OSI model - wikipedia OSI model OSI model by layer 7. Application layer NNTP SIP SSI DNS FTP Gopher HTTP NFS NTP SMPP SMTP SNMP Telnet DHCP Netconf more... 6. Presentation layer MIME XDR 5. Session layer Named pipe NetBIOS SAP PPTP RTP SOCKS SPDY 4. Transport layer TCP UDP SCTP DCCP SPX 3. Network layer IP IPv4 IPv6 ICMP IPsec IGMP IPX AppleTalk X. 25 PLP 2. Data link layer ATM ARP IS - IS SDLC HDLC CSLIP SLIP GFP PLIP IEEE 802.2 LLC MAC L2TP IEEE 802.3 Frame Relay ITU - T G.hn DLL PPP X. 25 LAPB Q. 921 LAPD Q. 922 LAPF 1. Physical layer EIA / TIA - 232 EIA / TIA - 449 ITU - T V - Series I. 430 I. 431 PDH SONET / SDH PON OTN DSL IEEE 802.3 IEEE 802.11 IEEE 802.15 IEEE 802.16 IEEE 1394 ITU - T G.hn PHY USB Bluetooth RS - 232 RS - 449 The Open Systems Interconnection model ( OSI model ) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology. Its goal is the interoperability of diverse communication systems with standard protocols. The model partitions a communication system into abstraction layers. The original version of the model defined seven layers. A layer serves the layer above it and is served by the layer below it. For example, a layer that provides error - free communications across a network provides the path needed by applications above it, while it calls the next lower layer to send and receive packets that comprise the contents of that path. Two instances at the same layer are visualized as connected by a horizontal connection in that layer. The model is a product of the Open Systems Interconnection project at the International Organization for Standardization ( ISO ), maintained by the identification ISO / IEC 7498 - 1. Communication in the OSI - Model ( example with layers 3 to 5 ) Contents 1 History 2 Description of OSI layers 2.1 Layer 1 : Physical Layer 2.2 Layer 2 : Data Link Layer 2.3 Layer 3 : Network Layer 2.4 Layer 4 : Transport Layer 2.5 Layer 5 : Session Layer 2.6 Layer 6 : Presentation Layer 2.7 Layer 7 : Application Layer 3 Cross-layer functions 4 Interfaces 5 Examples 6 Comparison with TCP / IP model 7 See also 8 References 9 External links History In the late 1970s, one project was administered by the International Organization for Standardization ( ISO ), while another was undertaken by the International Telegraph and Telephone Consultative Committee ( CCITT, from French : Comité Consultatif International Téléphonique et Télégraphique ). These two international standards bodies each developed a document that defined similar networking models. In 1983, these two documents were merged to form a standard called The Basic Reference Model for Open Systems Interconnection. The standard is usually referred to as the Open Systems Interconnection Reference Model, the OSI Reference Model, or simply the OSI model. It was published in 1984 by both the ISO, as standard ISO 7498, and the renamed CCITT ( now called the Telecommunications Standardization Sector of the International Telecommunication Union or ITU - T ) as standard X. 200. OSI had two major components, an abstract model of networking, called the Basic Reference Model or seven - layer model, and a set of specific protocols. The concept of a seven - layer model was provided by the work of Charles Bachman at Honeywell Information Services. Various aspects of OSI design evolved from experiences with the ARPANET, NPLNET, EIN, CYCLADES network and the work in IFIP WG6. 1. The new design was documented in ISO 7498 and its various addenda. In this model, a networking system was divided into layers. Within each layer, one or more entities implement its functionality. Each entity interacted directly only with the layer immediately beneath it, and provided facilities for use by the layer above it. Protocols enable an entity in one host to interact with a corresponding entity at the same layer in another host. Service definitions abstractly described the functionality provided to an ( N ) - layer by an ( N - 1 ) layer, where N was one of the seven layers of protocols operating in the local host. The OSI standards documents are available from the ITU - T as the X. 200 - series of recommendations. 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. Not all are free of charge. Description of OSI layers The recommendation X. 200 describes seven layers, labeled 1 to 7. Layer 1 is the lowest layer in this model. OSI Model Layer Protocol data unit ( PDU ) Function Host layers 7. Application Data High - level APIs, including resource sharing, remote file access 6. Presentation Translation of data between a networking service and an application ; including character encoding, data compression and encryption / decryption 5. Session Managing communication sessions, i.e. continuous exchange of information in the form of multiple back - and - forth transmissions between two nodes 4. Transport Segment ( TCP ) / Datagram ( UDP ) Reliable transmission of data segments between points on a network, including segmentation, acknowledgement and multiplexing Media layers 3. Network Packet Structuring and managing a multi-node network, including addressing, routing and traffic control 2. Data link Frame Reliable transmission of data frames between two nodes connected by a physical layer 1. Physical Bit Transmission and reception of raw bit streams over a physical medium At each level N, two entities at the communicating devices ( layer N peers ) exchange protocol data units ( PDUs ) by means of a layer N protocol. Each PDU contains a payload, called the service data unit ( SDU ), along with protocol - related headers or footers. Data processing by two communicating OSI - compatible devices is done as such : The data to be transmitted is composed at the topmost layer of the transmitting device ( layer N ) into a protocol data unit ( PDU ). The PDU is passed to layer N - 1, where it is known as the service data unit ( SDU ). At layer N - 1 the SDU is concatenated with a header, a footer, or both, producing a layer N - 1 PDU. It is then passed to layer N - 2. The process continues until reaching the lowermost level, from which the data is transmitted to the receiving device. At the receiving device the data is passed from the lowest to the highest layer as a series of SDUs while being successively stripped from each layer 's header or footer, until reaching the topmost layer, where the last of the data is consumed. Some orthogonal aspects, such as management and security, involve all of the layers ( See ITU - T X. 800 Recommendation ). These services are aimed at improving the CIA triad - confidentiality, integrity, and availability - of the transmitted data. In practice, the availability of a 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. Layer 1 : physical layer This section may need to be rewritten entirely to comply with Wikipedia 's quality standards. You can help. The discussion page may contain suggestions. ( August 2017 ) The physical layer defines the electrical and physical specifications of the data connection. It defines the relationship between a device and a physical transmission medium ( for example, an electrical cable, an optical fiber cable, or a radio frequency link ). This includes the layout of pins, voltages, line impedance, cable specifications, signal timing and similar characteristics for connected devices and frequency ( 5 GHz or 2.4 GHz etc. ) for wireless devices. It is responsible for transmission and reception of unstructured raw data in a physical medium. Bit rate control is done at the physical layer. It may define transmission mode as simplex, half duplex, and full duplex. It defines the network topology as bus, mesh, or ring being some of the most common. The physical layer is the layer of low - level networking equipment, such as some hubs, cabling, and repeaters. The physical layer is never concerned with protocols or other such higher - layer items. Examples of hardware in this layer are network adapters, repeaters, network hubs, modems, and fiber media converters. Layer 2 : data link layer The data link layer provides node - to - node data transfer -- a link between two directly connected nodes. It detects and possibly corrects errors that may occur in the physical layer. It defines the protocol to establish and terminate a connection between two physically connected devices. It also defines the protocol for flow control between them. IEEE 802 divides the data link layer into two sublayers : Medium access control ( MAC ) layer -- responsible for controlling how devices in a network gain access to a medium and permission to transmit data. Logical link control ( LLC ) layer -- responsible for identifying and encapsulating network layer protocols, and controls error checking and frame synchronization. The MAC and LLC layers of IEEE 802 networks such as 802.3 Ethernet, 802.11 Wi - Fi, and 802.15. 4 ZigBee operate at the data link layer. The Point - to - Point Protocol ( PPP ) is a data link layer protocol that can operate over several different physical layers, such as synchronous and asynchronous serial lines. The ITU - T G.hn standard, which provides high - speed local area networking over existing wires ( power lines, phone lines and coaxial cables ), includes a complete data link layer that provides both error correction and flow control by means of a selective - repeat sliding - window protocol. Layer 3 : network layer The network layer provides the functional and procedural means of transferring variable length data sequences ( called datagrams ) from one node to another connected in `` different networks ''. A network is a medium to which many nodes can be connected, on which every node has an address and which permits nodes connected to it to transfer messages to other nodes connected to it by merely providing the content of a message and the address of the destination node and letting the network find the way to deliver the message to the destination node, possibly routing it through intermediate nodes. If the message is too large to be transmitted from one node to another on the data link layer between those nodes, the network may implement message delivery by splitting the message into several fragments at one node, sending the fragments independently, and reassembling the fragments at another node. It may, but does not need to, report delivery errors. Message delivery at the network layer is not necessarily guaranteed to be reliable ; a network layer protocol may provide reliable message delivery, but it need not do so. A number of layer - management protocols, a function defined in the management annex, ISO 7498 / 4, belong to the network layer. These include routing protocols, multicast group management, network - layer information and error, and network - layer address assignment. It is the function of the payload that makes these belong to the network layer, not the protocol that carries them. Layer 4 : transport layer The transport layer provides the functional and procedural means of transferring variable - length data sequences from a source to a destination host, while maintaining the quality of service functions. The transport layer controls the reliability of a given link through flow control, segmentation / desegmentation, and error control. Some protocols are state - and connection - oriented. This means that the transport layer can keep track of the segments and re-transmit those that fail delivery. The transport layer also provides the acknowledgement of the successful data transmission and sends the next data if no errors occurred. The transport layer creates packets out of the message received from the application layer. Packetizing is the process of dividing a long message into smaller messages. OSI defines five classes of connection - mode transport protocols ranging from class 0 ( which is also known as TP0 and provides the fewest features ) to class 4 ( TP4, designed for less reliable networks, similar to the Internet ). Class 0 contains no error recovery, and was designed for use on network layers that provide error - free connections. Class 4 is closest to TCP, although TCP contains functions, such as the graceful close, which OSI assigns to the session layer. Also, all OSI TP connection - mode protocol classes provide expedited data and preservation of record boundaries. Detailed characteristics of TP0 - 4 classes are shown in the following table : Feature name TP0 TP1 TP2 TP3 TP4 Connection - oriented network Yes Yes Yes Yes Yes Connectionless network No No No No Yes Concatenation and separation No Yes Yes Yes Yes Segmentation and reassembly Yes Yes Yes Yes Yes Error recovery No Yes Yes Yes Yes Reinitiate connection No Yes No Yes No Multiplexing / demultiplexing over single virtual circuit No No Yes Yes Yes Explicit flow control No No Yes Yes Yes Retransmission on timeout No No No No Yes Reliable transport service No Yes No Yes Yes If an excessive number of PDUs are unacknowledged. An easy way to visualize the transport layer is to compare it with a post office, which deals with the dispatch and classification of mail and parcels sent. A post office inspects only the outer envelope of mail to determine its delivery. Higher layers may have the equivalent of double envelopes, such as cryptographic presentation services that can be read by the addressee only. Roughly speaking, tunneling protocols operate at the transport layer, such as carrying non-IP protocols such as IBM 's SNA or Novell 's IPX over an IP network, or end - to - end encryption with IPsec. While Generic Routing Encapsulation ( GRE ) might seem to be a network - layer protocol, if the encapsulation of the payload takes place only at endpoint, GRE becomes closer to a transport protocol that uses IP headers but contains complete frames or packets to deliver to an endpoint. L2TP carries PPP frames inside transport packet. Although not developed under the OSI Reference Model and not strictly conforming to the OSI definition of the transport layer, the Transmission Control Protocol ( TCP ) and the User Datagram Protocol ( UDP ) of the Internet Protocol Suite are commonly categorized as layer - 4 protocols within OSI. Layer 5 : session layer The session layer controls the dialogues ( connections ) between computers. It establishes, manages and terminates the connections between the local and remote application. It provides for full - duplex, half - duplex, or simplex operation, and establishes checkpointing, adjournment, termination, and restart procedures. The OSI model made this layer responsible for graceful close of sessions, which is a property of the Transmission Control Protocol, and also for session checkpointing and recovery, which is not usually used in the Internet Protocol Suite. The session layer is commonly implemented explicitly in application environments that use remote procedure calls. Layer 6 : presentation layer The presentation layer establishes context between application - layer entities, in which the application - layer entities may use different syntax and semantics if the presentation service provides a mapping between them. If a mapping is available, presentation service data units are encapsulated into session protocol data units and passed down the protocol stack. This layer provides independence from data representation by translating between application and network formats. The presentation layer transforms data into the form that the application accepts. This layer formats data to be sent across a network. It is sometimes called the syntax layer. The presentation layer can include compression functions. The Presentation Layer negotiates the Transfer Syntax. The original presentation structure used the Basic Encoding Rules of Abstract Syntax Notation One ( ASN. 1 ), with capabilities such as converting an EBCDIC - coded text file to an ASCII - coded file, or serialization of objects and other data structures from and to XML. ASN. 1 effectively makes an application protocol invariant with respect to syntax. Layer 7 : application layer The application layer is the OSI layer closest to the end user, which means both the OSI application layer and the user interact directly with the software application. This layer interacts with software applications that implement a communicating component. Such application programs fall outside the scope of the OSI model. Application - layer functions typically include identifying communication partners, determining resource availability, and synchronizing communication. When identifying communication partners, the application layer determines the identity and availability of communication partners for an application with data to transmit. The most important distinction in the application layer is the distinction between the application - entity and the application. For example, a reservation website might have two application - entities : one using HTTP to communicate with its users, and one for a remote database protocol to record reservations. Neither of these protocols have anything to do with reservations. That logic is in the application itself. The application layer per se has no means to determine the availability of resources in the network. Cross-layer functions Cross-layer functions are services that are not tied to a given layer, but may affect more than one layer. Examples include the following : Security service ( telecommunication ) as defined by ITU - T X. 800 recommendation. 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 ) MPLS, ATM, and X. 25 are 3a protocols. OSI divides the Network Layer into 3 roles : 3a ) Subnetwork Access, 3b ) Subnetwork Dependent Convergence and 3c ) Subnetwork Independent Convergence. 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. Sometimes one sees reference to a Layer 2.5. This is a fiction create by those who are unfamiliar with the OSI Model and ISO 8648, Internal Organization of the Network Layer in particular. ARP determines the mapping of an IPv4 address to the underlying MAC address. This is not a translation function. If it were IPv4 and the MAC address would be at the same layer. The implementation of the MAC protocol decodes the MAC PDU and delivers the User - Data to the IP - layer. Because Ethernet is a multi-access media, a device sending a PDU on an Ethernet segment needs to know what IP address maps to what MAC address. DHCP, DHCP assigns IPv4 addresses to new systems joining a network. There is no means to derive or obtain an IPv4 address from an Ethernet address. Domain Name Service is an Application Layer service which is used to look up the IP address of a given domain name. Once a reply is received from the DNS server, it is then possible to form a Layer 4 connection or flow to the desired host. There are no connections at Layer 3. Cross MAC and PHY Scheduling is essential in wireless networks because of the time varying nature of wireless channels. By scheduling packet transmission only in favorable channel conditions, which requires the MAC layer to obtain channel state information from the PHY layer, network throughput can be significantly improved and energy waste can be avoided. Interfaces Neither the OSI Reference Model nor OSI protocols specify any programming interfaces, other than deliberately abstract service specifications. Protocol specifications precisely define the interfaces between different computers, but the software interfaces inside computers, known as network sockets are implementation - specific. For example, Microsoft Windows ' Winsock, and Unix 's Berkeley sockets and System V Transport Layer Interface, are interfaces between applications ( layer 5 and above ) and the transport ( layer 4 ). NDIS and ODI are interfaces between the media ( layer 2 ) and the network protocol ( layer 3 ). Interface standards, except for the physical layer to media, are approximate implementations of OSI service specifications. Examples Layer OSI protocols TCP / IP protocols Signaling System 7 AppleTalk IPX SNA UMTS Miscellaneous examples No. Name 7 Application FTAM X. 400 X. 500 DAP ROSE RTSE ACSE CMIP INAP MAP TCAP ISUP TUP AFP ZIP RTMP NBP SAP APPC HL7 Modbus 6 Presentation ISO / IEC 8823 X. 226 ISO / IEC 9576 - 1 X. 236 MIME SSL TLS XDR AFP TDI ASCII EBCDIC MIDI MPEG 5 Session ISO / IEC 8327 X. 225 ISO / IEC 9548 - 1 X. 235 Sockets ( session establishment in TCP / RTP / PPTP ) ASP ADSP PAP NWLink DLC ? Named pipes NetBIOS SAP half duplex full duplex simplex RPC SOCKS Transport ISO / IEC 8073 TP0 TP1 TP2 TP3 TP4 ( X. 224 ) ISO / IEC 8602 X. 234 TCP UDP SCTP DCCP DDP SPX NBF Network ISO / IEC 8208 X. 25 ( PLP ) ISO / IEC 8878 X. 223 ISO / IEC 8473 - 1 CLNP X. 233 ISO / IEC 10589 IS - IS IP IPsec ICMP IGMP OSPF RIP SCCP MTP ATP ( TokenTalk / EtherTalk ) IPX RRC / BMC NBF Q. 931 NDP IS - IS Data link ISO / IEC 7666 X. 25 ( LAPB ) Token Bus X. 222 ISO / IEC 8802 - 2 LLC ( type 1 / 2 ) PPP SBTV SLIP MTP Q. 710 LocalTalk ARA PPP IEEE 802.3 framing Ethernet II framing SDLC PDCP LLC MAC ARP ARQ ATM Bit stuffing CDP CRC DOCSIS FDDI FDP Fibre Channel Frame Relay HDP HDLC IEEE 802.3 ( Ethernet ) IEEE 802.11 a / b / g / n ( Ethernet MAC and LLC ) IEEE 802.1 Q ( VLAN ) ISL ITU - T G.hn DLL Linux interface bonding PPP Q. 921 Token Ring Physical X. 25 ( X. 21bis EIA / TIA - 232 EIA / TIA - 449 EIA - 530 G. 703 ) MTP Q. 710 RS - 232 RS - 422 PhoneNet Twinax UMTS air interfaces RS - 232 Full duplex RJ45 ( 8P8C ) V. 35 V. 34 I. 430 I. 431 T1 E1 10BASE - T 100BASE - TX 1000BASE - T POTS SONET SDH DSL 802.11 a / b / g / n PHY ITU - T G.hn PHY CAN bus DOCSIS DWDM OTN Comparison with TCP / IP model The design of protocols in the TCP / IP model of the Internet does not concern itself with strict hierarchical encapsulation and layering. RFC 3439 contains a section entitled `` Layering considered harmful ''. 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. Despite using a different concept for layering than the OSI model, these layers are often compared with the OSI layering scheme in the following way : The Internet application layer includes the OSI application layer, presentation layer, and most of the session layer. Its end - to - end transport layer includes the graceful close function of the OSI session layer as well as the OSI transport layer. The internetworking layer ( Internet layer ) is a subset of the OSI network layer. The link layer includes the OSI data link layer and sometimes the physical layers, as well as some protocols of the 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. The presumably strict 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 ( for example OSPF ), or in the description of tunneling protocols, 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. See also Computing portal Layer 8 Hierarchical internetworking model Management plane Service layer Protocol stacks IBM Systems Network Architecture Internet protocol suite WAP protocol suite List of information technology initialisms References Jump up ^ ITU - T X-Series Recommendations Jump up ^ `` Publicly Available Standards ''. Standards.iso.org. 2010 - 07 - 30. Retrieved 2010 - 09 - 11. Jump up ^ `` The OSI Model 's Seven Layers Defined and Functions Explained ''. Microsoft Support. Retrieved 2014 - 12 - 28. ^ Jump up to : `` ITU - T Recommendataion X. 800 ( 03 / 91 ), Security architecture for Open Systems Interconnection for CCITT applications ''. ITU. Retrieved 14 August 2015. Jump up ^ `` 5.2 RM description for end stations ''. IEEE Std 802 - 2014, IEEE Standard for Local and Metropolitan Area Networks : Overview and Architecture. ieee. Jump up ^ International Organization for Standardization ( 1989 - 11 - 15 ). `` ISO / IEC 7498 - 4 : 1989 -- Information technology -- Open Systems Interconnection -- Basic Reference Model : Naming and addressing ''. ISO Standards Maintenance Portal. ISO Central Secretariat. Retrieved 2015 - 08 - 17. Jump up ^ `` ITU - T Recommendation X. 224 ( 11 / 1995 ) ISO / IEC 8073, Open Systems Interconnection - Protocol for providing the connection - mode transport service ''. ITU. Jump up ^ Grigonis, Richard ( 2000 ). Computer telephony - encyclopaedia. CMP. p. 331. ISBN 9781578200450. Jump up ^ `` ITU - T X. 200 - Information technology -- Open Systems Interconnection -- Basic Reference Model : The basic model ''. Jump up ^ Miao, Guowang ; Song, Guocong ( 2014 ). Energy and spectrum efficient wireless network design. Cambridge University Press. ISBN 1107039886. Jump up ^ `` ITU - T Recommendation Q. 1400 ( 03 / 1993 ) ), Architecture framework for the development of signaling and OA&M protocols using OSI concepts ''. ITU. pp. 4, 7. Jump up ^ ITU Rec. X. 227 ( ISO 8650 ), X. 217 ( ISO 8649 ). Jump up ^ X. 700 series of recommendations from the ITU - T ( in particular X. 711 ) and ISO 9596. ^ Jump up to : `` Internetworking Technology Handbook - Internetworking Basics ( Internetworking ) ''. Cisco. 15 January 2014. Retrieved 14 August 2015. Jump up ^ `` 3GPP specification : 36.300 ''. 3gpp.org. Retrieved 14 August 2015. Jump up ^ RFC 3439 Jump up ^ `` RFC 3439 - Some Internet Architectural Guidelines and Philosophy ''. ietf.org. Retrieved 14 August 2015. Jump up ^ Walter Goralski. The Illustrated Network : How TCP / IP Works in a Modern Network ( PDF ). Morgan Kaufmann. p. 26. ISBN 978 - 0123745415. External links Wikimedia Commons has media related to OSI model. Microsoft Knowledge Base : The OSI Model 's Seven Layers Defined and Functions Explained ISO / IEC standard 7498 - 1 : 1994 ( PDF document inside ZIP archive ) ( requires HTTP cookies in order to accept licence agreement ) ITU - T X. 200 ( the same contents as from ISO ) `` INFormation CHanGe Architectures and Flow Charts powered by Google App Engine ''. infchg.appspot.com. The ISO OSI Reference Model, Beluga graph of data units and groups of layers. Archived from the original on 2012 - 05 - 26. Zimmermann, Hubert ( April 1980 ). `` OSI Reference Model -- The ISO Model of Architecture for Open Systems Interconnection ''. IEEE Transactions on Communications. 28 ( 4 ) : 425 -- 432. CiteSeerX 10.1. 1.136. 9497. doi : 10.1109 / TCOM. 1980.1094702. Cisco Systems Internetworking Technology Handbook ISO standards by standard number List of ISO standards / ISO romanizations / IEC standards 1 -- 9999 5 6 7 9 16 31 - 0 - 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 128 216 217 226 228 233 259 269 302 306 428 518 519 639 - 1 - 2 - 3 - 5 - 6 646 690 732 764 843 898 965 1000 1004 1007 1073 - 1 1413 1538 1745 2014 2015 2022 2047 2108 2145 2146 2240 2281 2709 2711 2788 2848 2852 3029 3103 3166 - 1 - 2 - 3 3297 3307 3602 3864 3901 3977 4031 4157 4217 4909 5218 5428 5775 5776 5800 5964 6166 6344 6346 6385 6425 6429 6438 6523 6709 7001 7002 7098 7185 7200 7498 7736 7810 7811 7812 7813 7816 8000 8178 8217 8571 8583 8601 8632 8652 8691 8807 8820 - 5 8859 - 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 8 - I - 9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 8879 9000 / 9001 9075 9126 9293 9241 9362 9407 9506 9529 9564 9594 9660 9897 9899 9945 9984 9985 9995 10000 -- 19999 10005 10006 10007 10116 10118 - 3 10160 10161 10165 10179 10206 10218 10303 - 11 - 21 - 22 - 28 - 238 10383 10487 10585 10589 10646 10664 10746 10861 10957 10962 10967 11073 11170 11179 11404 11544 11783 11784 11785 11801 11898 11940 ( - 2 ) 11941 11941 ( TR ) 11992 12006 12182 12207 12234 - 2 13211 - 1 - 2 13216 13250 13399 13406 - 2 13450 13485 13490 13567 13568 13584 13616 14000 14031 14224 14289 14396 14443 14496 - 2 - 3 - 6 - 10 - 11 - 12 - 14 - 17 - 20 14644 14649 14651 14698 14750 14764 14882 14971 15022 15189 15288 15291 15292 15398 15408 15444 - 3 15445 15438 15504 15511 15686 15693 15706 - 2 15707 15897 15919 15924 15926 15926 WIP 15930 16023 16262 16612 - 2 16750 16949 ( TS ) 17024 17025 17100 17203 17369 17442 17799 18000 18004 18014 18245 18629 18916 19005 19011 19092 ( - 1 - 2 ) 19114 19115 19125 19136 19439 19500 19501 19502 19503 19505 19506 19507 19508 19509 19510 19600 : 2014 19752 19757 19770 19775 - 1 19794 - 5 19831 20000 + 20000 20022 20121 20400 21000 21047 21500 21827 : 2002 22000 23270 23271 23360 24517 24613 24617 24707 25178 25964 26000 26300 26324 27000 series 27000 27001 27002 27006 27729 28000 29110 29148 29199 - 2 29500 30170 31000 32000 38500 40500 42010 55000 80000 - 1 - 2 - 3 Retrieved from `` https://en.wikipedia.org/w/index.php?title=OSI_model&oldid=828275779 '' Categories : OSI model ISO standards ITU - T recommendations Reference models Computer - related introductions in 1979 Hidden categories : Pages using RFC magic links All articles with unsourced statements Articles with unsourced statements from April 2013 Wikipedia articles needing rewrite from August 2017 All articles needing rewrite Articles with unsourced statements from November 2013 Talk Contents About Wikipedia Wikiversity Afrikaans Azərbaycanca Беларуская Беларуская ( тарашкевіца ) ‎ Български Bosanski Čeština Dansk Deutsch Eesti Ελληνικά Español Euskara فارسی Français Galego ગુજરાતી 한국어 Հայերեն हिन्दी Hrvatski Bahasa Indonesia Italiano עברית ქართული Қазақша Latina Latviešu Lietuvių Magyar Македонски മലയാളം Bahasa Melayu Монгол မြန်မာဘာသာ Nederlands 日本 語 Norsk Norsk nynorsk Polski Português Română Русский Scots සිංහල Simple English Slovenčina Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska తెలుగు ไทย Türkçe Українська Tiếng Việt Yorùbá 中文 51 more Edit links This page was last edited on 1 March 2018, at 16 : 26. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: ipsec is defined at what layer of the osi model
Answer: transport layer