The Evolution Of A Standard

DFWMAC (distributed foundation wireless media access control) has an involved parentage that demonstrates the standards-definition process in the 1990s. AT&T Global Information Solutions/NCR Microelectronic Products Division's Wireless Communications and Networking Division entered the wireless market in 1990, specializing in direct-sequence spread-spectrum technology. NCR became a market leader and in 1992, was joined by Symbol Technologies (San Jose, CA) in proposing a wireless LAN standard. The NCR/Symbol integration began due to customer demand to both companies for interoperability of their products.

The NCR/Symbol proposal was not alone, however. In the past three and a half years, the Wireless Local-Area Networks Standards Working Group, IEEE Project 802.11 has received over 11 proposals for a MAC (media access cont rol) specification from various market players. These proposals have fallen into two main groups: distributed-access protocols, which, like Ethernet, distribute the decision to transmit over all the nodes using a carrier-sense mechanism, and centralized-access protocols, which involve single-node transmission regulated by a centralized decision maker. IBM submitted one example of a centralized protocol in July 1991.

Work began on the original NCR/Symbol proposal--called WMAC (wireless media access control)--in November 1992. WMAC used a distributed-access protocol as a foundation for more advanced functionality. This functionality included power management, synchronization, and optional support for time-bounded services. In March 1993, Xircom proposed the WHAT (wireless hybrid asynchronous time-bounded) MAC protocol. Xircom's WHAT protocol also used a distributed-access protocol, supporting hidden nodes as well as time-bounded services.

In May 1993, several companies proposed rival MAC specifica tions. While NCR and Symbol introduced the WMAC protocol, Spectrix offered the CODIAC (centralized or distributed integrated access control) MAC protocol; shortly thereafter, National Semiconductor (Sunnyvale, CA) proposed merging IBM's and Xircom's proposals into a hybrid protocol.

In September 1993, the Project 802.11 committee selected five of the original 11 proposals for further consideration with a goal of selecting a final protocol at the November meeting. The five selected proposals included two distributed-access protocols (the WMAC protocol from NCR/Symbol and the WHAT protocol from Xircom), two centralized access protocols (the IBM protocol and the CODIAC protocol from Spectrix), and one hybrid protocol (the WHO protocol from National Semiconductor). At that time, the CODIAC and WHO protocol proposals incorporated a secondary mode that mimicked aspects of the WHAT protocol at certain times.

Also, at the September 1993 meeting, NCR, Symbol, and Xircom decided to integrate their proposa ls, resulting in the enhanced WMAC protocol called DFWMAC (Distributed Foundation WMAC) that was introduced in the November meeting. The resulting DFWMAC protocol contained 95 percent of the functionality of the WMAC protocol, adding improvements in the areas of optional hidden-node protection from the WHAT protocol and PHY (physical) independence and synchronization support for extemporaneous ad hoc networks. Thus, the DFWMAC protocol ultimately has become an improvement over the individual protocols, and its popularity has been strengthened by the number of companies involved.

At the November 1993 meeting, the 802.11 committee reviewed the above proposals. At that time, National Semiconductor's WHO proposal was voted down, and it decided to support the DFWMAC protocol proposal. A voting procedure was held, and the required 75 percent majority then selected DFWMAC as the 802.11 foundation protocol for the MAC specification.

Global Considerations

To achieve worldwide standardization, the 802. 11 committee is coordinating its efforts with other standards organizations where appropriate. These include the T1P1 group in the T1 Accredited Standards Committee and the TR32/TR45 groups in the Telecommunications Industry Association. T1P1 aims to provide public telephone, ISDN, and cellular telephone interoperability. The TR32/TR45 groups are primarily interested in digital-voice communications on cordless and mobile telephones.

The 802.11 committee is also well connected with the ETSI (European Telecommunications Standards Group). The ETSI-RES 2 committee defines standards for land mobile systems operating in the 2.4-GHz bandwidth. The ETSI-RES 10 committee is drafting a standard for a HIPERLAN (high-performance LAN), that will provide 10- to 20-Mbps bandwidths in the 5.2-GHz bandwidth.

AMD, DEC, International Computers, National Semiconductor, NEC, Norand, Telxon, and Toshiba have already put their voices behind DFWMAC, and more companies are joining the motion. Together with efforts to br oaden the geographical reach of the standard, these endorsements will go a long way to ensure that any wireless LAN equipment you purchase will be interoperable.