Lesson 1-Introduction
Comp277 – Data Communications and Networking
Data Communications and Networking
Telecommunications
- tele means far in Greek;
- means telephony, telegraphy, television, or communications at a distance
Data
- refers to information presented in whatever form if agreed upon by parties creating and using it
Data Communications
- is the exchange of data between two devices via some form of transmission medium
Effectiveness of data communication system depends on four fundamental characteristics:
1. Delivery
- data must be delivered to the correct destination, and only to the intended recipient.
2. Accuracy
- data must be delivered accurately, should not have been altered during transmission
3. Timeliness
- data must be delivered in a timely manner; if is it late, it is useless; it should be real-time transmission without any delay
4. Jitter
- there should not be variation in the packet arrival time.
Components of Data Communication
1. Message
- message is the information (data) to be communicated between devices
- this may come in a form of text, numbers, pictures, audio and video.
2. Sender
- is the device that sends the (data) message
- it can be a computer, workstation, telephone handset, video cam, etc.
3. Receiver
- is the device that receives the message
- it can be a computer, workstation, telephone handset, video cam, etc.
4. Transmission Medium
- is the physical path by which a message travels from sender to receiver.
- examples are twisted pair, coaxial cable, fiber optics, radio waves, etc.
5. Protocol
- is the set of rules that govern data communications
- example is French vs. Japanese
Data Presentation
Data may be presented in a form of text, numbers, images, audio, or video.
1. Text
- is represented by a bit pattern of 0's and 1's.
- each set is called a code.
- Unicode is the prevalent coding system which uses 32 bits to represent a symbol or character.
- The ASCII (American Standard Code for Information Interchange) constitutes the first 127 characters (or 7 bits) in the Unicode, also called the Basic Latin.
2. Numbers
- numbers are represented by bit patters but ASCII is not used. Instead, the number is directly converted to a binary number to simplify mathematical operations;
- uses the number systems
3. Images
- also represented by bit patterns;
- image is composed of matrix of pixels (picture elements)
- each pixel is a small dot
- a black and white uses 1-bit pattern;
- if image is not pure black or white, or includes gray scale, two-bit pattern may be used; example – 00 is black, 01 dark grey, 10 dark grey, 11 is white;
- one method to represent a color is using RGB which uses the combination of Red Blue and Green;
- another method is the YCM which uses Yellow cyan and Magenta.
4. Audio
- refers to the recording or broadcasting of sound or music;
- audio unlike images, text and numbers, is not discrete but continuous.
5. video
- recording or broadcasting of picture or movie.
Data Flow
Communication between devices can be simplex, half-duplex or full-duplex.
1. Simplex – a simplex communication is a unidirectional or a one-way street. Only one of the two devices on a link can transmit; the other one can only receive.
2. Half-duplex – a half-duplex communication is similar to a CB, or a one-lane road with traffic allowed in both directions but when cars are travelling in one direction, the cars going the other way should wait.
3. Full-duplex – In a full-duplex mode (also called duplex), both stations can transmit and receive simultaneously. An example is a telephone system where both parties can talk and listen at the same time.
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Lesson 1-Introduction
Comp277 – Data Communications and Networking
Networks
A network is a set of devices (often referred to as nodes) connected by communication links. Most networks use distributed processing in which a task is divided into multiple computers.
Network Criteria
A network must meet certain criteria which include performance, reliability and security.
1. Performance – performance can be measured in terms of transit time (the amount of time required for a message to travel from one device to another); response time (time elapsed between an inquiry and a response) ; throughput (the average rate of successful message delivery over a communication channel); and delay (how long it takes for a bit of data to travel across the network from one node or endpoint to another).
2. Reliability – network reliability is measured in terms of accuracy of delivery, frequency of failure, the time it takes to recover from a failure, and the network's robustness in a catastrophe.
3. Security – network security is the protection of data from unauthorized access; data damage and development; implementation of policies and procedures for the recovery from breaches and data losses.
Types of Connection
1. Point-to-point – a point-to-point connection provides a dedicated link between two devices. An example is when you change your television channel by infrared remote control – there is a point-to-point connection between the remote control and the television's control system.
2. Multipoint – a multipoint (also known as multidrop) connection is one in which more than two specific devices share a single link.
Topology
Network topology refers to the way in which a network is laid out physically.
1. Mesh – In a mesh topology, every device has a dedicated point-to-point link to every other device. This is the most reliable, yet most expensive and difficult to setup. In order to determine the number of physical links required, user n(n-1)/2. Which means that for a network with 5 nodes, the physical link is equal to (5)(5-1)/2 = 20.
2. Star – In a star topology, each of the device has a dedicated point-to-point link only to a central controller, which may be a hub or switch. It does not allow direct traffic between devices. In order for one device to send data, it must transmit first to the central controller which will relay the data to the other connected device.
3. Bus – a bus topology is a multipoint connection which acts as backbone to link all devices in a network. Nodes are connected to the bus cable by drop lines and taps. Bus is easy to install but the signal becomes weaker and weaker as it travels farther and farther.
4. Ring – In a ting topology, each device has a point-to-point dedicated connection with only the two devices on either side. A signal is passed along the ring in one direction. This connection is easy to install and configure however, a break in the ring can disable the entire network.
5. Hybrid – Most networks use hybrid, for example, you can have a main star topology with each branch connecting several stations in a bus topology.
Categories of Network
The category of a network is determined by its size.
1. Local Area Network (LAN) – a LAN is usually privately owned and links the devices in a single office, building, or campus. Currently, LAN size is limited to a few kilometers.
2. Wide Area Network (WAN) – a WAN provides long distance data, audio, and video transmission over large geographic areas which can spread over a country, continent or even the whole world.
3. Metropolitan Area Network (MAN) – a MAN is a network with a size between a LAN and a WAN. It normally covers the area inside a town or a city.
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Lesson 1-Introduction
Comp277 – Data Communications and Networking
Interconnection of Networks: Internetwork
Today, it is very rare to see a WAN, a MAN, or a LAN, in isolation. Usually, they are connected to one another. When two networks are connected, they become an internetwork, or internet.
The Internet
A network is a group of connected communicating devices such as computers and printers. An internet (small i) is two or more network that can communicate with each other. The most notable internet is the Internet (big I).
History of the Internet
Internet began in 1969. During the 1960's computers, mainframes, and devices were stand-alone devices. Computers from different manufacturers were unable to communicate with one another.
ARPA (Advanced Research Projects Agency) in the DoD (Department of Defense) tried to find a way to make computers communicate so that they can distribute their research with ease and without duplicating.
In 1967, ARPA introduced the ARPANET at a meeting with Association for Computing Machinery (ACM). The ARPANET was a project in which they used specialized computer called the interface message processor (IMP) which will serve as hosts and which in turn are connected to one another.
In 1969, the project became a reality. Four nodes were connected via IMPs to form a network using the software Network Control Protocol (NCP). The four nodes were situated at the University of California at Los Angeles (UCLA), University of California at Santa Barbara (UCSB), Stanford Research Institute (SRI), and the University of UTAH.
In 1972, Vint Cerf and Bob Khan collaborated on the called Internetting Project. They detailed their work in 1973 paper that outlined the protocols to receive end-to-end delivery of packets.
Shortly thereafter, authorities made a decision to split TCP into two protocols: Transmission Control Protocol and the Internetworking Protocol (IP).
Internet Today
Internet has come along way since 1960s. Today, it is made up of many wide- and local- area networks joint by connecting devices and switching stations. Internet Service Providers(ISPs) provide end-users with Internet connection. Service Providers may be:
1. International – providers that connect nations together.
2. National – are backbone networks created and maintained by specialized companies. Examples are SprintLink, PSINet, UUNet Technology, etc.
3. Regional – are smaller ISPs that are connected to one or more national ISPs. They have smaller data rate.
4. Local – provide direct service to the end users. They can be connected to regional ISPs or directly to national ISPs. Local ISPs are companies that just provides Internet services.
Protocols and Standards
Protocol
A protocol is a set of rules that govern data communications. A protocol defines what is communicated, how it is communicated, and when it is communicated. Key elements of a protocol are:
1. Syntax – refers to the structure or format of the data, meaning in order in which they are presented.
2. Semantics – meaning of each section of bits. How is a particular pattern to be interpreted.
3. Timing – when should date be sent, and how fast can be sent.
Standards
Standards are developed through cooperation of standard creation committees, forums and government regulatory agencies. Examples of standard organizations are: International Organization for Standardization (ISO), American National Standards Institute (ANSI), Institute of Electrical and Electronics Engineer (IEEE) which is the largest professional engineering society in the world, etc.
Internet Standards
Internet standard is a thoroughly tested specification that is useful to and adhered to by those who work with the Internet. It is formalized regulation that must be followed.
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