T U 2010

A Protocol for Packet Network Intercommunication
VINTON G. CERF AND ROBERT E. KAHN,
MEMBER, IEEE
Abstract — A protocol that supports the sharing of resources that exist
in different packet switching networks is presented. The protocol provides
for variation in individual network packet sizes, transmission failures,
sequencing, flow control, end-to-end error checking, and the creation anddestruction of logical process-to-process connections. Some
implementation issues are considered, and problems such as internetwork
routing, accounting, and timeouts are exposed.

INTRODUCTION
IN THE LAST few years considerable effort has
been expended on the design and implementation of
packet switching networks [1]-[7],[14],[17]. A principle reason for developing such networks has been
tofacilitate the sharing of computer resources. A
packet communication network includes a transportation mechanism for delivering data between computers or between computers and terminals. To
make the data meaningful, computer and terminals
share a common protocol (i.e, a set of agreed upon
conventions). Several protocols have already been
developed for this purpose [8]-[12],[16]. However,these protocols have addressed only the problem of
communication on the same network. In this paper
we present a protocol design and philosophy that
supports the sharing of resources that exist in different packet switching networks.
After a brief introduction to internetwork
protocol issues, we describe the function of a
GATEWAY as an interface between networks and
discuss its role in theprotocol. We then consider the
various details of the protocol, including addressing,
formatting, buffering, sequencing, flow control,
error control, and so forth. We close with a
description of an interprocess communication
mechanism and show how it can be supported by
the internetwork protocol.
Even though many different and complex
problems must be solved in the design of an
individualpacket switching network, these
problems are manifestly compounded when
dissimilar networks are interconnected. Issues arise
which may have no direct counterpart in an
individual network and which strongly influence the
way in which internetwork communication can take
place.
A typical packet switching network is composed
of a set of computer resources called HOSTS, a set
Paper approved bythe Associate Editor for Data Communications of the
IEEE Communications Society for publications without oral presentation.
Manuscript received November 5, 1973. The research reported in this paper was supported in part by the Advanced Research Projects Agency of
the Department of Defense under Contract DAHC 15-73-C-0370.
V.G. Cerf is with the Department of Computer Science and ElectricalEngineering, Standford University, Stanford, Calif.
R.E. Kahn is with the Information Processing Technology Office,
Advanced Research Projects Agency, Department of Defense, Arlington,
Va.

of one or more packet switches, and a collection of
communication media that interconnect the packet
switches. Within each HOST, we assume that there
exist processes which must communicate with
processesin their own or other HOSTS. Any current
definition of a process will be adequate for our
purposes [13]. These processes are generally the
ultimate source and destination of data in the
network. Typically, within an individual network,
there exists a protocol for communication between
any source and destination process. Only the source
and destination processes require knowledge of thisconvention for communication to take place.
Processes in two distinct networks would ordinarily
use different protocols for this purpose. The
ensemble of packet switches and communication
media is called the packet switching subnet. Fig. 1
illustrates these ideas.
In a typical packet switching subnet, data of a
fixed maximum size are accepted from a source
HOST, together with a formatted...