 AND FUNCTIONS Communication network architecture (yes, including the Internet) includes six critical functional elements, or capabilities: clocking, multiplexing, routing, signaling, switching, and transmission. Clocks control basic timing in digital networks. Digital networks simply wouldn't work without accurate, consistent, long-term, stable clocking and timing mechanisms. The basic clocking scheme used to maintain timing and synchronization in networks is not much differ- ent than it was when first conceived in the 1950s, except it's signifi- cantly more accurate and much less expensive, especially at the higher levels of accuracy and precision. Multiplexing enables two or more signals to share time and/or bandwidth of a common facility. Multiplexing gains greater use of a limited resource. Multiplexing was a key characteristic of early analog telephone systems. Analog multiplexing shares fre- quency spectrum instead of time. Multiplexing can be active or passive. Active multiplexing involves electronic circuitry, while passive multiplexing, sometimes referred to as combining and filtering, requires no power supply, and attenuates the signals being combined. 4 NETWORK TECHNOLOGY AND METHODOLOGY Demultiplexing simply reverses the multiplex process. The multi- plexing techniques used in classical T-carrier networks are active the bit level. Timing differences between signals generated by dis- parate clocks running within frequency tolerance specification limits, along with a variation in propagation delay of the transmission path require the use of bit stuffing techniques to avoid clock slips and errors in transmission. Routing in its broadest context applies to multiple ways to get from here to there, or connect point A to point B. A router or routing switcher in a broadcast facility is a drastically different beast than a router that can pass Internet packets from one port to another. Routing telephone calls and configuring private line connections play an important part in the global communications network 