Structure Of The Telephone System
Structure Of The Telephone System: Shortly after Alexander Graham Bell patented the phone in 1876 (just hours before its competitor, Elisha Gray), his new invention became indispensable. The initial market was the sale of handsets in pairs. It was up to the customer to connect a single cable between them. If the owner of the phone wanted to speak with other owners of the phone, separate cables had to be connected to all the homes. During the year, the city was covered with cables that passed over homes and trees in wild confusion. Once it became clear that the model to connect all phones on all the rest of the phone, shown in the following figure.
Figure: Fully Interconnected Network.
To his credit, Bell identified this problem from the beginning and founded Bell Telephone, which opened its first foreign exchange office (in New Haven, Connecticut) in 1878. The company sent a telegram to each home or office of each client. To make a call, the customer had to start the phone so that a call signal sounded in the telephone company’s office to catch the operator’s attention. He then had to manually connect the caller to the caller using a connection cable. In short, to connect it. The model called Single Switching Office Model is shown in the following figure.
Figure: Centralized switch.
Very quickly, Bell switching centers appeared everywhere and people wanted to make long-distance calls between cities. The Bell System has started to connect switching centers. The initial problem quickly returned: the connection of each wire center to any other wire-connected switching center quickly became out of control, so second-level switching centers were invented. After a while, it took several second-level offices, as shown in the following figure.
Figure: Two-level hierarchy.
A telephone system consists of three main components:
- Local loops (analog twisted pairs going to houses and businesses).
- Trunks (digital fiber optic links connecting the switching offices).
- Switching offices (where calls are moved from one trunk to another).
Local loops give everyone access to the entire system, so they are crucial. Unfortunately, they are also the weakest link in the system. For long-distance lines, the main problem is how to collect multiple calls together and send them to the same fiber. This requires multiplexing, and we apply FDM and TDM for this purpose.
Read More The Public Switched Telephone Network