2012 Jan 19
| OSI Reference Model Layer Description |
OSI Layer |
Comment | TCP/IP Equivalent Layer Description Details |
|||
|---|---|---|---|---|---|---|
| Application | 7 | Does not include user applications, but rather provides the interface between those applications and the network's services. For example, and email client uses this layer to generate a request to the email server. | Process/ Application |
|||
| Presentation | 6 | Manages the way data is encoded. Provides translation between otherwise incompatible data-encoding schemes (e.g. ASCII vs EBCDIC, different floating point representations, as well as encryption and decryption). | Process/ Application |
|||
| Session | 5 | Relatively unused - many protocols bundle this functionality into their transport layers. Manages flow of communications between two computer systems. Determines whether communications can be uni- or bi-directional. It also ensures that one request is completed before a new one is accepted. |
|
|||
| Transport | 4 | Responsible for end-to-end integrity of transmissions, including through routers (which layer 2 does not do). Also provides resequencing of packets that may arrive out of order (e.g. due to different paths) before passing contents to session layer. | Host-to-Host | |||
| Network | 3 | Establish route to be used between originating and destination computers. Optional, and only required if computer systems are separted by a router, or the application requires some service, or capability of either this or transport layer. Has no error detection/correction and relies on layer 2 for that. Routable protocols include IP, Novell IPX, and AppleTalk. |
| |||
| Data Link | 2 | Provide successful delivery of data transmitted and received: (1) Destination node verifies integrity of received frame and send and ACK. (2) Originating node must receive an acklowledging receipt of frame. | Network Access |
|||
| Physical | 1 | Electrical and optical signalling of bits, including voltages, media type, impedance, and physical shape of connector | Network Access |
|||
| Transmission Media | 0 | Coaxial cable, fiber, photons, etc. - not included in usual definition of layer 1 | Network Access |
Web request, email, etc. packet
+-------------------------------+
| |
+-------------------------------+
Transport layer creates the TCP segment \
+--------+-------------------------------+ |
| Header | | |
+--------+-------------------------------+ |
> TCP/IP Stack
Network layer creates the IP datagram |
+--------+--------+-------------------------------+ |
| Header | ...... | | |
+--------+--------+-------------------------------+ /
Data link/Physical layer creates the Ethernet frame
+--------+--------+--------+-------------------------------+---------+
| Header | ______ | ...... | | Trailer |
+--------+--------+--------+-------------------------------+---------+
Routers Move the packet across the network, from hop to hop
(use lower 3 layers, do not require Transport or APplication layers).
2005-2012