Citation: 
V. Cerf and R. Kahn, "A Protocol for Packet Network Interconnection",
IEEE Transactions on Communications, May 1974, pp. 637-641.

* Summary

The seminal paper describing and justifying the use of IP and TCP in
heterogeneous packet-switched network. Previous work on packet-switched
networks led to protocols for use only within a single network, and
differences between protocols included addressing formats, maximum data
size, failure detection and error correction, etc. The concept of a 
gateway is described as a means for dealing with differences between two
networks. The foundations for internet routing and transmission control
are described.

* Gateways

To account for characteristic differences between networks, a piece of 
hardware known as a gateway can be employed. Gateways are responsible
for extracting the standard internetwork information and data from one 
network's local packet format and storing that information and data in 
the local format of another network. In doing so, it is possible that 
the size of the packets are different between the two networks, and the
gateway is then responsible for fragmenting the data into multiple
packets. 

* Internetwork Headers

Each packet is assumed to contain an internetwork header, composed of the
following information:
1) source and destination addresses (each address must be unique among all 
                                     hosts in all networks)
2) sequence number and byte count - used by destination to reconstruct 
   original data from the packets received
3) flags used to specify control information
4) checksum for end-to-end verification of a packet's contents

* Process Level Communication

In order to support communication between processes of unbounded but finite
length messages, it is necessary to provide a transmission control program
on end hosts which is responsible for multiplexing/demultiplexing multiple
data streams between multiple processes. The TCP assumes the use of ports
in identifying the processes to which a message is sent, and thus the 
notion of a TCP header is introduced. The TCP header also includes the 
information necessary for sequencing and window-based flow control.