Eicon Networks ISDN NT1 Spécifications télécharger pdf (Page 4)

• Network Services define how the user and the network interact with each other in

order to manage calls.

• The user can use Network Services to request the network to perform functions

such as making and clearing calls, transferring calls to another user, and so on.

• This activity is known as signalling.

Bearer Services

• Bearer services carry the call activity that the user is performing at any given

moment.

• This includes voice calls, fax and modem calls, and connections to the Internet.

• Broadly speaking, there are two forms of bearer service.

o Structured Data - the information passing over the bearer service is in a

format that is understood by the network.

Voice is an example of structured data. Because the network knows that the

connection carrying voice, it can convert the data into an analogue signal in

the event that the call is connected to an ordinary analogue phone.

o Unstructured Data - the format of the information is not understood by the

network, but is understood by the two users at either end of the service.

Summary

• Bearer services provide connections between users across the network.

• Network services provide control and signalling between the user and the network.

• ISDN is provided either as Basic rate or as Primary rate.

• Basic rate provides 2 user channels.

• Primary rate provides either 30 or 23 user channels.

Q/A

1. What is the essential difference between ISDN and the ordinary telephone system (PSTN)?

The essential difference between ISDN and the ordinary PSTN system is that ISDN is digital, whereas the

PSTN is analogue.

ISDN signals pass as a stream of bits. It is from this digital basis that most of the benefits of ISDN arise:

speed, multi-channeling, and the ability to carry many types of calls.

2. In addition to voice, name at least two other services which can be carried over ISDN.

In addition to voice, ISDN can also handle fax, computer data and e-mail, videoconferencing, and audio

transmission.

3. Name the two forms in which an ISDN service can be provided to the user.

ISDN can be supplied to the user in two forms:

Basic Rate - Two 'B' channels

Typical usage: domestic use, home-workers, remote offices

and

Primary Rate - 30 'B' channels (23 in North America)

Typical usage: corporate use, dial-in remote access servers, Internet service providers, digital PABXs

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