communications protocol

Hardware and software standards that govern data transmission between computers. The term "protocol" is very generic and is used for hundreds of different communications methods. A protocol may define the packet structure of the data transmitted or the control commands that manage the session, or both. A protocol suite such as TCP/IP is made up of several levels of functionality. Learning the 7-layer protocol hierarchy, known as the "OSI model," is essential for understanding protocols. See OSI model and interface.

TCP/IP and Ethernet
TCP/IP is the standard communications protocol of the Internet and most internal networks. Ethernet is the local network standard. TCP/IP is responsible for routing packets and ensuring that everything sent was received. Ethernet is an access method that is responsible for moving packets from one node to another. See TCP/IP, Ethernet, Token Ring, ATM, IPX, SPX, NetBIOS, NetBEUI and SS7.

Conceptually Speaking
The following are very conceptual exchanges managed by TCP/IP and Ethernet.

The TCP/IP Protocol
Are you there? Yes, I am. Are you ready to receive? Yes, I am. Here comes the message--blah, blah, blah-- did you get it? Yes, I did. Here comes the next part--blah, blah, blah-- did you get it? No, I didn't - resend it. Here it comes again-- blah, blah, blah-- did you get it? Yes, I did. There is no more. Goodbye. Goodbye.

The Ethernet Access Method
Is the network busy? Yes, it is. Wait random amount of time. Is the network busy? Yes, it is. Wait random amount. Is the network busy? No, it isn't. Here goes the frame... did it collide with another packet on the line? No, it didn't. Is the network busy? Yes, it is. Wait random amount. Is the network busy? No, it isn't. Here goes the next frame... did it collide? Yes, it did. Wait random amount. Is the network busy? No, it isn't. Here goes the frame again... did it collide?

Examples
The following communications protocols are widely used (name in parentheses is the protocol suite). There are a large number of protocols at all layers. For a comprehensive list with detailed descriptions, visit www.protocols.com.

    Layer    Protocol

     1       RS-232
     1       V.35
     1       SONET

     1-2     802.11 wireless
     1-2     Bluetooth wireless

     2       Ethernet
     2       Fast Ethernet
     2       Gigabit Ethernet
     2       Token Ring
     2       FDDI
     2       ATM

     3       IP      (TCP/IP)
     3       IPX     (NetWare)

     4       TCP     (TCP/IP)
     4       UDP     (TCP/IP)
     4       SPX     (NetWare)
     4       NetBEUI (NetBIOS)

     5       NetBIOS

     6       ASN.1

     7       SMB     (NetBEUI)
     7       AFP     (AppleTalk)
     7       NCP     (NetWare)
     7       NFS     (TCP/IP)
     7       HTTP    (TCP/IP)
     7       FTP     (TCP/IP)
     7       SMTP    (TCP/IP)
     7       DNS     (TCP/IP)