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 different than it was when first conceived in the 1950s, except it’s significantly 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 frequency 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.
Demultiplexing simply reverses the multiplex process. The multiplexing techniques used in classical T-carrier networks are active at the bit level. Timing differences between signals generated by disparate 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 today and are likely to remain so well into the future.
Signaling is the mechanism whereby customers, subscribers, and users (through equipment) communicate with the network to setup and tear down a connection, or configure it for initial use, or reconfigure it for different use (i.e., change the default service configuration). Signaling is also a process whereby network elements communicate with each other in response to commands from users for service, or the owner for changes in configuration or service capability. Successful signaling depends on a logical addressing or numbering scheme whereby all the elements in and outside the network carry a unique identification label.
Switching has been around since someone had a hunch that telephone service could take a cue from the railroads and get more use from fewer telephone lines by installing a switching point somewhere in the service area. From automatic switch-over when a transmission backbone segment fails, to provisioning private lease lines, to telephone service, data communications, audio and video conferencing, content creation, distribution, and delivery, modern communications networks simply wouldn’t do what they do so well without it. Switching concepts include circuit switching, cell switching, and packet switching.
Transmission is the act of propagating energy or moving information from point A to point B. In the context of communications networking, the term includes sending and receiving. If the heart of the network is the clocking system, transmission is analogous to the arteries and capillaries carrying oxygen from the lungs to the brain and other important organs. Modern communications network transmission seems to have started when someone figured out that a direct current voltage applied to one end of a pair of wires could be detected at the other end as long as the conductive characteristics of the path are intact. Without the underlying transmission facilities, today’s IP would be of no more value than Samuel B. Morse’s telegraph code without a baseband electrical signal transmission facility. Successful transmission requires a viable medium. Electrical transmission works well on copper wire. Radio transmission moves easily through free space, where electrical current doesn’t travel well. Light waves move through transparent glass, but opaque objects block them.
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