RFC 760 (rfc760) - Page 2 of 42
DoD standard Internet Protocol
Alternative Format: Original Text Document
January 1980
Internet Protocol
Introduction
1.4. Operation
The internet protocol implements two basic functions: addressing and
fragmentation.
The internet modules use the addresses carried in the internet header
to transmit internet datagrams toward their destinations. The
selection of a path for transmission is called routing.
The internet modules use fields in the internet header to fragment and
reassemble internet datagrams when necessary for transmission through
"small packet" networks.
The model of operation is that an internet module resides in each host
engaged in internet communication and in each gateway that
interconnects networks. These modules share common rules for
interpreting address fields and for fragmenting and assembling
internet datagrams. In addition, these modules (especially in
gateways) may have procedures for making routing decisions and other
functions.
The internet protocol treats each internet datagram as an independent
entity unrelated to any other internet datagram. There are no
connections or logical circuits (virtual or otherwise).
The internet protocol uses four key mechanisms in providing its
service: Type of Service, Time to Live, Options, and Header Checksum.
The Type of Service is used to indicate the quality of the service
desired; this may be thought of as selecting among Interactive, Bulk,
or Real Time, for example. The type of service is an abstract or
generalized set of parameters which characterize the service choices
provided in the networks that make up the internet. This type of
service indication is to be used by gateways to select the actual
transmission parameters for a particular network, the network to be
used for the next hop, or the next gateway when routing an internet
datagram.
The Time to Live is an indication of the lifetime of an internet
datagram. It is set by the sender of the datagram and reduced at the
points along the route where it is processed. If the time to live
reaches zero before the internet datagram reaches its destination, the
internet datagram is destroyed. The time to live can be thought of as
a self destruct time limit.
The Options provide for control functions needed or useful in some
situations but unnecessary for the most common communications. The