Eicon Networks ISDN NT1 Specifikace stáhnout pdf (Strana 23)

• Modems and CODECs always work in pairs - they can be nested together but each

must have a partner.

• A Terminal Adapter is an interface between the ISDN and any non-ISDN device,

such as a computer or an analogue phone

• If analogue devices need to be connected to the ISDN, then the Terminal Adapter

will need to perform the function of a CODEC, and have analogue (POTS) ports

available for modems and fax machines to plug into.

• Internal ISDN adapters can use dedicated chips on the card, or software running on

the PC, to implement the digital and analogue conversions, thereby removing the

requirement for any physical analogue devices like fax machines and modems.

• There are three kinds of device used in data communications with ISDN:

o Conventional Modems - these require Terminal Adapter to connect to the

ISDN

o ISDN Modems - which combine the functionality of CODEC and modem

o Terminal Adapter - allow analogue devices to connect to the ISDN and

contain a CODEC for this purpose

o ISDN Adapters - merely pass a stream of bits between a protocol driver and

the ISDN

Q/A

1. What is the device inside an ISDN telephone that converts voice into digits?

A CODEC.

A word deriving from the two functions performed : COder - DECoder

2. What happens to these bits when they are received by the ISDN telephone at the other end?

The CODEC within the ISDN telephone at the other end will translate the incoming digital signal into an

analogue format.

It can then be reproduced as voice through the speaker in the earpiece.

3. What device converts the signals between the ISDN and the PSTN networks?

This again is a CODEC.

It is operated by the local ISDN provider, and will be situated at the boundary of the ISDN network and the

PSTN network.

This device enables calls to pass from one network to the other by converting bits to waves, and vice versa.

4. For all the above conversions to succeed, what must be common?

CODECs are not simply generic devices. They need to perform their conversion according to a standard so

that a complementary CODEC at the receiving end can apply the same standard when it does the reverse

conversion.

The CODEC will encode the data according to a fixed set of rules - as long as the receiving CODEC applies

the same set of rules in reverse, then the data can be reconstituted exactly as it was originally transmitted.

5. What is the purpose of an ISDN Terminal Adapter?

The purpose of a Terminal Adapter is to connect items of equipment that are not ISDN-aware to the ISDN

network.

An ISDN telephone, for example, is ISDN-aware, and can be connected directly to the ISDN network.

The serial port on a PC, on the other hand, is not ISDN-aware, and will therefore require a Terminal Adapter

to provide the appropriate interface between the PC and the ISDN network.

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