are the exchange of data between two devices via some form of transmission medium such as a wire cable.
Data flow
simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive.
In half-duplex mode, each station can both transmit and receive, but not at the same time
In full-duplex (called duplex), both stations can transmit and receive simultaneously
communication system made up of a combination of
hardware (physical equipment) and software (programs).
communications system depends on four fundamental characteristics:
Delivery
Accuracy
Timeliness
Jitter
Delivery: The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user.
Accuracy: The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable.
Timeliness: The system must deliver data in a timely manner. Data delivered late are useless. In the case of video and audio.
Jitter: Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets.
Five components
Massage
Sander
Receiver
Transmission medium
Protocol
1. Message. The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video.
2. Sender. The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on.
3. Receiver. The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on.
4. Transmission medium. The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
5. Protocol. A protocol is a set of rules that govern data communications
set of devices (often referred to as 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.
Network Criteria
Performance
Reliability
Security
Network criteria
Depends on Network Elements
1-Depends on Network Elements.
2-Measured in terms of Delay and Throughput.
1- Failure rate of network components.
2- Measured in terms of availability/robustness.
Data protection against corruption/loss of data due to: · Errors. · Malicious users.
Network advantage
File sharing
Resources sharing
Increased storage capacity
Increased cost efficiency
Network disadvantages
Security issues
Repaid spread of computer viruses
Expansive set up
Dependency on the main file server
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