The Internet and Its Protocols

2.2 IPv4 25

Figure

2.1 IP provides a uniform network layer protocol to operate over any collection of data-link

protocols and physical links.

Many physical link types and data-link layer protocols are fundamentally

unreliable--that is, they may drop frames without warning. Some are capable

of detecting and reporting errors, but few can recover from such problems and

retransmit the lost data such that the higher-layer protocols (that is, the transport

and application protocols that use the links) are protected from knowledge of

the problems. This means that a protocol must be run at a higher level ...