NET 221D:Computer Networks Fundamentals Networks and Communication Department Lecture 1: Introduction

Introduction The merging of computers and communications has had a profound influence on the way computer systems are organized. Computer Network: a collection of autonomous computers interconnected by a single technology. Networks are usually connected together to make larger networks.

Uses of Computer Networks Business Applications. Home Applications. Mobile Users.

1. Business Applications of Networks Goals: sharing physical resources such as printers or sharing information (product information, inventories, financial statements, …). Example: one or more databases with company information and some number of employees who need to access them remotely.

1. Business Applications cont. A network with two clients and one server.

1. Business Applications cont. A computer network can provide a powerful communication medium among employees : E-mail. Telephone calls between employees may be carried by the computer network instead of by the phone company: IP telephony or Voice over IP (VoIP). Doing Business electronically: E-commerce.

2. Home Network Applications Home users can access information, communicate with other people, and buy products and services with e-commerce. Much of this information is accessed using the client-server model. A different model for accessing information is peer- to-peer communication.

2. Home Applications cont. Peer to peer model: Some forms of E-commerce:

3. Mobile Network Users Combinations of wireless networks and mobile computing. Example:

Example on PDA 6-Nov-18 Networks and Communication Department PDA an smartphone : what is the difference? PDAs do not connect to cellular networks. PDAs in general cheaper 6-Nov-18 Networks and Communication Department

Overview of Data Communications and Networking Behrouz A. Forouzan” Data communications and Networking

1. Data Communication Communication sharing information. Sharing can be local (face to face) or remote (over distance) Data communication: exchange of data between two devices via transmission medium (wire cable) Communicating devices made up of : H.W( physical equipments )and S.W Behrouz A. Forouzan” Data communications and Networking

Data Communication The Effectiveness of data communication depends on : Delivery : System must deliver data to correct destination. Data must be received by only intended device or user. Accuracy: The system must deliver data accurately Timeliness: the system must deliver data in a timely manner. Data delivered later are useless. Jitter: Variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. Behrouz A. Forouzan” Data communications and Networking

Components Behrouz A. Forouzan” Data communications and Networking

Components A data communications system has five components: 1. Message: the information to be communicated. 2. Sender: the device that sends the data message. 3. Receiver: the device that receives the message. 4. Transmission medium: the physical path by which a message travels from sender to receiver. 5. Protocol: set of rules that govern data communications. Behrouz A. Forouzan” Data communications and Networking

Direction of data flow Simplex, half duplex and full duplex Simplex: Communication is unidirectional. (one-way-street). Only one of the two devices on a link can transmit; the other can only receive. Ex: As Keyboard (only input) and monitors only output) Behrouz A. Forouzan” Data communications and Networking

Direction of data flow 2. half duplex : Each station can both transmit and receive , but not at the same time. When one device is sending the other can receive and vice versa.

Direction of data flow 3. Full-Duplex: Both stations can transmit and receive simultaneously. ( telephone network) Like two way street with traffic flowing in both directions at the same time.

2. Networks 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 Performance, Reliability and security

Network criteria Type of transmission media, 1. Performance: The performance depends on : Number of user Type of transmission media, Capabilities of connected H.W and the efficiency of software.

Network criteria 2.Reliability Measured by frequency of failure, the time it takes to recover from failure, and network’s robustness in a catastrophe. 3. Security: Protecting data from unauthorized access. 6-Nov-18 Networks and Communication Department

Physical Structures: A. Types of connections Point –to-point and Multipoint connections 6-Nov-18 Networks and Communication Department

Physical Structures: A. Types of connections 1. Point –to-point Dedicated link between two devices. Most of them uses an actual length of wire or cable to connect the two ends but other options ,such as microwave satellite are possible. Behrouz A. Forouzan” Data communications and Networking

Physical Structures: Types of connections 2. Multipoint A multipoint (also called multidrop) connection is one in which more than two specific devices share a single link. In a multipoint environment, the capacity of the channel is shared as: Spatially: If several devices can use the link simultaneously Temporally: If users must take turns, it is a timeshared connection.

Physical Structures: B. physical topology The way in which a network is laid out physically. It is the geometric representation of the relationship of all the links and linking devices (nodes) to one another. Behrouz A. Forouzan” Data communications and Networking

1. Fully connected mesh topology Every device has a dedicated point-to-point link to every other devices. Fully connected mesh network has n(n-1)/2 physical connection to link n devices. Every device on the network must have n-1 input/output (I/O) ports. Behrouz A. Forouzan” Data communications and Networking

1. Mesh topology Advantages: Privacy or security: every message travels along a dedicated line, and only the intended recipient sees it. Eliminating the traffic problems: the use of dedicated links guarantees that each connection can carry its own data load; that can occur when links must be shared by multiple devices. A mesh is robust. If one link becomes unusable, it does not incapacitate the entire system. Fault identification and fault isolation easy. This enables the network manager to discover the precise location of fault and aids in finding its cause and solution. Behrouz A. Forouzan” Data communications and Networking

1. Mesh topology Disadvantages Every device must be connected to every other device, installation and reconnection are difficult . The sheer bulk of the wiring can be greater than the available space can accommodate. The H.W required to connect each link (I/O ports and cable) expensive. Behrouz A. Forouzan” Data communications and Networking

2. Star topology 6-Nov-18 Networks and Communication Department

2. Star topology Each device has a dedicated point-to-point link only to a central controller (hub). Unlike a mesh , a star topology does not allow direct traffic between devices. If one device want to send data to another , it send it to the hub, which send it to other device. Behrouz A. Forouzan” Data communications and Networking

2. Star topology Advantages Easy to install and to reconfigure and it is less expensive. Robustness: if one link fails, only that link affected and other links remain active. Identification and fault isolation Disadvantages The dependency of the whole topology on one single point, the hub. If the hub goes down, the whole system is dead. Behrouz A. Forouzan” Data communications and Networking

2. Tree topology 6-Nov-18 Networks and Communication Department

3. Tree topology Not every device plugs directly into the central hub. The majority of devices connect to secondary hub that in turn is connected to the central hub. The advantages and disadvantages of tree topology are generally the same as those of star . Behrouz A. Forouzan” Data communications and Networking

2. Bus topology 6-Nov-18 Networks and Communication Department

4. Bus topology Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection running between the device and the main cable. A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core. Behrouz A. Forouzan” Data communications and Networking

4. Bus topology Advantages Easy of insulation: use less cabling than mesh or star. Disadvantages A fault in bus cable (break) stops all transmissions even between devices on the same side of the problem. Reconnection It can be difficult to add new devices (adding more require modification or replacement of the backbone). Behrouz A. Forouzan” Data communications and Networking

2. Ring topology 6-Nov-18 Networks and Communication Department

5. Ring topology Each device has a dedicated point-to-point connection only with the two devices on either side of it. A signal is passed along the ring in one direction from device until it reaches its destination. Each device in the ring incorporate as repeater. Repeater :regenerates the signal. It receives a weakened signal, creates a copy, bit for bit, at the original strength. Behrouz A. Forouzan” Data communications and Networking

5. Ring topology Advantages: Easy to install and reconfigure: Each device is linked only to its immediate neighbors. Fault isolation is simplified : A signal is circulating at all times (token) if one device does not receive a signal within specified period, it can issue an alarm. Disadvantages Unidirectional traffic: A break in the ring (such as disabled station) can disable the entire network. This can be solved by use dual ring.

Hybrid topology Behrouz A. Forouzan” Data communications and Networking

Network categories Today when we speak about networks, we are generally referring to two primary categories : local - area networks and wide – area networks. The categories are : PAN LAN MAN WAN 6-Nov-18 Networks and Communication Department

1. Personal Area Network Bluetooth is used to connect wirelessly a computer with its peripherals. PANs can also be built with other technologies that communicate over short ranges, such as RFID.

2. Local Area Networks A LAN is a privately owned network that operates within and nearby a single building like a home, office or factory. Every computer has a radio modem and an antenna that it uses to communicate with other computers. Each computer talks to a device in the ceiling called an AP (Access Point), wireless router, or base station. IEEE 802.11, popularly known as WiFi is a communication standard for LANs. It runs at speeds anywhere from 11to hundreds of Mbps.

Local Area Networks

Local Area Networks Most of wired LANs use copper wires, but some use optical fiber. Typically, wired LANs run at speeds of 100 Mbps to 1 Gbps, have low delay (microseconds or nanoseconds), and make very few errors. It is just easier to send signals over a wire or through a fiber than through the air. The topology of many wired LANs is built from point-to-point links. IEEE 802.3, popularly called Ethernet, is, by far, the most common type of wired LAN.

4. Wide Area Networks WAN (Wide Area Network) spans a large geographical area, often a country or continent. Consist of hosts and communication subnets. In most WANs, the subnet consists of two distinct components: transmission lines and switching elements. When data arrive on an incoming line, the switching element must choose an outgoing line on which to forward them.

Wide Area Networks The hosts and subnet are owned and operated by different people. The routers (one of the switching elements) will usually connect different kinds of networking technology. What is connected to the subnet? This could be individual computers, as was the case for connecting to LANs, or it could be entire LANs.

Wide Area Networks Relation between hosts on LANs and the subnet.

Wide Area Networks A stream of packets from sender to receiver.

Heterogeneous Networks A combination of LANs and WANs produces heterogeneous network.

The Internet

The Internet People connected to one network often want to communicate with people attached to a different one. A collection of interconnected networks is called an internetwork or internet. ISP (Internet Service Providers) : The Internet ( as an example of internet) uses ISP networks to connect enterprise networks, home networks, and many other networks.

The Internet NAP (network access points): complex switching stations (normally run by a third party) which connects different national ISPs. Peering Points: private switching stations which connects ISPs one to another.

The END Behrouz A. Forouzan” Data communications and Networking