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*Asynchronous Versus ISDN Analog converted to digital and backChannelbankSWSW Digital end-to-endChannelbankSWSWThe advantages of ISDN over analog connections include:Higher speedFaster call setupCheaper than leased linesVoice and data can be run simultaneously

*Integrated ServicesProvider networkDigital PBXSmall officeHome office Voice, data, video, and special servicesTelecommuterCentral site

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*ISDN Services and Channelized E1 and T156/64 kbps56/64 kbps16 kbps144 kbps2BD}{BRIT1 1.544 Mbps orE1 2.048 Mbps (includes sync)23B (T1) or 30B (E1) D64 kbps each 64 kbps}PRI2.048 Mbps (includes sync)31 64 kbpschannels}E11.544 Mbps (includes sync)24DS0s}T1

*31BRI Call ProcessingISDNservice provider4B channelD channel/SS7 signaling2SS7Q.931 signalingQ.931 signaling

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*TE1NT1LELocal loop terminatorISDN local exchangeISDN terminal equipmentNT2Customer premises switching equipmentTE2TANon-ISDN terminal equipmentTerminal adapterSURTBRI Functional Groups and Reference Points

*Physical Representation of BRI Reference PointsCisco ISDNrouterTo ISDNserviceWall jack4-wirecircuit2-wire circuitS/TUTAS/T busS/T busS/T interface as a multipoint connectionTo non-ISDNdevice (TE2)R

*PRILayer 1 Standards and Reference PointsLEU

ITU-T I.431 ANSI T1.601TECSU/ DSUS/T

ITU-T I.430

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*ISDN Protocol LayersLayer 3LAPD (Q.921)D ChannelB ChannelI.430/I.431/ANSI T1.601HDLC/PPP/FR/LAPBLayer 1Layer 2DSS1 (Q.931)IP/IPX

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*ISDNNT1Daisy-chainS/T busTEI/SAPITEI/SAPILEISDN Layer 2ITU-T Q.920 and Q.921Defines logical link between TE/TA and NT2/LECarries Layer 3 D-channel messages

*ISDN Layer 3D Channel Q.931Q.931 defines call control between the TE and local switchTEETNT1LTQ.931ISDN switch (LE)

*Q.931 MessagingCall Setup ExampleCalling partyCalled partySetupConnect acknowledgeConnect acknowledgeSetupSetup acknowledgeCall proceedingAlertingConnectAlertingConnectCall proceedingTimeISDN service providerISDN switchISDN switch

*Q.931 MessagingCall Teardown ExampleReleasedDisconnectCalling partyCalled partyDisconnectReleasedRelease completeRelease completeReleaseTimeISDN service providerISDN switchISDN switch

*DDR OperationInteresting ?Connected ?Phone # ?Connected ?DialNoYesYesNoNoSendIncoming packetReset Idle TimerYesNoInterfaceup?YesYesNo

*Using DDR with ISDNISDN service providerBRI or

PRI1.2.Remoterouter1. Packet arrives 2. Switch packet to DDR interface, determine if interesting 3. If interesting, dial DDR destination via ISDN 4. Connect to remote router3.4.

*ISDN Configuration TasksGlobal configurationSelect switch typeSpecify traffic to trigger DDR callInterface configurationSelect interface specificationsConfigure ISDN addressingOptional feature configurationISDN

*ISDN Configuration CommandsSet global parameters with this command:isdn switch-typeSet interface parameters with these commands:encapsulation ppp

*Router(config)#isdn switch-type switch-typeRouter(config-if)#isdn switch-type switch-typeSelecting the ISDN Switch TypeSpecifies the type of ISDN switch with which the router communicatesGlobal or interface command

*Setting Interface ProtocolsRouter(config-if)#encapsulation {ppp | hdlc} Selects framing for that ISDN BRI Router(config-if)#ppp authentication {pap | chap | ms-chap} Selects PPP authentication type

*DDR Configuration Tasks1. Define interesting traffic2. Assign interesting traffic definition to ISDN interface 3. Define destination 4. Define call parameters ISDN service providerBRI orPRIRemoterouterInteresting traffic arrivesDial destination

*Defining Interesting Traffic Router(config)#dialer-list dialer-group-number protocol protocol-name {permit | deny} list access-list-numberDefines interesting packets for DDR Associated with the dialer group assigned to the interface Router(config-if)#dialer-group group-numberAssigns an interface to the dialer access group specified in the dialer-list command

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*Purpose: This figure compares an analog and an ISDN call.Emphasize: The advantages of ISDN over analog connections include:Higher speedFaster call setupCheaper than leased linesVoice and data can be run simultaneously

*Purpose: The figure shows the vision of ISDN as a network that allows voice, data, video, and special services to use the same facilities.Emphasize: ISDN allows the usage of existing telephone cables (in most cases) for high-speed data as well as voice.Transition: The next figure shows the ISDN services.*Purpose: This figure compares the physical characteristics of ISDN BRI and PRI. Emphasize: Compare the number of channels in BRI and PRI.Transition: The next figure shows the sequence of a BRI call.*Purpose: This figure shows the sequence of events and the usage of the B and D channel in the establishment of a BRI call.Emphasize: Normally, the D channel is only used for signaling/call control. Q.931 signaling is between the end user and the local ISDN switch. In the provider network, Signaling System 7 (SS7) is used for call control between the switches.Note: The D channel can be used for low-speed data. Specifically, X.25 can be configured to run over the D channel if the ISDN service provider can provide the service.Transition: The next figure shows the BRI functional groups and reference points.*Purpose: This figure introduces the standard ISDN BRI functional elements.Emphasize: Discussions of BRI usually speak in terms of the device initialisms (NT1, TA, and so on) and the demarcation points (S, T, S/T, and U). It is very important to become familiar with these terms and identifiers.Note: Often the ST demarcation point is used to describe non-U.S. implementations. This ST reference point exists when there is no NT2 device and the S and T reference points converge.Transition: The next figure takes these reference points and functional groups and relates them to physical hardware.*Purpose: This figure assigns well-known devices to the abstract reference points and functional groups.Emphasize: The Network Termination 1 (NT1) is part of the customer premises equipment (CPE) equipment in the U.S. and is part of the central office (CO) equipment in Europe. Cisco routers for small offices, (700, 800, 1600, and 1700 series) come with or without internal NT1 devices.Transition: The next figure shows ISDN PRI reference points.*Purpose: This figure shows the reference points and standards for ISDN PRI.Emphasize: PRI requires a channel service unit/data service unit (CSU/DSU) and no NT1 device.Transition: The next figure shows the ISDN architecture and how the physical-layer standards for PRI and BRI relate to the upper layers.*Purpose: This figure shows the ISDN architecture through Layer 3.Emphasize: The control protocols (Q.921 and Q.931) run over the D channel, while data protocols (IP and IPX at Layer 3, and Layer 2 encapsulations) run over the B channel. Note: DSS1 is a comprehensive signaling system of which only specific parts (Q.921 and Q.931) are used.Transition: The next figure shows BRI Layer 1 framing.*Purpose: This figure highlights the Layer 2 protocol Q.921 and its usage.Emphasize: Q.921 is the protocol by which the ISDN switch assigns a terminal endpoint identifier (TEI) to an end device. Use the analogy of a protocol or service access point (SAP) field in a LAN protocol data unit (PDU) that is used to map to a higher-layer protocol suite to demonstrate the need for TEIs and service access point identifiers (SAPIs).Transition: The next figure takes us up to the Layer 3 protocol Q.931.*Purpose: This figure shows how Q.931 is used for D-channel call control from the ISDN switch to the TE device.Emphasize: This protocol is used to communicate between the ISDN switch and the TE device. This protocol is transparent to the NT1 device. During configuration of a Cisco router, we must specify the type of ISDN switch to which the router will interface. Different ISDN switches use different Q.931 messaging procedures. We must match the specific switch procedures or no D-channel communication can occur.Transition: The next two figures give an example of the Q.931 messaging that occurs between the ISDN switch and the TE device (Cisco router).*Purpose: This figure illustrates the sequence and types of Q.931 messages exchanged between calling party (perhaps a router) and its local ISDN switch, and the messages exchanged between the called party and its local ISDN switch during the setup of an ISDN call.Emphasize: The sequence and message types are dependent on the type of ISDN switch.Transition: The next figure shows an example of the Q.931 call teardown message sequence.*Purpose: This figure shows a typical Q.931 call teardown message sequence.Emphasize: Message type and sequence may vary with the ISDN switch type.Transition: The next section gives a brief overview of DDR operation.*Purpose: This figure shows the sequence of events in DDR operation.Emphasize: The key to efficient DDR operation is in the definition of interesting traffic. We have several mechanisms, including dialer and access lists, which we will discuss later in this section. Note that even if the traffic is not interesting it can be forwarded if the connection to the destination is already up.Transition: The next figure shows how DDR is used with ISDN.*Purpose: This figure shows the sequence of events for a call over an ISDN interface.Emphasize: There is no difference whether the call is ISDN or not. DDR works the same in either case. Differences may exist in the configuration of ISDN-specific parameters.Transition: The next section covers the commands used for an ISDN BRI with DDR configuration.

*Purpose: This figure is a signpost for the tasks necessary to configure ISDN.Emphasize: Each task will be covered in more detail later.Transition: The following pages present each task shown in the figure.*Purpose: This figure shows the specific commands required to configure ISDN.Emphasize: The commands discussed in this section are for ISDN BRI. The two categories of commands are global configuration, specifically for the ISDN switch type, and commands for the BRI interface itself.Transition: The next figure gives the command syntax and usage for the isdn switch-type command.

*Purpose: This figure shows the isdn switch-type command.Emphasize: This command can be used in either global or interface configuration mode. When this command is used globally, the switch type specified applies to all interfaces. To specify different switch types for individual interfaces, use the command in interface configuration mode and specify the switch type that connects to that interface. Note: The switch types shown in the Student Guide are representational and may vary with the version of Cisco IOS software used. Some providers switches may emulate other switch types. For example, a CO equipped with a 5ESS switch may emulate the National ISDN-1 protocols. Therefore, you must configure to match the emulation. Transition: The next figure shows BRI interface commands.*Purpose: This figure shows some interface configuration commands.Emphasize: These commands are used to specify the data link layer encapsulation protocol and, if PPP is the encapsulation protocol, which authentication protocol to use. Transition: The next figure shows how to configure for service profile identifiers (SPIDs).*Purpose: This figure is a signpost for the DDR configuration tasks.Emphasize: Point out each task in the figure and discuss the usage of the optional dialer timer commands.Transition: The next few figures discuss in detail each task listed on this page.*Purpose: This figure shows the commands necessary to define interesting DDR traffic.Emphasize: Interesting traffic will trigger a call on the specified interface. Use the global dialer-list command to define the traffic, and the interface dialer-group command to apply the definition to an interface. A basic dialer list contains all the filtering information needed to define interesting traffic. An option of this command allows using an access list for specific definition of interesting traffic.Transition: The next figure shows how to use access lists with dialer lists.