ISDN

The Integrated Services Digital Network was the first generation of mass-market digital telecommunications. It promised big improvements over traditional analog phone service; but botched marketing, installation difficulties, technical snags and newer technologies mean that, for most potential users, its time passed, before it arrived.

"Integrated Services" means that with ISDN you can talk and receive and send data, still images, video or faxes all on the same line, at the same time.

"Digital" means ISDN transmits information as a discrete number, encoded as a series of ONEs and ZEROs instead of as part of a continuously varying analog signal. This makes ISDN service fast and accurate.

ISDN offered dramatic increases in the speeds of data and document transfer over the typical 28.8MB modem speeds used in the mid 1990s, but with widespread availability of cable internet access and DSL, often for less money, ISDN is just not very important now.

The basic ISDN-to-user connection, called a Basic Rate Interface, or BRI, contains three separate channels, or "pipes."

Two of these channels (the B channels) carry user "conversations" from a telephone, a computer, a fax or almost any other device. The third channel (the D channel) carries call set-up information for the telephone company network, but can also carry a customer's data transmissions. The power of ISDN enables all three of these transmissions to happen at the same time, through the same copper twisted-pair telephone line that once could handle only one transmission at a time.

Depending on the capabilities of the phone company's central office switch, ISDN can support up to eight devices and as many as 64 separate telephone numbers through a single BRI connection.

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Why is a digital network important?

1. Digital signals ignore the static and noise that often affect analog transmissions, especially over long distances and older telephone lines. Voice conversations are quiet and crystal-clear, and data transmissions are usually error-free.

2. Data can move at much higher speeds than with traditional dial-up connections.

Two kinds of ISDN: Basic & Primary

1. Basic Service consists of two 64-Kbps (Kilobytes) B channels to carry voice, data and image communications, and one 16-Kbps D channel for packet data and call management. The two Basic Service B channels can be combined to transmit data or images at 128 Kbps.
2. Primary Service consists of 23 64-Kbps B channels and one 64-Kbps D channel, and allows users to combine the B channels for speeds up to 1.5 Mbps.

ISDN service varies around the country. Generally, you must be within a few miles of the central office to obtain service, and not all central offices can provide ISDN.

In some areas where local ISDN service is not available, phone companies can provide service from the closest central office that has ISDN equipment. This arrangement is called Virtual ISDN Service, and there is an additional one-time installation charge, as well as a monthly surcharge, from some phone companies.

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Making Connections

1. If you want to connect a standard phone or fax plus a PC, you'll need to get a Terminal Adapter, often called an "ISDN modem."
2. The Panasonic KX-TD1232 "dash three" and later versions can use various circuit modules, such as the KX-TD392 to connect to BRI.
3. The Panasonic KX-TD1232 "dash six" and "dash seven" can use the KX-TD290 module to connect to PRI.

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The competition from ADSL and cable

When ISDN was first proposed, most computer-users were poking along at 300bps (300 bits per second), so the prospect of 128kbps (128,000 bits per second) was extremely exciting. When ISDN became commonly available, many modems were running at 53kbs (53,000 bits per second), so the move to 128k just wasn't very impressive, particularly because of the added expense.

With Asymmetric Digital Subscriber Line, a rapidly developing technology that provides high-speed data transmission over existing copper telephone lines, you can have much faster speed than ISDN can deliver. ADSL can provide a dedicated 1.5Mbps (1,500,000 bits per second) link from the phone company's central office to its customers. A typical web page can be downloaded up to 50 times faster than a 28.8 kilobit modem.

With Cable internet access, It's theoretically possible to receive data at up to 10Mbps (10,000,000 bits per second), and send data at 768kbps. A web page filled with graphics loads instantaneously. Maximum speed will decrease depending on the number of other users.

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At AbleComm, we have cable internet service ("Optimum Online") from Cablevision, plus ADSL from AT&T/SBC/SNET as backup, and dialup service from Cyburban Link and AOL as backup backups.