Thanks to the success of asynchronous transfer mode (ATM) on wireline networks, wireless ATM (WATM) has become an imposed strategy towards the “ATM everywhere” movement. The WATM can be viewed as a solution for next generation PCNs, or a wireless extension of the broadband ISDN (B-ISDN) networks, which will support integrated transmissions of voice, data and video with guaranteed quality of service (QoS).
The ATM Forum has been working on defining the baseline of WATM systems. The specification for both mobility control in ATM infrastructure networks and seamless radio extension of ATM to mobile devices are some embryonic considerations being mooted.
The overall WATM system consists of a fixed ATM network infrastructure and a radio access segment. In the fixed ATM networks, the switches that communicate directly with wireless station or wireless end-user entities are mobility-enhanced ATM switches. They set up connections on behalf of the wireless devices. They serve as the “entrance” to the infrastructure wireline ATM networks.
The other ATM switching elements in the ATM networks, however, remain unchanged. While a fixed station may comfortably serve a 25-Mbps to 155-Mbps data rate ATM link, even an 25-Mbps data link in WATM environment is rather difficult to realise. In a wireless environment a several gigahertz spectrum is required to support a high-speed transmission.
A recommended band for WATM is 5 GHz, which can support 51 Mbps channels only with advanced modulation and special coding techniques. Although 155 Mbps is not reachable (at this time), it is anticipated that, when 60 GHz spectral operation is comprehended, even 622-Mbps rates could be achieved over WATM!
Consistent with this utopian dream, two physical (PHY) layer specifications have been recommended, one for the 5-GHz band and the other for the 60-GHz band for the Herculean effort involved. To understand why wireless ATM has become a technology of interest, it is pertinent to understand the market drivers behind the scene.
These market drivers indicate the existing co-operation between standards organisations, which has led to the agreements on wireless broadband ATM architectures on their performance. Foreseeing the comforts of wireless ATM-based teletraffic, several vendors and education institutions have co-operated in realising a number of prototype networks.
The Magic WAND, RACE II, and RDRN are a few to mention. The quest for large bandwidth coupled with the ever-increasing mobility of today’s society is the precursor for wireless ATM. It has been estimated that the need and market for wireless ATM can jump by about 100 % by 2005. The conceivable applications of wireless ATM refer to the following locales: The workplace, home, and “wireless to the curb.”
The workplace application will allow multimedia, bandwidth-intensive applications to run on mobile devices. Video conferencing, access to multimedia databases, and Internet access will not be limited by the number and location of LAN ports and wiring. Mobile devices might also include ATM-ready PDAs. Workplace applications are likely to be the first applications implemented. Home-based applications might also include the following:
- Portable enhanced television services, including video-ondemand, home-shopping, banking, games etc.
- Wireless in-home networking and Internet access for traditional PCs and mobile network computers.
- High-quality audio distribution throughout the home, allowing more flexible positioning of audio components, cordless telephony, and replacement of miscellaneous legacy wiring systems.
The “wireless to the curb” application of wireless ATM differs from the first two applications in that both the base station and subscriber devices would be fixed. On the consideration of possible uses for a wireless ATM network, there are several constraints that must be looked into when the standards are developed. The primary factor is the QoS. Other hurdles to be faced are:
- Access schemes in reference to protocols that can overcome high error rates and noise inherent in radio systems.
- Reliability and availability specified by coverage areas, fading temporary outages, error detection, and correction.
- Service ubiquity posed by wireless reaching difficult downtown areas, carriers’ responsibility to acquire licenses, acquiring rooftop space, and deploying access stations.
- QoS mobility to ensure consistent QoS and hand-off as a user wanders.
- Applications made to overcome the limitations inherent in wireless transmissions.
Standards on wireless ATM are still emerging. Several organisations have been working on standards from many different perspectives. Both European and North American standardisation efforts are on trial. The standards cover a wide range of topics pertaining to both additions to the ATM protocol standards for communication on air (both mobile and fixed) and enhancements to wireless standards for usage and globalisation.
The ITU-T has launched its International Mobile Telecommunications - 2000 (IMT-2000) initiative “to provide wireless access to the global telecommunication infrastructure through both satellite and terrestrial systems, serving fixed and mobile users in public and private networks” (ITU-IMT, 1999). Study Group 11 of the IMT met in July 1999 to address signalling for broadband and multimedia networks and services.
Working within the framework of IMT-2000 is the UMTS Forum (which was founded in 1996). It is a non-profit organisation with representation from over 180 member organisations. This group is working with other standards organisations including the ITU, ETSI, GSM Association, and ANSI to develop the Universal Mobil Telecommunication System (UMTS).
The UMTS Forum met August 9 –12, 1999 for a workshop on 3G Mobile Broadband. The ETSI has also established a standardisation project for Broadband Radio Access Networks (BRAN). Prior to the establishment of the BRAN project ETSI had released functional specification EN 300 652 HIPERLAN described earlier.
The BRAN project will enhance the HIPERLAN functionality to HIPERLAN Type 2 and begin working on standards for wireless access and broadband interconnects. At present there are several documents in various stages of approval under the BRAN project. The BRAN project has also been working closely with the ATM Forum, IEEE, and the ITU-T to avoid duplication of efforts and ensure a cohesive set of standards.
The ATM Forum had also begun looking into standards for wireless ATM. In 1996 the wireless ATM working group was formed. In part, the WATM working group will address two items, as follows:
- Radio access layer protocols including radio physical layer, medium access control for wireless channel errors, data link control for wireless channel errors, and wireless control protocol for radio resource management.
- Mobile ATM protocol extensions including hand-off control (signalling, network-to-network interface (NNI) extensions, etc.), location management for mobile terminals, routing considerations for mobile connections, traffic/QoS control for mobile connections, and wireless network management.
In addition, there are smaller groups such as the Wireless Broadband Association and the Delson Telcom Group’s Task Force − Wireless Mobile ATM (TFWMATM). These are small independent organisations working on generic solutions to wireless ATM access.
