IMG 1010 - SIP Redirect - IW Call Diversion Info to SS7

Owned by Kelli Higdon
Last updated: Mar 04, 2024
6 min read

When a call is Redirected (also known as Call Forwarding), the called party redirects the call to a third party. The redirecting could be the result of the line being busy, the called party configured for call forwarding, or a host of other reasons. When the call is redirected, the ACM and/or CPG backward call messages will be mapped back to the SIP leg in either the Diversion or History-Info headers. The parameters that will be mapped are displayed in the table below.

Backward Call Messages

Address Complete Message (ACM)

  • Optional Backward Call Indicators

  • Generic Notification Indicators

  • Redirection Number

  • Redirection Number Restriction Indicator

  • Call Diversion Information

Call Progress Message (CPG)

  • Optional Backward Call Indicators

  • Generic Notification Indicators

  • Redirection Number

  • Redirection Number Restriction Indicator

  • Call Diversion Information

 These parameters are all mapped back to the SIP leg. Refer to the Call Flow diagrams below as to when and how they are mapped.

Call Flow Diagrams

The first call flow below displays one scenario of a call being Redirected from an SS7 User to an ISDN User. The call flows to follow display the mappings from the SS7 backward call messages to SIP mappings.

Call Flow 1 - Basic Redirecting Scenario

In the Call Flows below, the call is first sent to the SS7 User. The SS7 User is configured to redirect the call to the Redirected User and redirects the call. The SS7 User also sends either an ACM or CPG message in the backward direction with the redirection information. The parameters in the ACM or CPG message will determine how the redirecting information will be mapped back to the original SIP User. Also, the IMG can be configured to map the parameters back to the SS7 User in either the SIP Diversion Header or SIP History-Info Header.

Call Flow 2 - ACM mapped to 183 Progress

Information in the backward ACM message

In the scenario where all of the parameters in the bulleted list below are received in the backward ACM message:

  • Backward Call Indicator (BCI=0) = No Indication

  • Redirection Number

  • Call Diversion Information

The parameters received are mapped to either the Diversion Header or the History-Info Header in the 183 Session Progress message. Refer to the call flow diagram below. For individual parameter mappings, refer to the Diversion and History-Info Mappings section in this topic.

 

Call Flow 3 - ACM mapped to 180 Ringing

Information in the backward ACM message

In the scenario where all of the parameters in the bulleted list below are received in the backward ACM message.

  • Backward Call Indicator (BCI=1) = Subscriber Free

  • Optional Backward Call Indicator (OBCI) = Call Diversion May Occur

The parameters received are mapped to either the Diversion Header or the History-Info Header in the 180 Ringing message. Refer to the call flow diagram below. For individual parameter mappings, refer to the Diversion and History-Info Mappings section in this topic.

Call Flow 4 - CPG mapped to 183 Progress

Information in the backward CPG message

In the scenario where the Event parameter includes either the CFB, CFNR, or CFU along with both the Redirection Number and Call Diversion Information in the backward CPG message. See list below.

  • Event = Call Forwarding Busy (CFB) -or- Call Forwarding Unconditional (CFU) -or- Call Forwarding No Reply (CFNR).

  • Includes Redirection Number

  • Includes Call Diversion Information (CDI)

The parameters received are mapped to either the Diversion Header or the History-Info Header in the 183 Progress message. Refer to the call flow diagram below. For individual parameter mappings, refer to the Diversion and History-Info Mappings section in this topic.

Call Flow 5 - CPG mapped to 183 Progress

Information in the backward CPG message

In the scenario where the Event parameter includes either the CFB, CFNR, or CFU but does not include the Redirection Number or the Call Diversion Information in the backward CPG message. See list below.

  • Event = Call Forwarding Busy (CFB), Call Forwarding Unconditional (CFU), or Call Forwarding No Reply (CFNR).

  • Does NOT include the Redirection Number

  • Does NOT include the Call Diversion Information (CDI)

The parameters received are mapped to either the Diversion Header or the History-Info Header in the 183 Progress message with Default Values. Refer to the call flow diagram below. For individual parameter mappings, refer to the Diversion and History-Info Mappings section in this topic.

Call Flow 6 - CPG  mapped to 180 Ringing

Information in the backward CPG message

In the scenario where the Event parameter is set to Alerting and either the Redirection Number, the Call Diversion Information or both are included in the backward CPG message. See list below.

  • Event = Alerting, Call Forwarding Unconditional (CFU), or Call Forwarding No Reply (CFNR).

  • Includes either the Redirection Number or Call Diversion Information (CDI).

The parameters received are mapped to either the Diversion Header or the History-Info Header in the 180 Ringing message. Refer to the call flow diagram below. For individual parameter mappings, refer to the Diversion and History-Info Mappings section in this topic.

 Call Flow 7 - CPG mapped to 180 Ringing without Diversion/History-Info Header

Information in the backward CPG message

In the scenario where the Event parameter is set to Alerting and neither the Redirection Number, nor the Call Diversion Information are included in the backward CPG message. See list below.

  • Event = Alerting

  • Does NOT include the Redirection Number

  • Does NOT include the Call Diversion Information (CDI)

The parameters received NOT mapped to the Diversion or History-Info Header. Refer to the call flow diagram below.

Call Flow 8 - CPG mapped to 183 Progress

Information in the backward CPG message

In the scenario where the Event parameter is set to Progress and either the Redirection Number, the Call Diversion Information or both are included in the backward CPG message. See list below.

  • Event = Progress

  • Includes either the Redirection Number, the Call Diversion Information (CDI), or both

The parameters received are mapped to either the Diversion Header or the History-Info Header in the 183 Progress message. Refer to the call flow diagram below. For individual parameter mappings, refer to the Diversion and History-Info Mappings section in this topic.

 

Call Flow 9 - CPG mapped to 183 Progress

Information in the backward CPG message

In the scenario where the Event parameter is set to Progress and neither the Redirection Number, nor the Call Diversion Information are included in the backward CPG message. See list below.

  • Event = Progress

  • Does NOT include the Redirection Number

  • Does NOT include the Call Diversion Information (CDI)

The parameters received NOT mapped to the Diversion or History-Info Header. Refer to the call flow diagram below.

Diversion and History-Info Mappings SS7 to SIP

As described above, the parameters in the ACM and CPG backward messages can be mapped to either the SIP Diversion Header or the SIP History-Info Header. Below are tables displaying how the parameters in the ACM and CPG messages are mapped to the SIP Diversion and SIP History-Info Headers.

Diversion Header Mappings

The IMG implementation of SIP Diversion Header is compatible with RFC 5806.

 

Call Diversion Info

 

Parameters in ACM/CPG

Diversion Header Parameters

Notification Subscription Options

 

 

 

Unknown

privacy=off

 

Presentation Not Allowed

privacy=full

 

Presentation Allowed with Redirection Number

privacy=off

 

Presentation Allowed without Redirection Number

privacy=off

Redirecting Reason

 

 

 

Unknown/ Not Available

reason=unknown

 

User Busy

reason=user busy

 

No Reply

reason=no answer

 

Unconditional

reason=unconditional

 

Deflection During Alerting

reason=deflection during alerting

 

Deflection Immediate Response

reason=deflection immediate response

 

Mobile Subscriber Not Reachable

reason=unknown

 

Call Forwarding DTE Out of Order

reason=unavailable

 

Call Deflection or Call Forwarding by the Called DTE

reason=deflection

 

Call Forwarding Unconditional or Systematic Call Redirection

reason=unconditional

Redirecting Number

 

Parameters in ACM/CPG

Diversion Header Parameters

Nature of Address ind=x

 

noa=x

Address Signals

1234

username=1234

 

Not Available

unknown@unknown.invalid

 

 

counter=1 (By Default)

History-Info Header Mappings

 

Call Diversion Info

 

Parameters in ACM/CPG

History-Info Header Parameters

Notification Subscription Options

 

 

 

Unknown

privacy=none or absent

 

Presentation Not Allowed

privacy=history

 

Presentation Allowed with Redirection Number

privacy=none or absent

 

Presentation Allowed without Redirection Number

privacy=none or absent

Redirecting Reason

 

 

 

Unknown/ Not Available

cause=404

 

User Busy

cause=486

 

No Reply

cause=408

 

Unconditional

cause=302

 

Deflection During Alerting

cause=302

 

Deflection Immediate Response

cause=302

 

Mobile Subscriber Not Reachable

cause=503

Redirecting Number

 

Parameters in ACM/CPG

Diversion Header Parameters

Nature of Address ind=x

 

noa=x

Address Signals

 

username

Configuration

There is no additional configuration needed for the functionality described above.

 

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