3.11 Globalised Call Routing Overview

This topic describes globalized call routing.

  • Allows one format (+E.164) to be used for routing to PSTN destinations.
  • Users can still type PSTN numbers in local format.
  • Localized input is globalized at call ingress.
  • Routing is based on numbers in +E.164 format.
  • At call egress, numbers are localized, depending on the egress device.
  • Substantially simplifies international dial plans, especially when using any of the following features.
    1. TEHO
    2. AAR
    3. SRST, CFUR
    4. Cisco Device Mobility
    5. Cisco Extension Mobility
  • Optionally, directory numbers are also configured in +E.164 format (although dialed differently internally).

With globalized call routing, all calls that involve external parties are based on one normalized format. This format is the +E.164 format, that is, a + prefix, followed by a number in E.164 format. Because +E.164 format is a globally unique format, call routing based on +E.164 numbers is called globalized call routing. With globalized call routing, numbers must use the following formats:

  • Normalized called-party numbers: The +E.164 format is used for all external destinations while a call is routed. It is also possible to use the +E.164 format for internal destinations during call routing.
  • Normalized calling-party numbers: When a call involves at least one external party, then the +E.164 global format is used for the source of the call. It is also possible to use +E.164 format on internal calls.

If sources of calls (users at phones, incoming PSTN calls at gateways, calls received through trunks, and so on) do not use the normalized format, this localized call ingress must be normalized before being routed. This requirement applies to all received calls (coming from gateways and trunks, as well as from phones).

After the call is routed and the path selection (if applicable) is performed, the destination device might need to change the normalized numbers to a local format. This change is referred to as localized call egress.

Localized call egress applies to these situations:

  • Calling-party and called-party numbers for calls that are routed to gateways and trunks: If the PSTN or the telephony system on the other side of a trunk do not support globalized call routing, then the called-party and calling-party numbers must be localized from the global format. An example would be to change the called-party number +494012345 to 011494012345 before sending the call out to the PSTN in the United States
  • Calling-party numbers for calls that are routed from gateways or trunks to phones, if the phone user does not want to see caller IDs in the global format: An example would be that the user at a U.S. phone wants to see PSTN callers that are located in the same area code as the seven-digit number and not in +1XXXXXXXXXX format.

Globalized call routing simplifies international dial plans because the core call-routing decision is always based on the same format, regardless of how the number was initially dialed and regardless of how the number looks at the egress device.

Globalized Call Routing: Number Formats

This section describes the number formats that are used in globalized call-routing Cisco Unified Communications Manager deployments.

The table explains the terms that are related to globalized call routing.

Term Description
Incoming PSTN call This term refers to a call from the PSTN to an internal phone. Like all calls, this call consists of two call legs (incoming and outgoing). See also the terms “call ingress” and “call egress” in this table. On an incoming PSTN call, the incoming call leg (call ingress) is from the PSTN gateway to Cisco Unified Communications Manager; the outgoing call leg (call egress) is from Cisco Unified Communications Manager to the internal phone.
Outgoing PSTN call This term refers to a call from an internal phone to the PSTN. Like all calls, this call consists of two call legs (incoming and outgoing). On an outgoing PSTN call, the incoming call leg (call ingress) is from the internal phone to Cisco Unified Communications Manager; the outgoing call leg (call egress) is from Cisco Unified Communications Manager to the PSTN gateway.
Call ingress This term refers to the incoming call leg, which is the call received by Cisco Unified Communications Manager.
Call egress This term refers to the outgoing call leg, which is the call routed to a destination by Cisco Unified Communications Manager.
Number normalization This term refers to the process of changing numbers to a well-defined, standardized (normalized) format. In this case, all external phone numbers are changed to +E.164 format (that is, the E.164 format with the plus [+] prefix).
Number globalization This term refers to the process of changing numbers to +E.164 format. Example: Because the normalized format is +E.164, normalization of a called number (for example, 4085551234) is achieved by globalizing the number, that is, changing the number to global format (for example, +14085551234).
Number localization This term refers to the process of changing from a normalized format (in this case, +E.164) to a local format. Usually the local format is the shortest possible format that does not conceal relevant information. Examples of a local format are 5551234 instead of +14085551234, or 9723334444 instead of +19723334444 (assuming that the device where localization occurs is located in the 408 area code of the NANP as indicated by the + prefix and country code 1).
PSTN format This format is the PSTN number in full (international) or partial (subscriber, national) E.164 format. Depending on the PSTN provider, it may or may not include a + prefix (in the case of a full E.164 format). It may also include an additional information element called TON.
Note

In Cisco IOS gateways, each call has an incoming and an outgoing dial peer, one for each call leg. In Cisco Unified Communications Manager, these call legs are referred to as call ingress and call egress.

On the left side of the figure, call ingress is illustrated by two types of call sources:

  • External callers: Cisco Unified Communications Manager receives calls through a gateway or trunk. Calls received from a PSTN gateway use the PSTN format.
  • Internal callers: Calls from internal callers are received from internal phones. In the case of calls to internal destinations (for example, phone-to-phone), calling-party and called-party numbers are typically provided as internal directory numbers. In the case of calls to external destinations (for example, phone-to-PSTN), the calling number is the directory number (at call ingress time) and the called number depends on the local dial rules for PSTN access. These dial rules can differ significantly per location.
    Note

    As mentioned earlier, it is also possible to configure directory numbers in +E.164 format. In this case, at call ingress the calling-party number of internal calls would be in +E.164 format and the called-party number would be in the format that is used for internal dialing (for example, 4-digit dialing).

The center of the figure illustrates the standards that are defined for globalized call routing. These defined standards are the following:

  • External to internal
    1. Calling-party number: +E.164
    2. Called-party number: Directory number
    Note

    If directory numbers or one of their aliases (enterprise alternate number or +E.164 alternate number) are specified in +E.164 format, then the +E.164 format is also used for the called party.

  • External to external (if applicable)
    1. Calling-party number: +E.164
    2. Called-party number: +E.164
  • Internal to internal
    1. Calling-party number: Directory number
    2. Called-party number: Directory number
    Note

    Similar to calls from external to internal endpoints, +E.164 format would be used if directory numbers are configured in +E.164 format.

  • Internal to external
    1. Calling-party number: +E.164
    2. Called-party number: +E.164

On the right side of the figure, call egress is illustrated by two types of call targets:

  • Gateways: When sending calls to the PSTN, the PSTN format that the PSTN provider requires is used for both the calling-party and the called-party numbers. The format of these numbers (especially of the called-party number) can significantly differ based on the location of the gateway (for example, different international access codes in the United States [011] versus in the European Union [00]).
  • Phones: When a call from an internal phone is sent to another internal phone, the call should be received at the phone with both the calling-party and called-party numbers by using internal directory number format (which may be +E.164 format). When a call from an external caller is sent to an internal phone, most users prefer to see the calling number in localized format (for example, seven or ten digits instead of +E.164 in case of the NANP). The called number is the DN and is usually not displayed at the phone.

It is evident from the figure that there are several situations in which the numbers that are provided at call ingress do not conform to the globalized format that is used for call routing. The same applies to call egress, where the globalized format is not always used when delivering the call to the endpoint. Therefore, localized call ingress must be globalized and the globalized format must be localized at call egress.

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