networks are more resilient and can better handle peak traffic periods than older networks, because diverse packets from the same message are routed via different paths, depending on both availability and congestion. In a national emergency such as the September 11, 2001 attacks in the United States on the Pentagon in Washington, DC, and the World Trade Center in New York City, the Internet, which is a packet network, still functioned when many portions of the older public voice and cellular networks were either out of service or SO overwhelmed with traffic that people could not make calls. If one route on a packet network is unavailable, traffic is rerouted onto other routes. In addition, unlike older voice networks, the Internet does not depend on a few large switches to route traffic. Rather, if one router fails, another router can route traffic in its place. Per Packet Flexible Routing Packet networks can handle peak congestion periods better than older types of networks because traffic is balanced between routes. This ensures that one path is not overloaded while a different route carries only a small amount of traffic. Sending data from multiple computers on different routes uses resources efficiently because packets from multiple devices continue to be transmitted without waiting until a single "heavy user" has finished its entire transmission. Thus, if one route is congested, packets are transmitted on other routes that have more availability. Routers in packet networks are connected to each separate route in the network. They have the ability to check congestion on each leg of the journey connected to them and send each packet to the least congested route. As shown in Figure 1-7, packets from the same message are transmitted over the different routes. www.TechnicalPDF.com Packet Network Packets routed individually least congested routes 3. Packets routed or 2. AT&T different routes Packet1 Packet 1 1. John sends email to S Sophie Packet2 Verizon 1. John 2. John's email AT&T 3. Packets in email each sent 