What is ISDN protocol stack?

Answer 1

Integrated Services Digital Network (ISDN) is a digital, point-to-point network capable of transmitting speeds of about 2Mbps. A computer connects to an ISDN line via an ISDN adapter and uses the same type of wiring as a Telephone wire. The only difference is ISDN can carry analog (voice) and digital signals, so it can be used to connect to the internet. It can be connected by the phone company but it is rarely used as it needs special equipment and is more expensive than other way.

Answer 2

ISDN-BRI (Integrated Services Digital Network--Basic Rate Interface) is not a protocol but, instead, is a telephony service that provides 128 kilobits per second (128 Kbps or 128 Kbaud) of bandwidth over two bonded 64K baud channels. It was never widespread in the US and has been dropped by many telephone companies in favor of DSL or other faster and better services.

ISDN-PRI (with PRI standing for Primary Rate Interface) is what G543 was mentioning in his answer and it is the more expensive ISDN service available though it is mostly used to connect Private Branch Exchanges (PBXes) of businesses and other larger facilities to the packet switched telephone network (PSTN), otherwise known as the telephone system with which we are all familiar. Outside the US, ISDN-PRI uses an E1 carrier and has a total of 2048 Kbaud of bandwidth but only 1920 Kbaud is actually usable as 64 Kbaud is used for signalling and the other 64 Kbaud is used for an alarm channel. Within the US, though, ISDN-PRI is serviced on a T1 carrier line which has a maximum throughput of 1536 Kbaud (as opposed to the 1544 Kbaud possible on an analog T1 leased line), 1472 Kbaud of which is for data and the final 64 Kbaud is for signalling. ISDN-PRI is still in common use in the US but its days are numbered since the uses for the services are limited.