Data
Communication
Networks
Lecture 1
Introduction
Dr/ Amr Wageeh
DATA COMMUNICATIONS
The term telecommunication, means communication at a distance.
The word data refers to information presented in whatever form is agreed
upon by the parties creating and using the data.
Data communications are the exchange of data between two devices via
some form of transmission medium such as a wire cable.
The effectiveness of a data communications system
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.
Timeline: 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.
Jitter: refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or
video packets.
Components
Message: is the information (data) to be communicated.
Sender: is the device that sends the data message
Receiver: is the device that receives the message.
Transmission medium: is the physical path by which a message travels from
sender to receiver.
Protocol: is a set of rules that govern data communications.
Data flow
Networks
A network is a 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
A network must be able to meet a certain number of criteria.
The most important of these are performance, reliability,
and security.
Performance
Performance is often evaluated by two networking metrics: throughput and delay. We
often need more throughput and less delay.
Reliability
Network reliability is measured by the frequency of failure, the time it takes a link to
recover from a failure.
Security
Network security issues include protecting data from unauthorized access,
protecting data from damage and development.
Types of connections: point to point and multipoint
Categories of topology
A fully connected mesh topology (five devices)
In mesh topology, we need n(n -1) /2 duplex-mode links
Advantage of mesh topology
1-Use of dedicated links guarantees that each connection can carry its own data
load.
2- Robust. If one link becomes unusable, it does not incapacitate the entire
system.
3- Security. When every message travels along a dedicated line, only the
intended recipient sees it.
4- Point-to-point links make fault identification and fault isolation easy.
A star topology connecting four stations
A bus topology connecting three stations
A ring topology connecting six stations
A hybrid topology: a star backbone with three bus
networks
Categories of Networks
• Local Area Networks (LANs)
Short distances
Designed to provide local interconnectivity
• Wide Area Networks (WANs)
Long distances
Provide connectivity over large areas
• Metropolitan Area Networks (MANs)
Provide connectivity over areas such as a city, a campus
An isolated LAN connecting 12 computers to a hub in a
closet
WANs: a switched WAN and a point-to-point WAN
A heterogeneous network made of four WANs and two LANs
Internet
The Internet has revolutionized many aspects of our daily lives.
It has affected the way we do business as well as the way we spend our leisure
time.
Count the ways you've used the Internet recently. Perhaps you've sent electronic
mail (e-mail) to a business associate, paid a utility bill, read a newspaper from a
distant city, or looked up a local movie schedule-all by using the Internet.
The Internet is a communication system that has brought a wealth of information
to our fingertips and organized it for our use.
Hierarchical organization of the Internet
PROTOCOLS AND STANDARDS
In this section, we define two widely used terms: protocols and standards.
First, we define protocol, which is synonymous with rule. Then we discuss
standards, which are agreed-upon rules.
