Avaya SIP Software 3.2 for 1200 Series Instrukcja Użytkownika Pobierz pdf (Strona 161)

Chapter 16: Session Timer Service

The Session Timer for the Session Initiation Protocol (SIP) feature (RFC4028) allows the Avaya 1200

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.

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Avaya SIP Software 3.2 for 1200 Series Instrukcja Użytkownika Strona 161