Transmission Shortcomings

Packets are placed on the network. What is their fate next? Even if the network is essentially a reliable bit pipe, it is possible for it to break, independent of the end hosts communicating. Practice shows that it is in fact far more likely to break than, for instance, the terminal interface device on a mainframe, or a disk controller... If the network is packet switched, then things can go wrong in more subtle ways. Depending on the type of network, a variety of disasters can befall a packet: The consequences are that there must be mechanisms for hosts to indicate where they wish to communicate with - just like file systems allow us to indicate which file we want to read or write. There may be a single wire leading out of a host, which then splits in some way to go to multiple destinations. This means we need to have some kind of Addressing mechanism, so that we can Multiplex communication between many hosts on a network. The user needs some level of Reliability. This can vary between some statistical level - digital voice or video may only require some percentage of data per second to be delivered from which a reasonable result can be constructed by the receiver. [For instance, humans only need 30% someone's voice to be able to understand 99% said]. The user may need to restrict the rate at which data arrives. Real Time applications like Voice and Video require fairly exact rates of arrival. Print servers may support much lower data rates than typical modern networks.