Cisco IOS Dial Technologies Configuration Guide, Release 12.2SR
Configuring ISDN Caller ID Callback
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Configuring ISDN Caller ID Callback

Table Of Contents

Configuring ISDN Caller ID Callback

ISDN Caller ID Callback Overview

Callback After the Best Match Is Determined

Legacy DDR

Dialer Profiles

Timing and Coordinating Callback on Both Sides

How to Configure ISDN Caller ID Callback

Configuring ISDN Caller ID Callback for Legacy DDR

Configuring ISDN Caller ID Callback for Dialer Profiles

Monitoring and Troubleshooting ISDN Caller ID Callback

Configuration Examples for ISDN Caller ID Callback

Best Match System Examples

Best Match Based on the Number of "Don't Care" Characters Example

Best Match with No Callback Configured Example

No Match Configured Example

Simple Callback Configuration Examples

ISDN Caller ID Callback with Dialer Profiles Examples

ISDN Caller ID Callback with Legacy DDR Example

Individual Interface Example

Dialer Rotary Group Example


Configuring ISDN Caller ID Callback


This chapter describes how to configure the ISDN Caller ID Callback feature. It includes the following main sections:

ISDN Caller ID Callback Overview

How to Configure ISDN Caller ID Callback

Monitoring and Troubleshooting ISDN Caller ID Callback

Configuration Examples for ISDN Caller ID Callback

The ISDN Caller ID Callback feature conflicts with dialer callback security inherent in the dialer profiles feature for dial-on-demand routing (DDR). If dialer callback security is configured, it takes precedence; ISDN caller ID callback is ignored.

Caller ID screening requires a local switch that is capable of delivering the caller ID to the router or access server. If you enable caller ID screening but do not have such a switch, no calls will be allowed in.

ISDN caller ID callback requires DDR to be configured and bidirectional dialing to be working between the calling and callback routers. Detailed DDR prerequisites depend on whether you have configured legacy DDR or dialer profiles.

For a legacy DDR configuration, ISDN caller ID callback has the following prerequisite:

A dialer map command is configured for the dial string that is used in the incoming call setup message. The dial string is used in the callback.

For a dialer profiles configuration, ISDN caller ID callback has the following prerequisites:

A dialer caller command is configured to screen for the dial-in number.

A dialer string command is configured with the number to use in the callback.

To identify the hardware platform or software image information associated with a feature, use the Feature Navigator on Cisco.com to search for information about the feature or refer to the software release notes for a specific release. For more information, see the "Identifying Supported Platforms" section in the "Using Cisco IOS Software" chapter.

For a complete description of the ISDN caller ID callback commands mentioned in this chapter, refer to the Cisco IOS Dial Technologies Command Reference, Release 12.2. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.

ISDN Caller ID Callback Overview

ISDN caller ID callback allows the initial incoming call from the client to the server to be rejected on the basis of the caller ID message contained in the ISDN setup message, and it allows a callback to be initiated to the calling destination.

Before Cisco IOS Release 11.2 F, ISDN callback functionality required PPP or Combinet Packet Protocol (CPP) client authentication and client/server callback negotiation to proceed. If authentication and callback negotiation were successful, the callback server had to disconnect the call and then place a return call. Both the initial call and the return call were subject to tolls, and when service providers charge by the minute, even brief calls could be expensive.

This feature is independent of the encapsulation in effect and can be used with various encapsulations, such as PPP, High-Level Data Link Control (HDLC), Frame Relay, and X.25.

The ISDN Caller ID Callback feature allows users to control costs because charges do not apply to the initial, rejected call.

ISDN caller ID callback allows great flexibility for you to define which calls to accept, which to deny, and which calls to reject initially but for which the router should initiate callback. The feature works by using existing ISDN caller ID screening, which matches the number in the incoming call against numbers configured on the router, determining the best match for the number in the incoming call, and then, if configured, initiating callback to the number configured on the router.

When a call is received, the entire list of configured numbers is checked and the configuration of the best match number determines the action:

If the incoming number is best matched by a number that is configured for callback, the incoming call is rejected and callback is initiated.

If the incoming number is best matched by another entry in the list of configured numbers, the call is accepted.

If the incoming number does not match any entry in the configured list, the call is rejected and no callback is started.

"Don't care" characters are allowed in the caller ID screening configuration on the router and are used to determine the best match.

For more information and examples, see the "Best Match System Examples" section later in this document.

Callback After the Best Match Is Determined

The details of router activities after the router finds a best match with callback depend on the DDR feature that is configured. The ISDN Caller ID Callback feature works with the following DDR features:

Legacy DDR

Dialer Profiles

Legacy DDR

If legacy DDR is configured for the host or user that is identified in the incoming call message, the router performs the following actions:

1. Checks the table of configured numbers for caller ID callback.

2. Searches the dialer map entries for a number that "best matches" the incoming call string.

3. Waits for a configured length of time to expire.

4. Initiates callback to the number provided in the dialer map command.

Dialer Profiles

If the dialer profiles are configured for the host or user identified in the incoming call message, the router performs the following actions:

1. Searches through all the dialer pool members to match the incoming call number to a dialer caller number.

2. Initiates a callback to the dialer profile.

3. Waits for a configured length of time to expire.

4. Calls the number identified in the dialer string command associated with the dialer profile.

Timing and Coordinating Callback on Both Sides

When an incoming call arrives and the router finds a best match configured for callback, the router uses the value configured by the dialer enable-timeout command to determine the length of time to wait before making the callback.

The minimum value of the timer is 1 second; the default value of the timer is 15 seconds. The interval set for this feature on the router must be much less than that set for DDR fast call rerouting for ISDN (that interval is set by the dialer wait-for-carrier-time command) on the calling (remote) side. We recommend setting the dialer wait-for-carrier timer on the calling side to twice the length of the dialer enable-timeout timer on the callback side.


Note The remote site cannot be configured for multiple dial-in numbers because a busy callback number or a rejected call causes the second number to be tried. That number might be located at a different site, defeating the purpose of the callback.


How to Configure ISDN Caller ID Callback

To configure ISDN caller ID callback, perform the tasks in the following sections. The required configuration tasks depend whether you have configured legacy DDR or dialer profiles.

Configuring ISDN Caller ID Callback for Legacy DDR (As required)

Configuring ISDN Caller ID Callback for Dialer Profiles (As required)

For configuration examples, see the section "Configuration Examples for ISDN Caller ID Callback" at the end of this chapter.

Configuring ISDN Caller ID Callback for Legacy DDR

This section provides configuration tasks for the local (server, callback) side and the remote (client, calling) side.

On the callback (local) side, to configure ISDN caller ID callback when legacy DDR is configured, use the following commands in interface configuration mode:

 
Command
Purpose

Step 1 

Router(config-if)# isdn caller remote-number callback


or

Router(config-if)# dialer caller number callback

Configures caller ID screening and callback when a dialer rotary is not configured.

Configures caller ID screening and callback when a dialer rotary (dialer interface) is configured.

Step 2 

Router(config-if)# dialer enable-timeout seconds

Configures the time to wait before initiating callback.

On the calling (remote) side, to set the timer for fast call rerouting, use the following command in interface configuration mode:

Command
Purpose

Router(config-if)# dialer wait-for-carrier-time seconds

Changes the ISDN fast call rerouting timer to double the length of the enable timeout timer.


Configuring ISDN Caller ID Callback for Dialer Profiles

This section provides configuration tasks for the local side and the remote side.

On the callback (local) side, to configure ISDN caller ID callback when the dialer profiles are configured, use the following commands in interface configuration mode:

 
Command
Purpose

Step 1 

Router(config-if)# dialer caller number callback

Configures caller ID screening and callback.

Step 2 

Router(config-if)# dialer enable-timeout seconds

Configures the time to wait before initiating callback.

On the calling (remote) side, to set the timer for fast call rerouting, use the following command in interface configuration mode:

Command
Purpose

Router(config-if)# dialer wait-for-carrier-time seconds

Changes the ISDN fast call rerouting timer to double the length of the enable timeout timer.


Monitoring and Troubleshooting ISDN Caller ID Callback

To monitor and troubleshoot ISDN caller ID callback, use the following commands in EXEC mode as needed:

Command
Purpose

Router# show dialer

Displays information about the status and configuration of the ISDN interface on the router.

Router# debug isdn event

Displays ISDN events occurring on the user side (on the router) of the ISDN interface. The ISDN events that can be displayed are Q.931 events (call setup and tear down of ISDN network connections).

Router# debug isdn q931

Displays Layer 3 signaling messages, protocol transitions and processes, the line protocol state, and the channel IDs for each ISDN interface.


Configuration Examples for ISDN Caller ID Callback

The following sections provide ISDN caller ID callback configuration examples:

Best Match System Examples

Simple Callback Configuration Examples

ISDN Caller ID Callback with Dialer Profiles Examples

ISDN Caller ID Callback with Legacy DDR Example

Best Match System Examples

The best match is determined by matching the incoming number against the numbers in the configured callback commands, starting with the right-most character in the numbers and using the letter X for any "don't care" characters in the configured commands. If multiple configured numbers match an incoming number, the best match is the one with the fewest "don't care" characters.

The reason for using a system based on right-most matching is that a given number can be represented in many different ways. For example, all the following items might be used to represent the same number, depending on the circumstances (international call, long-distance domestic call, call through a PBX, and so forth):

011 1 408 555 7654
    1 408 555 7654
      408 555 7654
          555 7654
            5 7654

Best Match Based on the Number of "Don't Care" Characters Example

The following example assumes that you have an incoming call from one of the numbers from the previous example entered (4085557654), and that you configured the following numbers for callback on the router (disregarding for the moment the commands that can be used to configure callback):

555xxxx callback
5552xxx callback
555865x 
5554654 callback
xxxxx

The first number listed is the best match for the incoming number (in the configured number, the three numbers and four Xs all match the incoming number); the line indicates that callback is to be initiated. The last line has five Xs; it is not the best match for the calling number.


Note The last number in the list shown allows calls from any other number to be accepted without callback. When you use such a line, you must make sure that the number of Xs in the line exceeds the number of Xs in any other line. In the last line, five Xs are used; the other lines use at most four Xs.

The order of configured numbers is not important; the router searches the entire list and then determines the best match.


Best Match with No Callback Configured Example

The following example assumes that a call comes from the same number (4085557654) and that only the following numbers are configured:

5552xxx callback
555865x 
5554654 callback
xxxxx

In this case, the best match is in the final line listed, so the incoming call is accepted but callback is not initiated.

No Match Configured Example

The following example assumes that a call comes from the same number (4085557654) and that only the following numbers are configured:

5552xxx callback
555865x 
5554654 callback

In this case, there is no match at all, and the call is just rejected.

Simple Callback Configuration Examples

The following example assumes that callback calls will be made only to numbers in the 555 and 556 exchanges but that any other number can call in:

isdn caller 408555xxxx callback
isdn caller 408556xxxx callback
isdn caller xxxxx

The following example configures the router to accept a call with a delivered caller ID equal to 4155551234:

isdn caller 4155551234

The following example configures the router to accept a call with a delivered caller ID equal to 41555512 with any digits in the last two positions:

isdn caller 41555512xx

The following example configures the router to make a callback to a delivered caller ID equal to 41555512 with any digits in the last two positions. (The router rejects the call initially, and then makes the callback.) The router accepts calls from any other numbers.

isdn caller 41555512xx callback
isdn caller xxx

ISDN Caller ID Callback with Dialer Profiles Examples

The following example shows the configuration of a central site that can place or receive calls from three remote sites over four ISDN BRI lines. Each remote site is on a different IP subnet and has different bandwidth requirements. Therefore, three dialer interfaces and three dialer pools are defined.

! This is a dialer profile for reaching remote subnetwork 10.1.1.1.
interface dialer 1
 ip address 10.1.1.1 255.255.255.0
 encapsulation ppp
 dialer remote-name Smalluser
 dialer string 4540
 dialer pool 3
 dialer-group 1
 dialer caller 14802616900 callback 
 dialer caller 1480262xxxx callback 
!
! This is a dialer profile for reaching remote subnetwork 10.2.2.2.
interface dialer 2
 ip address 10.2.2.2 255.255.255.0
 encapsulation ppp
 dialer remote-name Mediumuser
 dialer string 5264540 class Eng
 dialer load-threshold 50 either
 dialer pool 1
 dialer-group 2
 dialer caller 14805364540 callback
 dialer caller 1480267xxxx callback 
 dialer enable-timeout 2
!
! This is a dialer profile for reaching remote subnetwork 10.3.3.3.
interface dialer 3
 ip address 10.3.3.3 255.255.255.0
 encapsulation ppp
 dialer remote-name Poweruser
 dialer string 4156884540 class Eng
 dialer hold-queue 10
 dialer load-threshold 80
 dialer pool 2
 dialer-group 2
!
! This map class ensures that these calls use an ISDN speed of 56 kbps.
map-class dialer Eng
 isdn speed 56
!
interface bri 0
 encapsulation PPP
! BRI 0 has a higher priority than BRI 1 in dialer pool 1.
 dialer pool-member 1 priority 100
 ppp authentication chap
!
interface bri 1
 encapsulation ppp
 dialer pool-member 1 priority 50
 dialer pool-member 2 priority 50
! BRI 1 has a reserved channel in dialer pool 3; the channel remains inactive
! until BRI 1 uses it to place calls.
 dialer pool-member 3 min-link 1
 ppp authentication chap
!
interface bri 2
 encapsulation ppp
! BRI 2 has a higher priority than BRI 1 in dialer pool 2.
dialer pool-member 2 priority 100
ppp authentication chap
!
interface bri 3
encapsulation ppp
! BRI 3 has the highest priority in dialer pool 2.
dialer pool-member 2 priority 150
ppp authentication chap

ISDN Caller ID Callback with Legacy DDR Example

This section provides two examples of caller ID callback with legacy DDR:

Individual Interface Example

Dialer Rotary Group Example

Individual Interface Example

The following example configures a BRI interface for legacy DDR and ISDN caller ID callback:

interface bri 0
 description Connected to NTT 81012345678901
 ip address 10.1.1.7 255.255.255.0
 no ip mroute-cache
 encapsulation ppp
 isdn caller 81012345678902 callback
 dialer enable-timeout 2
 dialer map ip 10.1.1.8 name spanky 81012345678902
 dialer-group 1
 ppp authentication chap

Dialer Rotary Group Example

The following example configures BRI interfaces to connect into a rotary group (dialer group) and then configures a dialer interface for that dialer group. This configuration permits IP packets to trigger calls. The dialer interface is configured to initiate callback to any number in the 1-480-261 exchange and to accept calls from two other specific numbers.

interface bri 0
 description connected into a rotary group 
 encapsulation ppp
 dialer rotary-group 1
!
interface bri 1
 no ip address
 encapsulation ppp
 dialer rotary-group 1
!
interface bri 2
 encapsulation ppp
 dialer rotary-group 1
!
interface bri 3
 no ip address
 encapsulation ppp
 dialer rotary-group 1
!
interface bri 4
 encapsulation ppp
 dialer rotary-group 1
!
interface dialer 0
 description Dialer group controlling the BRIs
 ip address 10.1.1.1 255.255.255.0
 encapsulation ppp
 dialer map ip 10.1.1.2 name angus 14802616900
 dialer map ip 10.1.1.3 name shamus 14802616901
 dialer map ip 10.1.1.4 name larry 14807362060
 dialer map ip 10.1.1.5 name wally 19165561424
 dialer map ip 10.1.1.6 name shemp 12129767448
 dialer-group 1
 ppp authentication chap


!
 dialer caller 1480261xxxx callback
 dialer caller 19165561424

 
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any 
examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes 
only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental. 
 
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