Seven Layers of ISO OSI Model

The ISO / OSI model are described below. The seven levels of the OSI model are:

Application
Presentation
Session
Traffic
Network
Antiqua "> Data Link
Physical

1 Application layer:

This layer provides a means to inform users about access to the network through an application. Many users of applications that communicate across the network to application layer protocol to interact directly. What people are asking questions are not part of OSILayer, use the network services offered by the suite of network protocols. application-level functions typically include identifying communication partners, and determine the availability of resources. Some examples of application layer implementations include Telnet, File Transfer Protocol (FTP) and Simple Mail Transfer Protocol (SMTP).

2 Presentation Layer:

presentation layer converts local host computer data representations into a standard format for the networktransmission on the network. On the receiving side, it changes the network format into the appropriate host computer's format so that data can be utilized independent of the host computer. ASCII and EBCDIC conversions, cryptography, and the like are handled here.
Examples of Presentation layer coding and conversion schemes include common data representation formats, conversion of character representation formats, common data compression schemes, and common data encryption schemes.

Presentation layer implementations are not typically associated with a particular protocol stack. Some well-known standards for video include QuickTime and Motion Picture Experts Group (MPEG). QuickTime is an Apple Computer specification for video and audio, and MPEG is a standard for video compression and coding.

3. Session layer:

The session layer establishes, manages, and terminates communication sessions. Communication sessions consist of service requests and service responses that occur between applications located in different network devices. These requests and responses are coordinated by protocols implemented at the session layer. Some examples of session-layer implementations include AppleTalk's Zone Information Protocol (ZIP), and Decent Phase Session Control Protocol (SCP).

4.Transport layer:

Transport layer is responsible for providing reliable service between the hosts. Upper layer datagrams are broken down into datagrams manageable, and then the appropriate header information (such as sequence number, port number, etc.), the datagram before passing it to the network layer added. Two commonly used transport protocols, TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

Important features of the transport layer:

Transport layer ensures reliable service.

Cancel the message (from sessions layer) into small datagrams, and add the corresponding unitHeader information.

Responsible for communication with the session layer

Major features of the TCP / UDP:

TCP / IP protocol used to transport / network layer
TCP (Transport Control Protocol), TCP ensures that a packet reaches its destination by means of a confirmation. Otherwise, send the lost messages. Therefore, TCP is called a connection-oriented protocol.

UDP (Universal Datagram Protocol), UDP packets sent over the web. E 'do not wait for a confirmation. E 'responsibility to higher level protocols to ensure that the information was intended for the partner (s) made. Therefore, UDP is often referred to as a connectionless protocol.

Application programs that use is not normally necessary connection-oriented protocol UDP.

5. Network Layer:

network layer is responsible for routing packets across the network. The layer uses logical addressing for this purpose. Note that the physicaladdress (like MAC address) keeps changing from hop to hop when a packet travels from source to destination. As a result, an address that doesn't change is required to ensure continuity between hops. This is nothing but logical address. For IP networks, IP address is the logical address; and for Novell network, IPX address is the logical address, and so on. This layer also provides for congestion control, and accounting information for the network. IP (Internet Protocol) is an example of a network layer protocol.

6. Data link layer:

Data link layer provides delivery of information frames between communicating partners. This layer is responsible for flow regulation, error detection and correction, and framing of bits for transmission. The network data frame is made up of checksum, source address, destination address, and the data itself. The largest frame size that can be sent is known as the maximum transmission Unit (MTU).

Important features of Data link layer:

Assembles bits into frames, making them ready for transmission over the network.
Provides error detection, and correction to transmitted frames. If the checksum is not correct, it asks for retransmission. (Send a control message).
Consists of two sub layers:

Logical Link Control (LLC): Defines how data is transferred over the cable and provides data link service to the higher layers.


Medium Access Control (MAC): Controls media access by regulating the communicating nodes using pre-defined set of rules. (i.e. Token passing, Ethernet [CSMA/CD] all have MAC sub-layer protocol).




Different Data link layer protocols define different network and protocol characteristics, including physical addressing, network topology, error notification, sequencing of frames, and flow control. Physical addressing (as opposed to logical addressing) defines how devices are addressed at the data link layer. The protocols used in Data link layer are SLIP, PPP, and CSLP.

7. Physical layer:

This is the bottom-most layer of the OSI model. The Physical layer handles the bit-level communications across the physical medium. The physical medium could be made up of wired electrical signals, or light, or radio (wireless) signals. Physical layer specifications define characteristics such as media, data rates, maximum transmission distances, and physical connectors.

Some of the important standards that deal with physical layer specifications are:

RS-232(for serial communication lines), X.21, EIA 232, and G730.

Physical layer and Data link layer implementations can be categorized as either LAN or WAN specifications.