Acme Packet 4600
 
Acme Packet 6300
 
Acme Packet 4500
 
Acme Packet 3820
 

PLA-Support>Sun Systems>CommsGBU>Session Delivery Network>SN-SND: Acme Service Provider
 

SIP PRACK, reliable provisional responses, 100rel and the C-series SBCs

In this Document

Symptoms

Changes

Cause

Solution

Created from <SR 3-8685321961>

Applies to:

Symptoms

PRACK, reliable provisional response, 100rel, etc... not working properly with the SBC

Changes

 N/A

Cause

Lack of proper configuration

Solution

100rel - SIP Extension interoperability

When a PBX utilizes SIP extensions, it advertises the fact by listing option tags representing these extensions in either the Supported, Proxy-Require or Require SIP headers of a request.
In order for the SD to allow these headers through for ultimate processing at the UAS, it is necessary to configure the sip-feature object.
sip-feature configuration objects are associated with specific realms or the realm-name parameter can be left blank to make the specific sip-feature global on the SD.
Below is an example of enabling all realms to pass the 100rel option tag as presented in a SIP INVITE Require header. For more information on reliable provisional responses, see RFC3262.

sip-feature
            name 100rel
            realm
            support-mode-inbound Pass
            require-mode-inbound Pass
            proxy-require-mode-inbound Pass
            support-mode-outbound Pass
            require-mode-outbound Pass
            proxy-require-mode-outbound Pass

PRACK Interworking

This function allows the Net-Net SD to support a PBX which requires reliable provisional responses in a SIP Trunking environment where the Service Provider does not support this functionality.
Sessions initiated by the PBX indicate support for provisional response acknowledgement by the including the tag 100rel in either the Supported or Require header. When the Net-Net SD receives an INVITE with the 100rel tag, it will remove 100rel from the list of tags in the Require/Supported headers (or remove the header completely if 100rel was the only tag present) when forwarding the INVITE to the SIP trunk.

When forwarding provisional responses (e.g. 183 Session Progress and 180 Ringing) received from the SIP trunk, the Net-Net SD will add in reliable provisional response headers Require: 100rel and RSeq:
This will trigger the PBX to respond with a PRACK method. The Net-Net SD will respond directly to each PRACK with a locally generated 200 OK.

In the opposite direction, where the session is originated from the SIP trunk (which does not support the reliable provisional response feature), the Net-Net SD will add a Supported: 100rel header to the INVITE destined for the PBX.
For all provisional responses generated by the PBX, the Net-Net SD will generate and send PRACKs (to which the PBX will respond with 200 OKs) before stripping the Require: 100rel and RSeq: headers and forwarding the provisional responses to the SIP trunk.

This functionality is configured on the Net-Net SD simply by adding sip-interface option (100rel-interworking) to the PBX-side realm.

sip-interface
            state enabled
            realm-id enterprise-1
            description
            sip-port
                        address 192.168.50.100
                        port 5060
                        transport-protocol UDP
                        tls-profile
                        allow-anonymous agents-only
                        ims-aka-profile
            carriers
            ...
            options 100rel-interworking

            ...

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