1's. Network nodes can easily store digital data and resend it without degrading the quality of the data. This capability enables the use of multi- plexing techniques that are more efficient than FDM, such as Time Division Multiplexing (TDM). However, even TDM systems make rather inefficient use of the network resources. Voice transmissions fail to use all the available bandwidth in a circuit, none of which can be reassigned for any other purpose. As if that weren't enough, data communications brought new communi- cations patterns into the picture. Data traffic is bursty and non-uniform. Terminals do not transmit continuously, but are idle most of the time and very busy at certain points. Data rates are not kept constant through the duration of the connection either; they vary dynamically. A particular data transmission has a peak data rate and an average data rate associated to it, and these are not usually the same. Employing dedicated circuits to transmit traffic with these characteris- tics is a waste of resources, as we can see in Figure 2-1. The circuit in the Packet Switching, IP, and the IETF Capacity used Figure 2-1 at a certain moment Inefficient use of the network capacity. 64 Kbps Available capacity provided by the circuit Unused capacity = wasted capacity figure provides 64 Kbps continuously, but the data rate needed by the sys- tems communicating is rarely 64 Kbps; it is usually less and sometimes more. The figure also shows that the available capacity that is not in use by the system at a certain moment is simply lost. Packet switching was first designed to fulfill the requirements of bursty traffic presented by data. Although the first papers about packet-switching technology appeared in 1961, the first packet-switching node was not imple- mented until the end of the 1960s. In packet switching, the content of the transmitted data determines how network switching is performed. The source nodes chunk the information that will be transmitted into pieces called packets. Then the information needed to 