Home Add to Favorite Contact Submit  
             28 January, 2021

Category:  Articles » Computers » Certification Tests


Seven Layers of ISO OSI Model

         Views: 2348
2006-11-19 00:02:21     
Article by Vijayanand Yadla

The ISO OSI model are explained below. The seven layers of the OSI model are:

Antiqua">Data Link

1 Application layer:
This layer provides a means for the user to access information on the network through an application. Many user applications that need to communicate over the network interact with the Application layer protocol directly. The user applications are not part of OSI Application layer, use the networking services offered by the networking protocol suite. Application layer functions typically include identifying communication partners, and determining availability of required 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 network format for transmission 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 manageable datagrams and then appropriate header information (such as sequence number, port number, etc.) is added to the datagram before passing it on to the Network layer. Two frequently used transport protocols are the TCP (Transmission Control Protocol) and the UDP (User Datagram Protocol).

Important features of Transport layer:

Transport layer ensures reliable service.
Breaks the message (from sessions layer) into smaller datagrams, and appends appropriate unit header information.
Responsible for communicating with the Session layer

Important features of TCP/UDP:

TCP/IP widely used protocol for Transport/Network layers
TCP: (Transport Control Protocol) TCP ensures that a packet has reached its intended destination by using an acknowledgement. If not, it retransmits the lost messages. Hence, TCP is called a connection oriented protocol.
UDP (Universal Data gram Protocol): UDP simply transmits packets over the internet. It does not wait for an acknowledgement. It is the responsibility of upper layer protocols to ensure that the information had reached the intended partner(s). Hence, UDP is often called connectionless protocol.
Application programs that do not need connection-oriented protocol generally use UDP.

5. Network layer:
Network layer is responsible for the routing of packets through the entire network. The layer uses logical addressing for this purpose. Note that the physical address (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.

Specialized in: Vlan - Wan - Ccna Tutorial - Ccna - Access Lists - Simulationexams
URL: http://www.simulationexams.com
Print article      Bookmark this page
Related Articles 
How to Pass the Final Exam of the DipFA (Popularity: ): IntroductionI've been helping students through their DipFA qualification for almost two years' now and this article is designed to share all the best practises, tips and strategies that can help you achieve a really good mark in this challenging exam.I'm going to share with you various tips that have come from examiner's reports, students I've worked with over the years and share with you a really good structure that can ...
Computer Certifications Increase Salaries (Popularity: ): According to a website for technology and engineering professionals, Dice Learning, an MCSE certificate is one of the top 10 qualifications most likely to help an employee increase the size of their income. These findings are partially based on the fact that Dice Learning has almost 1,000 vacancies on its website requesting MCSE certification as a requirement. But what is it about this qualification that makes it so desirable to ...
Getting an ISECP Certification (Popularity: ): The Information Security Engineering Certified Professional (ISECP) certification is a vendor-neutral certification exam developed by INFINIDOX that covers the foundations of information security. A vendor-neutral means it is not tied to one computer or network brand or platform.The ISECP Certification Program is designed to objectively assess and measure professional knowledge. The ISECP exam is customized for network professionals and system administrators with at least 3 years security experience. To obtain ...
MCSA Certification Exam - 70-270 (Popularity: ): MCSA Certification Exam: 70-270Installing, Configuring and Administering Microsoft Windows XP ProfessionalAfter you study your text books it is important to test your newly acquired knowledge and see just how well you have absorbed the material. Practice exams....* Reinforces what you learnt - fill in the gaps of what you missed * Gets you used to answering questions to build confidence and familiarityHere are 10 Multiple choice exams questions for you to ...
CCNA Security Practice Exam - 10 Questions on the IOS Firewall Set (Popularity: ): Earning your CCNA Security certification is a tremendous boost to your career and your career prospects! To help you prepare for total success on exam day, here are 10 complimentary questions on the IOS Firewall set. Answers are at the end of the article. Enjoy!1. Define the term "DMZ" as it pertains to network security, and name three different common network devices that are typically found there.2. Identify the true ...

Related Business 
Orga-Naqsis business consultancy, audit and training in ISO-OSI coupled management standards (Popularity: ): Orga-Naqsis is a business consultancy, audit and training company in quality management ISO 9001, environmental management ISO 14001, food safety management ISO 22000 and HACCP. Also open systems information OSI linked to quality management ISO projects
Audu, Osi (Popularity: ): Official web site of Nigerian artist Osi Audu. Includes CV details, exclusive works and news.
OSI Golf: Golf Accessories (Popularity: ): OSI Golf is a product development company specializing in developing the most innovative, patent golf training aids and accessories on the market. OSI Golf researches, designs and develops the best golf training aids on the market. Whether you are struggling to keep the ball in the fairway or if you simply want to hit the ball farther, our products can help.
ISO 14001 (Popularity: ): Hassle-free, ISO accreditations can take just 30 days to complete. Choose QMS International PLC for you ISO certifications and training. ISo's covered include: ISO 9001, ISO 14001, OHSAS 18001, ISO 18001 and BS 25999.
Overman & Associates, LLC (Popularity: ): Offering ISO consulting and training specializing in ISO 9001, ISO 14001, ISO/TS 16949 and ISO 17025.
Oneinfoplace (Popularity: ): Information on Java Server Faces, OSI model, Web services, Web services secutity and XHTML.
ISO 9001 Consultants (Popularity: ): ISOconsultant.us is the most trusted and leading name in ISO Documentation and Certification Solution. We are the best ISO Consultant, BRC Consultant as well as HSE Consultant. ISO Consultants provide quality and safety international standards like ISO 9001, ISO 14001, OHSAS 18001, HSE, ISO/IEC 17025, ISO 22000, ISO 27001, ISO 50001, BRC global standard for food and BRC packaging standard.
ISO Certification Made Simple (Popularity: ): ISO in a Box™ from Equas is a template management system that can be tailored to fit any type or size of organisation and enable it to meet the requirements of a range of ISO, BS, OHSAS and other standards – including ISO 9001, ISO 14001, ISO 50001 and OHSAS 18001.
ISO Certification Consultants In India (Popularity: ): ISO Consultants play a very vital role in overall effectiveness of the ISO management system. ISO Certificate is not just a piece of paper that we hang on the wall and display proudly but it is a corporate culture that we as one of the largest iso consultants in the world develop in the company using ISO standards as a tool to become more competitive and process oriented. If you ...
Quality Consultant Management Services (Popularity: ): Baton Rouge, LA consultant specializing in ISO Conversion, all ISO activities, Malcolm Baldrige, TQM, emphasis on ISO 9000, ISO 9001, and ISO 14000 consulting.