Aastra Telecom SIP 480I - Manual (Page 148)

Operational Features
5-36 41-001129-00 Rev 09, Release 1.4.1
IP Phone Administrator Guide
Operational Features
Aastra Web UI
1 Click on Advanced Settings->Global SIP->Advanced SIP Settings.
2 Enter a value, in seconds, from 120 (2 min) to 3600 (1 hour) in the "BLF Subscription Period" field.
3 Click to save your changes.
You must restart your IP phone for the changes to take affect.
4 Click on Operation->Reset.
5 In the "Restart Phone" field click to restart the IP phone and apply the changes.