Wide Area Networks (cont.) - 7 : Integrated Services Digital Network (ISDN) скачать в хорошем качестве

Wide Area Networks (cont.) - 7 : Integrated Services Digital Network (ISDN)

This playlist provides an overview of the wide-area #network (#WAN), the technology used for communicating over a WAN, and the role of #WANs in organizations today. Continues the discussion of WANs and introduces three common WAN technologies: #ISDN, frame relay, and leased lines.    • 34 : WAN - Fundamentals of Communications   Let's start with a long definition again. The ISDN protocol is a point-to-point, circuit-switched, connection-oriented, dial-up connection designed to support multiple service types. Once again, we are looking at a point-to-point connection, with no sharing of bandwidth. And, just like a leased line, ISDN is circuit-switched with signaling between switches establishing the circuit, and as such it is also connection-oriented. The difference between leased lines and ISDN is that ISDN is a dial-up connection. Using ISDN, the connection is only established when data needs to be sent and is disconnected immediately afterwards. Leased lines, in contrast, are permanent connections. "Multiple services" means ISDN is designed from the beginning to support voice and data services simultaneously. The basic operation of ISDN is just like making a phone call. As a matter of fact, ISDN services are available in most locations for phone lines. Essentially, the idea of ISDN is to replace the older modem connections and keep communication digital from end to end. The advantages of ISDN are that you only pay for it when you need to send data, and it is a dedicated connection, so no sharing of the connection is required. The disadvantage is it is still very expensive on a packet-for-dollar basis. Charges here are very similar to long distance phone charges. Communication between sites with lots of traffic can get quite expensive. ISDN is best utilized between sites that only require a small amount of random communication. (We'll learn more about ISDN in the next lesson.) So far we have covered linking sites with a lot of traffic and linking sites with only a little traffic. We also need something in between.