“PSTN” means “Public Switched Telephone Network,” and “ISDN” means “Integrated Services Digital Network.”
1.PSTN lines are analogue while ISDN lines are digital.
2.When comparing the two networks, the PSTN lines are used for small companies and ISDL are used for bigger companies.
3.The ISDN provides 128 kbps, which is really good for the Internet. PSTN (maximum rate of 56kbps) has a disadvantage that it does not make the most possible use of the broadband.
4.While PSTN does not allow two simultaneous connections, it is allowed in ISDN service.
5.When using ISDN, one can make faster calls than when using the PSTN.6.Both are mostly obsolete now with Ethernet and TCP/IP based networks and the Internet providing all that and a lot more.