We have said that protocols allow one to specify or understand communication

without knowing the details of a particular vendor s network hardware. They are to

computer communication what programming languages are to computation. It should

be apparent by now how closely the analogy fits. Like assembly language, some protocols

describe communication across a physical network. For example, the details of the

Ethernet frame format, network access policy, and frame error handling comprise a protocol

that describes communication on an Ethernet. Similarly, like a high-level

language, the Internet Protocol specifies higher-level abstractions (e.g., IP addressing,

datagram format, and the concept of unreliable, connectionless delivery)