Understanding Dial-in and Callback

If you are a service provider or a corporate data center into which a remote location dials in during an emergency, you can configure your Juniper Networks device to accept incoming ISDN calls originating from the remote location. The dial-in feature enables the device to receive calls from the remote end of a backup ISDN connection. The remote end of the ISDN call might be a service provider, a corporate central location, or a customer premises equipment (CPE) branch office. Each dialer interface accepts calls from only callers whose caller IDs are configured on it.

Note: Incoming voice calls are currently not supported.

Alternatively, you can configure the device to reject the incoming ISDN calls and call back the remote location. The callback feature lets you control access by allowing only specific remote locations to connect to the device. The feature also enables the device to call back the caller from the remote end of a backup ISDN connection. Instead of accepting a call from the remote end of the connection, the device rejects the call, waits a configured period of time, and calls a number configured on the device's dialer interface.

When it receives an incoming ISDN call, the Juniper Networks device matches the incoming call's caller ID against the caller IDs configured on the device’s dialer interfaces. If an exact match is not found and the incoming call's caller ID has more digits than the configured caller IDs, the device performs a right-to-left match of the incoming call's caller ID with the configured caller IDs and accepts the incoming call if a match is found. For example, if the incoming call's caller ID is 4085550115 and the caller ID configured on a dialer interface is 5550115, the incoming call is accepted. Each dialer interface accepts calls from only callers whose caller IDs are configured on it.

This topic contains the following sections:

• Dial-in and Callback Encapsulation
• Dial-in Configuration
• Callback Configuration

Dial-in and Callback Encapsulation

The dialer interface of the device and the dialer interface of the remote device must have the same encapsulation—PPP, Multilink PPP, or Cisco HDLC. If the encapsulation is different, the ISDN call is dropped. Table 15 describes how the device performs encapsulation monitoring.

Dial-in Configuration

When you enable the dial-in feature on a dialer interface associated with an ISDN physical interface, the device accepts incoming calls. You can specify that the interface accept all incoming calls, or you can configure up to 15 specific incoming numbers per dialer interface that you want the device to accept.

If multiple devices are connected to the same ISDN line, you can configure an ISDN interface to screen incoming calls based on the incoming called number. Each interface accepts only the calls whose called numbers are configured on it. If an exact match is not found, the incoming call is ignored.

The same caller ID must not be configured on different dialer interfaces. However, you can configure caller IDs with more or fewer digits on different dialer interfaces. For example, you can configure the caller IDs 14085550115, 4085550115, and 5550115 on different dialer interfaces. Additionally, if you configure one of the interfaces to accept all calls, the device only uses that interface if the incoming call's caller ID does not match the caller IDs configured on other dialer interfaces.

You can also configure the device to reject (ignore) calls from specific numbers. You might choose to use this option if a the number belongs to another device connected to the same ISDN line. For example, if another device on the same ISDN line has the called number 4085551091, you can configure the called number 4085551091 with the reject option on the ISDN interface so that it does not accept calls with that number.

Callback Configuration

When you enable the callback feature on a dialer interface, the ISDN interface rejects incoming calls, waits for 5 seconds (the default callback wait period) or the interval you specify, and then calls back the incoming number.

Before configuring callback on a dialer interface, ensure that the following conditions exist:

• The dialer interface is not configured as a backup for a primary interface.
• The dialer interface does not have a watch list configured.
• Only one dial string is configured for the dialer interface.
• Dial-in is configured on the dialer interface of the remote device that is dialing in.

Related Topics

• Junos OS Feature Support Reference for SRX Series and J Series Devices