John J. MacNamara

Seamless mobility across IMS and legacy circuit networks

The growing desire of network providers to introduce support for voice over IP (VoIP) has created interesting challenges in the area of interoperability with existing wireless circuit networks. The 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2) standards have defined the IP Multimedia Subsystem (IMS) as the platform for convergence. By definition, IMS is access agnostic; it provides services and features through a common core network, regardless of the means of transport. However, the IMS standards are just beginning to address the challenges associated with interworking with existing cellular circuit networks. Achieving seamless mobility involves supporting both roaming and handoff between networks. This paper discusses the issues involved in providing seamless mobility for subscribers across the packet and circuit domains and proposes network-based solutions.

Support for CDMA circuit mobiles in a SIP-based packet core network: A step on the path to IMS

This paper introduces an architecture based on the Internet Protocol Multimedia Subsystem (IMS) standards that provides packet transport for wireless circuit mode voice services. The motivating force behind this architecture is transcoder-free operation (TrFO), which improves voice quality for mobile-to-mobile calls while reducing the cost of the equipment required to support them. Included in this paper are a description of the architecture, examples of call scenarios supported by the architecture, examples of call flows that demonstrate the use of the Session Initiation Protocol (SIP) in the architecture, and a description of the IMS components that are reused in the architecture.

Issues in supporting multimedia services in SIP networks with mixed endpoint types

The evolution from traditional circuit-based networks to packet-based networks is a salient feature of todays telecommunications industry. As new types of Session Initiation Protocol (SIP) networks and endpoints (e.g., 3rd Generation Partnership Project Internet Protocol Multimedia Subsystem [3GPP IMS], cable, public switched telephone network [PSTN] gateways, and 802.11-capable personal digital assistant [PDAs]) are introduced, SIP extensions are being introduced to solve the problems unique to each of them. As SIP networks mature to support mixed endpoint types, interesting issues relating to interoperability among the various endpoints arise. This paper includes a discussion of some of these issues, including out-of-band versus in-band call progress information, handling early media, support of Internet Protocol (IP) and asynchronous transfer mode (ATM) transport networks, interworking with ISDN User Part (ISUP), and support of different SIP extensions. It also explores issues of performance, reliability, and service quality that arise as networks serving mixed endpoints are deployed.