Network Reference Model
Before discussing OSI Model first of all know what is protocol and why we need OSI reference model. Protocols are set of rules by which a computer can understand each other. In other words Protocols is language used by computer to communication each other.
When OSI Model not exit in computer network then communication take place without a standard way. It means that if a Hardware manufactures produce a PC then that PC can communicate with same vendor PC only. The reason behind this is they uses their own developed proprietary protocols for communication so other vendor PC don't understand that language.
To Solved this problem a open standard protocols were developed which support by all hardware vendor since it is open standards it is not tied with a specific manufacturer company. we can use any manufacturer company to build our network.
Protocols can be relatively simple or highly complex. Many organizations are involved in developing protocols for networking. From those following six are the most important organizations.
Institute of Electrical and Electronics Engineers (IEEE)
The Institute of Electrical and Electronics Engineers (IEEE) develop and maintain standards in every technology field related with electricity. The Institute of Electrical and Electronics Engineers (IEEE) develop and maintain Local Area Network (LAN) networking standards including Ethernet (IEEE 802.3 family standards) and Wireless LAN (IEEE 802.11 family standards).
Internet Corporation for Assigned Names and Numbers (ICANN) & Internet Assigned Numbers Authority (IANA )
The Internet Corporation for Assigned Names and Numbers (ICANN ) is an international non-profit corporation which is in charge of Internet Protocol (IP) address allocation (IPv4 and IPv6), Domain Names allocation (examples, omnisecu.com, msn.com, google.com) Global public Domain Name System management, DNS Root Server maintenance, Port Number allocation etc.
Previously Internet Assigned Numbers Authority (IANA) was in control of above functions. Now above functions are under ICANN.
Internet Architecture Board (IAB)
Internet Architecture Board (IAB) defines the architecture for the Internet. The Internet Architecture Board (IAB) purpose is to provide oversight of the architecture for the protocols and other procedures used by the Internet.
Internet Society (ISOC)
The Internet Society (ISOC) is mainly involved in policy, governance, technology, education & training and development of internet.
Internet Research Task Force (IRTF) & Internet Engineering Task Force (IETF)
The Internet Research Task Force (IRTF) is a technology research organization which is working on focused long-term research on technical topics related to standard Internet protocols, applications, architecture and technology.
A Request for Comments (RFC) is a technical publication of the Internet Engineering Task Force (IETF) and the Internet Society. Request for Comments (RFCs) are mainly used to develop a network protocol, a function of a network protocol or any feature which is related with network communication.
World Wide Web Consortium (W3C)
World Wide Web Consortium (W3C) is global organization working to define technologies related with World Wide Web like HTML, scripting languages, protocols for Web servers etc.
OSI Stands for Open Systems Interconnection. It is developed by ISO(International Organization of Standardization) and publish in 1984.
OSI Model is a seven layer architecture. It is a logical model that standardizes the communication function. Open Systems Interconnection (OSI) model categorizes these hundreds of problems to Seven Layers. A layer in Open Systems Interconnection (OSI) model is a portion that is used to categorize specific problems. It is used for networking and to show how two different systems can communicate with each other without requiring changes to their underlying hardware and software models.
Feature of OSI Model:
- Each layer performs a unique function.
- Each layer has its own protocol.
- The use of layers is designed to reduce complexity and make standardization easier.
- Troubleshooting is easier by separate networks.
- It can be used to compare basic functional relationships on different networks.
- Allowing software and hardware to integrate well and be portable on differing systems.
- Create a model which all the countries of the world use.
Advantages And Disadvantages Of OSI Model
- It does not depend or rely on a specific computer system.
- Every layer of OSI Model Perform specific function.
- Function of a layer not overlapping with function of other layer.
- Reduced complexity.
- Allow Modular Engineering.
- It encrypts the data for security purpose.
- Many applications do not require/need the data integrity, which is provided by OSI-model.
- It is used as a reference model.
- The higher level layers can't control all aspects of the lower layers.
Functions of Different Layers :
Layer 1: The Physical Layer :
- Defines physical medium and interfaces.
- It is lowest layer of OSI Model.
- Determines how bits are represented.
- Controls transmission rate & bit synchronization.
- Controls transmission mode: simplex, half-duplex, & full duplex.
- It is responsible for transmission and reception of the raw data over network.
- What Voltages and what data rates needed for transmission is defined in the physical layer.
- It converts the digital/analog bits into electrical signal.
- Protocol supported DSL, ISDN, Wi-Fi, Infrared,SONET/SDH, Ethernet etc.
- Devices: hubs, repeater, cables, connectors etc.
Layer 2: Data Link Layer :
- It is second layer of OSI model.
- PDU: Frames.
- Check transmission errors.
- Control the flow of data.
- Provide a well-defined interface to the network layer.
- Logical Link Control(LLC) refers to the functions required for the establishment and control of logical links between local devices on a network.
- Media Access Control(MAC) refers to as method used by devices to control access to the network medium.
- Devices: Switch, Bridge etc.
Layer 3: The Network Layer :
- PDU: Packet.
- It route packet from source to destination(Routing).
- End to end delivery of packets.
- Creates a logical paths.
- Uses logical hierarchical addresses which can change when a device moved from one subnet to another.
- Devices: Routers, Firewalls.
Layer 4: Transport Layer :
- PDU: Segment.
- Port addressing: Since every process has its own port number.
- TCP/UDP are two protocols where internet lies on.
- Must reassemble segments into data using sequence numbers.
- Can use either connectionless or connection oriented sessions.
- TCP support connection oriented session. It require the sender to first request a connection, the receiver to acknowledge the connection, and that they negotiate how much data can be sent/received before its reception is acknowledged.
- UDP support connectionless session.It rely on upper layer protocols for error control and are often used for faster less reliable links.
Layer 5: The Session Layer :
- PDU: Data.
- This Layer establishes, maintains, and terminates the sessions.
- Synchronize the conversation between two different applications.
- Dialog control between the two computers in a session.
- Ex: RPC,LDAP,NFS etc.
Layer 6: The Presentation Layer :
- Data formatting, translation, encryption, and compression.
- It send data in such a way that the receiver will understand the information(Data).
- Responsible for the syntax and semantics of the information exchanged between two Computers.
- Ex: ASCII, EBCDIC, HTML, JPEG
Layer 7: Application Layer :
- It is the topmost layer.
- Provides communication services to applications.
- It provide Mail services, Directory services and File services.
- Ex: HTTP, FTP, SMTP.
TCP / IP Networking Model
The New/Updated TCP / IP Networking model consist of the 5 layers: –
- Data Link
Compare Original/Old TCP/IP Model with New/updated TCP/IP Model
The Application Layer of the TCP/IP mainly a bunch of communication protocols. These communication protocol that actual access the network and see whether it can send information, and how to send particular information and from where to send particular information. An example of this is the HTTP protocol defines how a web browser can access content from a web page from a web server.
Application Layer Protocols Example :- HTTP, IMAP, LDAP, Telnet, SSH, SMTP, SNMP, NTP, DHCP, DNS, BGP, FTP etc.
The Transport Layer of the TCP/IP for host to host communication. Transport Layer perform several function like Multiplexing(using Port),Error recovery(reliability), Connection establishment and termination, Flow control(using Windowing) and Ordered data transfer and data segmentation. The most important function of transport layer are error recovery and flow control.
TCP and UDP are two important protocol of Transport layer. Difference between these two describe later.
Network/Internet layer perform internetworking. Network/Internet layer encapsulate data into data packets known as IP datagram's, which contain source and destination address (logical address) information which is used to forward the datagram's between hosts and across networks. It is also responsible for routing of IP datagram's.
Network/Internet Layer main protocols are IP(IPv4 and IPv6),ICMP,IGMP ECN, IPsec, Routing protocols(EIGRP,RIP,OSPF etc) and Routed Protocols(IP or IPx).
Data Link/Physical Layer
Old Link Layer divided into Data Link and Physical Layer so that easily identified what is Physical aspect like cable, connector etc and what are the Data Link aspect like ARP/RARP, MAC address etc.
The Physical portion defines physical medium and interfaces, how bits are represented, Controls transmission rate & bit synchronization, Controls transmission mode: simplex, half-duplex, & full duplex. What Voltages and what data rates needed for transmission is defined in the physical layer, It converts the digital/analog bits into electrical signal.
Data Link portion check transmission error, control the flow of data. the important protocols are ARP, OSPF Tunneling, PPP, Frame-Relay and MAC Addressing(Physical addressing).
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