Related protocols and initiatives

 In bringing together the worlds of the Internet, mobile and the traditional circuit-switched PSTN, there are a number of issues to be resolved. SIP addresses a prime concern: the establishment of sessions on an IP network as a basis for rich service offerings. But IP isn't yet ubiquitous: mobile networks are evolving to an all-IP architecture and, in the medium term at least, there will be a huge legacy of services and users remaining on the PSTN. There are a number of complementary initiatives that seek to ensure portability of services across these differing realms.

PINTs and SPIRITS - Service interworking

Number resolution - TRIP and ENUM

Seamless signaling - SIGTRAN and SIP-T

IMPP - Instant Messaging and Presence

SIMPLE - SIP for Instant Messaging and Presence Leveraging Extensions