IMSSF Protocol Translator Guide

This document details basic procedures for system administrators managing, maintaining, configuring, and deploying OpenCloud’s IM-SSF Module.

IM-SSF provides protocol translation from SIP to ETSI INAP CS1 and CAP v1/v2/v3 with the Service Interaction SLEE (SIS).

Topics

About the IM-SSF — IM-SSF features; and how it is triggered, looks up subscription information, classifies the call as originating or terminating, and runs the BCSM
Installing the IM-SSF — prerequisites, installation procedures, licenses and activation, and details for CGIN and CDR resource adaptor entities
Configuring the IM-SSF — configuring general properties, subscription information, and user interface
IM-SSF Statistics — parameter sets related to originating and terminating BCSMs, charging and writing call detail records, looking up subscription information, user interaction, and routing to the called party
IM-SSF Alarms — alarm types and descriptions
Using the IM-SSF — how to include the IM-SSF in a service composition, support more than one IM-SSF use in a service composition, override the IM-SSF method for classifying originating or terminating access tracing in the IM-SSF, support IM-SSF acting as an assisting SSF for announcements, and use rate limiting with the IM-SSF.

For more information

The IM-SSF Changelog
Documentation on the Service Interaction SLEE (SIS)

About the IM-SSF

The IM-SSF module provides support for protocol translation from SIP to ETSI INAP CS1 and CAP v1/v2/v3.

Support for translation into other SS7 protocols are part of the IM-SSF module roadmap.

The IM-SSF module implements most of the features of the IMS specification (3gpp 23.278 'IM CN Interworking'), plus some additional features (such as support for ETSI INAP CS1).

Standalone IM-SSF

The IM-SSF is also available as a dedicated standalone product. Contact your OpenCloud sales representative for more details.

Below are tables outlining features related to 3gpp 23.278, plus additional features of the IM-SSF.

Feature supported Description

Feature supported	Description
CAPv1, CAPv2, CAPv3	supports CAMEL phase 1, 2, and 3
Call Control	supports messages such as `InitialDP`, `RequestReportBCSM`, `EventReport`, `Connect`, `Continue`
Charging	supports `FurnishChargingInformation`, `ApplyCharging`, and `ApplyChargingReport`
User Interaction	supports `ConnectToResource` and `PlayAnnouncement`, acting as an assisting SSF when it receives and `EstablishTemporaryConnection`, and responding with a second dialog starting with an `AssistRequestInstructions`
O-IM-CSI, VT-IM-CSI	supports both originating and terminating subscription information

CAPv1, CAPv2, CAPv3

supports CAMEL phase 1, 2, and 3

Call Control

supports messages such as InitialDP, RequestReportBCSM, EventReport, Connect, Continue

Charging

supports FurnishChargingInformation, ApplyCharging, and ApplyChargingReport

User Interaction

supports ConnectToResource and PlayAnnouncement, acting as an assisting SSF when it receives and EstablishTemporaryConnection, and responding with a second dialog starting with an AssistRequestInstructions

O-IM-CSI, VT-IM-CSI

supports both originating and terminating subscription information

Feature NOT supported Description

Feature NOT supported	Description
CAP v4	does not yet support CAMEL phase 4
D-IM-CSI	does not yet support dialed subscription information
`PromptAndCollect`	does not yet include a method for translating `PromptAndCollect`

CAP v4

does not yet support CAMEL phase 4

D-IM-CSI

does not yet support dialed subscription information

PromptAndCollect

does not yet include a method for translating PromptAndCollect

Additional features

Feature supported Description

INAP

The IM-SSF provides the same set of features for various INAP variants as it does for CAMEL. INAP variants currently supported are: ETSI INAP CS1, Ericsson INAP CS1 (optional), and Ericsson INAP CS1+ (optional).

A version of IM-SSF that supports other proprietary vendor variants of INAP is available on request. Please contact your OpenCloud sales representative for more information.

Multiple media servers

The IM-SSF uses lookup tables (which can support many entries) to map the parameters received from the SCP to the address of the media server to use. Can also provision a default media server.

Configurable routing to the media server

Some operators prefer the IM-SSF to route directly to the media server; others prefer the route to go back through the S-CSCF. Routing method is configurable per media server. Can also define default routing behaviour.

Per-CSI-tracing

Can enable detail tracing per CSI using an additional field in the CSI data stored in the IM-SSF. If per-CSI tracing is enabled, then the IM-SSF will generate more trace output whenever that CSI is applied to an incoming INVITE.

Ability to override per-MSISDN lookup of CSI

The IM-SSF uses the MSISDN (extracted from the INVITE) to lookup appropriate CSI. If an alternate approach is required, several IM-SSF features allow overriding the normal CSI lookup behaviour.

Ability to override method for classifying the trigger and originating or terminating

The IM-SSF looks for a parameter in the incoming Route to classify a call. The parameter to look for, and the expect value, are completely configurable. Can also override this mechanism entirely, making the classification externally (outside the IM-SSF, for example by using signaling interceptors in the SIS).

See Using the IM-SSF for more details on using the additional IM-SSF features.

See IM-SSF in Action for details on how IM-SSF istriggered, looks up subscription information, classifies the call as originating or terminating, and runs the BCSM.

IM-SSF in Action

:sortorder:2

The IM-SSF is a protocol translator that mediates between a SIP session with the SIS and a CAP or INAP session with an external SCP.

Below is an outline of how IM-SSF is triggered, looks up subscription information, classifies the call as originating or terminating, and runs the BCSM.

`INVITE` triggers a composition that invokes IM-SSF

The process starts when …

1	…the SIS receives an `INVITE`. This triggers a SIS process that selects a service composition to run — which includes an `invoke` of the IM-SSF. For example, in the following diagram we see that a service composition is using the IM-SSF to run SS7-based VPN services, in a composition with a SIP-based OCS.
2	The SIS forwards the `INVITE` message to the IM-SSF. The IM-SSF uses `request-uri` and the headers of the `INVITE` to: determine the "lookup key" it will use to Look up subscription information determine if the call is originating or terminating.
3	The IM-SSF runs either the O-IM-BCSM or T-IM-BCSM on the `INVITE`.

1

…the SIS receives an INVITE. This triggers a SIS process that selects a service composition to run — which includes an invoke of the IM-SSF. For example, in the following diagram we see that a service composition is using the IM-SSF to run SS7-based VPN services, in a composition with a SIP-based OCS.

2

The SIS forwards the INVITE message to the IM-SSF. The IM-SSF uses request-uri and the headers of the INVITE to:

determine the "lookup key" it will use to Look up subscription information
determine if the call is originating or terminating.

3

The IM-SSF runs either the O-IM-BCSM or T-IM-BCSM on the INVITE.

IM-SSF uses a key to look up subscription information

To look up subscription information, IM-SSF first checks to see if the INVITE has an "IM-CSI-Key"header. If so, IM-SSF will use the value of theheader as the key to lookup subscription information. Otherwise, it will:

1

Get the destination MSISDN from the request-uri, and get the source MSISDN from the Fromheader address uri.

2

Classify the call as originating or terminating.

3

If the call is originating:

Check the destination number against the list of provisioned B number prefixes. If it matches, then use the destination number as the key for lookup of O-IM-CSI.
Otherwise use the source number as the key for lookup of O-IM-CSI

To provision the set of B number prefixes, use the sis-console command configure-bnumber-prefixes. (See General IM-SSF Configuration for more details.)

4

If the call is terminating:

Use the destination number as the key for lookup of VT-IM-CSI.

If IM-SSF fails to locate any subscription information for the call, it rejects the INVITE.

Getting an MSISDN from a SIP URI

If the uri is a Tel URL then, the MSISDN is the Tel URL address without any separator charactors. If the Tel URL includes a leading "+", then treat the numbers as international.
Otherwise, the uri is a SIP URI. Take the user part of the SIP URI, and parse it according to the rules in rfc2806. By default, the IM-SSF relaxes these rules to allow non-digits ("A"…"D") in the address sequence.

If the IM-SSF cannot extract an MSISDN, it rejects the INVITE.

Classifying the call as originating or terminating

To classify a call as originating or terminating, the IM-SSF first checks to see if the INVITE includes an "IM-Access-Override" header. If the value of theheader is:

orig — IM-SSF applies originating treatment
term — IM-SSF applies terminating treatment
otherwise, the IM-SSF checks the parameters in the topmost Routeheader (see below).

The IM-SSF is configured with the parameter to look for (RqdParameter) and the expected parameter value (RqdParameterVal) that tells the IM-SSF if the call is originating access. RqdParameterVal may be empty, indicating that presence of the parameter is enough to classify the call as originating.{ocpanel}

You can define the parameter the IM-SSF looks for using the sis-console command configure-originating-access. See General IM-SSF Configuration for more details.

Inspecting the Routeheader

The IM-SSF inspects the topmost Routeheader and checks each parameter:

if (RqdParameterVal is Empty) then

  if (param == RqdParameter) then call is *originating*, else call is *terminating*

else

  if (param == RqdParameter and paramVal == RqdParameterVal) then call is *originating* else call is *terminating*

In the following example, we can see an incoming INVITE that includes a parameter mode with expected value originating in the topmost route (in this case, the IM-SSF should be configured: configure-originating-access mode originating).

  INVITE sip:1453800888888@ims1.operator.com SIP/2.0
  To: <sip:1453800888888@ims1.operator.com;user=phone>
  From: <sip:+886230050000@ims1.operator.com;user=phone>;tag=snl_0008395652_NSN_CLIENT
  Call-ID: NSNSIP-c2421c0a-c4421c0a-1-11-1254881719-108155-1254989874
  CSeq: 1235 INVITE
  ...
  Route: <sip:6N0j0Hg5C+O3p0hBLp~usAFA@172.28.81.7:5060;oc-node=101;lr;transport=udp;mode=originating>, ...
...

Running the BCSM

The IM-SSF executes the IM-BCSM following description 3gpp 23.278. An important aspect of this process is the subscription information it uses for the call. The subscription information tells the IM-SSF, among other things, the address of the external SCP to contact, the ServiceKey to use in the InitialDP message and how to respond in failure scenarios. The following tables explain the fields in both O-IM-CSI and VT-IM-CSI.

Properties common to both `O-IM-CSI` and `VT-IM-CSI`

Field Description

Field	Description
Msisdn	The unique id of the subscriber. This field is a string that is normally a digit sequence. It may, however, be a string that corresponds to the `IM-CSI-KEY`header.
getGsmSCFAddress	The SCCP address of the external SCF.
ServiceKey.	The service key to include in the `InitialDP` message sent to the SCF. This indicates the service to execute in the SCF.
DefaultCallHandling	Indicates whether the IP multimedia session shall be released or continued in case of error in the IM-SSF to gsmSSF dialogue. One of (`Default_Released`, `Default_Continued`).
CAMELCapabilityHandling	Indicates the phase of CAMEL which is asked by the gsmSCF for the service. One of (`CAPv2`, `CAPv3`, `CAPv4`, `ETSIINAPCS1`).
CSIActiveStatus	Whether the CSI is active or not.
TraceEnabled	Whether detailed tracing should be done, if tracer level is `Fine`, `Finer`, or `Finest`.

 Msisdn

The unique id of the subscriber. This field is a string that is normally a digit sequence. It may, however, be a string that corresponds to the IM-CSI-KEYheader.

 getGsmSCFAddress

The SCCP address of the external SCF.

 ServiceKey.

The service key to include in the InitialDP message sent to the SCF. This indicates the service to execute in the SCF.

 DefaultCallHandling

Indicates whether the IP multimedia session shall be released or continued in case of error in the IM-SSF to gsmSSF dialogue. One of (Default_Released, Default_Continued).

 CAMELCapabilityHandling

Indicates the phase of CAMEL which is asked by the gsmSCF for the service. One of (CAPv2, CAPv3, CAPv4, ETSIINAPCS1).

 CSIActiveStatus

Whether the CSI is active or not.

 TraceEnabled

Whether detailed tracing should be done, if tracer level is Fine, Finer, or Finest.

O-IM-CSI

Field Description

Field	Description
*Trigger Detection Points*
CollectedInfo	One of (`INTERRUPTED`, `NOTIFY_AND_CONTINUE`, `TRANSPARENT`).
AnalyzedInformation	One of (`INTERRUPTED`, `NOTIFY_AND_CONTINUE`, `TRANSPARENT`). Note that this TDP is only relevant for INAP.
RouteSelectFailure	One of (`INTERRUPTED`, `NOTIFY_AND_CONTINUE`, `TRANSPARENT`).

Trigger Detection Points

 CollectedInfo