Mobile IP telephony: mobility support of SIP

The Internet has recently become the most important, most popular way of communication. A significant new feature of the Internet is the support of telephony. Two main competing signaling protocol standards have been developed for this purpose: H.323, proposed by the ITU, and SIP, proposed by the IETF. Another new feature for the Internet is the support of terminal mobility. The IETF efforts in this field have resulted in the Mobile IP standard. Liao (1999) has shown that Mobile IP does not provide fast enough handoffs to support voice communications. Liao has also demonstrated how H.323 may be extended to offer a solution. In this paper we address several major issues for supporting mobility on SIP. We detail the mechanisms for extending SIP to support location management, registration of roaming mobiles, and handoffs. The mechanisms are either extensions of existing SIP, or based on Mobile IP, and thus may be readily employed over the Internet. We believe that the work presented here is an important step towards supporting mobile telephony over the Internet.