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This chapter describes configuration of the ISDN Caller ID Callback feature. It includes the following main sections:
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:
For a dialer profiles configuration, ISDN caller ID callback has the following prerequisites:
For a complete description of the ISDN caller ID callback commands in this chapter, see the Cisco IOS Dial Services Command Reference publication. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.
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:
"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" section later in this document.
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:
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.
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.
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 this 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.
The required configuration tasks depend whether you have configured legacy DDR or dialer profiles. Perform the tasks in the following sections:
For configuration examples, see the section "ISDN Caller ID Callback Configuration Examples" at the end of this chapter.
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 | isdn caller remote-number callback | Configures caller ID screening and callback when a dialer rotary is not configured. |
Step2 | dialer enable-timeout seconds | Configures the time to wait before initiating callback. |
| Command | Purpose |
|---|---|
dialer wait-for-carrier-time seconds | Changes the ISDN fast call rerouting timer to double the length of the enable timeout timer. |
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 | |
|---|---|---|
Step1 | dialer caller number callback | Configures caller ID screening and callback. |
Step2 | 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 |
|---|---|
dialer wait-for-carrier-time seconds | Changes the ISDN fast call rerouting timer to double the length of the enable timeout timer. |
To monitor and troubleshoot ISDN caller ID callback, use the following commands in EXEC mode:
| Command | Purpose |
|---|---|
show dialer | Displays information about the status and configuration of the ISDN interface on the 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 teardown of ISDN network connections). |
debug isdn q931 | Displays Layer 3 signalling messages, protocol transitions and processes, the line protocol state, and the channel IDs for each ISDN interface. |
This section provides the following 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 1 408 556 7654
1 408 556 7654
408 556 7654
556 7654
6 7654
556xxxx callback 555xxxx callback 559765x 5577654 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.
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NoteThe 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. |
The following example assumes that a call comes from the same number (4085567654) and only the following numbers are configured:
555xxxx callback 559765x 5577654 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.
The following example assumes that a call comes from the same number (4085567654) and only the following numbers are configured:
555xxxx callback 559765x 5577654 callback
In this case, there is no match at all, and the call is just rejected.
The following example assumes callback calls will be made only to numbers in the 555 and 556 exchanges, but 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
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 1.1.1.1. interface Dialer1 ip address 1.1.1.1 255.255.255.0 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 2.2.2.2. interface Dialer2 ip address 2.2.2.2 255.255.255.0 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 3.3.3.3. interface Dialer3 ip address 3.3.3.3 255.255.255.0 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
This section provides two examples of caller ID callback with legacy DDR:
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 7.1.1.7 255.255.255.0 no ip mroute-cache encapsulation ppp isdn caller 81012345678902 callback dialer enable-timeout 2 dialer map ip 7.1.1.8 name spanky 81012345678902 dialer-group 1 ppp authentication chap
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 8.1.1.1 255.255.255.0 encapsulation ppp dialer map ip 8.1.1.2 name angus 14802616900 dialer map ip 8.1.1.3 name moe 14802616901 dialer map ip 8.1.1.4 name larry 14807362060 dialer map ip 8.1.1.5 name curly 19165561424 dialer map ip 8.1.1.6 name shemp 12129767448 dialer-group 1 ppp authentication chap ! dialer caller 1480261xxxx callback dialer caller 19165561424 dialer caller 12129767448 ! dialer-list 1 protocol ip permit
Posted: Tue Jul 18 15:17:44 PDT 2000
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