 basically a computer with several network interfaces attached to it. It receives packets from one interface, analyzes the headers, and forwards them through the proper outgoing interface. Falling computer prices in the last few years directly benefit packet-switching nodes. Chapter 2 Weaknesses of Packet Switching We've cited more delay and higher overhead as the two primary reasons why packet switching may not perform as well as circuit switching under certain circumstances. Circuit-switching nodes do not examine contents of the information transferred at all, whereas packet-switching routers exam- ine the headers of every packet before forwarding them. This process takes necessarily longer than, say, just switching information from one time slot to another in a TDM network. Besides, packets that will be forwarded through a certain interface in a router must line up in the outgoing queue of that interface. There, they wait until all of the previous packets are gone. When the network has a heavy load, router queues are usually full, which is compounded by the fact that packets have to queue in each and every node they traverse. It is possible to mitigate the delay introduced by imple- menting different priorities for different types of traffic in the queues, for instance, but these delays are inherent to packet switching and can't be eliminated altogether. How much of a disadvantage is the overhead intro- duced by full-packet headers? The headers, of course, consume network resources, and if the payload of a packet is small enough, the header can actually outweigh it. For instance, if a 20-octet header is used to transfer 5 octets of user data, the network will transmit a packet of 25 octets, in which just 5 octets are user data. In the 1970s, the telephony carriers developed packet-switched networks based on virtual circuits. These networks offered many similarities to the public-switched telephone network (PSTN) and a smart network. The spec- ification X.25 defined the interface between the terminals and the n