1.1.1 Why Use A Network?
• Medium for Communication:
- Satellite link
- Phone line
- High Speed (Multiplexed) phone lines
- Coax Cable
- Fibre Optical Cable
- Twisted pair cable
- (Theoretically anything can be used)
• General OSI Diagram contains seven layers
22.214.171.124 - Physical Layer
• Physical layer is concerned with transmission of raw bits over a physical circuit.
• Deals with voltages, timing, connections, etc.
• Responsible for bit synchronization and the identification of a signal element as either a 0 or a 1.
• Protocols: RS-232, RS-449, CCITT X.25 and X.21, IEEE 802
126.96.36.199 - Data Link Layer
• Data link layer breaks input data into “data frames” and processes acknowledgments.
• Object is to provide a error-free transmission line to the network layer.
• Responsible for the reliable delivery of information over a point-to-point or multipoint link.
• Supervises interchange of both link control data and user information
• Protocols: ANSI X3.28, HDLC, X.25, ISDN, IEEE 802
188.8.131.52 - Network Layer
• Network layer determines the interface between the computer and the intermediate system, how packets are routed.
• Chooses a route from the available data links that form the network.
• Object is to take messages, convert them to packets and send them towards the destination.
• Protocols: CCITT X.25, X.21, IP, CCITT Q.931, ISO 8473
184.108.40.206 - Transport Layer
• Transport layer takes data from the session layer, splits it up if necessary, and passes this to the network layer.
• Ensures that pieces all arrive correctly at the other end.
• Isolates the user from any concern for the actual movement of the information.
• Protocols: TCP, ISO 8073
220.127.116.11 - Session Layer
• Session layer defines a connection between users (presentation layer processes).
• Includes specification of the remote machine, authorization, options for the communication, and recovering from errors in broken transport connections.
• The set-up of communications is called binding.
• Protocols: ISO 8327, CCITT X.225, T.62, ECMA 75, NFS, RPC.
18.104.22.168 - Presentation Layer
• Ensures compatible syntax among the communicating processes by adjusting data structures, formats, and codes.
• Presentation layer is generally represented by library routines which the user accesses to perform network operations.
• This layer can also perform transformations such as compression and encryption.
• Protocols: DIS 8823, 8824, 8825, CCITT X.409, T.61
22.214.171.124 - Application Layer
• Application layer is written by the user, or is a program that performs some function for the user.
• Provides a window by which the user gains access to the communication services provided by the architecture.
• Protocols: DIS 8571, 8832, 9040