===================================================================================================
| No. | ISO Layer Name | TCP/IP Layers | Responsibility |
===================================================================================================
| | | | |
| | | | Applications running on a PC or other |
| 7 | Application | | device. Applications like telnet, FTP, |
| | | | and HTTP operate at this layer. |
| | | | |
|----------------------| There is no clear |-----------------------------------------|
| | | distinction | |
| | | between these | Provides an abstraction for data |
| 6 | Presentation | layers in the | representation differences between |
| | | TCP/IP protocol. | applications. |
| | | | |
|----------------------| |-----------------------------------------|
| | | | |
| | | | Offers an optional bidirectional or |
| 5 | Session | | full-duplex service if not provided |
| | | | by the transport layer. |
| | | | |
|----------------------|--------------------------------|-----------------------------------------|
| | | | |
| 4 | Transport | TCP, UDP, and ICMP(1) | Provides end-to-end management. For |
| | | | example, TCP provides flow control, |
| | | | acknowledgement, sequencing, and error |
| | | | correction; TCP also provides |
| | | | connection-oriented "reliable" |
| | | | communications. UDP provides |
| | | (1): ICMP could very well be | connectionless communication, a very |
| | | positioned at layer 3 | thin layer on top of IP. However, it |
| | | but it is positioned at | provides "unreliable" communication, |
| | | layer 4 because ICMP | that is, the data may get to its |
| | | must be first placed | destination, or it may not. |
| | | within an IP packet | |
| | | of which IP is a layer 3 | TCP also provides a concept of |
| | | protocol. | of session management at this layer. |
| | | | |
|----------------------|--------------------------------|-----------------------------------------|
| | | | |
| | | | Is responsible for the routing of |
| 3 | Network | IP, ARP, and RARP. | packets (which encapsulates frames) |
| | | | across the network. |
| | | | |
|----------------------|--------------------------------|-----------------------------------------|
| | | | |
| 2 | Data Link | The data link | Regulates access to the network. |
| | | | Provides point-to-point frame |
| | | (Ethernet, ATM+IP, FDDI, | formation and management for various |
| | | & Token Ring all span | protocols. All frames contain |
| | | the data link and physical | source addresses and a destination |
| | | layers) | addresses. |
| | | | |
|----------------------|--------------------------------|-----------------------------------------|
| | | | |
| | | | Controls the physical attachment |
| 1 | Physical | Physical, as mentioned | to the network, including wiring |
| | | above. | and signaling. |
| | | | |
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Sources: The OSI Reference Model and Building Switched Networks by Darryl P. Black (1999)