TCP/IP PROTOCOL SUIT

TCP/IP PROTOCOL SUIT

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. The most notable difference between TCP/IP and OSI models is the Application layer, as TCP/IP integrates a few steps of the OSI model into its Application layer. A simplified TCP/IP interpretation of the stack is shown below

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The physical layer

The Physical layer describes the physical characteristics of the communication, such as conventions about the nature of the medium used for communication (such as wires, fiber optic links ect.), and all related details such as connectors, channel codes and modulation, and maximum distances. The Internet protocol suite does not cover the physical layer of any network.

The data link layer

The data link layer specifies how packets are transported over the physical layer, including the framing (i.e. the special bit patterns which mark the start and end of packets). Ethernet, for example, includes fields in the packet header which specify which machine or machines on the network a packet is destined for.

The network layer

As originally defined, the Network layer solved the problem of getting packets across a single network. With the advent of the concept of internetworking, additional functionality was added to this layer, such as getting data from the source network to the destination network. In the internet protocol suite, IP performs the basic task of getting packets of data from source to destination.

The transport layer

The protocols at the Transport layer can solve problems like reliability ("did the data reach the destination?") and ensure that data arrives in the correct order. In the TCP/IP protocol suite, transport protocols also determine which application any given data is intended for. The dynamic routing protocols which technically fit at this layer in the TCP/IP Protocol Suite (since they run over IP) are generally considered to be part of the Network layer TCP is a "reliable", connection-oriented, transport mechanism providing a reliable byte stream, which makes sure data arrives complete, undamaged, and in order. TCP tries to continuously measure how loaded the network is and throttles its sending rate in order to avoid overloading the network. Furthermore, TCP will attempt to deliver all data correctly in the specified sequence. UDP is a connectionless datagram protocol. It is a "best effort" or "unreliable" protocol - not because it is particularly unreliable, but because it does not verify that packets have reached their destination, and gives no guarantee that they will arrive in order. If an Application requires these characteristics, it must provide them itself, or use TCP.

UDP is typically used for applications such as streaming media (audio and video, etc) where on-time arrival is more important than reliability, or for simple query/response applications like DNS lookups, where the overhead of setting up a reliable connection is disproportionately large.

The application layer

The Application layer is the layer that most common network-aware programs interface use in order to communicate across a network with other programs. Processes that occur in this layer are application specific; data is passed from the network-aware program, in the format used internally by this application, and is encoded into a standard protocol. Some specific programs are considered to run in this layer. They provide services that directly support user applications. These programs and their corresponding protocols include: HTTP (The World Wide Web), FTP (File transport), SMTP (Email), SSH (Secure remote login), DNS (Name <-> IP Address lookups) and many others. Once the data from an application has been encoded into a standard application layer protocol it will be passed down to the next layer of the IP stack. At the Transport Layer, applications will most commonly make use of TCP or UDP, and are often associated with a well-known port number. The most common ports are listed below:

• File Transfer Protocol (FTP) on port 21

• Secure Shell (SSH) on port 22

• Telnet on port 23

• Simple Mail Transport Protocol (SMTP) for outgoing e-mail on port 25

• Domain Name System (DNS) lookups on UDP (or sometimes TCP) port 53

• Dynamic Host Configuration Protocol (DHCP) on ports 67 and 68

 1. File transfer (FTP):

Connect to a remote machine and send or fetch an arbitrary file. FTP deals with authentication, listing a directory contents, ASCII or binary files, etc.

2. Remote login (telnet):

A remote terminal protocol that allows a user at one site to establish a TCP connection to another site, and then pass keystrokes from the local host to the remote host.

3. Mail (SMTP):

Allow a mail delivery agent on a local machine to connect to a mail delivery agent on a remote machine and deliver mail.

4. News (NNTP):

Allows communication between a news server and a new client.

5. Web (HTTP):

Base protocol for communication on the World Wide Web.