The local loop is truly a loop; it is a loop of copper wire that allows current to ﬂow from the tele-phone to the central ofﬁce and back. It is the dual-wire physical interface that connects a telephone to the central ofﬁce. The central office, also referred to as the local exchange, serves a group of subscribers (customers) in a local area. Local exchange carriers (LEC) are local telephone companies that provide service along with other LECs within a designated geographical area. The designated geographical area is typically referred to as the local access and transport area (LATA).
In the telephone system, the point where either an LEC or a long-distance carrier meets another long-distance carrier is deﬁned as the point of presence (POP). The POP provides the interconnection to the long-distance carrier or interexchange carrier (IXC).Making a phone call today from a cellular or fixed land-line phone can happen instantaneously. The caller is unaware of how their call is routed to the recipient. The phone system works so well that it is often taken for granted and few customers rarely take the time to learn how the telephone system is organized.
Cellular telephones are wireless telephones that are served by a cellular telephone system. This
system is broken into many small geographical areas called cells. Cells are connected to a Mobile
Telephone Switching Ofﬁce (MTSO). The connection from the cell to the MTSO is typically done
over telephone lines. These lines could be copper or ﬁber optic, and in some applications, micro-
waves are used.
A cellular telephone is essentially a two-way radio that carries a full-duplex conversation. Full-
Duplex means that the persons using the telephones can talk and listen at the same time. This is
different from a walkie-talkie, where only one person can talk at a time, which is referred to as
Typically, the geographical area of a cell is kept small to minimize the amount of...