3GPP IP Multimedia Subsystem (IMS) Architecture

The IP Multimedia Subsystem (IMS) is an architectural framework defined by the wireless standards body 3rd Generation Partnership Project (3GPP) for delivering IP multimedia services to mobile users based on the UTMS network. A similar system called Multimedia Domain (MMD) was defined by the 3GPP2 (a different organization) for the CDMA2000 network, which was based on the 3GPP IMS.

For the network access, the user can connect to an IMS network in various ways using IP. Direct IMS terminals (such as mobile phones, personal digital assistants (PDAs) and computers) can register directly on an IMS network, even when they are roaming in another network or country (the visited network). The only requirement is that they can use IPv6 (also IPv4 in early IMS) and run Session Initiation Protocol (SIP) user agents. Fixed access (e.g., Digital Subscriber Line (DSL), cable modems, Ethernet), mobile access (e.g. W-CDMA, CDMA2000, GSM, GPRS) and wireless access (e.g. WLAN, WiMAX) are all supported. Other phone systems like plain old telephone service (POTS -- the old analogue telephones), H.323 and non IMS-compatible VoIP systems, are supported through gateways.

The IP Multimedia Core Network Subsystem is a collection of different functions, linked by standardized interfaces, which grouped form one IMS administrative network. The key functions of the core network are:

Home Subscriber Server (HSS), or User Profile Server Function (UPSF), is a master user database that supports the IMS network entities that actually handle calls. It contains the subscription-related information (user profiles), performs authentication and authorization of the user, and can provide information about the user's physical location.

Call Session Control Function (CSCF) is used to process SIP signaling packets in the IMS. There are three types of CSCF: Proxy-CSCF (P-CSCF), Serving-CSCF (S-CSCF) and Interrogating-CSCF (I-CSCF).

Application servers (AS) host and execute services, and interface with the S-CSCF using SIP.

MRF (Media Resource Function) provides media related functions such as media manipulation (e.g. voice stream mixing) and playing of tones and announcements.

A BGCF (Breakout Gateway Control Function) is a SIP server that includes routing functionality based on telephone numbers.

Media Resources are those components that operate on the media plane and are under the control of IMS Core functions. Specifically, Media Server (MS) and Media gateway (MGW).

CDMA2000: 3G Standard Based on CDMA IS-95

CDMA2000 is the 3rd Generation solution based on CDMA IS-95, which supports 3G services as defined by the ITU 3G standards IMT-2000. CDMA2000 defines both an air interface and a core network. Cdma2000 has already been implemented to several networks as an evolutionary step from cdmaOne as cdma2000 provides full backward compatibility with IS-95B.

The CDMA2000 standard is evolving to continually support new services in a standard 1.25 MHz carrier. The first phase of CDMA2000, or CDMA2000 1X will deliver average data rates of 144 kbps. Phase two, labeled CDMA2000 1xEV, will provide for data rates greater than 2Mbps.

CDMA2000 1X (or the IS-2000 standard) published by the Telecommunications Industry Association (TIA), offers average data rates of 144 kbps, backward compatibility with cdmaOne networks, and many other performance improvements. CDMA2000 1X can be implemented in existing cdmaOne spectrum (1.25 MHz) or in new spectrum allocations. A CDMA2000 1X network will support simultaneous voice and data services with low latency and improved performance.

The evolution of CDMA2000 beyond 1X is called CDMA2000 1xEV. 1xEV is divided into two steps: 1xEV-DO and 1xEV-DV. 1xEV-DO stands for 1X Evolution Data Only. 1xEV-DV stands for 1X Evolution Data and Voice. Again CDMA2000 1XEV can be implemented in existing cdmaOne spectrum (1.25 MHz) or in new spectrum allocations.

1xEV-DO, requiring a separate carrier for data, will provide for higher data rates on 1X systems. By allocating a separate carrier for data, operators will be able to deliver peak data rates in excess of 2 Mbps at its best effort. 1xEV-DV allows data and voice services for CDMA2000 in one carrier. A 1xEV-DV carrier will provide not only high speed data and voice simultaneously, but will also be capable of delivering real-time packet services.

The standards for a CDMA packet core network are being developed by the TR45.6 working group of the TIA. These standards are being developed by using existing standards from the IETF (Internet Engineering Task Force) on Mobile IP. 3GPP2 is also busy defining the evolution of a CDMA2000 network to All-IP. The CDMA2000 PCN will be the first step in this evolution.

CDMA2000 Mobile Wireless Network Architecture

CDMA2000 is a hybrid 2.5G / 3G technology of mobile telecommunications that use CDMA (code division multiple access) to send digital radio, voice, data, and signaling data between mobile phones and cell sites. CDMA2000 is standardized by the 3rd Generation Partnership Project 2 (3GPP2).

The cdma2000 network comprises three major parts: the core network (CN), the radio access network (RAN) and the mobile station (MS). The core network is further decomposed in two parts, one interfacing to external networks such as the Public Switched Telephone Network (PSTN) and the other interfacing to the IP based network such as Internet. The mobile station terminates the radio path on the user side of the network and enables subscribers to access network services over the Um interface.

In a CDMA2000 access network, two radio access network technologies are supported: 1xRTT and EV-DO. CDMA2000 is considered a 2.5G (or 2.75G) technology when the 1xRTT access network is used and a 3G technology when the EV-DO access network is used.

CDMA2000 1xRTT, the core CDMA2000 wireless air interface standard, is also known as 1x, 1xRTT, and IS-2000. The designation "1x", meaning "1 times Radio Transmission Technology", indicates the same RF bandwidth as IS-95 (CDMA-One): a duplex pair of 1.25 MHz radio channels. 1xRTT almost doubles the capacity of IS-95 by adding 64 more traffic channels to the forward link, orthogonal to the original set of 64. Although capable of higher data rates, most deployments are limited to a peak of 144 kbit/s. IS-2000 also made changes to the data link layer for the greater use of data services, including medium and link access control protocols and QoS.

CDMA2000 EV-DO (Evolution-Data Optimized or Evolution-Data only), a broadband access radio technology standardized by 3rd Generation Partnership Project 2 (3GPP2), provides access to mobile devices with air interface speeds of up to 2.4 Mbit/s with Rev. 0 and up to 3.1 Mbit/s with Rev. A. The industry is working newer generations of EV-DO such as Rev. B and Rev. C, etc.

The CDMA2000 access network may perform mobility management functions for registering, authorizing, authenticating and paging IP based terminals, independent of circuit based terminals. The access network may perform handoffs within an access network and between access networks of the same technology and may support handoffs between access networks of differing technologies.

The key components of the cdma2000 access network are:
Base Transceiver System (BTS): an entity that provides transmission capabilities across the Um reference point. The BTS consists of radio devices, antenna and equipment.

Base Station Controller (BSC): an entity that provides control and management for one or more BTSs.

Packet Control Function (PCF): an entity that provides interface function between the access network and the packet switched network.