Introduction
Packet switching provides the basic building blocks upon which data transmission takes place across the Internet. This technology was not designed for the Internet per se but was the result of the research carried out by Paul Baran of The RAND Corporation into the survivability of communication networks in the event of a nuclear attack. Concurrent research into computer time-sharing by Donald Davies of NPL reached similar conclusions. This page examines the influence of packet switching in the development of the Internet.
Circuit Switching
During a telephone call between two or more people, a dedicated link is made through exchanges between the users. Circuit switched communication of this type happens in real time. During this time the line cannot be used for any other purpose. This would be inefficient in computer communications. Data transmissions are sent in short bursts. A new direct connection would need to be made for each burst.
Packets Switching
To take advantage of these short bursts, data for transmission is separated into individual packets of data.
Image representing the construction of a data packet. Addressing and other information is included in the header and trailer.
This is the key feature of packet switching in Internet communications. These packets are then sent out onto a distributed network. An image of different network layouts, demonstrating Baran's ideas for a distributed network, can be seen at Rand.org. 30/9/01
There is no dedicated connection between the communicating devices. Each packet of data can follow a different route through the network. This routing is the responsibility of the network "nodes or routers"; computers used as stepping stones through the network. Each receiving node briefly stores each incoming packet. The packet is forwarded on to its destination following a path based on the information the node holds on the current state of the network. If a node is out of action the storing node can forward the packet to the next available node.
"Thus, in the system to be described, each node will attempt to get rid of its messages by choosing alternate routes if its preferred route is busy or destroyed. Each message is regarded as a "hot potato," and rather than hold the "hot potato," the node tosses the message to its neighbor, who will now try to get rid of the message."From On Distributed Communications: Chapter IV. On a Future System Development by Paul Baran. From The RAND Corporation. 30/9/01
Influence on Internet Development
In the late 1960's the US Defense Advanced Research Projects Agency started work on the ARPANET, a computer network. The network was not designed for wartime use, but was meant to link ARPA researchers across the United States of America. The person in charge, Larry Roberts, implemented Baran's ideas into the design. Barans network nodes became known as "Interface Message Processors", (IMP) acting as gateways between computers in the network.
Packet Control
ARPA carried out research into the control of packets travelling across a network. This resulted in the establishment of a Network Control Protocol. This was a set of standards on how packets would be handled by the IMP's. Further work, notably by Vinton Cerf and Robert Kahn, saw the development of TCP/IP (Transmission Control Protocol and Internet Protocol). TCP/IP protocols are still in use today.
Conclusion
Paul Barans ideas for packet switching were initially rejected by AT and T as unworkable. Now, it appears inconceivable that the Internet could operate without this technology. ARPA needed a robust method to network computer data. Baran's and Davies' packet switching technology was readily available. ARPANET demonstrated its effectiveness. The success of packet switching in the operation of the Internet is a testament to the work done by both Baran and Davies.
References
- Paul Barans work into distributed networks From The RAND Corporation. 30/9/01
- Donald Davies From The National Physics Laboratory. 30/9/01
- Packet switching From Webopedia.com. 30/9/01
- Circuit switching From Webopedia.com. 30/9/01
- Paul Baran From Internet Pioneers at Ibiblio.org. 30/9/01
- On Distributed Communications: Chapter IV. On a Future System Development by Paul Baran. From The RAND Corporation. 30/9/01
- US Defense Advanced Research Projects Agency - accessed 30/9/01
- Larry Roberts From ibiblio.org - accessed 30/9/01
- Network Control Protocol RFC54 - accessed 30/9/01
- Transmission Control Protocol RFC793 - accessed 30/9/01
- Internet Protocol RFC791 - accessed 30/9/01
- Vinton Cerf From ibiblio.org - accessed 30/9/01
- Robert Kahn From The Corporation for National Research Initiatives - accessed 30/9/01
