OSI model: Difference between revisions

Revision as of 06:33, 21 June 2014

Revision as of 07:10, 21 June 2014

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The OSI standards documents are available from the ITU-T as the X.200-series of recommendations.<ref>

[http://www.itu.int/rec/T-REC-X/en ITU-T X-Series Recommendations]</ref> Some of the protocol specifications were also available as part of the ITU-T X series. The equivalent ISO and ISO/IEC standards for the OSI model were available from ISO, but only some of them without fees.<ref>{{cite web|url=http://standards.iso.org/ittf/PubliclyAvailableStandards/index.html |title=Publicly Available Standards |publisher=Standards.iso.org |date=2010-07-30 |accessdate=2010-09-11}}</ref>.

==Description of OSI layers==

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| style="background:#eddc9c;"|<small>Addressing, routing and (not necessarily reliable) delivery of datagrams between points on a network.</small>

|-

| style="background:#e9c189;" |[[Bit]]/[[Frame_Frame (networking)|Frame]]

| style="background:#e9c189;"|2. [[Data link layer|Data link]]

| style="background:#e9c189;"|<small>A reliable direct point-to-point data connection.</small>

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[[Security service (telecommunication)|Security services]] are not related to a specific layer: they can be related by several layers, as defined by [[ITU-T]] X.800 Recommendation.<ref name="x800"/>

These services are aimed to improve the [[Information Security|CIA triad]] ([[confidentiality]], [[integrity]], and [[availability]]) of transmitted data. In practice, the availability of communication service is determined by the interaction between [[network design]] and [[network management]] protocols. Appropriate choices for both of these are needed to protect against [[denial of service]].{{factcitation needed|date=April 2013}}

===Layer 1: physical layer===

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The data link layer is divided into two sublayers:

* [[Media Access Control]] (MAC) layer - responsible for controlling how computers in the network gain access to data and permission to transmit it.

* [[Logical Link Control ]] (LLC) layer - control error checking and packet synchronization.

The [[Point-to-Point Protocol]] (PPP) is an example of a data link layer in the TCP/IP protocol stack.

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* Management functions, i.e. functions that permit to configure, instantiate, monitor, terminate the communications of two or more entities: there is a specific application-layer protocol, [[common management information protocol]] (CMIP) and its corresponding service, [[common management information service]] (CMIS), they need to interact with every layer in order to deal with their instances.

* [[Multiprotocol Label Switching]] (MPLS) operates at an OSI-model layer that is generally considered to lie between traditional definitions of layer 2 (data link layer) and layer 3 (network layer), and thus is often referred to as a "layer-2.5" protocol. It was designed to provide a unified data-carrying service for both circuit-based clients and packet-switching clients which provide a [[datagram]]-based service model. It can be used to carry many different kinds of traffic, including IP packets, as well as native ATM, SONET, and Ethernet frames.

* [[Address_Resolution_ProtocolAddress |Resolution Protocol|ARP]] is used to translate IPv4 addresses (OSI layer 3) into Ethernet MAC addresses (OSI layer 2).

==Interfaces==

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| Sockets. Session establishment in [[Transmission Control Protocol|TCP]], [[Real-time Transport Protocol|RTP]], [[PPTP]]

|

| [[AppleTalk|ASP]], [[AppleTalk|ADSP]], [[Password_authentication_protocolPassword authentication protocol|PAP]]

| [[NWLink]]

| [[Data Link Control|DLC]]?

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| [[Synchronous Data Link Control|SDLC]]

| [[PDCP|Packet Data Convergence Protocol]] (PDCP),<ref name=TS36300>[http://www.3gpp.org/ftp/Specs/html-info/36300.htm 3GPP TS 36.300 : E-UTRA and E-UTRAN Overall Description, Stage 2, Release 11]</ref> [[Logical Link Control|LLC]] (Logical Link Control), [[Media Access Control|MAC]] (Media Access Control)

| [[Ethernet|802.3 (Ethernet)]], [[IEEE 802.11|802.11a/b/g/n MAC/LLC]], [[IEEE 802.1Q|802.1Q (VLAN)]], [[Asynchronous Transfer Mode|ATM]], [[Hopling Discovery Protocol|HDP]], [[FDDI]], [[Fibre Channel]], [[Frame Relay]], [[HDLC]], [[Cisco Inter-Switch Link|ISL]], [[Point-to-Point Protocol|PPP]], [[Q.921]], [[Token Ring]], [[Cisco Discovery Protocol|CDP]], [[G.hn|ITU-T G.hn DLL]] <br>[[Cyclic redundancy check|CRC]], [[Bit stuffing]], [[Automatic repeat-request|ARQ]], [[DOCSIS|Data Over Cable Service Interface Specification (DOCSIS)]], [[Link_aggregationLink aggregation#Aggregation_Modes_in_Linux_Aggregation Modes in Linux .28Bonding_Modes28Bonding Modes.29_29 .5B6.5D|interface bonding]]

|-

| 1

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==Comparison with TCP/IP model==

In the [[TCP/IP model]] of the Internet, protocols are deliberately not as rigidly designed into strict layers as in the OSI model.<ref>RFC 3439</ref> RFC 3439 contains a section entitled "Layering [[considered harmful]]".<ref>http://tools.ietf.org/html/rfc3439#section-3</ref> However, TCP/IP does recognize four broad layers of functionality which are derived from the operating scope of their contained protocols: the scope of the software application; the end-to-end transport connection; the internetworking range; and the scope of the direct links to other nodes on the local network. <ref>

[http://www.exa.unicen.edu.ar/catedras/comdat1/material/TP1-Ejercicio5-ingles.pdf]</ref>

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*The internetworking layer ([[Internet layer]]) is a subset of the OSI network layer (see above)

*The [[link layer]] includes the OSI data link and physical layers, as well as parts of OSI's network layer.

These comparisons are based on the original seven-layer protocol model as defined in ISO 7498, rather than refinements in such things as the internal organization of the network layer document.{{factcitation needed|date=November 2013}}

The presumably strict peer layering of the OSI model as it is usually described does not present contradictions in TCP/IP, as it is permissible that protocol usage does not follow the hierarchy implied in a layered model. Such examples exist in some routing protocols (e.g., OSPF), or in the description of [[tunneling protocol]]s, which provide a link layer for an application, although the tunnel host protocol might well be a transport or even an application-layer protocol in its own right.{{factcitation needed|date=November 2013}}

==See also==

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==External links==

{{commons category}}

{{commonscat}}

* [http://standards.iso.org/ittf/PubliclyAvailableStandards/s020269_ISO_IEC_7498-1_1994(E).zip ISO/IEC standard 7498-1:1994] ([[Portable Document Format|PDF document]] inside [[ZIP (file format)|ZIP archive]]) (requires [[HTTP cookies]] in order to accept licence agreement)

* [http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-X.200-199407-I!!PDF-E&type=items ITU-T X.200 (the same contents as from ISO)]