1. High speed service. ISDN is fast. As there is no need of conversion of analog to digital inside a digital network, the speed is high. Table 12.1 shows the speed comparison of various devices.
MODEM ISDN lB channel ISDN 2B channel
28.8 kbps B4 kbps l28 kbps
Before ISDN, normal phone carries only 2.4 kbps. After ISDN, digital phone lines can carry 128 kbps over the same wire. Hence ISDN's speed allows very quick file transfers. The ISDN call setup (connect) also faster (2 to 4 sec) than analog devices (15 to 30 sec). ISDN can transfer two times faster than a 56 K modem.
2. Cost advantage. Low costs results due to reduced retransmission of information and fast information transfer. Simplified network management and maintenance results in reduced costs for international and nation-wide communication. Reduced infrastructure and maintenance costs by offering multiple services through a single network.
3. High quality transmission. ISDN transmits data digitally (except the link between you and telephone company) and as a result, is less vulnerable to static and noise than analog transmission. Due to digital technology, transmission is highly reliable. Voice conversation over ISDN also crystal clear, having the sound quality of an audio CD.
4. Simultaneous transmission. ISDN has two B channels for voice, circuit or packet conversations and one D channel to carry signals between your equipment and the phone company. Thus ISDN can perform simultaneous functions. You can send a fax, you can receive a fax or utilize a 56 kbps internet connection while talking.
5. Multiple device connection. Because ISDN lines are divided into logical channels, up to eight devices (fax, telephone, computer etc.) can be connected on a single Basic Rate ISDN in any combination. This reduces the additional wiring.
6. Conferencing. As eight devices could be in use simultaneously, this may result in multiple call appearences. Thus ISDN allows to handle several calls at once or conference them together with one number. This multiple call appearence is useful for small office with large number of outside sales people.
7. ISDN provides clear, quiter voice telephone service and easy to use call control features. Its caller identification features can screen incoming calls.
8. Call management features.
(a) Call forwarding. Forwards call to a preselected number.
(b) Call pickup. Call can be picked at another phone or station.
(c) Directed call pickup. Calls from specific extension be automatically forwarded to a second number.
(d) Message Waiting indicator.
(e) Directed Dial. Incoming calls can be automatically forwarded to a central office, car etc.
f) Ringing options.
(g) Additional call offering. Allows the user to use a distinctive ring to a particular call.
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