Eicon Networks ISDN NT1 Especificações descarregar pdf (Página 45)

Bit stuffing

The bits required to fill up the 64kbps channel must be added in a systematic way so that

the receiving device can remove the bits using exactly the same methodology to retain the

information being transmitted.

There are two protocols commonly used that define systems to insert and remove extra

bits:

• V.120

• V.110

You will use either one or the other, depending on the protocol required by the service you

are calling.

Rate Adaptation is usually implemented in a Terminal Adapter. The activity happens within

the B channel and is an end-to-end protocol. The ISDN is therefore unaware of this and

the call type will be Unstructured Data.

Connecting 64k and 56k channels

The V.120 protocol is also used with unstructured data where you are connecting together

B channels which have different information rates.

This is commonly used between Europe, where the B channel operates at 64 000bps, and

North America, where some B channels operate at 56 000bps.

This is handled transparently by the ISDN providers at the network boundary points.

Connecting GSM data to ISDN

The V.110 protocol is often used when a mobile phone (GSM) connects to the ISDN in

order to access a data service, such as a WAP gateway.

This conversion is handled transparently by the data gateway that connects the GSM

network to the ISDN network.

Some GSM to ISDN gateways convert the call into a low speed modem format. Which

format is used depends on the internetworking function chosen by the two network

operators. The user has no control over this. Handling both types of call transparently is a

challenge for the recipient of the call.

For voice calls between the GSM and ISDN networks, a different conversion is performed

to convert the GSM format for voice calls to the ISDN format for voice calls.

Conversion

If you need to make an Internet connection using the serial port of your PC, but your ISP

doesn't support V.110 or V.120, you will need to use protocol conversion.

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Eicon Networks ISDN NT1 Especificações Página 45