0 accesses are planned, there are 9900 possible connectivities to be analyzed to carry out signal level balance. One way to simplify the job is to segment the network, placing a regenerative repeater (or bridge) at each boundary. This reduces the signal balance job to realizable proportions and ensures that a clean signal of proper level is available at each access tap. For baseband LANs, 50-S2 coaxial cable is favored over the more common 75-S2 cable. The lower-impedance cable is less prone to signal reflections from access taps and provides better protection against low-frequency interference. 11.5 OVERVIEW OF ANSI/IEEE LAN PROTOCOLS 11.5.1 Introduction Many of the widely used LAN protocols have been developed in North America through the offices of the Institute of Electrical and Electronic Engineers (IEEE). The American National Standards Institute (ANSI) has subsequently accepted and incorporated these standards, and they now bear the ANSI imprimatur. The IEEE develops LAN standards in the IEEE 802 family of committees. Of interest in this chapter are the following IEEE committees, each with published standards, which continue to evolve: 802.1 High-Level LAN Interface 802.2 Logical Link Control (LCC) 802.3 CSMA/CD Networks Ethernet working group 802.4 Token Bus Networks (inactive) 802.5 Token Ring Networks (inactive) 802.11 Wireless LAN (many subset such as 802.11b, 802.11d, others) 802.15 Wireless Personal Area Network 802.16 Broadband Wireless Access 802.17 Resilient Packet Ring 802.18 Radio Regulatory 802.19 Coexistence 802.20 Mobile Broadband Wireless Access (MBWA) 802.21 Media Independent Handoff list as of 3/22/04 11.5.2 How LAN Protocols Relate to OSI LAN protocols utilize only OSI layers 1 and 2, the physical and data-link layers, respec- tively. The data-link layer is split into two sublayers: logical link control (LLC) and ENTERPRISE NETWORKS I: LOCAL AREA NETWORKS 7 Application Network Network 6 Presentation layers layers defined 5 Session 4 Transport Logical 802.2 control 3 Network Media access 8