OSI Protocols
The OSI Model provides a conceptual framework for communication between computers, but the model itself is not a method of communication. Actual communication is made possible by using communication protocols. Each layer on the OSI Model has some protocols associated with it. Some important protocols on each layer are as in below:
OSI Devices
Similar to protocols, each layer has associated equipment with it. For example, Hubs, Repeaters & Media Converters operate at Layer1, L2 Switches & Bridges generally operate on Layer2, Routers & Layer3 Switches operate on Layer3, Firewalls work on Application Layers and some on Transport Layer4 as well.
How to remember Layer Names
In addition to remembering the functions, features, basics, protocols and devices of each OSI layer, we also need to remember the names of the layers. We can simply memorize them but relevant phrases are easy to remember. We can remember them by memorising some interesting phrases as in below:
In these phrases, the first letter of each word is the same as the first letter of an OSI layer name as highlighted in YELLOW in above. So, it becomes very easy to remember these layer names & order.
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How is the multi-tasking done in network equipment & on which layer to be precise?
It is mainly done on Layer4. The core concept behind Transport is “support of Multitasking” … it allows same computer, browser & internet connection to work on multiple applications simultaneously … & this is achieved through Port Numbers, Transport Layer Addressing & Multiplexing.
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Detailed explanation … like it!
How many type of port numbers are there on transport layer in total?
The range of Transport Layer Port numbers is from 0-65,535. 65000, because Port number is a 16-bit number & maximum range through which it can span is 65,535. The port numbers are divided into three ranges:
Well Known Ports Registered Ports, Private/Dynamic Ports with ranges 0-1023, 1024-49151, 49152-65535.
What does Transport Layer do exactly?
The main function is Layer4 Addressing. Transport Layer is responsible for Layer4 Addressing which is also called Process Level Addressing. It allows a computer to use multiple network layer protocols simultaneously. Other functions include Sequencing, Multiplexing and De-multiplexing, Error Control, : E2E Connection Mgmt, Transmission, Segmentation, Flow Control & so on….
What is CRC? On which layer does CRC work?
CRC is Cyclic Redundancy Check. It is used to detect the errors in a network. It works at Data Link Layer – LLC Sub Layer of L2 to be specific!!
So, the real model we use is TCP/IP model?
Yes, true. Although OSI is the standard today but we never find it on real equipment. The model in action today is TCP/IP. OSI is used only for standardization & reference purposes.
What is the different b/w TCP & UPD header?
Header size of TCP is 20 bytes while that of UDP is 8 bytes.
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What are media layers or upper layers? Are these OSI layers or TCP/IP layer names?
The Seven Layer of OSI Model are generally divided into two groups:
Layer 1-4 are called Media Layers or Lower Layers
Layer 5-7 are called Upper Layers or Host Layers
Lower/Media Layers are responsible for Networking & they handle data transport issues. The physical layer and the data link layer are implemented in hardware and software. The physical layer is responsible for actually placing information on the medium.
Upper/Host layers are about Applications. Upper layers deal with application issues and generally are implemented only in software.