line.
The mainPRI configuration tasks are as follows:– Specify the correct PRI switch type that the router interfaces with atthe CO of the ISDN provider.– Specify the T1/E1 controller, framing type, and line coding for thefacility of the ISDN provider.– Set a PRI group timeslot for the T1/E1 facility and indicate the speedused.Configure ISDN PRIConfigure T1/E1 Controller• Specify an interface for PRI D-channeloperation. The interface is a serial interface to aT1/E1 on the router:Router(config)#interface serial{slot/port: | unit:}{23 | 15}• The interface carries IP configuration that needto traverse the link:Router(config)#ip address ip_address subnet_maskInterface channels• Channel 16, the E1 signaling channel, is channel15 on the interface.• Channel 24, the T1 signaling channel, becomeschannel 23 on the interface.• Channels use a colon instead of a dot toindicate the channel number:– S0/0.23 refers to a Subinterface– S0/0:23 refers to a channelISDN PRI exampleVerifying ISDN configuration: show isdn status• The show isdn status command to inspect thestatus of the BRI interfaces:– verify that the TE1, or router, is communicating correctlywith the ISDN switch– displays the number of active callsShow isdn statusVerifying ISDN configuration: show isdn active• The show isdn active command displays currentcall information, including all of the following:–––––Called numberTime until the call is disconnectedAdvice of charge (AOC)Charging units used during the callWhether the AOC information is provided during calls orat end of callsShow isdn activeVerifying ISDN configuration: show dialer• The show dialer command displays informationabout the dialer interface:––––Current call statusDialup timer valuesDial reasonRemote device that is connectedShow dialerVerifying ISDN configuration: show interface bri• The show interface bri0/0 displays statistics forthe BRI interface configured on the router.– The B channel is using PPP encapsulation.– LCP has negotiated and is open.– There are two NCPs running, IPCP and Cisco DiscoveryProtocol Control Protocol (CDPCP).Show interface briTroubleshooting ISDN configurationDDR ConfigurationDial-on-demand routing• DDR is triggered when traffic that matches apredefined set of criteria is queued to be sentout a DDR-enabled interface.• The traffic that causes a DDR call to be placed isreferred to as interesting traffic.• Once the router has transmitted the interestingtraffic, the call is terminated.DDR operationDDR operationConfiguring legacy DDR• Legacy DDR is a term used to define a verybasic DDR configuration with the followingsteps:– Define static routes– Specify interesting traffic– Configure the dialer informationDefining static routes for DDR• When configuring static routes, consider thefollowing:– By default, a static route will take precedence over adynamic route because of its lower administrativedistance.– To reduce the number of static route entries, define asummarized or default static route.Specifying interesting traffic for DDR• Interesting traffic may be defined as any of thefollowing:– IP traffic of a particular protocol type– Packets with a particular source address or destination– Other criteria as defined by the network administrator• Use the dialer-list command to identifyinteresting traffic.
The command syntax is asfollows:Router(config)#dialer-list dialer-group-num protocolprotocol-name {permit | deny | list access-list-number}dialer-group-num: an integer between 1 and 10Specifying interesting trafficDialer-group• A dialer list specifying the interesting traffic forthis DDR interface needs to be associated withthe DDR interface.Router(config-if)#dialer-group group-number• Group-number must match the dialer-list groupnumber.• Each interface can have only one dialer group.Dialer-map• The correct dialing information for the remoteDDR interface needs to be specified.• The dialer map command maps the remoteprotocol address to a telephone number.Router(config-if)#dialer map protocol next-hop-address [namehostname] [speed 56 | 64] [broadcast] dial-stringDialer-map commandOther commands• If dialing only one site, use an unconditionaldialer string command that always dials the onephone number regardless of the trafficdestination.• The dialer idle-timeout seconds command maybe used to specify the number of idle secondsbefore a call is disconnected.
The default is 120.Configuration sampleDialer profiles• Remove the configuration from the interface receiving ormaking calls and only bind the configuration to theinterface on a per-call basis.Dialer profile tasks• Configure B channels of an ISDN interface with differentIP subnets.• Use different encapsulations on the B channels of anISDN interface.• Set different DDR parameters for the B channels of anISDN interface.• Eliminate the waste of ISDN B channels by letting ISDNBRIs belong to multiple dialer pools.Dialer profile elements•A dialer profile consists of the following elements :– Dialer interface– Dialer pool– Physical interfacesConfiguring interface dialer• Each dialer interface is the complete configuration for adestination.• Configure one or more dialer interfaces with all the basicDDR commands:––––IP addressEncapsulation type and authenticationIdle-timerDialer-group for interesting traffic• Configure the physical interfaces and assign them to adialer pool using the dialer pool-member command.Dialer priority• If more than one physical interface exists in thepool, use the priority option of the dialer poolmember command to set the priority of theinterface within a dialer pool.• The dialer pool with the highest priority is theone that dials out first.Configuring dialer interfaceConfiguring physical interfaceVerifying DDR configuration• The show dialer interface [BRI] command displaysinformation on incoming and outgoing calls.• The show isdn active command displaysinformation about the current active ISDN calls.• The show isdn status command displaysinformation about the three layers of the BRIinterface.Troubleshooting the DDR configuration• There are two major types of DDR problems.– A router is not dialing when it should,– A router is constantly dialing when it should not.• Several debug commands can be used to helptroubleshoot problems with a DDRconfiguration.Debug isdn q921Debug isdn q931Debug dialer eventsIsdn call interfaceSummary• ISDN uses standards for addressing,concepts, and signaling• ISDN uses the physical and data-link layers• Interfaces and reference points for ISDN• Router configuration for ISDN BRI and PRI• Legacy DDR and dialer profiles• ISDN and DDR verification andtroubleshooting.CCNA4 – Module4.
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