Abstract: The present method provides for a session initiation protocol timing arrangement which facilitates instant communications in a packet data communication system (50). Each network server (15-25) sets a time out timer (92) which is coordinated with each of the downstream network servers. Network server (15), for example, sets a time out timer value which is selectable by the system operator. Subsequent network servers (20 and 25) then set the value of the time out timer to be that of the originating server (15) or client (10) less a fixed time such as one second. Further, a provisional message (118) is sent through the network to avoid expiration of the time out timer in upstream stages.

Abstract: For a network server (35) communicating with a wireless unit (10) via a Session Initiation Protocol, a retransmission method (50) first sets a timer based upon a time likely for a mobile unit to respond (54). Then the network server waits for a response (56). When the timer set for the kind of mobile unit being used expires (64), a retransmit of the original SIP request takes place (68). Optionally, modes for waiting may include a linear mode (72) and an exponential mode (74).