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Agency (DARPA), a Department of
Defense agency devoted to developing advanced technology for military
use.27 The Internet grew out of an ARPANET project and was perhaps the
most important civilian application that came from DARPA.
    In 1966 DARPA hired MIT's Lawrence Roberts to build a network of
different computers that all communicated with one another.28 This would
be a resource-sharing network. Each individual system would follow its
own design with the only requirement being that the various networks be
able to "internetwork" with one another29 through the use of Interface
Message Processors (IMPs). Designing the IMPs fell to a Cambridge, Massachusetts, consulting company, Bolt Beranak and Newman (BBN), one of
whose researchers, Robert Kahn, moved to DARPA.
    Kahn realized that only the IMPs would need a common language to
communicate, and this greatly simplified the entire scheme. The other
machines within the individual networks would not need to be transformed in any way in order to communicate with the rest of the system.
These principles made so much sense that forty years later they still govern
the Internet:
    • Each individual network would stand on its own and would not need
internal changes in order to connect to the internetwork.
    • Communications were on a "best-effort" basis. If a communication did
not go through, it would be retransmitted.
    • The IMPs would connect the networks. These gateway machines (now
known as routers and switches) did not store information about the packets
that flowed through them, but simply directed the packets.
    • All control would be local; there would be no centralized authority directing traffic.30 (This model is essentially opposite to the PSTN architecture of the time; there are many reasons for this difference, not all of them
technical.31)

    With his colleague Vinton Cerf, Kahn developed the fundamental design
principles and communication protocols for the network that became the
Internet; they are the true "fathers of the Internet."
    Kahn and Cerf developed the underlying protocol for end-to-end transmissions in 1973. It consisted of the Transmission Control Protocol (TCP)
and the Internet Protocol (IP) and is usually simply abbreviated as TCP/IP.
TCP determines whether a packet has reached its destination, while the IP
address is a numeric address that locates a device on a computer network.
Kahn and Cerf 's original version of IP used 32 bits for the address; this is
still in use today. As more and more devices connect to the Internet, the
32-bit address space, which allows for over four billion individual devices
to be located on the Internet, is running out of room.32 The new version
of addressing, IPv6 (Internet Protocol version 6), has 128 bits for addressing, which increases the number of possible Internet addresses by a factor
of 296, or more than a billion billion billion times as many.
    Although the numbers used in an IP address are meaningful to a networking expert-to those in the know, an address of the form 18.x.y.z,
where x, y, z are between 0 and 255, designates MIT-most people find the
sequence of numbers largely incomprehensible. Instead people use names
(such as www.mit.edu) rather than IP addresses to define Internet locations; machines around the Internet resolve these names into the numeric
IP addresses.33
    Internet routing is very different from PSTN routing. There is no restriction that a path take just five hops. More importantly, the routing of a
communication is dynamic: packets travel whichever way is least congested and, in theory-though not often in practice-the different packets
of a file transfer, VoIP call, email, or any other IP-based communication
could each take different paths. Packet switching puts the destination
address into each packet of data, and the Internet routers and switches
constantly broadcast the best ways to get from here to there.34
    The flexibility of the system engendered many