New SIP Headers for Reducing SIP Message Size

Current SIP messages are text based and inherently large, especially when these messages are to be transmitted over the bandwidth-strained wireless access technologies (a typical orginiating SIP Invite is about 1200 bytes). For most wireless technologies, transmitting the session initiation messages (such as SIP Invite) over the signaling channel can reduce the call setup time substantially. The size limitation of these wireless signaling channels are typically very small (~210 bytes in the uplink and ~110 bytes in the downlink). To address this problem, a new function called Encoding Assitant (EA) has been introduced in the User Agent (UA) and in the SIP Proxy server within the network. Additionally, the method provided in this document defines new SIP option tags and headers. These new option tags and headers allow the UA and a SIP Proxy server within the network (such as the P-CSCF), to exchange information using the signaling channels supported by most wireless access networks.