Home arrow more... arrow Jul - Sep 2007 arrow 3G Americas Recommends the SIP-I Session Control Protocol
3G Americas Recommends the SIP-I Session Control Protocol

3G Americas, an organization representing the GSM family of technologies in the Americas, today provides a white paper entitled "Why SIP-I? A Switching Core Protocol Recommendation for GSM/UMTS Operators."  3G Americas recommends to the wireless industry, and GSM/UMTS/LTE operators in particular, the adoption of a single session control protocol which will support the creation, modification and termination of packetized voice sessions in an existing GSM/UMTS or future LTE network. 

Session control refers to the process used to create, modify, and terminate IP-based communication sessions of various methods, including two-way voice communication, multimedia (text, audio, or video) conference collaboration, instant messaging, application sharing, and other contemplated but not yet fully specified services.  It is accomplished through signaling between various network elements and endpoints using a session control protocol. 

The most widely known session control protocol is Session Initiation Protocol (SIP), but SIP has a major limitation that is of great importance to any GSM/UMTS operator. It does not provide any method of directly inter-working with the PSTN because it was not created with the intention of it being fully backward compatible with legacy PSTN signaling mechanisms.

The recommendation of the white paper is based on analysis and comparison of three session control protocols that can inter-work with the PSTN: BICC, SIP-I and SIP-T.  BICC is the current protocol standardized in the 3GPP Release 4 architecture and deployed in some networks today.  However, BICC is not an optimal choice for ongoing evolution because it has been limited to, and is predicted to remain limited to, operation within a GSM/UMTS context.  BICC does not address domains beyond GSM/UMTS such as LTE; as a result, it does not automatically offer the future level of flexibility of continued development and evolution that would accompany the SIP with ISUP encapsulation variants (i.e. either SIP-T or SIP-I).

The paper presents a detailed technical analysis of capabilities existing within the two SIP technologies with ISUP encapsulation variants, and provides the recommended direction for evolution: SIP-I. There are four areas where SIP-I is better suited for a GSM/UMTS environment than SIP-T:

  • Assumptions regarding the trust and security environment
  • Encapsulation procedures & message mapping
  • Support of RFCs
  • User plane interoperability

Chris Pearson, President of 3G Americas, commented, "In the current transformation of voice communications networks from circuit switched to packet based systems, SIP-I is clearly the best way forward to support and enable new capabilities of the network."

3G Americas recommends that all GSM/UMTS network operators put SIP-I on their network evolution roadmap as the session control protocol, and, as operational requirements and service delivery requirements emerge, and evolve to SIP-I technology over time.

The white paper, Why SIP-I? A Switching Core Protocol Recommendation for GSM/UMTS Operators is available for free download on the 3G Americas website, www.3gamericas.org/.


BICC: Bearer Independent Call Control (BICC)
ISDN: Integrated Services Digital Network
ISUP: ISDN User Part
PSTN: Public Switched Telephone Network
SIP: Session Initiation Protocol
SIP-I: Session Initiation Protocol with encapsulated ISUP
SIP-T: Session Initiation Protocol for Telephones