1. Time Division Multiplexing Guide
  2. Overlap Dialing for Call Routing

8 Overlap Dialing for Call Routing

Some countries use variable length numbers in call plans, which can cause the Oracle® Enterprise Session Border Controller (ESBC) to trigger the SIP INVITE before all of the digits arrive. Overlap dialing provides a mechanism that the Acme Packet 1100 and Acme Packet 3900 can use in a Time Division Multiplexing (TDM)-to-SIP deployment to wait for all of the digits and answer a Q.931 SETUP message with the SETUP ACKNOWLEDGE instead of an immediate PROCEEDING or ALERTING message.

Without overlap dialing enabled, the Acme Packet 1100 and Acme Packet 3900 consider only the digits in the SETUP message and ignore subsequent digits. The behavior causes the Acme Packet 1100 and Acme Packet 3900 to build the SIP INVITE too soon and the SIP call either stops or connects to the wrong destination.

With overlap dialing enabled, the Acme Packet 1100 and Acme Packet 3900 can work with the information in the SETUP message. When the SETUP message contains no "Sending Complete" element, the system waits for three seconds to receive an additional digit. Each additional digit restarts the digit collection timer until all digits are collected. The system creates the SIP INVITE only after collecting all of the digits, resulting in successful calls.

In some circumstances, even three seconds might be too short to collect all of the digits. The system may need more time, but the underlying hardware does not allow you to alter the digit collection time span. You can extend the digit collection time span by way of the software with the incoming-pattern parameter in the tdm-profile configuration. When the collected digits do not map to a pattern, for example when a number is longer than the pattern, the system triggers a longer timer. With the incoming-pattern set, the system can respond in the following ways:
  • The number does not match any pattern—The digit collection timer waits up to eight seconds for more digits. If the timer expires before collecting the necessary digits, the system releases the call. If the system receives more digits, the extension matching procedure repeats.
  • The number matches a pattern and there might be enough digits received to route the call, but the match is still ambiguous—The digit collection timer waits three seconds for more digits. If the timer expires, the system sends the SIP INVITE. If the system receives more digits, the extension matching procedure repeats.
  • The number matches, does not allow any more digits, and no other pattern would match even if more digits were received—The system sends the SIP INVITE without waiting.

Configuration

The configuration process includes setting the following parameters in tdm-profile:
  • Set the overlap-dial parameter to incoming to enable overlap dialing.
  • Specify the match pattern in the incoming-pattern parameter. See "Incoming Call Patterns for TDM" for rules and syntax.

Note:

Overlap dialing does not prevent en-bloc dialing from working.

Supported Platforms

Acme Packet 1100—with the single-port or four-port PRI interface, the four-port Euro ISDN BRI interface, and the analog interface

Acme Packet 3900—with the four-port PRI interface.