Packet Network Foundations

Аннотация

Part I of this book introduces four widely deployed packet network technologies: X.25, frame relay, asynchronous transfer mode (ATM), and Internet protocol (IP). Before packet networks, communications technology used circuitswitched telephone networks with dedicated, analog circuits that functioned on a “always on once activated” basis. A dedicated circuit cannot be used for other purposes even if no communications are taking place at the moment. In regard to telephone conversations, it is estimated that on the average a dedicated circuit carried active traffic only 20 to 25 percent of the time and is idle the other 75 to 80 percent. Moreover, other services such as video data streams cannot be efficiently carried on circuitswitched networks.