Redes

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 creationand destruction 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 prin-ciple reason for developing such networks has beento facilitate the sharing of computer resources. A packet communication network includes a transpor-tation mechanism for delivering data between com-puters 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, theseprotocols 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 differ-ent 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 individual packetswitching 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 by the AssociateEditor for Data Communications of the IEEE Communications Society for publications without oral presentation. Manuscript received November 5, 1973. The research reported in this pa-per 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 Electrical En-gineering,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 processes in their own orother 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 this convention forcommunication 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 destination address which is...