name—IP, for Internet Protocol. IP provides logical communication between hosts.
The IP service model is a best-effort delivery service. This means that IP makes its
“best effort” to deliver segments between communicating hosts, but it makes no
guarantees. In particular, it does not guarantee segment delivery, it does not guarantee
orderly delivery of segments, and it does not guarantee the integrity of the data
in the segments. For these reasons, IP is said to be an unreliable service. We also
mention here that every host has at least one network-layer address, a so-called IP
address. We’ll examine IP addressing in detail in Chapter 4; for this chapter we need
only keep in mind that each host has an IP address.