Eicon Networks ISDN NT1 Especificaciones descargar pdf (Pagina 18)

Voice, Fax, and Modems

In this section you will learn about

• How ISDN and analogue networks interact

• Digital and analogue conversions in the network

• Where and how these conversions take place

• MODEMs and CODECs

• How they impact making fax and modem calls

• ISDN equipment types and their fax and modem capabilities

Analogue Calls and ISDN

The key characteristic of ISDN is that it is a digital network. However, many of the devices

and networks with which an ISDN user needs to communicate are not digital but analogue.

In order for these two types of device to communicate, the information that they are

exchanging must be converted from one form to the other.

In fact, except for data calls between computers to across the ISDN network, almost all

other types of calls - voice, fax, modems - will all involve some kind of conversion from

digital to analogue, or vice versa.

Much of this conversion takes place without the user's knowledge or intervention and is

handled by the networks and devices involved. However, there are instances where an

understanding of what is involved will assist in making successful connections and

diagnosing problem areas.

You need to pay careful attention to the requirements of the ISDN device in use,

particularly when sending and receiving faxes. This section provides the background to the

various scenarios involved, and the practical implications for the different types of ISDN

device that are available.

Voice over ISDN

ISDN is a Digital network. Everything (including sounds such as voice and modem

signals) is carried as a stream of bits.

This means that ISDN telephones need to be able to digitise and "un-digitise" sounds. This

is performed by a device called a CODEC (Cod

er-Decoder) which is located inside the

telephone. The CODEC translates the sounds into bits in one direction, and translates bits

into sounds in the opposite direction.

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Eicon Networks ISDN NT1 Especificaciones Pagina 18