ich ness services being brought to market in months rather communications between telephones or other devices than years or decades. are conducted-the telecommunications industry is now preparing for a big technology changeover, what's being called a "next-generation network" based on so-called Data traffic characteristics data packets. Instead of setting up an explicit channel for each In the early days of data communications, all networks conversation or data flow, all the traffic types-data, were circuit-switched, and many still are. More recently, Data and voice traffic CHAPTER 3.1 for networks that cover wide areas, the emphasis has certain ways to form the larger, but still local, network. A shifted to packet switching, simply because it permits subnetwork is a portion of a network in which all of the the interconnection of far more nodes into a single nodes are directly connected; for example, all of the network. With packet switching, fewer communication nodes may be connected by one piece of wire. channels are required (because channels are shared by Metropolitan area networks (MANs) continue to many users), and interconnection of networks is much evolve and will be developed primarily by data carriers in easier to accomplish. response to the demand to interconnect LANs across The data layering of communications gives rise to a metropolitan area. For example, a university might situations where the lower layers of a network are interconnect its campuses. Wide area networks (WANs) connectionless, but the higher layers establish a con- are often interconnected LANs or MANs. They can be nection; the opposite, where the lower layers establish homogeneous, but are often heterogeneous, that is, a connection and the upper layers do not, can also interconnecting LANs or MANs that have been built occur. using different technologies. A WAN can span campuses, cities, states, or even continents. Typically, only one node on each LAN or MAN, called a gateway, connects to the Broadcast channels WAN. Other nodes communi