TCP/IP information is sent via datagrams. A single
message may be broken into a series of datagrams
that must be reassembled at their destination. Three
layers are associated with the TCP/IP protocol stack:
• Application layer: This layer specifies protocols
for e-mail, file transfer, remote login, and other
applications. Network management is also supported.
• Transport layer: This layer allows multiple
upper-layer applications to use the same data
stream. TCP and UDP protocols provide flow
control and reliability.
• Network layer: Several protocols operate at the
network layer, including IP, ICMP, ARP, and
RARP.
IP provides connectionless, best-effort routing of
datagrams.
TCP/IP hosts use Internet Control Message
Protocol (ICMP) to carry error and control messages
with IP datagrams. For example, a process
called ping allows one station to discover a host
on another network.
Address Resolution Protocol (ARP) allows communication
on a multiaccess medium such as
Ethernet by mapping known IP addresses to MAC
addresses.