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Tuesday, July 7, 2015

Short Note on Computer Networking 

  • A network is

A set of devices (nodes) connected by communication links.
A node can be a
·        Computer
·        Printer
·        Or any other device

Capable of sending and/or receiving data generated by other nodes on the network.


Ø Components needed in communication
·        Two or more parties
·        A communication medium
·        Compatible standards(language, protocols)


Ø Telecommunication means communication at a distance.
Ø Data communication means the exchange of data between two devices using transmission medium.



Ø Types of communication (Based on data flow)/Transmission Modes
o   Simplex
o   Half-Duplex
o   Full-Duplex
For more refer this (click here )
   




  Ø Use of Networks
o   Resource sharing(HW/SW)
o   Information sharing(Files)
o   Communication(Emails)
o   Remote computing
o   Distributed computing(GRID)
o   Social networking
o   E-commerce


  Ø Network Topologies
o   Mesh
o   Star
o   Bus
o   Ring
o   Tree
o   Hybrid
Refer for further information (Click here)






  Ø Mesh Topology
o   Connects all devices to each other (redundant).
o   Use in WAN to interconnect LAN.
o   Use in mission critical networks.
o   Implantation is expensive.

  Ø Star Topology
o   Commonly use in Ethernet LANs.

  Ø Tree Topology
o   Extended star topology.
o   Reduce traffic on wires (sending packets only to the wires of the destination).

  Ø Bus Topology
o   Referred as linear bus.
o   Use single cable.

  Ø Ring Topology
o   Frames travel around the rings.
o   Node adds data and destination address to the frame.


OSI Model


Application
(Telnet ,ftp ,NFS,NIS)

Allow access to network resources

Presentation


Translate encrypt and compress data

Session

Establish, Manage & terminate sessions

Transport
(TCP,UDP)

Provide process to process reliable message delivery and error recovery

Network
(IP,ICMP)

Move packet from source to destination

Data Link
(Ethernet)

Organize bits into frames. Hop to hop communication

Physical

Transmit bit over medium & provide mechanical & electrical specification



Refer For further information (Click here )

  Ø IP Packet/IP Datagram refers to a message send by protocols operating at the network layer of the OSI model.

  Ø PDU (Protocol Data Unit) Formal term use in OSI model to describe protocol messages.

  Ø Segment refer to TCP PDU.

Ø Network Protocol
o   Set of rules & actions.
o   Define format & order of the message exchange.
o   Routing Protocols defines the path from source to destination.
o   HW implemented protocols in NIC control the flow of bits in wire.
o   Congestion – control protocol in end systems control the rate of packet transmission.


Network Components

  Ø Transmission medias
  Ø Interconnecting devices
  Ø End devices
  Ø Network Software
  Ø Applications


  Ø Interconnecting Devices
o   Repeaters
§  Operating at the physical layer
§  Connect separate segments
§  Do not understand frames packets or headers
§  Functionality
·        Take incoming frames
·        Regenerate or amplify the signal

o   Hubs
§  Operate at the physical layer.
§  Similar to repeaters.
§  Coppices incoming frames.
§  Collision can occur.
§  Not amplify the signal.

o   Bridges
§  Operate at data link layer.
§  Connect 2 or more LANs.
§  Inspect incoming frame headers and forward it into relevant LAN.


o   Switches
§  Operate at data link layer.
§  Similar to bridge.
§  Learn addresses dynamically.
§  No collision.

o   Routers
§  Operate at the network layer.
§  Make forwarding decisions based on Network Layer.
§  When multiple paths available router decide which path to use
§  Provide methods to
·        Filter traffic based on addresses
·        Route redundancy
·        Load balancing
·        Hierarchical addressing
 


                       




  Ø Network Applications
o   Email
o   E-Commerce
o   Video conferencing

  Ø Classification of networks(Classification Mainly based on scale and ownership)
o   PAN(USB, Firewall, Bluetooth)
o   HAN(wireless access point, residential LAN)
o   LAN(Privately owned network, broadcast)
o   CAN(Covering limited geographical area)
o   MAN(Metro-Ethernet)

o   WAN(Large geographical area)

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