Ericsson CDMA2000 specifications Technical realization, IP multimedia system

efficiency over the air interface. This prob- lem has been addressed through signaling compression (SigComp), another IETF stan- dard initiated by Ericsson. SigComp is a ver- satile compression framework that can use any compression algorithm to compress ASCII-based protocols, such as SIP, to a frac- tion of their original size, reducing both bit rate requirements and transport latency.

SigComp sessions are initialized during the registration phase of the Instant Talk service. The SigComp compressor generates a decompression byte code that contains a preferred compression algorithm and trans- mits it to the decompressor. The decom- pressor, called the universal decompression virtual machine (UDVM), decodes the byte code and adopts the decompression algo- rithm, making it ready to receive com- pressed SIP messages. Extended operations (an important feature) enable SigComp to learn from SIP messages.4 Therefore, SigComp becomes increasingly efficient as compression and SIP signaling proceed.

SigComp is a critical component of Ericsson Instant Talk because it can signif- icantly reduce the number of bits sent over the wireless link (compression ratios of 8:1 are not unusual).5 It greatly reduces the transmission delay of SIP messages, and con- sequently, the time it takes to establish an Instant Talk session.

Technical realization

Ericsson has taken a total business approach in its technical realization of Intant Talk, providing the infrastructure, terminal clients and professional services, and ensur- ing availability of terminals. Guided by this approach, Ericsson will continue to opti- mize performance by implementing en- hancements in the radio access network, mo- bile core network, application servers and clients. EricssonÕs ability and willingness to influence the nodes in the end-to-end path of telecommunications systems set it apart from other vendors of push to talk solutions. The commercial launch of Ericsson Instant Talk will include vertical service assurance.

One more important factor is that Ericsson bases its products on open stan- dards. Therefore, handset interoperability will not be an issue. Operators and end-users will be able to choose terminals and termi- nal vendors freely.

Instant Talk consists of three main parts: the IPMM, the Instant Talk application server, and the handset client.

				Instant Talk￿
				application￿
				server
				Call/session￿
				control￿
Instant Talk client				function￿
				(CSCF)
			Signaling
				Home￿
				subscriber￿
				server￿
				(HSS)
Access network￿	Core￿	SIP
(GPRS,￿
	network			Media￿
CDMA2000￿
		RTP
WCDMA)			Media	resource ￿
				function￿
				(MRF)
Figure 1
Ericsson Instant Talk high-level architecture.

IP multimedia system

Figure 1 shows a schematic drawing of the nodes involved in the Instant Talk service. At the heart of the solution is the Ericsson IPMM system (Figure 2), which complies with the principles of the IMS standard (3GPP) that was drafted to bring SIP-based communications to the wireless market.2 The IMS can be deemed a ÒnewÓ domain that has been added to the mobile core network to support a wide range of SIP-based appli- cations, such as Instant Talk, instant mes- saging, and presence services.

The IPMM architecture includes the call/session control function (CSCF), the media resource function (MRF), and the home subscriber server (HSS). The CSCF is the teminalÕs first point of contact in the IPMM domain. All SIP signaling is routed through the CSCF, which also performs SigComp. The role of the CSCF is to handle subscriber registration, and to support the establishment, modification and release of Instant Talk sessions. The CSCF ensures interoperability with telephone systems and network addressing mechanisms by query- ing domain name service (DNS) servers to map SIP uniform resource identifiers (URI) or E.164 numbers to network addresses.

In an IPMM-based service, media is di- rected to, replicated in, and distributed from

Ericsson Review No. 1, 2004 17