Eicon Networks ISDN NT1 Specifikace stáhnout pdf (Strana 52)

More Termins

http://www.freesoft.org/CIE/Topics/index.htm

Analogue

What does "Analogue" mean?

Often this refers to a quantity that is can vary continuously. That doesn't mean that it's always changing. It

means that it can have any value.

One example of this is temperature. The temperature outside today might be 25°C or it might be 35°C. It

could also be any other temperature, perhaps 33.5°C or 36.1274°C*.

If you were a farmer, you might have six cows or seven cows, or 200. You wouldn't have 11.5 cows unless

you're called Damian Hurst (an artist noted for exhibiting animals that have been split down the middle).

The number of cows you have can only be discrete values, while the temperature can be any value.

Baseband and Broadband

Baseband communication is fundamentally digital. Data is transmitted directly as on/off signals in a

transmission medium (usually a copper wire). Because the transition from on to off and vice versa is usually

very nearly instantaneous, a large bandwidth is required. Generally, only one communication channel is

available at any given moment.

An alternative to this is broadband communication which (paradoxically) requires a lower bandwidth. In

broadband communications, data is carried by a particular portion of the available bandwidth. This allows

more than one communication channel to be carried a time. This is comparable to the way radio stations can

transmit on different frequencies so that they don't interfere with each other.

PBX or PABX

PBX stands for Private Branch Exchange. PABX means Private Automatic Branch Exchange. Nowadays,

these both mean the same thing.

This is a telephone exchange as would be used within an office to connect a number of internal users to a

(usually) smaller number of outside lines on the public network. They can range in size from very small (two

outside lines and maybe eight extensions) to very large (hundreds of outside lines and thousands of

extensions).

This expression covers both conventional (analogue) exchanges and those supporting ISDN.

Transmitting data over the D channel

There are two ways in which the D channel can be used to carry data between two users:

Some networks can optionally connect each user's D channel to an X.25 data network. Then, data can be

transmitted on the D channel as far as the ISDN network, where the data is re-directed onto the X.25

network.

The ISDN specifications allow for a small amount of user-data to be attached to the SETUP message that

initiates the call. This could be used for applications requiring very short exchanges of data (such as credit

card authorisation).

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Eicon Networks ISDN NT1 Specifikace Strana 52