what is meant by:
digital modem
analog modem
synchronous modem
and asynchronous modem
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digital modem= it's not really a modem (modulator/demodulator) because the bits don't
have to be modulated to analog sound, an ISDN-card is a digital modem
analog modem=see above modulates and demodulates bits to sound and vice versa
synchronous modem= uses 2 phone lines one for calling and control signals and one for data
asynchronous= What you are probably using using 1 line for all signals
An ISDN is a telephone network that is digital instead of
regular PSTN (analog), it's available in most European country's and the US. You can choose between ISDN-2 and ISDN-30, the number stands for the number of thelephone lines and thus maximum available connections. One ISDN-line has a speed of 64 Kilobit/sec which is faster than analog modems, it's also possible to bundle lines to get a maximum speed of ca. 2 Megabit/s (30 lines). Also making a connection with ISDN is
faster (1 or 2 seconds). For using ISDN has the telephone company has to install special hardware in your house, also you need cables with 4 wires instead of 2.
An ISDN-card is what I use right now, it's a sort of modem for ISDN connections.
Analog modems comes in two flavors synchronous and asynchronous,
the most used is asynchronous because you only need 1 phone line for it.
Synchronous modems are kind of obsolete because you need two phone lines for it and is still used for connections with older hardware like ATM's that use synchronous modems.
why don't you call your local telco provider and they'll be more then happy to tell you all about isdn. and sell it to you.
tell them you want isdn option m-2. this will give you 2 64k B chanels and one d-control channel. you'll be able to connect at 128 k
also find out about dsl technology, the use modems which will access networks at anywhere from 384k to 10 mb
www.techguide.com
the short answers:
digital modem - one that functions on a digitial phone line
analog modem - one that functions on an analog phone line
synchronous modem - one that uses two phone lines to send data in both directions at the same time..
asynchronous modem - one that uses the phone line to send data in one direction at a time..
ISDN - an advent of the telephone company to provide a data grade circuit that supports high speed network like connections to the home or office..
for more detailed stuff, I agree with the comments above.. see your local telephone representative, or get a book on telecommunications from your local library..
the right modem for you depends on the job it want it to do..
eg. if you want internet type access to your home, you could probably manage it with an asynchronous 56k modem.. it's not real fast, but it's livable.. but if you wanted to run an ISP out of your house, that's a different story.. you'ld need a bunch of async modems for incoming callers, and probably some sort of ISDN or cable modem for your feed to the network..
modems range from the $40 version you can buy for your home PC to the $50000+ satellite modems used to communicate with spacecraft.. and more..
I've used most of them at one time or another, and there is no easy answer.. you need to pick the right one for the task you're doing, but to tell you blindly about all modems is difficult without knowing what you want to do..
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by: aftPosted on 1999-02-11 at 13:09:18ID: 1148011
Adjusted points to 25