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Osi Model

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OSI
Ned Leeds

CMGT/245 CMGT/245 Version 2
IS Security Concepts

October 28, 2013

LAYER 1 - PHYSICAL The physical layer is mainly responsible for establishing, maintaining and ending physical connections (point to point) between computers. This layer is concerned with the actual interpretation of the bit stream into an electrical signal that can be carried across a physical medium. The protocols at this layer deal with the binary transmission, voltage levels, and data rates. This layer would also specify physical medium properties such as cables and network cards.
LAYER 2 - DATA LINK
The data link layer defines the format of data on the network. All of the data sent through the network are made into a frame which is performed at this level. The frame is a uniform way of sending the data along with address information and error checking capabilities. CRC is used for the error detection at this level. The receiving end the CRC fails at this level there is a request back to the sender for retransmission of this packet.
LAYER 3 - NETWORK
The network layer basically handles all of the addressing issues. This layer addresses packets, determines the best path or route will manages network problems such as data congestion. There are three ways in which the packets are routed to their destinations. There could be a static route through the entire network that will never be changed. This could also be a static line only used during a particular session between the sender and receiver. Packets could be dynamically sent through the network using changing paths in order to prevent bottlenecks in data traffic. The bottlenecks are formed when there are too many packets present in one subnet causing them to get in each other's way. The network level is also responsible for converting the network address and names to the MAC addresses of the machines. The most

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