MODULE 1 NOTES 15EC64
3. Timeliness. The system must deliver data in a timely manner. Data delivered late are
useless. In the case of video and audio, timely delivery means delivering data as they
are produced, in the same order that they are produced, and without significant delay.
This kind of delivery is called real-time transmission.
4. Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay in the
delivery of audio or video packets. For example, let us assume that video packets are sent
every 30 ms. If some of the packets arrive with 30-ms delay and others with 40 ms delay,
an uneven quality in the video is the result.
A data communications system has five components (see Figure 1.1)
Figure 1.1 Five components of data communication
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. It represents
an agreement between the communicating devices. Without a protocol, two devices
may be connected but not communicating, just as a person speaking French cannot be
understood by a person who speaks only Japanese
COMPUTER COMMUNICATION NETWORKS