|Powering The Next-Gen Wireless Network
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
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.
|Driving The Third Generation
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
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
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
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.