User's Manual

Session Timer Service
The Session Timer for the Session Initiation Protocol (SIP) feature (RFC4028) allows the Avaya
1100 Series IP Deskphone to support a keep-alive mechanism for SIP sessions. SIP sessions
are periodically refreshed by UPDATE requests (or re-INVITES for the IP Deskphones that do
not support UPDATE). The UPDATE requests are sent during an active call to allow endpoints
or proxies to determine the status of a SIP session.
The Session Timer Service contains the following elements:
• Session-Expires header
• Min-SE header
• response message (422—Session interval too small)
• tag (timer) for existing headers
The SIP IP Deskphone generates, processes and handles the SIP messages that include the
preceding elements.
Session-Expires header
The SIP Session-Expires header delivers the Session-Expires interval and provides
information about the entity performing the refreshes. A value of "uac" indicates that the
originating endpoint performs the refresh; a value of "uas" indicates that the terminating
endpoint performs the refresh. The session interval is the maximum amount of time that occurs
between session refresh requests in a dialog box before the session times-out. The minimum
for this field is 90 seconds; the recommended value is 1800 seconds (30 minutes).
Min-SE header
The Min-SE header indicates the minimum value for the session expiration in units of delta-
seconds. When your make a call, the presence of the Min-SE header informs the terminating
endpoint, and proxies, of the minimum value that the originating endpoints accept for the
session timer duration in units of delta seconds. When present in a 422 response, the Min-SE
header indicates the minimum session value the terminating endpoint accepts. When present
in a request or response, the value of the Min-SE header is 90 seconds or more. If the Min-
SE header is not present, the default value is 90 seconds. It is a configurable parameter.
Session Timer Service
SIP Software for Avaya 1100 Series IP Deskphones-Administration November 2012 187