Data Communications and Networking CSCS 311 Lecture 2 Amjad Hussain Zahid

Lecture Focus:  Networking  Distributed Processing  Network Criteria  Physical Structures  Categories of Networks Data Communications and Networking Lecture 2

Data Communications and Networking Lecture 2 NETWORKING: In its simplest form, data communication takes place between two devices that are directly connected by some form of point-to-point transmission medium. Often, however, it is impractical for two devices to be directly, point-to-point connected due to the following reasons:  The devices are very far apart. It would be expensive, for example, to string a dedicated link between two devices thousands of miles apart.  There is a set of devices, each of which may require a link to many of the others at various times.  Example:  All the telephones in the world  All of the computers owned by a single organization. Except for the case of a very few devices, it is impractical to provide a dedicated wire between each pair of devices. Solution to this problem is to attach each device to a communications network.

Data Communications and Networking Lecture 2 NETWORKING: Network is a highway on which data can travel.  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.  Interconnected nodes can share data, hardware and software. Links connecting the devices are often called communication channels.

Data Communications and Networking Lecture 2 NETWORKING: Distributed Processing  Most networks use distributed processing, in which a task is divided among multiple computers. Instead of one single large machine being responsible for all aspects of a process, separate computers (usually a personal computer or workstation) handle a subset.

Data Communications and Networking Lecture 2 NETWORKING: Network Criteria  A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security.

Data Communications and Networking Lecture 2 Network Criteria Performance can be measured in many ways, including transit time and response time. Transit time is the amount of time required for a message to travel from one device to another. Response time is the elapsed time between an inquiry and a response. The performance of a network depends on a number of factors, including: The number of users The type of transmission medium The capabilities of the connected hardware, and The efficiency of the software. Performance:

Data Communications and Networking Lecture 2 Network Criteria Performance: Performance is often evaluated by two networking metrics: Throughput Delay We often need more throughput and less delay. However, these two criteria are often contradictory. If we try to send more data to the network, we may increase throughput but we increase the delay because of traffic congestion in the network.

Data Communications and Networking Lecture 2 NETWORKING: Network Criteria Reliability: In addition to accuracy of delivery, network reliability is measured by the frequency of failure, the time it takes a link to recover from a failure, and the network's robustness in a catastrophe. Security: Network security issues include protecting data from unauthorized access, protecting data from damage, and implementing policies and procedures for recovery from breaches and data losses.

Data Communications and Networking Lecture 2 NETWORKING: Physical Structures Type of connection:  A network is two or more devices connected through links.  A link is a communications pathway that transfers data from one device to another.  For visualization purposes, it is simplest to imagine any link as a line drawn between two points.  For communication to occur, two devices must be connected in some way to the same link at the same time.

Data Communications and Networking Lecture 2 NETWORKING: Physical Structures Type of connection: There are two possible types of connections: point- to-point and multipoint. 1.Point-to-Point 2.Multipoint

Data Communications and Networking Lecture 2 Point-to-point connection  A point-to-point connection provides a dedicated link between two devices.  The entire capacity of the link is reserved for transmission between those two devices.  Most point-to-point connections use an actual wire or cable to connect the two ends, but other options, such as microwave or satellite links, are also possible. When you change television channels by infrared remote control, you are establishing a point-to-point connection between the remote control and the television's control system. A transmission medium is point-to-point if, first, it provides a direct link between two devices and, second, those are the only two devices sharing the medium.

Data Communications and Networking Lecture 2 Point-to-point connection There is no central server.Used in small business, homes etc.

Data Communications and Networking Lecture 2 Multi-point connection  A multipoint (also called multidrop) connection is one in which more than two specific devices share a single link.  More than two devices share the same medium  In a multipoint environment, the capacity of the channel is shared spatially or temporally.  If several devices can use the link simultaneously, it is a spatially shared connection.  If users must take turns, it is a timeshared connection.  A central computer acts as a server and remaining computers are called clients in the network.

Data Communications and Networking Lecture 2 Multi-point connection Server

Figure 1.7 Categories of topology Next Lecture

Figure 1.8 Fully connected mesh topology (for five devices)

Figure 1.9 Star topology

Figure 1.10 Bus topology

Figure 1.11 Ring topology

Figure 1.12 Categories of networks

Figure 1.13 LAN

Figure 1.13 LAN (Continued)

Figure 1.14 MAN

Figure 1.15 WAN

1.3 The Internet A Brief History The Internet Today

Figure 1.16 Internet today

1.4 Protocols and Standards Protocols Standards Standards Organizations Internet Standards