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| Contents | ||
| Application layer | HTTP, SMTP, FTP, SSH, IRC, SNMP ... |
| Transport layer | TCP, UDP, SCTP, RTP, DCCP ... |
| Network layer | IPv4, IPv6, ARP, IPX ... |
| Data link layer | Ethernet, 802.11 WiFi, Token ring, FDDI, ... |
The Internet protocol suite is the set of protocols that implement the protocol stack on which the Internet runs. It is sometimes called the TCP/IP protocol suite, after the two most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were also the first two defined.
The internet protocol suite can be described by analogy with the OSI model, which describes the layers of a protocol stack, not all of which correspond well with internet practice. In a protocol stack, each layer solves a set of problems involving the transmission of data, and provides a well-defined service to the higher layers. Higher layers are logically closer to the user and deal with more abstract data, relying on lower layers to translate data into forms that can eventually be physically manipulated.
The internet model was produced as the solution to a practical engineering problem. The OSI model, on the other hand, was a more theoretical approach, and was also produced at an earlier stage in the evolution of networks. Therefore, the OSI model is easier to understand, but the TCP/IP model is the one in actual use. It is helpful to have an understanding of the OSI model before learning TCP/IP, as the same principles apply, but are easier to understand in the OSI model.
There is some discussion about how to map the TCP/IP model onto the OSI model. Since the TCP/IP and OSI protocol suites do not match precisely, there is no one correct answer.
In addition, the OSI model is not really rich enough at the lower layers to capture the true layering; there needs to be an extra layer (the Internetworking layer) between the Transport and Network layers. Protocols specific to a particular network type, but which are run on top of the basic hardware framing, ought to be at the Network layer. Examples of such protocols are ARP, and the Spanning Tree Protocol (used to keep redundant bridges idle until they are needed). However, they are local protocols, and operate beneath the internetwork functionality. Admittedly, placing both groups (not to mention protocols which are logically part of the internetwork layer, but run on top of the internetwork protocol, such as ICMP) all at the same layer can be confusing, but the OSI model is not complex enough to do a better job.
The following diagram attempts to show where various TCP/IP and other protocols would reside in the original OSI model:
| 7 | Application | e.g. HTTP, SMTP, SNMP, FTPThe File Transfer Protocol (FTP is a software standard for transferring computer files between machines with widely different operating systems. It belongs to the application layer of the Internet protocol suite. FTP is an 8- bit client- server protocol,, TelnetTelnet is a network protocol used on the Internet. IETF document STD 8 (aka and ) states: : The purpose of the TELNET Protocol is to provide a fairly general, bi-directional, eight- bit byte oriented communications facility. It is typically used to provid, Ssh and Scp, NFSNetwork File System NFS is a protocol originally developed by Sun Microsystems in 1984 and defined in RFCs 1094, 1813, (3010) and 3530, as a file system which allows a computer to access files over a network as easily as if they were on its local disks., RTSP |
| 6 | Presentation | e.g. XMLXML eXtensible Markup Language is a W3C recommendation for creating special-purpose markup languages. It is a simplified subset of SGML, capable of describing many different kinds of data. Its primary purpose is to facilitate the sharing of structured tex, XDReXternal Data Representation (XDR) is an implementation of the presentation layer in the OSI model. XDR allows data to be wrapped in an architecture independent matter so data can be transferred between heterogenous computer systems. Converting from the l, ASN.1, SMB, AFP |
| 5 | Session | e.g. TLS, SSH, ISO 8327 / CCITT X.225, RPC, NetBIOS, ASP |
| 4 | Transport | e.g. TCP, UDP, RTP, SCTP, SPX, ATP |
| 3 | Network | e.g. IP, ICMP, IGMP, X.25, CLNP, ARP, RARP, BGP, OSPF, RIP, IPX, DDP |
| 2 | Data Link | e.g. Ethernet, Token ring, PPP, HDLC, Frame relay, ISDN, ATM |
| 1 | Physical | e.g. electricity, radio, laser |
Commonly, the top three layers of the OSI model (Application, Presentation and Session) are considered as a single Application Layer in the TCP/IP suite. Because the TCP/IP suite has no unified session layer on which higher layers are built, these functions are typically carried out (or ignored) by individual applications. A simplified TCP/IP interpretation of the stack is shown below:
| Application "layer 7" | e.g. HTTP, FTP, DNS (routing protocols like BGP and RIP, which for a variety of reasons run over TCP and UDP respectively, may also be considered part of the network layer) | |
| 4 | Transport | e.g. TCP, UDP, RTP, SCTP (routing protocols like OSPF, which run over IP, may also be considered part of the Network layer) |
| 3 | Network | For TCP/IP this is the Internet Protocol (IP) (required protocols like ICMP and IGMP run over IP, but may still be considered part of the network layer; ARP does not run over IP) |
| 2 | Data Link | e.g. Ethernet, Token ring, etc. |
| 1 | Physical | e.g. physical media, and encoding techniques, T1, E1 |