Cisco Systems BTS 10200 manual Reliable Provisional Responses, 2-15

Chapter 2 SIP Protocol Subscriber Features

Jointly-Provided Features

When session timer is enabled for the SIP subscriber and an initial INVITE is received by

Cisco BTS 10200 without a Supported header with ‘timer’ value or a Session-Expires header, a 200 class response is sent without a Require header with ‘timer’ value, or a Session-Expires header.

Cisco BTS 10200 sends periodic refresh request at half the negotiated session duration.

When session timer is disabled on the SIP subscriber and an initial INVITE is sent by Cisco BTS 10200, no Supported header with ‘timer’ value or a Session-Expires header is added, indicating to the remote SIP endpoint that the Cisco BTS 10200 does not support session timer.

When the feature is disabled on the SIP subscriber and an initial INVITE is received by

Cisco BTS 10200, any session timer related headers are ignored. The 200 class response does not include a Require header with ‘timer’ value or a Session-Expires header.

Call agent configurable parameters are available allowing the user to select the desired session duration and the minimum tolerable session duration if negotiated down by the remote SIP endpoint or proxy. If the parameters are not explicitly specified, the default session duration is 30 minutes and the minimum tolerable session duration allowed is 15 minutes.

A session that is not refreshed at the end of the duration interval results in a call release and session clean up.

For provisioning details, refer to the Cisco BTS 10200 SIP Phone Provisioning Guide.

Reliable Provisional Responses

SIP defines two types of responses, provisional and final. Final responses convey the result of the request processing, and are sent reliably. Provisional responses provide progress information about the request processing, but are not sent reliably in the base SIP protocol. The reliable provisional responses feature provides end-to-end reliability of provisional responses for Cisco BTS 10200 SIP subscribers.

Provisional responses in SIP telephony calls represent backward alerting and progress signaling messages, which are important when interoperating with PSTN networks. Therefore, for SIP-T calls on the Cisco BTS 10200, reliable provisional responses are mandatory. They are optional for regular SIP calls.

Cisco BTS 10200 support for this feature follows the specifications described in RFC 3262. A provisioning flag is provided to enable or disable this feature, and is disabled by default. For SIP trunks provisioned as “SIP-T,” the system internally ignores the flag and enables the feature always. In this case, the feature is mandatory. Therefore, the ability to enable or disable the feature applies to regular SIP trunks only. There is one exception: SIP-T trunks receiving SIP-T calls (calls with ISUP attachments) may also receive incoming regular SIP calls. In this case, the feature (enabled or disabled) for that regular SIP call is determined by the provisioning flag on that SIP-T trunk. The provisioning flag (PRACK_FLAG) is a member of the Softswitch Trunk Group profile. For provisioning details, refer to the Cisco BTS 10200 Softswitch SIP Provisioning Guide.

For calls received on a Cisco BTS 10200 regular SIP trunk, or regular SIP (non-SIP-T) calls received on

aSIP-T trunk, the following feature behavior applies:

•If the received INVITE indicates this feature is required, all provisional responses are sent reliably, regardless of the provisioned feature setting on the trunk.

•If the received INVITE indicates this feature is supported, then all provisional responses are sent reliably if the feature is provisioned enabled on the trunk.

•If the received INVITE indicates the feature is not supported, the call is refused if the feature is enabled on the trunk.

•If the received INVITE indicates the feature is not supported, the call is accepted if the feature is disabled on the trunk. Provisional responses are not sent reliably.

Cisco BTS 10200 Softswitch SIP Protocol User Guide

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