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Cisco BTS 10200 Softswitch SIP Protocol User Guide
OL-5352-03
Chapter 2 SIP Protocol Subscriber Features
Jointly-Provided Features
Jointly-Provided Features
In addition to the Softswitch-based and phone-based features, Release 4.4 also offers jointly-provided
features. These are features provided jointly by the phone and by the Cisco BTS 10200. To use these
features, you must provision both the phone and the Cisco BTS 10200.
These features include:
• Session Timer
• Reliable Provisional Responses
• Text-GUI Features
• Call Transfer (Blind and Attended)
• Distinctive Ringing
• Distinctive Ringing for Centrex DID Calls
Session Timer
This SIP extension allows for a periodic refresh of SIP sessions through a SIP re-INVITE or UPDATE
request. The refresh allows the Cisco BTS 10200 SIP interface to determine if a SIP session is still
active. If the session is inactive, possibly because the session did not end normally, the Cisco BTS 10200
sends a SIP BYE request and cleans up resources dedicated to the session. Stateful SIP proxies and the
remote SIP endpoint handling the BYE request can clean up resources dedicated to this session as well.
Cisco BTS 10200 support for this feature follows the specifications described in the IETF draft
draft-ietf-sip-session-timer-08. Session durations are configured within a range of 30 minutes to 2 hours.
Cisco BTS 10200 does not allow for negotiating a session less than 15 minutes. Cisco BTS 10200 SIP
interface does not impose the session timer feature be required on the remote SIP endpoint. This feature
does not require the session timer capability on the remote SIP endpoint.
In the unlikely event of a call agent redundancy failover, the session timer is deactivated. This may result
in eventual session expiration and call release.
This feature can be enabled or disabled for all SIP subscribers; the feature is disabled by default. This
feature is enabled by provisioning the SUB-SESSION-TIMER-ALLOWED entry in the CA-CONFIG
table.
If the feature is enabled for a SIP subscriber, Cisco BTS 10200 (as UAC) adds, to the initial INVITE
message, a supported header with a ‘timer’ value, as well as a Session-Expires header with the Refresher
parameter set to ‘Uac’. Whenever the SIP call is sent from a Cisco BTS 10200 SIP subscriber,
Cisco BTS 10200 specifies itself to be the refresher. If Session Timer is not supported on the remote end,
the value sent in the Session-Expires header is set for the session duration. A periodic refresh request is
sent at half of the negotiated Session-Expires value.
When this feature is enabled for the SIP subscriber and an initial INVITE is received by the
Cisco BTS 10200 with a Supported header with ‘timer’ value and a Session-Expires header, it sends a
200 class response with a Require header specifying ‘timer,’ and a Session-Expires header and refresher
parameter. The Session-Expires header contains a session duration and refresher value set to whatever
was received in the initial INVITE. If refresher parameter is not received in the initial INVITE,
Cisco BTS 10200 sets it to ‘Uas’ indicating Cisco BTS 10200 is the refresher. Cisco BTS 10200 sends
periodic refresh request at half the negotiated session duration.