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Definition of a Network  A network is nothing more than two or more computers connected by a cable or by a wireless radio connection so that they can exchange information.  Of course, computers can exchange information in ways other than networks. Like you copy a fi...

Definition of a Network  A network is nothing more than two or more computers connected by a cable or by a wireless radio connection so that they can exchange information.  Of course, computers can exchange information in ways other than networks. Like you copy a file to a flash drive or other portable storage device and then walk the data over to someone else’s computer. However, connecting computers with cables was cheaper and faster.  On the network: Every computer connected to the network is said to be a node. 1 Definition of a Network 2  Benefits of a Network  Sharing files  Networks enable you to share information with other computers on the network.  The data travels to your receiver's computer over the network cable and not on a CD or DVD or flash drive.  Sharing resources  You can set up certain computer resources — such as hard drives or printers — so that all computers on the network can access them.  For example, the laser printer attached to Ward’s computer in the last Figure is a shared resource, which means that anyone on the network can use it. Without the network, June, Wally, and the Beaver would have to buy their own laser printers.  You can share other resources, too, such as an Internet connection or hard drives. 3  Benefits of a Network  Sharing programs  Instead of keeping separate copies of programs on each person’s computer, put programs on a drive that everyone shares.  For example, if ten computer users all use a particular program, you can purchase and install ten copies of the program, one for each computer. Or you can purchase a ten-user license for the program and then install just one copy of the program on a shared drive. Each of the ten users can then access the program from the shared hard drive.  Is it ok to purchase a single user copy of a program and then putting it on a shared network drive?  User Communications.  Cost Saving and increasing productivity. 4  What is the Internet?  The Internet is a computer network that interconnects hundreds of millions of computing devices throughout the world.  ُُThe Internet is a network of networks. It consists of hundreds of thousands of separate computer networks, all interlinked, so that a user on any of those networks can reach out and potentially touch a user on any of the other networks. This network of networks connects more than a billion computers to each other.  Not too long ago, these computing devices were primarily traditional desktop PCs, Linux workstations, and servers that store and transmit information such as Web pages and e-mail messages. 5  Internet Services  But we can also describe the Internet from an entirely different angle— namely, as an infrastructure that provides services to applications.  These applications include electronic mail, Web surfing, social networks, instant messaging, Voiceover- IP (VoIP), video streaming, distributed games, peer-to-peer (P2P) file sharing, television over the Internet, remote login, and much, much more. 6  Protocols  Establishing communication between network devices required more than a length of cabling; a method or a set of rules was needed to establish how systems would communicate. Protocols provide that method.  A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event.  It would be nice if a single protocol facilitated communication between all devices, but this is not the case. You can use a number of protocols on a network, each of which has its own features, advantages, and disadvantages. Networking Fundamentals 7 ASHWAG GASHGARI  Protocols  Connection-oriented Vs. Connectionless protocols.  Connection-oriented communication, data delivery is guaranteed. The sending device resends any packet that the destination system does not receive. Communication between the sending and receiving devices continues until the transmission has been verified.  Connectionless protocols such as User Datagram Protocol (UDP) offer only a best-effort delivery mechanism. Basically, the information is just sent; there is no confirmation that the data has been received. If an error occurs in the transmission, there is no mechanism to resend the data, so transmissions made with connectionless protocols are not guaranteed. Networking Fundamentals 8 ASHWAG GASHGARI  Protocols  Internet Protocol (IP) is a network layer protocol responsible for delivering packets to network devices. The IP protocol uses logical IP addresses to refer to individual devices rather than physical (MAC) addresses.  IP also performs fragmentation and addressing. ► Transmission Control Protocol (TCP) is a connection-oriented transport layer protocol. Being connection-oriented means that TCP establishes a mutually acknowledged session between two hosts before communication takes place. ► TCP provides reliability to IP communications. Specifically, TCP adds features such as flow control, sequencing, and error detection and correction. Networking Fundamentals 9 ASHWAG GASHGARI  Protocols ► User Datagram Protocol (UDP) is a transport protocol, but the big difference is that UDP does not guarantee delivery like TCP does. In a sense, UDP is a “fire- and-forget” protocol; it assumes that the data sent will reach its destination intact. The checking of whether data is delivered is left to upper-layer protocols. UDP operates at the transport layer of the OSI model. ► Unlike TCP, with UDP no session is established between the sending and receiving hosts, which is why UDP is called a connectionless protocol.  File Transfer Protocol (FTP) provides for the uploading and downloading of files from a remote host running FTP server software. As well as uploading and downloading files, FTP enables you to view the contents of folders on an FTP server and rename and delete files and directories if you have the necessary permissions. Networking Fundamentals 10 ASHWAG GASHGARI  Protocols ► Simple Mail Transfer Protocol (SMTP) is a protocol that defines how mail messages are sent between hosts. ► Post Office Protocol(POP) V 3/ Internet Access Protocol V4 Both of them are mechanisms for downloading, or pulling, email from a server. ► They are necessary because although the mail is transported around the network via SMTP, users cannot always immediately read it, so it must be stored in a central location. From this location, it needs to be downloaded or retrieved, which is what POP3 and IMAP4 enable you to do. Networking Fundamentals 11 ASHWAG GASHGARI  Protocols ► Hypertext Transfer Protocol (Http)is the protocol that enables text, graphics, multimedia, and other material to be downloaded from an HTTP server. ► HTTP defines what actions can be requested by clients and how servers should answer those requests. ► In a practical implementation, HTTP clients (that is, web browsers) make requests on port 80 in an HTTP format to servers running HTTP server applications (that is, web servers). Files created in a special language such as Hypertext Markup Language (HTML) are returned to the client, and the connection is closed. ► Hypertext Transfer Protocol Secure (Https) : it is a secure protocol which uses a system known as Secure Sockets Layer (SSL), which encrypts the information sent between the client and host. ► HTTP requests are sent in clear text. For some applications, such as e-commerce, this method to exchange information is unsuitable—a more secure method is needed. Which is HTTPs. Networking Fundamentals ASHWAG GASHGARI 12  Protocols ► Telnet is a virtual terminal protocol. It enables sessions to be opened on a remote host, and then commands can be executed on that remote host. ► Secure Shell is a secure alternative to Telnet. SSH provides security by encrypting data as it travels between systems. This makes it difficult for hackers using packet sniffers and other traffic-detection systems. ► It also provides more robust authentication systems than Telnet. ► Internet Control Message Protocol (ICMP) is a protocol that works with the IP layer to provide error checking and reporting functionality. In effect, ICMP is a tool that IP uses in its quest to provide best-effort delivery. ► Dynamic Host Configuration Protocol (DHCP) A protocol that provides dynamic IP addressing to DHCP-enabled workstations on the network. Networking Fundamentals 13 ASHWAG GASHGARI  Types of Network Topologies  The term network topology refers to the shape of how the computers and other network components are connected to each other. A topology refers to a network’s physical and logical layout.  A network’s physical topology refers to the actual layout of the computer cables and other network devices.  A network’s logical topology refers to the way in which the network appears to the devices that use it.  There are several different types of network topologies, each with advantages and disadvantages. 14  Types of Network Topologies  Bus Topology  A bus topology uses a trunk or backbone to connect all the computers on the network in a line, The key to understanding how a bus topology works is to think of the entire network as a single cable, with each node “tapping” into the cable so it can listen in on the packets being sent over that cable. To avoid signal reflection, a physical bus topology requires that each end of the physical bus be terminated , with one end “Terminator” also being grounded.  It is very old technology and not used that much.  Note that a hub or switch is not needed in this installation. 15 Types of Network Topologies Bus 16 Types of Network Topologies Bus 17  Types of Network Topologies  Ring Topology  It is old and rarely used today.  In a ring topology, each computer is connected to each other in shape of a ring. Packets are sent around the circle from computer to computer. Each computer looks at each packet to decide whether the packet was intended for it. If not, the packet is passed on to the next computer in the ring.  Note that a hub or switch is not needed in this installation either.  In a true ring topology, if a single computer or section of cable fails, the signal is interrupted. The entire network becomes inaccessible. Network disruption can also occur when computers are added to or removed from the network, making it an impractical network design in environments where the network changes often. 18 Types of Network Topologies Ring 19 Types of Network Topologies Ring 20  Types of Network Topologies  Star Topology  In the star topology, all computers and other network devices connect to a central device called a hub or switch. Each connected device requires a single cable to be connected to the hub or switch, creating a point-to- point connection between the device and the hub or switch.  Using a separate cable to connect to the hub or switch allows the network to be expanded without disruption. A break in any single cable does not cause the entire network to fail. 21 Types of Network Topologies Star 22 Types of Network Topologies Star 23  Types of Network Topologies  Mesh Topology  It has a unique network design in which each computer on the network connects to every other, creating a point-to-point connection between every device on the network. The purpose of the mesh design is to provide a high level of redundancy. If one network cable fails, the data always has an alternative path to get to its destination; each node can act as a relay.  The wiring for a mesh network can be complicated. Furthermore, the cabling costs associated with the mesh topology can be high, and troubleshooting a failed cable can be tricky. Because of this, the mesh topology is not the first choice for many wired networks but is more popular with servers/routers. 24