nsmission technologies (e.g., micro- wave, infrared, open-air laser-type transmissions) in which the path between a transmitter and a receiver must be clear and unobstructed. (2) A clear, open-air, direct transmission path that is free of obstructions such as buildings but may in some cases be impeded by adverse weather or environmental conditions. line speed The maximum data rate that can be reliably transmitted over a line. link (1) A physical circuit between two points. (2) A conceptual (or virtual) circuit between two users of a packet-switched (or other) network that allows them to communicate even when different paths are used. link redundancy level The ratio of the actual number of paths to the minimum number of paths required to connect all nodes of a network. link state A state in which each router is aware of the topology of the entire network. Each router sends out information about the links that the router has to all other routers on the net- work. The final routing table is based on the shortest path to each destination. Most new routing protocols are based on this algorithm. Glossary link-state protocol link-state protocol A generic class of routing protocols in which information about the sta- tus of the entire network is propagated to every node and used in routing decisions. OSPF, IS-IS, and NLSP are link-state routing protocols. LLC (Logical Link Control) A protocol developed by the IEEE 802, common to all of its local network standards, for data link-level transmission control. It is the upper sublayer of the OSI Layer 2 protocol that complements the MAC protocol (IEEE 802.2). LLC 1 is a minimal- function LLC that supports connectionless link layer service. LLC 2 supports connection- oriented data link service. LMDS (Local Multipoint Distribution Service) A technique for supplying broadband access via a point-to-point microwave digital system. Referred to as Multipoint Video Distribu- tion service in Europe, it operates over a very large frequency allocation, a 1.3GHz band that is generally lo