Area code plus the first three digits identify the central office within a specific region. Broadcasting Sending a packet to all destinations simultaneously is known as broadcasting . Send a unicast packet to each destination. However, this approach makes poor use of resources. Flood packets to all nodes.
Flooding generates many packets and consumes too much bandwidth.
This approach is similar to sending unicast packets, except that we don't send individual copies of each messages. However, the copy operations slow down the ability of a router to process many packets. Use a spanning tree. Works only if each router uses the same spanning tree. When a packet arrives from router X, if the packet arrived on a line of the sink tree leading to X, the packet is traveling along the shortest path, so it must be the first copy we've seen.