OSI protocols

Internet history timeline

Early research and development:

1960–1962: J. C. R. Licklider networking ideas
1960–1964: RAND networking concepts developed
1962–1964: ARPA networking ideas
1965 (1965): NPL network concepts conceived
1966 (1966): Merit Network founded
1967 (1967): ARPANET planning begins
1967 (1967): Symposium on Operating Systems Principles
1969 (1969): NPL followed by the ARPANET carry their first packets
1970 (1970): Network Information Center (NIC)
1971 (1971): Tymnet switched-circuit network
1972 (1972): Merit Network's packet-switched network operational
1972 (1972): Internet Assigned Numbers Authority (IANA) established
1973 (1973): CYCLADES network demonstrated
1973 (1973): PARC Universal Packet development begins
1974 (1974): Transmission Control Program specification published
1975 (1975): Telenet commercial packet-switched network
1976 (1976): X.25 protocol approved and deployed on public data networks
1978 (1978): Minitel introduced
1979 (1979): Internet Activities Board (IAB)
1980 (1980): USENET news using UUCP
1980 (1980): Ethernet standard introduced
1981 (1981): BITNET established

Merging the networks and creating the Internet:

1981 (1981): Computer Science Network (CSNET)
1982 (1982): TCP/IP protocol suite formalized
1982 (1982): Simple Mail Transfer Protocol (SMTP)
1983 (1983): Domain Name System (DNS)
1983 (1983): MILNET split off from ARPANET
1984 (1984): OSI Reference Model released
1985 (1985): First .COM domain name registered
1986 (1986): NSFNET with 56 kbit/s links
1986 (1986): Internet Engineering Task Force (IETF)
1987 (1987): UUNET founded
1988 (1988): NSFNET upgraded to 1.5 Mbit/s (T1)
1988 (1988): Morris worm
1988 (1988): Complete Internet protocol suite
1989 (1989): Border Gateway Protocol (BGP)
1989 (1989): PSINet founded, allows commercial traffic
1989 (1989): Federal Internet Exchanges (FIX East|FIXes)
1990 (1990): GOSIP (without TCP/IP)
1990 (1990): ARPANET decommissioned
1990 (1990): Advanced Network and Services (ANS)
1990 (1990): UUNET/Alternet allows commercial traffic
1990 (1990): Archie search engine
1991 (1991): Wide area information server (WAIS)
1991 (1991): Gopher
1991 (1991): Commercial Internet eXchange (CIX)
1991 (1991): ANS CO+RE allows commercial traffic
1991 (1991): World Wide Web (WWW)
1992 (1992): NSFNET upgraded to 45 Mbit/s (T3)
1992 (1992): Internet Society (ISOC) established
1993 (1993): Classless Inter-Domain Routing (CIDR)
1993 (1993): InterNIC established
1993 (1993): AOL added USENET access
1993 (1993): Mosaic web browser released
1994 (1994): Full text web search engines
1994 (1994): North American Network Operators' Group (NANOG) established

Commercialization, privatization, broader access leads to the modern Internet:

1995 (1995): New Internet architecture with commercial ISPs connected at NAPs
1995 (1995): NSFNET decommissioned
1995 (1995): GOSIP updated to allow TCP/IP
1995 (1995): very high-speed Backbone Network Service (vBNS)
1995 (1995): IPv6 proposed
1996 (1996): AOL changes pricing model from hourly to monthly
1998 (1998): Internet Corporation for Assigned Names and Numbers (ICANN)
1999 (1999): IEEE 802.11b wireless networking
1999 (1999): Internet2/Abilene Network
1999 (1999): vBNS+ allows broader access
2000 (2000): Dot-com bubble bursts
2001 (2001): New top-level domain names activated
2001 (2001): Code Red I, Code Red II, and Nimda worms
2003 (2003): UN World Summit on the Information Society (WSIS) phase I

2003 (2003): National LambdaRail founded
2004 (2004): UN Working Group on Internet Governance (WGIG)
2005 (2005): UN WSIS phase II
2006 (2006): First meeting of the Internet Governance Forum
2010 (2010): First internationalized country code top-level domains registered
2012 (2012): ICANN begins accepting applications for new generic top-level domain names
2013 (2013): Montevideo Statement on the Future of Internet Cooperation
2014 (2014): NetMundial international Internet governance proposal
2016 (2016): ICANN contract with U.S. Dept. of Commerce ends, IANA oversight passes to the global Internet community on October 1st

Examples of Internet services:

1989 (1989): AOL dial-up service provider, email, instant messaging, and web browser
1990 (1990): IMDb Internet movie database
1994 (1994): Yahoo! web directory
1995 (1995): Amazon online retailer
1995 (1995): eBay online auction and shopping
1995 (1995): Craigslist classified advertisements
1995 (1995): AltaVista search engine
1996 (1996): Outlook (formerly Hotmail) free web-based e-mail
1996 (1996): RankDex search engine
1997 (1997): Google Search
1997 (1997): Babel Fish automatic translation
1998 (1998): Yahoo Groups (formerly Yahoo! Clubs)
1998 (1998): PayPal Internet payment system
1998 (1998): Rotten Tomatoes review aggregator
1999 (1999): 2ch Anonymous textboard
1999 (1999): i-mode mobile internet service
1999 (1999): Napster peer-to-peer file sharing
2000 (2000): Baidu search engine
2001 (2001): 2chan Anonymous imageboard
2001 (2001): BitTorrent peer-to-peer file sharing
2001 (2001): Wikipedia, the free encyclopedia
2003 (2003): LinkedIn business networking
2003 (2003): Myspace social networking site
2003 (2003): Skype Internet voice calls
2003 (2003): iTunes Store
2003 (2003): 4chan Anonymous imageboard
2003 (2003): The Pirate Bay, torrent file host
2004 (2004): Facebook social networking site
2004 (2004): Podcast media file series
2004 (2004): Flickr image hosting
2005 (2005): YouTube video sharing
2005 (2005): Reddit link voting
2005 (2005): Google Earth virtual globe
2006 (2006): Twitter microblogging
2007 (2007): WikiLeaks anonymous news and information leaks
2007 (2007): Google Street View
2007 (2007): Kindle, e-reader and virtual bookshop
2008 (2008): Amazon Elastic Compute Cloud (EC2)
2008 (2008): Dropbox cloud-based file hosting
2008 (2008): Encyclopedia of Life, a collaborative encyclopedia intended to document all living species
2008 (2008): Spotify, a DRM-based music streaming service
2009 (2009): Bing search engine
2009 (2009): Google Docs, Web-based word processor, spreadsheet, presentation, form, and data storage service
2009 (2009): Kickstarter, a threshold pledge system
2009 (2009): Bitcoin, a digital currency
2010 (2010): Instagram, photo sharing and social networking
2011 (2011): Google+, social networking
2011 (2011): Snapchat, photo sharing
2012 (2012): Coursera, massive open online courses
2016 (2016): TikTok, video sharing and social networking

The Open Systems Interconnection protocols are a family of information exchange standards developed jointly by the ISO and the ITU-T. The standardization process began in 1977.

While the seven-layer OSI model is often used as a reference for teaching and documentation,^[2] the protocols originally conceived for the model did not gain popularity, and only X.400, X.500, and IS-IS have achieved lasting impact. The goal of an open-standard protocol suite instead has been met by the Internet protocol suite, maintained by the Internet Engineering Task Force (IETF).

Overview

The OSI protocol stack is structured into seven conceptual layers. The layers form a hierarchy of functionality starting with the physical hardware components to the user interfaces at the software application level. Each layer receives information from the layer above, processes it and passes it down to the next layer. Each layer adds encapsulation information (header) to the incoming information before it is passed to the lower layer. Headers generally include address of source and destination, error control information, protocol identification and protocol parameters such as flow control options and sequence numbers.

OSI model
Layer			Protocol data unit (PDU)	Function^[3]
Host layers	7	Application	Data	High-level protocols such as for resource sharing or remote file access, e.g. HTTP.
	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	Reliable transmission of data segments between points on a network, including segmentation, acknowledgement and multiplexing
Media layers	3	Network	Packet, Datagram^[4]	Structuring and managing a multi-node network, including addressing, routing and traffic control
	2	Data link	Frame	Transmission of data frames between two nodes connected by a physical layer
	1	Physical	Bit, Symbol	Transmission and reception of raw bit streams over a physical medium

Layer 1: physical layer

This layer deals with the physical plugs, sockets, electrical/optical specifications and the required line codes.

The physical layer includes the medium over which the digital signals are transmitted. It can be twisted pair, coaxial cable, optical fiber, wireless, or other transmission media.

Layer 2: data link layer

The data link layer packages raw bits from the physical layer into frames (logical, structured packets for data). It is specified in ITU-T Rec. X.212 [ISO/IEC 8886], ITU-T Rec. X.222 and others. This layer is responsible for transferring frames from one host to another. It might perform error checking. This layer further consists of two sublayers: MAC and LLC.

Layer 3: network layer

Connectionless Network Service (CLNS) – ITU-T Rec. X.213 [ISO/IEC 8348]. SCCP is based on X.213.
Connectionless Network Protocol (CLNP) – ITU-T Rec. X.233 [ISO/IEC 8473-1].
Connection-Oriented Network Service (CONS) – ITU-T Rec. X.213 [ISO/IEC 8348].
Connection-Oriented Network Protocol (X.25) – ITU-T Rec. X.233 [ISO/IEC 8878]. This is the use of the X.25 protocol to provide the CONS.
Network Fast Byte Protocol – ISO/IEC 14700
End System to Intermediate System Routing Exchange Protocol (ES-IS) - ISO/IEC 9452 (reprinted in RFC 995).
Intermediate System to Intermediate System Intra-domain Routing Protocol (IS-IS) - ISO/IEC 10589 (reprinted in RFC 1142), later adapted for the TCP/IP model.
End System Routing Information Exchange Protocol for use with ISO/IEC 8878 (SNARE) – ITU-T Rec. X.116 [ISO/IEC 10030].

This level is in charge of transferring data between systems in a network, using network-layer addresses of machines to keep track of destinations and sources. This layer uses routers and switches to manage its traffic (control flow control, error check, routing etc.) So here it takes all routing decisions, it deals with end to end data transmission.

Layer 4: transport layer

The connection-mode and connectionless-mode transport services are specified by ITU-T Rec. X.214 [ISO/IEC 8072]; the protocol that provides the connection-mode service is specified by ITU-T Rec. X.224 [ISO/IEC 8073], and the protocol that provides the connectionless-mode service is specified by ITU-T Rec. X.234 [ISO/IEC 8602].

Transport Protocol Class 0 (TP0)
Transport Protocol Class 1 (TP1)
Transport Protocol Class 2 (TP2)
Transport Protocol Class 3 (TP3)
Transport Protocol Class 4 (TP4)
Transport Fast Byte Protocol – ISO 14699

The transport layer transfers data between source and destination processes. Generally, two connection modes are recognized, connection-oriented or connectionless. Connection-oriented service establishes a dedicated virtual circuit and offers various grades of guaranteed delivery, ensuring that data received is identical to data transmitted. Connectionless mode provides only best-effort service without the built-in ability to correct errors, which includes complete loss of data without notifying the data source of the failure. No logical connection, and no persistent state of the transaction exists between the endpoints, lending the connectionless mode low overhead and potentially better real-time performance for timing-critical applications such as voice and video transmissions.

Layer 5: session layer

Session service – ITU-T Rec. X.215 [ISO/IEC 8326]
Connection-oriented Session protocol – ITU-T Rec. X.225 [ISO/IEC 8327-1]
Connectionless Session protocol – ITU-T Rec. X.235 [ISO/IEC 9548-1]

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, and 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

Presentation service – ITU-T Rec. X.216 [ISO/IEC 8822]
Connection-oriented Presentation protocol – ITU-T Rec. X.226 [ISO/IEC 8823-1]
Connectionless Presentation protocol – ITU-T Rec. X.236 [ISO/IEC 9576-1]

This layer defines and encrypts/decrypts data types from the application layer. Protocols such as MIDI, MPEG, and GIF are presentation layer formats shared by different applications.

Layer 7: application layer

Common-Application Service Elements (CASEs)

Association Control Service Element (ACSE) – ITU-T Rec. X.217 [ISO/IEC 8649], ITU-T Rec. X.227 [ISO/IEC 8650-1], ITU-T Rec. X.237 [ISO/IEC 10035-1].
Reliable Transfer Service Element (RTSE) – ITU-T Rec. X.218 [ISO/IEC 9066-1], ITU-T Rec. X.228 [ISO/IEC 9066-2].
Remote Operations Service Element (ROSE) – ITU-T Rec. X.219 [ISO/IEC 9072-1], ITU-T Rec. X.229 [ISO/IEC 9072-2]. TCAP is related to X.219.
Commitment, Concurrency, and Recovery service element (CCRSE)
Security Exchange Service Element (SESE)

This keeps track of how each application talks to another application. Destination and source addresses are linked to specific applications.

Application processes

Common management information protocol (CMIP) – ISO 9596 / X.700
Directory services (DS) – X.500, later modified for the TCP/IP stack as LDAP
File transfer, access, and management (FTAM)^[5]
Message handling system (MHS) – X.400
Virtual terminal protocol (VT) - ISO 9040/9041
Remote Database Access (RDA)
Distributed Transaction Processing (OSI TP)
Interlibrary Loan Application Protocol (ILAP)
Document Transfer And Manipulation (DTAM)
Document Printing Application (DPA)
Document Filing and Retrieval (DFR)

Routing protocols

Intermediate System to Intermediate System (IS-IS) – ISO 10589 (reprinted in RFC 1142)
End System to Intermediate System (ES-IS) – ISO 9542 (reprinted in RFC 995)
Interdomain Routing Protocol (IDRP) – ISO 10747

References

^ "X.225 : Information technology – Open Systems Interconnection – Connection-oriented Session protocol: Protocol specification". Archived from the original on 1 February 2021. Retrieved 10 March 2023.
^ Shaw, Keith (2018-10-22). "The OSI model explained: How to understand (and remember) the 7 layer network model". Network World. Archived from the original on 2020-06-15. Retrieved 2020-05-16.
^ "Windows Network Architecture and the OSI Model". Microsoft Documentation. Retrieved 24 June 2020.
^ "What is a packet? | Network packet definition". Cloudflare.
^ FTAM support claimed by IBM, Novell, Sun, Unisys etc Archived 2013-03-02 at the Wayback Machine, Joint Interoperability Test Command

[1] "X.225 : Information technology – Open Systems Interconnection – Connection-oriented Session protocol: Protocol specification". Archived from the original on 1 February 2021. Retrieved 10 March 2023.

[2] Shaw, Keith (2018-10-22). "The OSI model explained: How to understand (and remember) the 7 layer network model". Network World. Archived from the original on 2020-06-15. Retrieved 2020-05-16.

[3] "Windows Network Architecture and the OSI Model". Microsoft Documentation. Retrieved 24 June 2020.

[4] "What is a packet? | Network packet definition". Cloudflare.

[5] FTAM support claimed by IBM, Novell, Sun, Unisys etc Archived 2013-03-02 at the Wayback Machine, Joint Interoperability Test Command

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v t e International Organization for Standardization (ISO) standards
List of ISO standards – ISO romanizations – IEC standards
1–9999	1 2 3 4 6 7 9 16 17 31 -0 -1 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 68-1 128 216 217 226 228 233 259 261 262 302 306 361 500 518 519 639 -1 -2 -3 -5 -6 646 657 668 690 704 732 764 838 843 860 898 965 999 1000 1004 1007 1073-1 1073-2 1155 1413 1538 1629 1745 1989 2014 2015 2022 2033 2047 2108 2145 2146 2240 2281 2533 2709 2711 2720 2788 2848 2852 2921 3029 3103 3166 -1 -2 -3 3297 3307 3601 3602 3864 3901 3950 3977 4031 4157 4165 4217 4909 5218 5426 5427 5428 5725 5775 5776 5800 5807 5964 6166 6344 6346 6373 6385 6425 6429 6438 6523 6709 6943 7001 7002 7010 7027 7064 7098 7185 7200 7498 -1 7637 7736 7810 7811 7812 7813 7816 7942 8000 8093 8178 8217 8373 8501-1 8571 8583 8601 8613 8632 8651 8652 8691 8805/8806 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 9036 9075 9126 9141 9227 9241 9293 9314 9362 9407 9496 9506 9529 9564 9592/9593 9594 9660 9797-1 9897 9899 9945 9984 9985 9995
10000–19999	10006 10007 10116 10118-3 10160 10161 10165 10179 10206 10218 10279 10303 -11 -21 -22 -28 -238 10383 10585 10589 10628 10646 10664 10746 10861 10957 10962 10967 11073 11170 11172 11179 11404 11544 11783 11784 11785 11801 11889 11898 11940 (-2) 11941 11941 (TR) 11992 12006 12052 12182 12207 12234-2 12620 13211 -1 -2 13216 13250 13399 13406-2 13450 13485 13490 13567 13568 13584 13616 13816 13818 14000 14031 14224 14289 14396 14443 14496 -2 -3 -6 -10 -11 -12 -14 -17 -20 14617 14644 14649 14651 14698 14764 14882 14971 15022 15189 15288 15291 15398 15408 15444 -3 -9 15445 15438 15504 15511 15686 15693 15706 -2 15707 15897 15919 15924 15926 15926 WIP 15930 15938 16023 16262 16355-1 16485 16612-2 16750 16949 (TS) 17024 17025 17100 17203 17369 17442 17506 17799 18004 18014 18181 18245 18629 18760 18916 19005 19011 19092 -1 -2 19114 19115 19125 19136 19407 19439 19500 19501 19502 19503 19505 19506 19507 19508 19509 19510 19600 19752 19757 19770 19775-1 19794-5 19831
20000–29999	20000 20022 20121 20400 20802 20830 21000 21001 21047 21122 21500 21778 21827 22000 22275 22300 22301 22395 22537 23000 23003 23008 23009 23090-3 23092 23094-1 23094-2 23270 23271 23360 23941 24517 24613 24617 24707 24728 25178 25964 26000 26262 26300 26324 27000 series 27000 27001 27002 27005 27006 27729 28000 29110 29148 29199-2 29500
30000+	30170 31000 32000 37001 38500 39075 40314 40500 42010 45001 50001 55000 56000 80000
Category

OSI model by layer
7. Application layer NNTP SIP SSI DNS FTP Gopher HTTP (HTTP/3) NFS NTP SMPP SSH SMTP SNMP Telnet DHCP NETCONF more....
6. Presentation layer MIME XDR ASN.1 ASCII TLS PGP
5. Session layer Named pipe NetBIOS SAP PPTP RTP SOCKS X.225^[1]
4. Transport layer TCP UDP SCTP DCCP QUIC SPX
3. Network layer IP IPv4 IPv6 ICMP (ICMPv6) IPsec IGMP IPX IS-IS AppleTalk X.25 PLP
2. Data link layer ATM ARP SDLC HDLC CSLIP SLIP GFP PLIP IEEE 802 LLC MAC L2TP Frame Relay ITU-T G.hn DLL PPP X.25 LAPB Q.922 LAPF
1. Physical layer RS-232 RS-449 ITU-T V-Series I.430 I.431 PDH SONET/SDH PON OTN DSL IEEE 802 IEEE 1394 ITU-T G.hn PHY USB Bluetooth X.21
v t e