Patent ID: 8885553

Claim:
A method of routing a session initiation protocol (SIP) packet, wherein the SIP packet comprises routing information between a mobile host and a correspondent host in respective first and further network domains, at least the first network domain comprising a plurality of subnets, said mobile host being attached to one of said subnets, the method comprising: using a mapping between a SIP-Uniform Resource Identifier (URI), a local IP address and a global IP address to identify the mobile host inside the first network domain; receiving a new local IP address of the mobile host upon the mobile host attaching to another one of said subnets, wherein the global IP address has validity outside the first network domain and wherein the new local IP address has validity inside the another one of said subnets, said routing information comprising the global IP address; refreshing the mapping by replacing the local IP address with the new local IP address in the mapping; reformatting said SIP packet by replacing the global IP address in a single IP header of the SIP packet with the new local IP address in the single IP header of the SIP packet upon receipt of the SIP packet in the first network domain; and communicating the reformatted SIP packet to the mobile host via the subnet to which the mobile host is attached.