The internet protocol suite is the protocol stack used on the internet. It is usually called TCP/IP after two of its most important protocols but there are other protocols as well. The TCP/IP is based on a five-layer model for networking. These layers are the physical, data link, network, transport, and application layers.
The physical layer contains all the functions needed to carry the bit stream over a physical medium to another system. This layer has four parts: mechanical, electrical/optical, functional, and procedural. The mechanical part specifies the physical size and shape of the connector itself so that components will plug into each other easily. The electrical/optical part determines what value of voltage or line condition determines whether a pin is active or what represents a 0 or 1 bit. The functional specifies the function of each pin or lead on the connector. The procedural details the sequence of actions that must take place to send or receive bits on the interface. The Ethernet twisted- pair interfaces from IEEE are common implements of the physical layer that includes these four part
With only the physical layer, a system would have no way to tell another system to get bits ready. The data link layer solves this problem by organizing the bit stream into a data unit called a frame. The data link layer moves bits across the link and can add reliability to the raw communications link. The data link layer can be very simple, or make the link appear error free to the layer above, the network layer. The data link layer usually adds both a header and trailer to the data presented by the network layer. The frame header typically contains a source and destination address and some control information. The control information is data passed from one data link layer to the other data link layer, and not user data. The body of the frame contains the sequence of bits being transferred across the network. The trailer usually contains information used in detecting bit errors. The data link layer performs framing, physical addressing, and error detection. This layer also performs access control, this determines whose turn it is to send over or control the link. In addition, the data link layer can perform some type of flow control. Flow control makes sure senders do not overwhelm receivers; a receiver must have adequate time to process the data arriving in its buffers. Not all destination systems are directly reachable by the sender. This means that when bits at the data link layer are sent from an originating system, the bits do not arrive at the destination system as the “next hop” along the way. Directly reachable systems are called adjacent systems, and adjacent systems are always one hop away from the sender. When the destination system is not directly reachable by the sender, one or more nodes are needed. The network layer delivers data in the form of a packet from source to destination, across as many links as necessary. The biggest difference between the network layer and the data link layer is that the data link layer is in charge of data delivery between adjacent systems while the network layer delivers data to systems that are not directly connected to the source. There can be many different types of data link and physical layers on the network, depending on the variety of the link types, but the network layer is essentially the same on all systems. The key concept at the network layer is the network address, which provides the information about the packets. In TCP/IP, the network address is the ip address and every system in the network receives a network address. This network address is different from the physical address. This layer also contains hardware devices such as routers, bridges, firewalls and switches. The network layer is at the very heart of any protocol stack, and TCP/IP is no exception. The protocol at this layer is ip, either IPv4 or IPv6.
The transport layer ensures the reliable arrival of messages and provides error checking mechanisms and data flow controls. The transport layer provides services for both connection mode transmissions, which is known as TCP, and for connectionless mode transmissions, which is UDP. Connection mode transmissions, a transmission may be sent or arrive in the form of packets. TCP is a connection-oriented, reliable service that provides ordered delivery of packet contents. UDP is a connectionless, unreliable service that does not provide ordered delivery of packet contents. In addition to UDP and TCP, there are other transport-layer protocols that can be used in TCP/IP, all of which differ in terms of how they handle transport-layer tasks. In TCP/IP, it is often said that the network layer offers an unreliable or best effort service, while the transport layer adds reliability in the form of flow and error control. Besides flow and error control, the transport layer also have the functions of connection control, segment handling, and process addressing and multiplexing.
The application layer consists of protocols that focus on process-to-process communication across an ip network and provides a communication interface and end-user services. This layer has many responsibilities, including error handling and recovery, data flow. It is also used to develop network-based applications. The application layer provides many services, including simple mail transfer protocol (SMTP), file transfer, web surfing, web chat, email clients, network data sharing, virtual terminals, and various file and data operations. There are also more than 15 protocols used in this layer such as file transfer protocol, telnet, trivial file transfer protocol and simple network management protocol. Its major network device is the gateway.
The TCP/IP protocol suite is a hierarchical model made up of interactive modules. Each module provides a specific function. In TCP/IP, the layers contain relatively independent protocols that can be “mixed and matched” depending on the needs of the system to provide whatever function is desired. TCP/IP is hierarchical in the sense that each higher layer protocol is supported by one or more lower layer protocols.