BY AMNON GAVISH, PH.D. AND AVI FISHER, MSC.

The explosive growth of wireless systems worldwide, and the race to provide new services over these networks, have created a pressing need to provide a full interworking capability among cellular systems, the PSTN, and data services. This need will only grow as third-generation (3G) cellular systems are deployed with their varied assortment of data services such as voice over IP (VoIP), fax over IP (FoIP), video, and audio along with support for legacy modem and fax connections. As the need for concurrent processing of multiple protocols in a multiple channel environment grows, infrastructure equipment design and logistics become more complex. A software access solution (SAS) is the best option to meet the challenges of today's and tomorrow's cellular infrastructure network

DATA SERVICES AND THE IWF
The analog 1G (e.g., AMPS, TACS, NMT) provides very slow-rate data services using expensive analog fax/modem technology in the mobile handset, and can be considered obsolete today. The popular 2G (PCS or GSM systems using TDMA or CDMA) mobile wireless systems used today provide modem and fax data services between the mobile unit and the PSTN through a device known as the InterWorking Function (IWF), situated at the mobile switch. The IWF performs the translation between the mobile air channel format and the PSTN PCM format. An example of this is when a fax or modem connection is made using a mobile device, but the actual signal modulation occurs in the IWF and not in the mobile device. This situation is analogous to a personal computer with an external fax/modem. The personal computer does not perform any modulation or signal processing tasks; instead it transmits and receives character data via the interconnecting serial cable to the external modem which, in turn, performs that actual signal processing and modulation. Analogously, the mobile device sends and receives character data via the cellular air interface, and then modulates it for the PSTN at the IWF. The IWF concept is being used for the more advanced networks (2.5G and 3G) as well, although the actual name may be different depending on the country of use and the manufacturer of the infrastructure equipment.

The IWF is located in the mobile network's central switch as a common resource to thousands of subscribers accessing various data services in parallel. Therefore, a multi-channel, multi-protocol access pool is required since many subscribers will be accessing many different protocols in the IWF according to the particular subscriber application. The fact that the IWF concentrates all services in a single location makes it a prime candidate for a high-density, convergent access pool.

CONVERGENCE THROUGH SAS
Convergence can be realized by dividing service support among several hardware subsystems such as a fax board, a modem board, and a voice board. While this type of solution may work, it is rigid, complicates system design, and does not deal effectively with changes in subscriber usage patterns. For example, as the number of Internet data-oriented calls grows, is it possible to predict exactly how many modem or VoIP calls will need to be handled by the IWF at any one time? If a design existed that automatically adapted to the actual subscriber usage pattern, excessive engineering spares or a lack of resources would be avoided.

The service dedicated subsystem approach also complicates product logistics. If each type of media service requires a different type of hardware subsystem, production, field support, and maintenance become cumbersome and adversely affect time-to-market and customer satisfaction. These problems are eliminated if a single type of general resource board is used to process all types of media services.

The design challenges posed by multi-service, multi-channel convergence can be successfully addressed by a SAS that runs on general purpose DSPs (digital signal processors). The SAS is designed to handle multiple channels (including T1 or E1 spans on a single DSP) by running the protocols in a parallel and non-blocking manner. Using the SAS approach, a given DSP chip can, for example, handle 24 V.90 modem calls at a single time. When the calling pattern shifts, the same DSP chip would be able to handle 30 VoIP calls or 48 fax calls or any mixture (e.g., 10 V.90 modems, 10 VoIP, and 12 fax) in a seamless fashion. No matter what the usage pattern, the DSP chip's resources can always be effectively utilized without call blocking. The infrastructure equipment manufacturer can then design the IWF's convergent access pool using multiple generic and identical DSP boards. Higher channel densities are realized by using multiple DSPs on the same board.

IWF SOFTWARE IMPLEMENTATION
Not only is the IWF required to handle many services, but many of these services are non-standard, and no hardware chipset exists for them. A good example is that of the fax adaptation that is commonly used in GSM cellular networks. The fax solution required in the IWF is not a complete fax call terminator, but an adapter that performs basic modulation and rate adaptation functions. The adapter does not deal with typical fax tasks such as image compression. Fax adaptation is best implemented as a specialized software protocol integrated with the SAS.

The 3G wireless environment will require even more services beyond modem fax and voice, with some demanding customized adaptation. For example, video or high-fidelity audio services may be transmitted across the air interface in a common baseline format to reduce the price and size-sensitivity of the hand-held device. Since services outside the cellular network may arise from any type of source, the IWF will be called upon to perform protocol adaptation from several formats to the baseline format selected for the given 3G network.

An interim solution between the future 3G network and today's 1G and 2G networks is the 2.5G network, which includes data services such as high-speed circuit-switched data (HSCSD), general packet radio services (GPRS), and enhanced data rate for global evolution (EDGE). These services will require special protocols such as high-speed V.90 analog modem pools and packet compression co-processors. Once again, specific hardware chipsets for these applications do not exist and require a software application.

The 3G network will support services which have yet to be finalized by the relevant standards bodies. This means that the IWF must be based on a software solution that can be upgraded once standards are finally agreed upon, without requiring any changes to the underlying hardware. System engineers, who are faced with the dilemma of designing a 3G system today so that it will be ready for deployment in the coming year, can immunize themselves from changing industry standards or subscriber usage patterns by choosing a convergent SAS product. This will ultimately provide a higher quality of service to the customer with a short time to market, culminating in a more positive consumer experience.

The interworking access services for the wireless networks are, therefore, best served by a SAS running on a high-performance, generic DSP platform. Many wireless data services such as VoIP, fax, and modem connectivity are similar to those handled by IP telephony, enterprise, and carrier equipment found in the "wireline" world. Wireline systems can also be based on the SAS approach - which will provide them with similar benefits in cost, channel density, convergence, logistics, and "future-proofing." c

Amnon Gavish and Avi Fisher are the founders of Surf Communica-tion Solutions, Ltd. Surf specializes in software access solutions integrated into OEM systems such as IWF, remote access servers, IP telephony products, and telephone switches. For more information, visit Surf's Web site at www.surf.co.il.

Telecommunications providers and subscribers around the world are looking forward to the arrival of third-generation (3G) wireless services. But what is driving the growth and what will eventually result in the widespread acceptance of 3G? The answer lies in the "anytime, anywhere" voice, data, and multimedia services that 3G will make possible for wireless subscribers.

While the following categorizations of potential 3G services are by no means definitive, potential wireless Internet services and applications include:

Communications. Basic communications are perhaps the most familiar and immediate services subscribers will see from wireless Internet. Messaging services, including text-based messages, event notification, e-mail, media conversion, and voice mail, will be among the first available 3G services. Voice services, video telephony, and video conferencing are also prime wireless Internet service possibilities.

E-commerce. The fast-growing e-business marketplace will also benefit from next-generation standards. Potential applications include wireless Internet access to broker services, interactive shopping, online banking, electronic ticketing, e-retail, and online auctions.

Mobile Office. The wireless Internet will open a powerful new world of business mobility, including Internet and intranet access, PIM synchronization, and file services such as fax, printing, and FTP downloads. Other mobile office capabilities might include remote maintenance and diagnostics of various systems, real-time support, collaborative connectivity, and the extension of corporate applications.
Leisure and Entertainment. Wireless Internet will open the doors to an exciting array of information and entertainment services, including universal access to news, sports, and weather updates. Other applications include electronic and interactive gaming, the dissemination of e-magazines, and audio- and video-on-demand services.

Travel and Location-Based. Operators will also be able to offer powerful and customized location-based 3G services. Potential offerings include navigational and location services, traffic information, scheduling and timetables, directory services, and virtual tours of travel destinations.

Telemetry. With the advent of the wireless Internet, companies and institutions will have access to a wide range of global telemetry applications. Those may include the monitoring and control of remote systems, data acquisition, security and surveillance uses, and healthcare-related monitoring.

As the evolution of 3G continues, business wireless services will evolve based on three market categories -- standard, enhanced, and advanced. Current or "standard" services include basic communications such as mobile voice, voice mail, short messages, news and weather, or stock quotes. Enhanced services will include voice dialing, group calling, e-mail, intra/Internet, calendar synchronization, customized information, mobile fax, and image or picture transfer capabilities. The advanced services include full-range mobile voice, voice command and control, streaming audio, anywhere e-mail and intra/Internet access, file transfer capabilities, electronic newspapers, video clips, and many more.

Along with offering a new portfolio of products and services, the emerging 3G wireless landscape will require a fundamentally new approach to network design. The desire for more immediate, convenient, and versatile wireless communications has brought the advent of 3G closer and closer. As more subscribers learn how 3G technology can benefit them, the push for the arrival and acceptance of 3G will continue.

This article was written by various contributors from Nortel Networks. Nortel Networks delivers the combined expertise and proven leadership in telephony and IP-based data, wireline, and wireless networking to bring all communications together over a single network. They are leaders in building and supporting Unified Networks - global, scalable, high-capacity public and private networks built on the innovation, IP technology, and application focus driving the Internet. For more information, visit the company's Web site at www.nortelnetworks.com.