switched networks are packet transport links and switches that relay packets. We will use the common term router for physical nodes that contain a packet switch, whether they are CON or CNL switches. The difference between transport links in circuit-switched and packet-switched net- works is the disposition of the bandwidth: In circuit-switched networks, the total capacity of a transport link is statically divided into a set of channels. One channel is normally dedicated for each CN connection. No other user can use that channel, even when the connection owner is not transmitting anything. The transport load that is created by each network user is proportional to the time that a CN connection exists. Transport links in circuit-switched networks are, therefore, most economical if they are used for isochronous (continuous stream of data) data transfer (such as voice or video). For data traffic (discrete chunks of data), they are economical only for bulk data transfer, like the transfer of large files, provided that set up and release of CN connections is done for each chunk of data. This requires fast set up and release of CN connections, often characterized as "fast circuit switching". In packet transport links, data are sent as discrete packages (a fixed- or variable- length sequence of octets, where an octet is eight bits). Each packet contains its own destination identifier, which allows the network to mix packets that belong to different users on the same transport link. The transport load that is created by each network user is therefore proportional only to the amount of data that is transferred, whether the connectivity service that is provided is connection-ori- ented or connection-less. This makes packet-switching networks very economi- cal for data communication services, which often have a very long session time, but little data to transfer (most Internet applications can be characterized in this way). Isochronous traffic can also be handled economically by packet-switching networks. The main problem, i