INRIA researchers were among the first to think up broadband wireless
communication networks between mobile computers. They are still on
the forefront today in the standardization of the protocols necessary
for a new generation of wireless networks, the ad hoc networks.
Let’s go back in time. Before wireless networks, corporate network
architectures were especially complex and fixed. Each computer was
connected to the others via a quantity of wires managed by a powerful
network server. In a second stage around twenty years ago, a revolutionary
solution was developed, considerably lighter and economical—Ethernet.
A single coaxial cable connected every machine to the server. This
time, several communications had to share the cable and computer resources.
A team of a dozen INRIA researchers got interested in the subject
of how to improve wire networks and decentralize the management of
communications, in order to avoid having to go through this central “policeman” that
was the server to go in or out of the network. “We rapidly realized
that the last element penalizing these networks was... the wire,” says
Philippe Jacquet, Head of project HIPERCOM at Rocquencourt. “We
started to think about a high speed wireless Ethernet network, possibly
with mobile users. We felt there could be many applications in offices,
vehicles...”
As surprising as it may seem today, at that time Ethernet networks
were just starting to be deployed and most of the industry was very
dubious about the idea of wireless computer networks. Some companies
were interested however, such as Dassault for military applications
and Apple for personal computers. “We continued our work and
participated in the development of an original standard called Hiperlan,
defended at the ETSI, the European Telecommunications Standards Institute.
Hiperlan brought two concepts together, one developed for Ethernet
and the other (a self-routing principle) stemming from the Internet
world,” continues Philippe Jacquet.
Hiperlan: a standard ahead of its time
Self-routing between computers was designed for the Internet at the
beginning of the 1990s. It looked like a solution to increase the
range of wireless network communications. Indeed, quite surprisingly,
physics commands that the higher data rate, the shorter range, due
to signal scrambling problems caused by the echoes engendered by
such obstacles as walls and furniture.
HIPERCOM researchers started to work on this solution in the framework
of a 1994-1996 European project with Dassault, Electronica (I), Symbionics
(UK) and the Universities of Bradford and Bristol (UK). This concept
of distributed network with internal routing was also at the heart
of the Hiperlan European standard (cf. What is a wireless telecommunication
standard?) defended by several companies including Apple, Motorola,
ATT, Canon and Daimler-Benz. Hiperlan was however probably too ambitious.
It aimed at transfer rates of 25 Mbits/s. “It was kind of the
Concorde of the wireless networks,” remembers Philippe Jacquet
with nostalgia. At the time, no company dared develop a product.
Wireless networks, the infamous Wi-Fi, were finally deployed in 1996
according to a competing standard called 802.11, defended at the IEEE by some of the same companies that were working on Hiperlan. The IEEE
(Institute of Electrical and Electronics Engineers) edicts international
standards, in particular for telecommunications. When Europeans were
trying to develop a totally new standard and products, the Americans
modified their products, and were able this time to impose industrial
solutions more rapidly.
Nonetheless, the competition with Hiperlan certainly influenced the
Wi-Fi standard significantly, in particular concerning the type of
network created, easy user access and routing mode. Wi-Fi networks
are thus designed around a single access point with which several computers
can communicate using a very simple distributed protocol, just as Hiperlan
proposed, that makes it possible for users to freely enter and leave
the network.
Another consequence inherited from Hiperlan concerns the ability of
the network to function in ad hoc mode—a mobile network in which
the various computers connected at a given moment can serve as relays
between one another and automatically route data. This type of functionality
had been developed in Hiperlan to alleviate the short range problem
due to the high rates envisioned. In the same way, ad hoc networks
can be used to extend the range of Wi-Fi networks or to design a wireless
network with an off-center access point, as is often the case. Thus,
mobiles that are out of range of the access point can use other mobiles
as relays to forward their communication to the access point.
Concepts applied to the new wireless networks
In parallel with the development of these radio technologies, the Internet
protocols also had to be adapted to computer physical mobility that
causes frequent changes in network topology. The interoperability
of the various networks had to be ensured as well as their stability
in order to avoid interruptions in transmissions, without eating
up all the available bandwidth with the traffic necessary to describe
this topology. In 1996, the Internet protocol international standardization
body, the
IETF (Internet Engineering Task Force), launched a work
group on the topic called
MANET (Mobile Ad hoc Network). “They
were interested in the concepts we had developed in Hiperlan, so
they quickly got in touch with us,” remembers Philippe Jacquet. “They
wanted to propose our
OLSR (Optimized Link State Routing) routing
protocol, adapted to the Internet and optimized for mobile networks.
OLSR was the first protocol that made it possible to experiment on
plug and play ad hoc networks.” The protocol was an instant
success and was downloaded more than 2,500 times! For the time being,
ad hoc networks are primarily of interest to the military, automobile
manufacturers and Wi-Fi enthusiasts. The latter are carrying experiments
between several buildings in Berlin and in Paris, using INRIA's protocol.
Today, about fifteen researchers keep working on OLSR. The protocol
is experimental (RFC 3626, Request For Comments), as are the three
other competing protocols at the IETF, all of which are American. “The
breakthrough of OLSR at the IETF in 2000 owes a lot to Thomas Clausen,
a Danish doctoral candidate who joined us in 2000 and who knew how
to communicate adequately in such forums.” OSLR is probably the
most implemented protocol presently, with around fifty implementations
in France, the United States, Japan, Canada, Norway and Finland, among
others, including by several companies such as Boeing and Cisco. Cisco
is planning to market hybrid OSLR-based servers within a few months
that will be able to operate with or without wires. The ideas developed
in OLSR have also been reused in other IETF works, and several standard
proposals by large American corporations include OSLR concepts.
Planning for the integration of third generation devices
In addition to all of the above, wireless networks must face new needs,
such as transmitting multimedia data to cell phones or PDAs, the
so-called 3rd generation devices. The companies and research departments
that develop such technology participate in the standardization of
such networks within the 3GPP (3rd Generation Partnership Project).
The 3GPP was created in 1999 and regroups several organizations such
as the
ETSI. It defines the standards adapted to mobile telephony:
GSM, GPRS and UMTS.
One part of the ARMOR team at Rennes is working on the mechanisms
required to manage the displacements of mobile terminals in such a
way that the latter may be able to transparently use several types
of radio networks (UMTS, Wi-Fi, Wi-Max, and so on). In this way, it
will become possible to use multimedia applications—voice over
IP, videoconference, video on demand, etc.—through the best communication
means available at every instant and every place. The different technologies
thus cooperate with each other in order to supply the best possible
covering.
Researchers are also developing data compression techniques for efficient
transmission of multimedia information on GPRS and UMTS networks. More
precisely, they are proposing an IPv6 header compression method at
the 3GPP. The method is already standardized at the IETF under the
name of ROHC (Robust Header Compression).
What is a wireless telecommunication standard?
By definition, wireless communications imply radio wave transmissions.
The radio resource is very much in demand by radio stations, TV channels,
satellite links and the military. To develop wireless telecommunication
equipment, it is thus compulsory to go through standardization in
order to obtain a specific frequency band. The ETSI is in charge
of this in Europe, in agreement with the various national jurisdictions,
such as the AFNOR, the French standardization body.
Concretely, each standard (GSM, Wi-Fi, Bluetooth, OLSR )must specify
the power, modulation mode and protocols to be implemented in dedicated
equipment in order to use this frequency and interoperate without interfering
with other devices.
