different between modem and lease line?

[thebeatlesguru]

i know that if i use modem connect to internet,the speed is 56kbps,and if i use lease line ,for example DDN,the speed is 64kbps,however the cost is higher so much than modem, of coure the speed is higher than modem ,but i was confused that the differnet of this two is only 8kbps,why the cost and speed are so different

[S.K. Chan · Accepted solution]

I'm not sure what DDN stands for but I think it's probably close to ISDN architecture except that you get a dedicated digital line. The thing with regular modem dialup is even though you have a 56kbps modem it does not mean you're getting a clean 56kpbs throughput. This is because once you data travel from the modem to the public analog phone lines it will depends on how "clean" or how good is the quality of these public lines. If there are a lot of "noises" then it will slow down significantly plus some public phone lines can only support up to 50kbps. This makes having a 56kbps modem seems useless :). So bottom line I can gurantee you'll not get a throughput above 50kbps.
As for the DDN .. (I'm trying to use ISDN as my explaination) I think the advantage is you get dedicated 64kbps. For example in the case of ISDN it has the capabilities of using the existing public analog lines to carry its multiple digital signal thus making it faster. Another advantage is you can share multiple devices using the single digital line (eg: digital phone, fax, computer), you can do that with regular modem dialup. So basically2 things..
1) speed (the difference is much bigger, we are talking possible up to 20kbps not just 8kbps)
2) flexibility (device connectivity)

[John Carr_2]

Hi

I upgraded yesterday from 56K modem to ADSL and im getting 576Kbps throughput which means I can now work on this forum without constantly getting timeouts. Im not sure what DDN is but upgrading to ADSL is definetly work the cost.

cheers
John.