Trunks Number Call Identification

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  • Prefix: This setting is used as a representation of the system when making outbound calls. If an ANI has not been set, the system puts the prefix (if there is one) in front of the primary account number and uses that as the ANI before it leaves the trunk. This is very useful in cases when a trunk deals with a range of numbers (typically outside of the NANPA area, e.g., Europe). The "extension" number is put after the prefix.
  • Trunk ANI: You can configure each trunk with an ANI (Automatic Number Identification). ANI is a service that tells the recipient of a telephone call the telephone number of the person making the call. In most cases, the ANI is used in the From field in the SIP packets or the caller ID.
  • Remote Party/Privacy Indication: This setting tells the system how to present the caller-ID on the trunk. The following values are available for configuring this setting :
―RFC3325 (P-Asserted-Identity): RFC 3325 describes a way to represent these two numbers. In most cases, it makes sense to use the P-Asserted-Identity header. In this case, the From header in the INVITE represents the display number, while the P-Asserted-Identity header has the network number. A similar representation can be done with the P-Preferred-Identity header. The system changes only the name of the header from P-Asserted-Identity to P-Preferred-Identity. The rest remains the same, as in the first method.
―No Indication: No Indication: This method simply discards the display number and uses only the network number in the From header. This method is a fallback when the provider cannot handle any other method. The disadvantage here is clearly that any redirection information gets lost.
―Remote-Party-ID: Remote-Party-ID: This method is described in a draft that expired years ago; however, there is still a lot of equipment outside that is supporting this method. In this case, the From header in the INVITE represents the network number, while the P-Asserted-Identity header is the display number.
―RFC3325, but don't hide: RFC 3325, but don’t hide: This method should not be used. It has been used in environments where the fields have gotten mixed up, and it is creating even more confusion.
Custom Headers: Custom headers are discussed in detail on the Custom Trunk Headers page. A few trunk provider specific samples are shown here.
  • Rewrite global numbers: When you are using a trunk, you may have to represent the telephone number in a specific format. For example, in the NANPA area, you might want to use 10 or 11 digits to represent a national number. When Use + symbol at the beginning is selected, the system will automatically use 11 digits.
  • Charging Vector: The "ICID" (IMS Charging Identifier) setting is used in the IMS(IP Multimedia Subsystem) environment. The setting is sent in the P-Charging-Vector header of the SIP packets on this trunk and it is essentially a token that identifies the trunk. If your provider uses this header, you should put it into this field.
  • Generate unique extension identifier: This setting allows you to use the extension’s EPID instead of the ANI if the extension’s EPID has already been set. If extension’s EPID is not set, “generate” a new EPID and use it (and set it for extension for the future use too)
  • Interpret SIP URI always as telephone number: When a call comes into the system, the system needs to know how to interpret the number. In SIP, the URI contains a domain name; however, in most cases, the domain name should be ignored when interpreting the URI coming from this trunk (because the user portion is just a telephone number). Usually, this is indicated by the parameter “user=phone,” but not all service providers set this flag. By turning on the “Interpret SIP URI always as telephone number,” you make the system believe that this flag was set on the trunk call.
  • Caller ID update on trunk: This setting is used to update the caller ID information on the trunk. For example, if you want to update the caller ID that is sent to a remote party, when a call is transferred, you can use this setting. This is dependent on whether the trunk provider supports that feature.