2.14 Dial Plan Solutions for Multisite Deployments

This topic provides an overview of dial plan solutions in multisite deployments.

  • Overlapping and nonconsecutive numbers
    1. Solved by access code and (unique) site code
    2. Allows routing that is independent of directory numbers
    3. Appropriate digit manipulation required
  • Variable-length numbering
    1. Dial string length is determined by timeout or use of # key.
    2. Overlap sending and receiving
  • DID ranges and PSTN addressing
    1. Use of interactive voice response applications (AA, B-ACD, etc.) or attendant required if no DID numbers
    2. Directory numbers appended to PSTN number (with variable-length dial plans, if supported by PSTN)
  • Number presentation (ISDN TON)
  • Least Cost Routing, TEHO, PSTN backup (based on prioritized paths).
  • Globalized call routing based on uniform format (+E.164)
    1. Globalized at call ingress
    2. Routed in +E.164 format
    3. Localized at call egress

Dial plan issues in multisite deployments can be solved in the following ways:

  • Overlapping and nonconsecutive numbers: This issue can be solved by implementing access codes and site codes for intersite dialing. This approach allows call routing that is independent of directory numbers. Appropriate digit manipulation (removal of site codes in the called number of outgoing calls) and prefixing of site codes in the calling number of incoming calls are required.
  • Variable-length numbering plans: Dial string length is determined by timeout. Overlap sending and receiving is enabled, allowing dialed digits to be signaled one by one instead of being sent as one whole number.
  • DID ranges and E.164 addressing: Solutions for mapping of internal directory numbers to PSTN numbers include DID, use of attendants or IVR applications to transfer calls, and extensions that are added to PSTN numbers in variable-length numbering plans.
  • Different number presentation in ISDN (TON): Digit manipulation that is based on TON enables the standardization of numbers that are signaled using different TONs.
  • Least Cost Routing, TEHO, and PSTN backup: These solutions can be implemented by appropriate call routing and path selection that is based on priorities.
  • Globalized call routing: In this dial plan implementation, all received calls are normalized toward a standardized format. The format that is used in call routing is globalized format, because all numbers are represented in +E.164 format. The process of normalizing the numbers dialed by end users (localized ingress) is therefore also referred to as globalization. Once the localized input has been globalized during ingress, the call is routed based on globalized numbers. After call routing and path selection, the called number is localized during call egress, depending on the selected egress device.