Glossary of Internet Terms

©2007 by Walt Howe

Select the first character of the term you want to look up or use the Search link below.

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Letter O

OffLine Reader. Software which will collect messages for you from mail, newsgroups, and message bases, send new ones you have written, and let you read and respond offline.

Acronym for Open Systems Interconnect. This is a model for connecting computers together in a network. The model consists of seven distinct and separate layers of protocols.

  • Physical or Data Transport Layer. This most basic layer moves data over cables based on the physical aress of each Network Interface Card (NIC). The most common types are ethernet and token ring. Ethernet terminals and server (if present) are connected by a hub.
  • Data Link Layer. This layer frames the packets of data that are sent through the network with a header and a footer that include CRC data for error checking. PPPframe relay, and X.25 operate at this layer. Bridges connect local networks of the same type at this layer.
  • Network or Internet Protocol Layer. This layer puts an Internet Protocol wrapper around the data with source and destination aresses and sequencing information in its header. Routers, which connect networks of different types together, operate at this layer.
  • Transport Layer. This layer governs the setting of suitable packet sizes, segmenting and reassembling data, detecting errors, and flow control. Packets are often received out of order and with errors. At this level, packets are sequenced correctly, and requests for error free packets are transmitted until error-free packets have all been received.
  • Session Layer. This layer polices the communications between sender and destination. Only one end can speak at a time. It executes transactions like saving a file. If something interrupts the save, the session layer returns the action to its previous state, preventing corruption of data, and the transaction can be attempted again.
  • Presentation Layer. This layer provides a standard interface between the network and application layers, allowing a wide variety of applications to exist.
  • Application Layer. This layer provides for standard interfaces for such functions as message handling and file transfer and remote login. It allows, for example, for different e-mail programs to be used, as long as they conform to the standard application layer interface. If you send a message constructed in VMSMAIL on a VAX system, it can be read by Eudora on a Windows system as long as the standard application interface for message handling is followed by both programs.

TCP/IP differs from the OSI model in that it combines the session, presentation, and application layers into a single application layer.

Acronym for On The Other Hand often used in chat.

(last updated 22 October 2012)