Basics of LANs and Telecommunications Signal generation and carrier methods used with local area networks deals primarily with basic telecommunications and I.T. theories. Local area networks (or LANs) are inherent to the I.T. (Information Technology) or "computer" world. A good example is a small office with multiple desktop computers linked together through a common server unit. No telecom carrier circuits are required at this level to connect these individual computers to one another inside a particular LAN. "Carrier" circuits come into play when 2 or more LANs are connected. For example, this same small company has 2 different departments in separate offices across town from one another - two different LANs - and they wish to share access to particular data. They would use a telecommunication network (e.g. the phone company) and incorporate various sized carrier circuits to transport their data between the two networks. These circuits are commonly referred to as "broadband carriers". The size of the circuit required would be primarily dependent on the individual network's average level of expected data transfer, with future growth potential factored in as well. These circuits are commonly measured in Mbs (Mega-Bits per second) - - - not to be confused with MB (Megabytes). Without going into too much detail on basic telecom hierarchy . . . the base unit for most applications of interconnecting 2 or more LANs is a DS1/T1 circuit (1.5 Mbs). This is an electrical connection using twisted-pair wire as the primary medium for transport. In simple terms, a T1 is equivalent to 24 individual 64k phone lines (8-bits for overhead on each channel making it the commonly-known 56k worth of payload per channel). If more bandwidth is required for data transfer, the next step is a DS3/T3 carrier circuit (45 Mbs). (A T3 contains twenty-eight T1 channels.) This is an electrical circuit that rides coaxial cable. The next step from there is to jump to fiber optic circuits. The base unit for optical circuits is the OC3 - (Optical Carrier 3). The number relates to the number of T3s, or in optical terms, the number of sts1 payloads that are carried by that single fiber. So, here's a basic example:
Company A wants to share data with Company B - one of its contractors. Company A has a 100Mbs LAN. Company B has a 10Mbs LAN. Company A places an order with the phone company to provide a carrier circuit between the two LANs. This circuit is really nothing more than an empty "pipe" between the two networks. The size of this pipe, as discussed earlier, can be altered to accommodate more or restrict traffic flow. The limitations of the actual data transfer are generally set, however, by the slowest element of a given network. In this example, Company B's LAN only operates at 10Mbs. But, there is the potential for future need/growth. A compromise could be to order a DS3 circuit (45Mbs)to begin with. Granted, the 100Mbs network of Company A would be slowed considerably in any data transfer applications with Company B's LAN, but, from a cost-analysis perspective, that level of bandwidth would still ensure that Company B's transfer rate is used to its max level without incurring the cost of a larger circuit that would be much more bandwidth than is necessary until they upgrade to a similar 100Mbs LAN.
A LAN connects to a carrier circuit through the use of a "router." In simple terms, a router is an interpreter of sorts which converts TCP/IP signal (the language computers use between one another on the LAN) to a Bi-polar electrical signal (for T1/T3 applications) or Sonet - the language of optical carrier circuits. The LAN server typically connects to the router via ethernet cable - and goes out the other side via CAT-5, COAX, or Fiber to a multiplexor that sends it on its merry way across the telecom network to the other location where it then goes through an exactly opposite process of de-mixing down and then converting back from "telecom" language to that of TCP/IP through the use of another router and then off to the server and into the second LAN.
Signal generation is simply what all CPE (customer premis equipment) does. It generates the "live" signal or data that is transported across LANs and between LAns via various carrier methods. Telecom equipment does not "generate" signal. It "re-generates" whatever the customer equipment sends out. It acts like an amplifier of sorts to ensure a stable signal level and prevent signal degradation as the data travels across its network on its way to its eventual destination. T1 and T3 level circuits are very sensitive to fluctuations in signal level and are somewhat limited in the allowable distance between equipment. They are also affected by moisture. Optical carriers are the best medium for data flow. Though they too are sensitive to light-level fluctuations - they are not affected by things such as moisture and other issues inherent to electrical connections. As long as the fiber optic cable is kept clean while connecting ends together and not damaged or bent too drastically, an optical signal can travel several hundred miles before needing to be "regenerated" as opposed to only a few miles on twisted-pair cable or only a few hundred feet in terms of coax cable.