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OSI Model
Data unit Layer Function
Data 7. Application Network process to application
6. Presentation Data representation and encryption
5. Session Interhost communication
Segment 4. Transport End-to-end connections and reliability
Packet 3. Network Path determination and logical addressing
Frame 2. Data Link Physical addressing
Bit 1. Physical Media, signal and binary transmission
The OSI Model is the Open System Interconnection Reference Model. In its most basic form, it divides network architecture into seven layers which, from top to bottom, are the Application, Presentation, Session, Transport, Network, Data-Link, and Physical Layers. It is therefore often referred to as the OSI Seven Layer Model.

The OSI model can be used to conceptualize complex networks of people, places, and machines. UML diagram elements can be structured in layers that correspond to the 7-layer OSI model. [1] Currently there is growing interest in the use of UML for system modeling. Structuring specifications is difficult, but The ITU (International Telecommunications Union), the IEC (International Electrotechnical Commission) and the ISO have jointly defined some UML profiles for a Reference Model of Open Distributed Processing (RM-ODP). [2]


Media, signal and binary transmission

Protocols: RS-232, V.35, V.34, I.430, I.431, T1, E1, 802.3 Ethernet, 10BASE-T, 100BASE-TX, POTS, SONET, DSL, 802.11a/b/g/n PHY, ITU-T PHY

Data Link[edit]

Physical addressing

Protocols: ARP, CSLIP, SLIP, Frame Relay, ITU-T DLL


Path determination and logical addressing

Protocols: IP, ICMP, IPsec, IGMP


End-to-end connections and reliability

Protocols: TCP, UDP, PPTP, L2TP, SCTP


Interhost communication

Protocols: Named Pipes, NetBIOS, SAP


Data representation and encryption

Protocols: MIME, XDR, SSL, TLS


Network process to application

Protocols: NNTP, SIP, SSI, DNS, FTP, Gopher, HTTP, NFS, NTP, SMPP, SMTP, SNMP, Telnet, (more)


  1. A Layered Approach to Information Modeling and Interoperability on the Web 2000 - Melnik, Decker, Database Group, Stanford University
  2. X.906 : UML4ODP - Use of UML for ODP system specifications ITU Recommendation X.906 (11/07) itu subscription version