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OSI MODEL

August 7, 2009

Network Topology:

Network topology is the study of the arrangement or mapping of the elements (links,nodes etc) of a network.Topology refers to the shape of a network,or the networks layout.
Basic Types of Topologies:
ᅡᄋ Bus
ᅡᄋ Star
ᅡᄋ Ring
ᅡᄋ Mesh
ᅡᄋ Tree
ᅡᄋ Hybrid
ᅡᄋ Point to Point
OSI Model:
The Open Systems Interconnection model consists of the Application,Presentation,Session,Transport,Network,Data link and Physical layers.A layer is a collection of functions that provides services to the layer above it and receives service from the layer below it.OSI layer provides error-free communications across a network path.
Apart from these  3 layers are added above Application Layer for business utility.They are : Utility Application Layer,Business Application and Data Layer.These three layers are named as Additional Real World Layers.
OSI Model
Data Unit
Layer
Function
Host Layers
Data
7.Application
Network process to application.
6. Presentation
Data representation and encryption.
5.Session
Interhost communication.
Segment
4.Transport
End to end connections and reliability.(TCP)
Media Layers
Packet/Datagram
3.Network
Path determination and logical addressing(IP).
Frame
2.Data Link
Physical addressing (MAC & LLC).
Bit
1.Physical
Media,signal & binary transmission.
Advantages of network:
ᅡᄋ Sharing – Network enables to share all data and     programs along with different resources.
ᅡᄋ Communication Medium – Networks provide very fast and effective communication mediums.
ᅡᄋ File Integrity – The file transfer and sharing is very frequent and immediate file updating in networks.Thus networks maintain the integrity of file and saves time.
ᅡᄋ Cost effective – Network allow to share the resources of expensive peripheral devices like printers.Thus decreasing the overall cost of the system.
ᅡᄋ Reliable  – Network provides the reliability by providing multiple sources of supply.
ᅡᄋ Greater Flexibility  – Networks provide greater flexibility because of possibility to connect devices from various vendors.
ᅡᄋ Backup – It is easier to backup the files from the central file server instead of from the scattered work station.
ᅡᄋ Security – Networks provide security measures so as to ensure that the network user may only have access to certain files and applications.
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