The transport of packets between hosts is handled by the Network and
two lower layers in the
OSI Networking Model:
The Network Layer describes how a series of exchanges
over various data links can deliver data between any two nodes
in a network. Ex: this layer defines the addressing and routing
structure of the Internet.
The Data Link Layer describes the logical organization
of data bits transmitted on a particular medium. Ex: this layer
defines the framing, addressing and checksumming of Ethernet packets.
The Physical Layer describes the physical properties of
the various communications media, as well as the electrical properties
and interpretation of the exchanged signals. Ex: this layer
defines the size of Ethernet coaxial cable, the type of BNC connector
used, and the termination method.
The Network Layer can be further subdivided into transport and switching.
Transport protocols concern themselves with encapsulating user data,
which switching protocols exchange network connectivity information
and are rarely seen by users. Internet switching protocols are
not covered here; see
Routing Concepts and
The primary Internet transport protocol is IP. In fact, an Internet
segment can be defined as any communications link that can exchange
IP packets. ICMP provides important error handling and control
functions, while IGMP offers rudimentary multicasting support.