Introduction to the Internet Protocols

This is an introduction to the Internet networking protocols (TCP/IP).It includes a summary of the facilities available and briefdescriptions of the major protocols in the family.

What is TCP/IP?

TCP/IP is a set of protocols developed to allow cooperating computersto share resources across a network. It was developed by a communityof researchers centered around the ARPAnet. Certainly the ARPAnet isthe best-known TCP/IP network. However as of June, 87, at least 130different vendors had products that support TCP/IP, and thousands ofnetworks of all kinds use it.

First some basic definitions. The most accurate name for the set ofprotocols we are describing is the "Internet protocol suite". TCP andIP are two of the protocols in this suite. (They will be describedbelow.) Because TCP and IP are the best known of the protocols, ithas become common to use the term TCP/IP or IP/TCP to refer to thewhole family. It is probably not worth fighting this habit. Howeverthis can lead to some oddities. For example, I find myself talkingabout NFS as being based on TCP/IP, even though it doesn't use TCP atall. (It does use IP. But it uses an alternative protocol, UDP,instead of TCP. All of this alphabet soup will be unscrambled in thefollowing pages.)

The Internet is a collection of networks, including the Arpanet,NSFnet, regional networks such as NYsernet, local networks at a numberof University and research institutions, and a number of militarynetworks. The term "Internet" applies to this entire set of networks.The subset of them that is managed by the Department of Defense isreferred to as the "DDN" (Defense Data Network). This includes someresearch-oriented networks, such as the Arpanet, as well as morestrictly military ones. (Because much of the funding for Internetprotocol developments is done via the DDN organization, the termsInternet and DDN can sometimes seem equivalent.) All of thesenetworks are connected to each other. Users can send messages fromany of them to any other, except where there are security or otherpolicy restrictions on access. Officially speaking, the Internetprotocol documents are simply standards adopted by the Internetcommunity for its own use. More recently, the Department of Defenseissued a MILSPEC definition of TCP/IP. This was intended to be a moreformal definition, appropriate for use in purchasing specifications.However most of the TCP/IP community continues to use the Internetstandards. The MILSPEC version is intended to be consistent with it.

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