Introduction to Data Communications
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24. Telephone Networks

The telephone network consists of your phone at home, that is connected by the Local Loop to the Central Office which is connected to a Hierarchical Phone Network. Worldwide there are over 300 million (300,000,000) telephones - 98% of them interconnected.

24a. POTS - Plain Old Telephone Set

The POTS or Plain Old Telephone Set consists of 5 sections:

  1. Ringer Unit
  2. Hook Switch
  3. Dialer Unit
  4. Hybrid/Speech Network
  5. Hand Set

The connection to the CO (Central Office) is with only 2 wires: Tip and Ring. This connection is called the Local Loop.

The Tip is +ve and coloured green.. The Ring is -ve and coloured Red. If you look at a phone jack in your house, you will see that it is wired for 4 wires: Red, Green, Black and Yellow. Black and Yellow are not normally used.

The black and yellow wires can be used for a second telephone line or they can be used for running a Network Physical layer protocol called Phonenet by Farralon. Phonenet uses the Black and Yellow for Network communications. It is for use with Appletalk and is a replacement for Localtalk. It runs at the Localtalk speed of 230 Kbps which is reasonable for small networks.

Introduction to Data Communications
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