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Routing is the process of moving packets across a network from one host to a another. It is usually performed by dedicated devices called routers. Packets are the fundamental unit of information transport in all modern computer networks, and increasingly in other communications networks as well. They are transmitted over packet switched networks, which are networks on which each message (i.e., data that is transmitted) is cut up into a set of small segments prior to transmission. Each packet is then transmitted individually and can follow the same path or a different path to the common destination. Once all of the packets have arrived at the destination, they are automatically reassembled to recreate the original message. Routing is a key feature of the Internet and it, together with a great deal of deliberate redundancy of high capacity transmission lines (e.g., optical fiber cable and microwave), is a key factor in the robustness (i.e., resistance to equipment failure) of the Internet. Each intermediary router performs routing by passing along the message to the next router. Part of this process involves analyzing self-configuring routing tables to determine the best (i.e., optimal) path. Routing is sometimes confused with bridging, which performs a somewhat similar function. The main difference is that the latter occurs at a lower level of the OSI (open systems interconnect) model and is thus more of a hardware function; the former occurs at a higher level where the software component is more important, and thus it can perform more complex analysis to determine the optimal path for each packet. Routing is also used by circuit switched networks, in which a dedicated circuit is established for the duration of the transmission of each message. The dominant circuit switched network is the public switched telephone network (PSTN), which is the worldwide collection of interconnected public telephone networks that was designed primarily for voice traffic. Created October 21, 2005. |