Skip to main content

seven-layer reference model

seven-layer reference model The standard model for communications protocols that is formally approved by the International Standards Organization acting in concert with the CCITT. The ISO approach identifies the functionality required in terms of seven separate layers, as summarized in the table; the two systems that are to communicate each support an implementation of these seven layers. The layers are conceptually organized with the “lowest” layer representing the physical link between the two systems, and with successive “higher” layers progressively being concerned less with the details of the network traffic, and more with the details of the end-user applications that wish to communicate. Each local implementation of these layers is often referred to as a protocol stack. Each layer can communicate only with the layers immediately above and below it in the stack. The set of permissible messages and responses in this local “vertical” communication is defined by the corresponding interface. The lowest, physical layer, communicates downward with the physical link, and information passes via the link to the corresponding lowest layer in the remote system. The highest layer communicates upward with the local end-user application.

By passing a message down through the lower layers at the transmitting end, across the link, and up through the layers at the receiving end, each layer can communicate with the corresponding layer in the remote system. The set of permissible messages and responses in this remote, “horizontal” communication is defined by the corresponding protocol. The entire system is therefore defined by the information that can pass vertically via the interface between adjacent layers in a given stack, and horizontally between corresponding layers in the two remote stacks.

The primary objective of the seven-layer model is to provide a flexible means of describing the behavior of communications systems, capable of dealing with all existing and future technologies, rather than to provide a specific set of protocols and interfaces. The process of reaching international agreements that meet the conflicting requirements of different groups of end-users, accommodate the interests of competing commercial suppliers, and define technically sound products is slow, often taking several years to reach a final set of recommendations. When agreement on proposals has been achieved, the development of commercially viable products conforming to the proposals is again time-consuming. It is then necessary to test the products for conformance, to demonstrate successful interworking between products from different suppliers, and to resolve discrepancies where systems that each separately appear to conform with the proposals do not interwork correctly.

Inevitably during this time, individual users or suppliers will have made their own systems, and in this sense the international standards will always lag behind the ad hoc or proprietary systems. Despite this, the model has itself been used as the basis for networks themselves (X25 for packet networks, ISO 8802.3 for CSMA/CD, ISO 8802.7 for slotted rings, ISO 8802.5 for token rings, ISO 8802.4 for token bus, and X75 for internetwork communication), and for some applications such as electronic mail (X400), directory services (X500), and manufacturing automation (MAP and TOP).

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"seven-layer reference model." A Dictionary of Computing. . Encyclopedia.com. 18 Oct. 2018 <http://www.encyclopedia.com>.

"seven-layer reference model." A Dictionary of Computing. . Encyclopedia.com. (October 18, 2018). http://www.encyclopedia.com/computing/dictionaries-thesauruses-pictures-and-press-releases/seven-layer-reference-model

"seven-layer reference model." A Dictionary of Computing. . Retrieved October 18, 2018 from Encyclopedia.com: http://www.encyclopedia.com/computing/dictionaries-thesauruses-pictures-and-press-releases/seven-layer-reference-model

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.