Introduction to the Internet Protocols
Published on Sep 21, 2019
TCP/IP is a set of protocols developed to allow cooperating computers to share resources across a network. It was developed by a community of researchers centered around the ARPAnet. Certainly theARPAnet is the best-known TCP/IP network. However as of June, 87, at least 130 different vendors had products that support TCP/IP, and thousands of networks of all kinds use it. First some basic definitions.
The most accurate name for the set of protocols we are describing is the "Internet protocol suite". TCP and IP are two of the protocols in this suite. Because TCP and IP are the best known of the protocols, it has become common to use the term TCP/IP or IP/TCP to refer to the whole family. It is probably not worth fighting this habit. However this can lead to some oddities. For example, I find myself talking about NFS as being based on TCP/IP, even though it doesn't use TCP at all.
The Internet is a collection of networks, including the Arpanet, NSFnet, regional networks such as NYsernet, local networks at a number of University and research institutions, and a number of military networks. The term "Internet" applies to this entire set of networks. The subset of them that is managed by the Department of Defense is referred to as the "DDN" (Defense Data Network).
This includes some research-oriented networks, such as the Arpanet, as well as more strictly military ones. (Because much of the funding for Internet and DDN can sometimes seem equivalent.) All of these networks are connected to each other. Users can send messages from any of them to any other, except where there are security or other policy restrictions on access. Officially speaking, the Internet protocol documents are simply standards adopted by the Internet community for its own use. More recently, the Department of Defense issued a MILSPEC definition of TCP/IP.
This was intended to be a more formal definition, appropriate for use in purchasing specifications. However most of the TCP/IP community continues to use the Internet standards.
The MILSPEC version is intended to be consistent with it.Whatever it is called, TCP/IP is a family of protocols. A few provide "low-level" functions needed for many applications. These include IP, TCP, and UDP. (These will be described in a bit more detail later.) Others are protocols for doing specific tasks, e.g. transferring files between computers, sending mail, or finding out who is logged in on another computer.
Initially TCP/IP was used mostly between minicomputers or mainframes. These machines had their own disks, and generally were self-contained.
Thus the most important "traditional" TCP/IP services are:
- file transfer. The file transfer protocol (FTP) allows a user on any computer to get files from another computer, or to send files to another computer.
- remote login. The network terminal protocol (TELNET) allows a user to log in on any other computer on the network. You start a remote session by specifying a computer to connect to.
- computer mail. This allows you to send messages to users on other computers. Originally, people tended to use only one or two specific computers.
- network file systems. This allows a system to access files on another computer in a somewhat more closely integrated fashion than FTP. A network file system provides the illusion that disks or other devices from one system are directly connected to other systems.
- remote printing. This allows you to access printers on other computers as if they were directly attached
to yours. (The most commonly used protocol is the remote lineprinter protocol from Berkeley Unix).