IMPORTANCE OF OSI LAYERS IN NETWORKING
Network
A network is an interconnection of 2 or more devices in order to communicate with each other.
OSI (Open Systems Interconnection)
-To divide complicated process of networking into different layers.
-To allow different vendors networks to interoperate.
-Developing protocols and devices for different layers.
-OSI reference model was introduced by international organization for standardization (ISO).
-It allows various types of network hardware and software to communicate.
OSI divide a network into 7 layers.
7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical
1. Physical layer
It co-ordinates the rule for transmitting bits.
The physical layer defines physical layer structure (topologies-bus, star, mesh, ring and cellular), mechanical and electrical specification for using the transmission media, bit transmission encoding and timing rules.
– converts to bits and traveling as voltage.
Devices – concentrators, hub, repeaters and modem.
2. Data Link layer
-Organize physical layer bits into logical groups of information called frame.
-Detect errors.
-control data flow
-identify computers on the network
Devices- bridge, switch and NIC
Data Link layer divided into two sub-layers
a. MAC (Media Access Control)
– includes logical topology, media access protocol [contention method, CSMA/CD, token passing and polling (here one master will check anyone is free and send data)] and physical addressing (MAC address-is a 48 bit.).
– controls the way transmitters a single transmission layer.
b. LLC (Logical Link Control)
-it establishes and maintains the link for transmitting data frame from one division to the other one.
-it includes transmission synchronization and connection services (It adds an error checking code called CRC (Cyclic Redundancy Check).
-which routing protocol (OSPF, RIP, EIGRP etc.) is using is identifying by LLC.
3. Network layer
– Packets are forming
– Path determination and routing takes place.
– Provides network-wide addressing (network addressing) and mechanism to move packets between multiple networks.
Devices- router and manageable switch (layer 3 switches).
Protocol- IP, IPX (routed protocol) and routing protocols.
4. Transport layer
– Provides end-to-end communication and reliable data delivery.
– Transmission of data taking place a. Connection-oriented sample packet sends and if they got replay means they send data.
b. Connectionless data sending without checking media. The broadcast purpose it is using.
Protocol-TCP, SPX (novel) and UDP.
5. Session layer
– A session starting, maintaining and ending process or controlling take place. Manage user session and track user session.
– All data are dividing into their own respective type or services like FTP, web service etc.
– Communication establishment like ready to send messages. Allows application to maintain an ongoing communication.
6. Presentation layer
– Files are converting into their own respective file format like JPJ (picture), MP3 (sound), encryption, decryption, compression, and translation take place.
-Provides common data formatting between communicating devices like MIME (multipurpose Internet Mail Extension).
-make sure the receiving station can read the transferred data.
-workstation or server service.
-email client.
7. Application layer
– All applications and user interaction like HTTP, FTP, NNTP, Telnet etc.
– gives end-user applications access to network resources like operating systems (shell part).
Data transmission from source to destination by using OSI layer:
In application layer, all application and user interaction like HTTP, FTP, telnet etc. take place. Users are interacting with system using this layer. In presentation layer files are converting into their own file format like JPJ (picture), MP3 (sound), encrypting, compressing and translating take place. In session layer a session starting and maintaining process take place. All data are dividing into their own respective type or services like FTP, web service etc. Then in transport layer, transmission of data take place.TCP header is adding. Addressing and path determination take place in network layer. Here IP header is adding. In data link layer, MAC header is adding. Data is traveling in the form of frames. Finally in physical layer, header is adding and then frames converting to bits and then it travel as voltage.
Physical layer checking and comparing source side physical layer header and destination header. If it is same, it is removing. Then going to data link layer. Their MAC header checking and removing. Network layer, source and destination side IP checking. Then in transport layer both side TCP header checking and removing, after that in session layer, will end that session if it is not required. If we want to continue, it will not disconnect. Then in presentation layer, decompressing, decrypting and that file we can see by using application layer.
Note:
Data traveling form in different layers:
Physical Bits
Data Link Frame
Network Packets
Transport Segments
Session, Presentation and Application Data
Transport TCP header adding/removing
Network IP header adding/removing
Data Link MAC header adding/removing
Physical Header adding/removing.
Article Authored by Jebin
Author, Jebin, is a Systems Engineer with SupportPRO. Jebin specializes in Cpanel and Linux servers. SupportPRO offers 24X7 technical support services to Web hosting companies and service providers.
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