LAYER CONCEPTS-NETWORKS

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LIFE CYCLE OF LAN

Analysis phase
• Looking into the problem and analyzing the options available for solving the problem.
• It is aimed at what the system should do and how it should it.
Eg.(1)The students have to work with a central server in a programming lab.(2)how many students?(3)what application?(4)need a high speed connection?
Design Phase
• The purpose of this phase is to determine how the requirements of the specification are to be met.
• Should include drawings and documentation of the network.
• The overview of the s/w to be installed should be prepared.

Implementation
• This involves physical installation of LAN.
• Cables are run, soft wares are installed, Commuters and other hardwares are put in place.
• Users are trained for using it.
Integration and System tesing
• Testing whether the meet the specifications. resources are added more and more to test the efficiency.
• Simulated hacking and intuitions are made to test security.

Operation and maintenance.
• This phase is important .
• If the network crashes ,or security is broken, results in serious consequences.
• There should be specially trained employees to watch the operation of n/w and maintain it



DATA LINK or LINK LAYER



• LLC protocols deals with establishing a connection oriented low level service between the peer machine.
• LAN model have additional layer called MAC which controls access to a medium, resolving the conflicts between the mutually competing machines on a LAN.
• MAC is responsible for routing the LAN.
• IEEE 802.x networks are peer-to-per networks on a shared medium.
• IEEE standards take account toplogies,access methods,transmission media and speeds.



TOKEN RING(MAC)
• Empty information frames are continuously circulated on the ring.
• When a computer has a message to send, it inserts a token in an empty frame (this may consist of simply changing a 0 to a 1 in the token bit part of the frame) and inserts a message and a destination identifier in the frame.
• The frame is then examined by each successive workstation. If the workstation sees that it is the destination for the message, it copies the message from the frame and changes the token back to 0.
• When the frame gets back to the originator, it sees that the token has been changed to 0 that the message has been copied and received. It removes the message from the frame.
• The frame continues to circulate as an "empty" frame, ready to be taken by a workstation when it has a message to send.