SIP Paging and Tracking

The paper introduces a new paging technique to track and wake up a mobile node attached to an access point in wireless LAN network after a SIP INVITE message is initiated by a caller. Tracking Agent keeps track of the mobiles’ handoffs between the access points. Paging Agent triggers tracking agent to page the mobile when a SIP INVITE is received for one of its users. Context transfer feature of our paging protocol allows the paging messages to deliver the station context in order to enable faster session reestablishment. Access point then does onlink paging in wireless link. SIP extensions are needed to trigger the paging agent to start paging and mobile nodes to notify their dormant status using an extended SIP REGISTER method. Onlink paging can be implemented using TIM or DTIMs of 802.11. Tracking protocol is analyzed to compare soft-state and hard-state approaches for state inconsistency ratio, message rate and the overall cost. Simulation model we developed enables us to evaluate the traffic introduced by the tracking protocol and the cache (state) size. Paging protocol is analyzed for CPU processing times and the transmission delays in SIP session setup with paging. Simulation of the paging with context transfer is used to show the gains in reauthentication.