When we download a movie from the Internet, we don't care about, say, packet sizes. However, even ifwe are not aware of howlow-level details of networks are implemented, our data is actually being sent as lots of small packets, some of which might be lost or arrive out of order. Therefore, it is important that the protocols we use guarantee that we won't have to deal with any of these problems. In other words, all we want is a simple interface that solves our problem; this interface for network programming will be provided by the operating system. Some of these abstractions are:

process-to-process communication

remote function calls

security

hosts have human-readable names

ordered, reliable communication

streams of bytes, instead of discrete packets

support for large messages

routing to ?nal destination

independence from the low-level network and hardware details