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This chapter considers a data communication channel, using the example of a modem link across the telephone network to connect two computers. The channel can be considered in two parts: from the computers to the modems, and between the modems. In both cases we need a transmission path and some means of coding the data to ensure that it can be transmitted over the link.

to explain who you are and whom you want to talk to to ask someone to take a message to pass on and understand telephone numbers to find out when someone is free to arrange a date for a visit to use a public telephone and you will be given information about the telephone system in Germany.

How often do you use the telephone? Most people now have a telephone at home and many more use telephones in their working lives. Businesses would have difficulty surviving without the use of this communication tool, and our private lives would be very different without it.