1. Purpose: This chapter provides a brief overview of ISDN BRI operation and legacy DDR. It also explains how to configure ISDN BRI and legacy DDR on a Cisco IOS device.
Timing: This chapter takes approximately 1.5 hours to present.
Note: This section has a laboratory exercise in which students configure ISDN and Legacy DDR. They then place a DDR call.
Contents:
Objectives—This section explains what the student will be able to do at the end of this chapter.
ISDN BRI Overview—This section describes how ISDN BRI operates.
ISDN Components—This section describes ISDN components and reference points. It also describes how to configure ISDN.
Written Exercise—This section tests students’ knowledge of ISDN components and reference points.
Dial-on-Demand Overview—This section describes Legacy DDR.
Configuring Legacy DDR—This section describes how to configure Legacy DDR.
Laboratory Exercise—Students will complete an ISDN BRI call.
Summary—This section summarizes what was taught in the chapter.
Review Questions—This section offers open-ended review questions. They should foster discussion after presenting the chapter.
Transition: Following are the list of performance objectives that describe what students will be able to do at the end of the chapter.

2. Objectives
Upon completion of this chapter, you will be able to perform the following tasks:
Describe the components that make up ISDN connectivity
Configure ISDN BRI and legacy dial-on-demand routing (DDR)
Verify DDR operation
Purpose: this figure states the chapter objectives.
Emphasize: Read or state each objective so each student has a clear understanding of the chapter objectives.

3. What is ISDN? Voice, data, video, and special services Small office
Digital PBX
Provider network
Telecommuter
Purpose: this figure describes various ISDN environments.
Emphasize: The icons in the cloud represent ISDN switches. The figure displays different sites that may use ISDN.
Home office
Central site
Voice, data, video, and special services

4. ISDN Standards Standards from the ITU (formerly CCITT) Issue Protocol
Key Examples
Telephone Network and ISDN
E.163—International Telephone Numbering Plan E.164—International ISDN Addressing
E-Series
ISDN Concepts, Aspects, and Interfaces
I.100 Series—Concepts, Structures, Terminology I.400—User-Network Interfaces (UNIs)
I-Series
Purpose: This figure describes the ISDN standards.
Emphasize: The following is ISDN standards relate back to the ISO/OSI model:
Layer 3—The ITU-T Q.931 provides a network-layer protocol. This ISDN call control protocol follows the ITU-T recommendations for the ISDN signaling layer. Signaling information is sent so the network will operate correctly. ISDN uses out-of-band signaling, even from home to the central office. There are many variations on how a provider’s switch implements Q.931. At this layer, ISDN addressing generally follows conventions from E.164.
Layer 2— In the ITU-T Q.921 LAPD data link protocol, the recommendation specifies the framing format for the ISDN call control message (in other words, LAPD encapsulated the Q.931 signaling message).
Layer 1—The ITU-TI.430/I.431 recommendation specifies the ISDN physical-layer interfaces: I.430 for the basic interface; I.431 for the primary interface.
Q.921—LAPD (Link Access Procedure on the D channel) Q.931—ISDN Network Layer between Terminal and Switch
Switching and Signaling
Q-Series
Standards from the ITU (formerly CCITT)

5. Signaling information (LAPD)
ISDN Access Options
Channel
Capacity
Mostly Used for B
64 kbps
Circuit-switched data (HDLC, PPP) D
16/64 kbps
Signaling information (LAPD)
BRI
NT1 D 2B
Service provider
network
Purpose: The figure explains BRI and PRI.
Emphasize: Be aware of geographic variations regarding ISDN services. With PRI, for example, there are 23 B channels in the United States and Japan and 30 in Europe.
Highlight that LAPD is the data link protocol on the D channel and PPP is typically seen on the B channels.
PRI
CSU/DSU D
23 or 30B
BRI and PRI are used globally for ISDN

6. BRI Call Processing ISDN service provider 1 3 4 ISDN Switch
Purpose: This figure describes the ISDN BRI call setup process.
Emphasize: The D channel is always up. The D channel is the signaling channel. The B channels are used to send data. 2
SS7
B channel(s)
D channel/SS7 signaling

7. ISDN Functions and Reference Points
Local loop
TE1
NT2
NT1
Service provider network S T U
ISDN Terminal
TE2 R TA
Functions are devices or hardware
Reference points are demarcations or interfaces
Purpose: This figure highlights ISDN hardware standards and reference points.
Emphasize: The TE1 designates a native ISDN device that can connect directly to its S/T interface. The TE1 characterizes a Cisco router that has a BRI.
The NT1 is a required external device that converts the 4-wire connection on the T interface to a 2-wire U line interface. The U interface also ensures rate conversion, clock synchronization, frame alignment, and adequate power supply, an provides an operational and maintenance control point for the service provider.
The TE2 designates a nonnative ISDN device that requires a TA for its S interface signals. The TE2 characterizes a Cisco router without a BRI.
The TA is an external device required on nonnative ISDN devices. The TA adapts the standard R-type device signals (RS-232, V.35, and so on) for the ISDN S/T interface. The S interface enables the connection for user devices and provides access the the useful transmission rate (for example, 144 kbps for BRI). The T interface corresponds to the S interface from the provider perspective. The T interface offers the total transmission rate (for example, 192 kbps from 2B*64+1D*16+1Y*48).
There is also a V interface that is part in the ISDN cloud. It is not covered here because it does not affect the CPE side of the connection
Terminal
Adapter
Existing
Terminal

8. Cisco ISDN BRI Interfaces
Native ISDN interface—int bri 0
Service provider network
TE1
bri 0
NT1
S/T
NT1
TE1
Purpose: This figure further highlights ISDN hardware standards and reference points for native and non-native ISDN devices.
Emphasize: Non-native ISDN devices, TE2s lack an ISDN BRI interface. To configure this device add an external TA to the serial interface; the TA contains the BRI S/T interface.
If the router does not have an NT1 interface, an external one must be provided. A simple way to check if the router is equipped with a built in NT1 is to check if it has an S/T or U interface. If the router has an S/T interface, it does not have a built in NT1. If it has a U interface, it has a built in NT1.
Note: Never connect a router with a U interface to an NT1 device because it could result in problems with the hardware.
bri 0
TE2
S/T R TA
NT1 U S0
Nonnative ISDN interface—int serial 0
(EIA/TIA-232, V.35, X.21)

9. ISDN Switch Types Many providers and switch typesCO S S S S CO
Many providers and switch types
Services vary by regions and countries
Purpose: The figure introduces an overview of ISDN switches.
Emphasize: The figure shows two representations of the ISDN world. In the top image, the cloud represents the providers by using different colors for the various switches they use.
An example of switch diversity occurs in Western Europe where all PTTs now offer ISDN. Despite efforts to adopt a common Euro-ISDN standard, switches in one nation may not easily interoperate with switches in another nation, Early adopters of ISDN, such as France, face major equipment upgrade efforts before they fully accommodate the European Telecommunication Standards Institute (ETSI) specifications.
For the administrator, a key requirement is to configure for compatibility with the switch on the ISDN local loop—the end-user ISDN device connected to the ISDN switch in the provider’s central office.
The lower image shows the globe and continental geographic representations to indicated the worldwide scope of ISDN standards-based networks. The bullet cautions that services and prices vary. ISDN coverage is not as seamless as it might appear on paper.
Note: Switch variations complicating ISDN switch configuration occur because of the different approaches used by ISDN providers at the network-layer functions between the terminal and the switch. Q.931 is the most prevalent protocol used for this network-layer function.

10. Configuring ISDN BRI Step 1: Specify the ISDN switch type
Router(config)#isdn switch-type switch-type
Router(config-if)#isdn switch-type switch-type
Specifies the type of ISDN switch with which the router communicates
Other configuration requirements vary for specific providers
Purpose: This figure describes how to configure the switch type.
Emphasize: The service provider must tell you what switch type it is using, or emulating, and what the SPIDs are.
The figure shows the command to specify the ISDN switch type. In newer versions of IOS, the switch type can also be configured at the interface level.
Note: If you need to change the switch type specified, you may need to reboot the router before the different switch type takes effect on the router.
Some service providers may use one switch type but emulate another. The switch type that must be configured is the one that is emulated.

11. Configuring ISDN BRI (cont.)
Step 2: (Optional) Setting SPIDs
Router(config-if)#isdn spid1 spid-number [ ldn ]
Sets a B channel SPID required by many service providers
Purpose: This figure describes how to configure SPIDs.
Emphasize: The isdn spid1 and isdn spid2 commands are used on some switches and are replacements for subaddresses.
Some service providers require SPIDs to authenticate that a call requests are within contract specifications. SPIDs are required for National ISDN-1 and DMS-100 ISDN switches.
Some service providers require that both spid1 and spid2 be specified, while others only require spid1.
Router(config-if)#isdn spid2 spid-number [ ldn ]
Sets a SPID for the second B channel

12. Label the functional elements and reference points
Written Exercise
BRI 0
Purpose: This exercise tests students knowledge of the ISDN hardware standards and reference points.
Emphasize: Students should fill in the empty boxes and circles with the ISDN functions and reference points.
Note: Answers are listed on the following figure. They are also listed in the “Answers” appendix in the Student Guide.
S 0
Customer Premises
Local Loop
Service Provider
Label the functional elements and reference points

13. Written Exercise: Answers
S/T
NT1 U
BRI 0 U R TA
S/T
NT1
Purpose: This figure provides the answers to the exercise on the pervious page.
Note: Answers are also listed in the “Answers” appendix in the Student Guide.
S 0
Customer Premises
Local Loop
Service Provider
Label the functional elements and reference points

14. What Is Dial-on-Demand Routing?
Dallas
Corporate
PSTN
Chicago
ISDN
I need to send
data to Dallas.
Purpose: This figure introduces students to DDR.
Emphasize: Explain that DDR is used to refer to a collection of dialup features.
Connect when needed
Disconnect when finished
ISDN or PSTN

15. When to Use DDR Periodic connections Small amounts of data
Telecommuter
Purpose: This figure explains when one would want to use DDR.
Emphasize: DDR is used for low-volume, periodic connections when traffic demands do not dictate the use of a dedicated line. DDR addresses the need for periodic network connections over a circuit-switched WAN service. By using WAN connections only on an as-need basis, DDR saves WAN-usage costs.
Note: Provide some scenarios when DDR may be used.
Headquarters
Periodic connections
Small amounts of data
Vendor

16. “Interesting” packet arrives
Generic DDR Operation
“Interesting” packet arrives
DCE
1. Route to destination is determined
Layer 1 of 4:
Purpose: This figure explains DDR operation.
Emphasize: Layer 1 shows interesting packets arriving at the router.

17. “Interesting” packet arrives
Generic DDR Operation
“Interesting” packet arrives
DCE
1. Route to destination is determined
2. Interesting packets dictate DDR call
Layer 2 of 4:
Purpose: This figure explains DDR operation.
Emphasize: Layer 2 shows the router looking for a route to a destination.
Introduce the concept of “interesting” traffic. This traffic is defined by some criteria, such as a particular kind of protocol or being permitted by an access list. Once this traffic has been identified, the router can monitor for interesting packets.

18. “Interesting” packet arrives
Generic DDR Operation
“Interesting” packet arrives
Dial connection
ISDN or Basic Service
DCE
1. Route to destination is determined
2. Interesting packets dictate DDR call
3. Dialer information is looked up
Layer 3 of 4:
Purpose: This figure explains DDR operation.
Emphasize: Layer 3 adds “dial connection” and dashed WAN connection between routers. The DCE device places a call to a predefined destination.

19. “Interesting” packet arrives
Generic DDR Operation
“Interesting” packet arrives
Dial connection
ISDN or Basic Service
DCE
1. Route to destination is determined
2. Interesting packets dictate DDR call
3. Dialer information is looked up
4. Traffic is transmitted
5. Call is terminated
Layer 4 of 4:
Purpose: This figure explains DDR operation.
Emphasize: Layer 4 adds fourth and fifth lines. After a user-defined idle period, the call is disconnected.
Point out that static routes are configured between the routers to avoid periodic transmissions over the WAN that would be caused by dynamic routing.

20. Configuring Legacy DDR
“Interesting” packet arrives
DCE 1
Define static routes—What route do I use?
Layer 1 of 3:
Purpose: This figure explains how to configure Legacy DDR.
Emphasize: It is important to note that these configuration steps are aligned with how the router processes a DDR call (refer to the “DDR Operation” discussion.
In layer 1, you must define the static route.

21. Configuring Legacy DDR
“Interesting” packet arrives
DCE 1
Define static routes—What route do I use?
Specify interesting traffic—What traffic enables the link?
Layer 2 of 3:
Purpose: This figure explains how to configure Legacy DDR.
Emphasize: In layer 2, you must define “interesting” traffic by specifying a protocol or access list. 2

22. “Interesting” packet arrives
Configuring DDR
“Interesting” packet arrives
Dial connection
ISDN or Basic Service
DCE 1
Define static routes—What route do I use?
Specify interesting traffic—What traffic enables the link?
Configure the dialer information—What number do I call?
Layer 3 of 3:
Purpose: This figure explains how to configure Legacy DDR.
Emphasize: Configure the dialer information. 2 3

23. Task 1: Defining Static Routes (Route to Destination)
Subnet
Subnets
ISDN
Home
Central
bri
bri 0
ip route
Purpose: This figure reviews how to configure a static route.
Emphasize: Static routes were covered in the “Determining IP Routes” chapter.
Static routes are commonly used with DDR. Dynamic routing protocols are not commonly used with DDR because the line could come up every time there is a routing update.
Specify address of next hop router
ip route
ip route
Network prefix
and prefix mask

24. Task 2: Specifying Interesting Traffic (What Enables the Connection?)
Without Access Lists
dialer-list 1 protocol ip permit
Any IP traffic will initiate the link
With Access Lists (for better control)
dialer-list 1 protocol ip list 101
access-list 101 deny tcp any any eq ftp
access-list 101 deny tcp any any eq telnet
access-list 101 permit ip any any
Purpose: This figure explains how to specify interesting traffic on a Cisco router.
Emphasize: This step involves some planning because access lists allow for much flexibility.
You must know exactly what kind of traffic should engage the line.
The dialer-list protocol command identifies interesting traffic based on protocol type. It can be used to specify an entire protocol suite. It can also be used to link an access list that more narrowly defines interesting packets to a dialer group.
Deny FTP
Deny Telnet
Any IP traffic, except FTP and Telnet, will initiate the link

25. Task 3: Configuring the Dialer Information
hostname Home !
isdn switch-type basic-5ess
username central password cisco
interface BRI0
ip address
encapsulation ppp
dialer idle-timeout 180
dialer map ip name Central
dialer-group 1
no fair-queue
ppp authentication chap
router rip
network
no ip classless
ip route
ip route
dialer-list 1 protocol ip permit
Applies rules defined by dialer-list to individual interfaces
Purpose: This figure explains how to configure the dialer interface.
Emphasize: Remind students to configure PPP on the dialer interface as they did on the serial interface in the “Establishing Serial Point-to-Point Connections” chapter. PPP is the data link protocol operating on the B channels.
The dialer-group command assigns an interface to a dialer access group (specified with the dialer-list command), and connects the interface to access list statements that identify interesting protocol traffic.
You can apply the same dialer list to one or more interfaces.
Both values must match

26. Task 3: Configuring the Dialer Information (cont.)
How do I get to
subnetwork ?
Subnets
ISDN
Home
Central
bri
bri 0
interface BRI0
ip address
encapsulation ppp
dialer idle-timeout 180
dialer map ip name Central
dialer-group 1
no fair-queue
ppp authentication chap
Purpose: This figure further explains how to configure the dialer interface.
Emphasize: The dialer-map command maps the remote protocol address to a telephone number. You need this command if you will be dialing multiple sites. If you will be dialing only one site, you could use and unconditional dialer string command that always dials the one phone number regardless of the traffic destination.
Note: This step is unique to Legacy DDR. Although the information is always required, the steps to configure destination information are different if using dialer profiles instead of Legacy DDR.
If you are dialing only one site, you could use the dialer-string command, although this method is rarely used because it does not allow for authentication.
Number to dial
Remote host name
Used for PPP CHAP

27. Legacy DDR Configuration Tasks Summarized
hostname Home !
isdn switch-type basic-5ess
username central password cisco
interface BRI0
ip address
encapsulation ppp
dialer idle-timeout 180
dialer map ip name Central
dialer-group 1
no fair-queue
ppp authentication chap
router rip
network
no ip classless
ip route
ip route
dialer-list 1 protocol ip permit 3
Purpose: This figure summarizes the tasks just presented.
Emphasize: Many times a configuration can look very confusing and complex. This page attempts to simplify the DDR configuration by showing a comprehensive configuration and matching the commands to the tasks just discussed.
Match the commands to the configuration tasks. 1 2

28. Optional Legacy DDR Commands
Router(config-if)#dialer load-threshold load [ outbound | inbound | either ]
Establishes the amount of traffic on link before a second link is enabled
Establishes the idle time before disconnect
Purpose: This figure presents some optional DDR commands.
Emphasize: The dialer idle-timeout as a default value of 120.
The dialer idle-timeout command specifies the amount of time the link stays idle before the connection is terminated. The dialer idle-timeout command is like a stopwatch. When the last interesting packet leaves the router, the router sets a timer to measure how long the interface is idle (defined by the absence of interesting traffic). If interesting traffic arrives, the timer is reset. If no interesting packets arrive at the interface before the timer expires, then the call is hung up even if non-interesting traffic is on the line.
The dialer load-threshold controls the conditions under which another call can be placed to the same destination. If you had too much traffic trying to squeeze over one phone line, then based on this parameter you may wish to place another simultaneous call to increase your bandwidth.
In releases before 11.1, load was only monitored in the outgoing direction.
Router(config-if)#dialer idle-timeout seconds

29. Legacy DDR Using ACLs Configuration Example
access-list 101 permit tcp any any eq smtp access-list 101 permit tcp any any eq telnet dialer-list 1 list 101 ! ip route ip route ! interface bri 0 ip address dialer-group 1 dialer map ip name B ! dialer idle-timeout 300
Access list defining interesting packets on Cisco A
Static routes to reach destination
Interface configuration for DDR
Purpose: This figure explains how to use access control lists with DDR.
Time to wait before dropping call
Subnets
ISDN A B

30. Verifying Legacy DDR and ISDN Operation
Triggers a link (assuming it is part of interesting traffic)
Router#ping or telnet
Displays current status of link, including amount of time link is connected
Router#show dialer
When using ISDN, displays call status while call is in progress
Router#show isdn active
Purpose: This figure highlights some of the verification commands used in ISDN.
Emphasize: Summarize the commands shown and provide examples of when each is used.
Displays the status of an ISDN connection
Router#show isdn status
Displays all routes, including static routes
Router#show ip route

31. Verifying Legacy DDR and ISDN Operation (cont.)
Router#debug isdn q921
Shows ISDN layer 2 messages
Router#debug isdn q931
Shows ISDN call setup and teardown activity
Shows call setup and teardown activity
Router#debug dialer
Purpose: This figure further highlights some of the verification commands used in ISDN.
Emphasize: Summarize the commands shown and provide examples of when each is used.
Clears currently established connections from the interface
Router(config-if)#shutdown

32. Visual Objective pod ro’s bri0 A 10.130.0.2 B 10.135.0.2 C 10.140.0.2
wg_pc_a
pod ro’s bri0 A B C D E F G H I J K L
e0/1
e0/2 e0
wg_ro_a
bri0
/24
wg_sw_a
PPP with CHAP
wg_pc_l
wg_ro_l
PPP with CHAP
e0/1
e0/2 e0
bri0
/24
Objectives: Establish an ISDN call.
Purpose: Teach students how to configure ISDN BRI and Legacy DDR on a Cisco router.
Laboratory Instructions: Refer to the Lab Setup Guide.
ISDN
wg_sw_l
...
s3/0 (pri)
fa0/24
fa0/23
fa0/0
/24 … /24
core_ server
core_sw_a
core_ro

33. Summary
After completing this chapter, you should be able to perform the following tasks:
Identify the components in an ISDN network
Configure ISDN BRI and legacy dial-on-demand routing (DDR)
Verify DDR operation using show and debug commands
Purpose: Review the summary items with your students.
Emphasize: Read or restate the summary statements. By now, your presentation and classroom discussion should have students able to meet the chapter learning objectives.

34. Review Questions
1. Differentiate between a native and a nonnative ISDN BRI interface.
2. How do you configure a Cisco router to interface to an ISDN switch? Why do you need to be specific about the switch type?
3. List and describe the three tasks associated with configuring DDR.
4. Why might you choose to use an access list to define interesting traffic for DDR?
Purpose: Review the chapter with open ended questions.
Note: The questions in this section are open ended questions designed to foster further discussion.
Answers the the review questions are in the “Answers” appendix.