IMG 1010 - SIP Diversion Header

Overview

The IMG supports the INVITE Diversion Header (Diversion and CC-Diversion) to support PSTN Redirecting Services (also known as Call Forwarding). The INVITE Diversion header carries information about the redirection of a call. The Diversion header prevents the pertinent SS7 or ISDN redirection information from being lost in the SS7/ISDN to SIP conversion. When SS7 redirection information is received on the incoming side, it is relayed in the Diversion header on the outgoing SIP side. The Call Flows below describe the functionality that is supported when utilizing the SIP Diversion Header. To enable or disable SIP Diversion Header refer to the IMG 1010 - SIP Headers topic.

In software 10.5.1 a new enhancement was added which includes a charge number parameter in the outgoing IAM message upon receiving an INVITE message from on the incoming SIP channel group. If the user wants to eliminate the charge number parameter, the charge number can be filtered out using the IMG 1010 - SS7 Parameter Filter object.

Scenarios

The call flow diagrams below display the supported functionality when utilizing the Diversion Header.

SS7 to SIP Call Forwarding Scenario

In the call flow below, the Redirecting number and Original called number is interworked from the SS7 to SIP. When a Redirecting number and Original Called number are present the following is true.

The Redirecting number will always be interworked to the SIP side as the topmost Diversion Header.
The Original Called number will always be interworked to the SIP side as the bottommost Diversion Header.

SS7 to SIP with NOA Scenario (10.5.3 SP9)

When an SS7 IAM is received, one of the following scenarios will occur.

If the incoming IAM message contains only the Redirecting Number parameter, the Nature Of Address parameter on the incoming IAM message will be interworked to the outgoing SIP Diversion Header as noa=x.
If the incoming IAM message contains only the Original Called Number parameter, the Nature Of Address parameter in the incoming IAM message will be interworked to the outgoing bottommost SIP Diversion Header as noa=y.
If the incoming IAM message contains both the Redirecting Number and Original Called Number, the Nature Of Address parameters will be interworked into two separate Diversion headers. The topmost Diversion Header in the SIP INVITE will contain the Nature Of Address parameter (noa=x) of the Redirecting Number. The bottommost Diversion Header in the SIP INVITE message will contain Nature Of Address parameter (noa=y) of the Original Called number.
The interworking of the Nature Of Address parameter is configured using the SIP Header Parameters object

Refer to the Call Flow below.

SIP to SS7 - Map single Diversion Header into both the Redirecting and Original called parameters (10.5.3 SP9)

In the call flow below, a single SIP Diversion Header is interworked to the SS7 side. In this scenario, the following is true.

The number in the SIP Diversion Header is interworked to both the Redirecting Number and the Original Called Number.
If the Original Called Number is not needed on the SS7 side, it can be filtered by setting the Original Called Number field in the IMG 1010 - SS7 Parameter Filter object to Don't Pass.
If the Redirecting Number is not needed on the SS7 side, it can be filtered by setting the Redirecting Number field in the IMG 1010 - SS7 Parameter Filter object to Don't Pass.

SIP to SS7 with NOA Scenario (10.5.3 SP4.1)

When a SIP INVITE message is received and one or more Diversion Headers are present with the Nature of Address parameter, the IMG will map the values to the ISUP Redirecting and Original Called Numbers as described below.

The Nature of Address parameter in the topmost Diversion Header received is mapped to the Redirecting Number on the SS7 side.
The Nature of Address parameter in the bottommost Diversion Header received is mapped to the Original Called Number on the SS7 side.
If the SIP INVITE message received has a Diversion Header without a Nature Of Address parameter then a Default value of NOA=3 will be added to the outgoing ISUP messaging.
If the Original Called Number is not needed on the SS7 side, it can be filtered by setting the Original Called Number field in the IMG 1010 - SS7 Parameter Filter object to Don't Pass.
If the Redirecting Number is not needed on the SS7 side, it can be filtered by setting the Redirecting Number field in the IMG 1010 - SS7 Parameter Filter object to Don't Pass.

ISDN to SIP Call Forwarding Scenario

In the call flow below the following scenario occurs.

The 1st Redirecting Number received in the ISDN SETUP message will be interworked into the topmost Diversion header on the SIP side.
The 2nd Redirecting Number received in the ISDN SETUP message will be interworked into the bottommost Diversion header on the SIP side.