A link is a network of nodes in which every pair of nodes can exchange messages via interfaces attached to media. Frequently, links are made to encompass more nodes by bridging or routing between two or more distinct media.
Links are characterized by their:
- capacity, latency, jitter, and error characteristics
- unicast, multicast, or broadcast message propagation abilities
- media access control (MAC) protocol, which participating interfaces use to avoid message collisions
- framing protocol, which participating interfaces use to detect message boundaries
- maximum transmission unit (MTU), which is the size of the largest single message that the link can propagate
and by what kind of message they carry.
Important media for data-carrying links include wires and the 2.4 GHz band of the radio spectrum. Important data bridges include Ethernet hubs, switches, and wireless access points. Important data routers include IPv4 and IPv6 routers and IPv4 network address translators (NATs).
Important media for matter-carrying links include roads, rails, airspace, and bodies of water. Important matter bridges include road and rail junctions, bridges, tunnels, and canals. Important matter routers are usually people or organizations working in the field of transit or devices controlled by such people or organizations.