Computer Networks

1. Computer Networks • A computer network is two or more computers connected to one another to share resources. • Networks allow users to access files and programs. • They also let users share printers and other equipment. • Various ways of connecting computers can be accomplished through physical media. • The medium can be any type of telecommunications connector: twisted pair telephone lines, coaxial cable, fiber-optic cable, or a microwave, radios, or infrared system. • Working together, the network media and the computers determine how much data can be sent through the connector.

2. Building Networks • To create a computer network, you need a network interface card, or NIC, in each workstation. • The NIC handles the flow of data to and from the computer in both wired and wireless networks. • The NICs connect to a network cable that, in many systems, connects to a central hub. • Each workstation must be able to work with the network.

3. Building Networks cont. • A network may be small, with just a few computers, or it may be large, with thousands of workstations. • The network functions the same way, no matter how many workstations are connected. • If the network is put together by actual cables, those cables connect to the NIC. • NICs often have a light that blinks green and amber to alert you to activity.

4. Building Networks cont. • Everyone on a network can work together. • Syneregy is the affect a group effort can create. • People working together on a network can accomplish more than people working alone on unconnected computers. • As you use a network, you may open windows and click icons to find files or other resources. • Behind the scenes, the network’s hardware and software are performing many complex tasks.

5. Organizing Users • All of the pieces of equipment connected together must be able to understand one another. • A network is organized into workstations, each with its own name and address. • A workstation is a computer connected to a computer network. • It is often set up with the same operating system, applications, and access to resources as the other computers in the network. • Sometimes network users work at a terminal, which usually includes a keyboard, a monitor, and a mouse.

6. Organizing Users cont. • A terminal can feel as if the computer is local, but it’s not. • Users are actually sharing time on a central computer, with their own work displayed on their terminal’s monitor. • This kind of network is sometimes called a timesharing system. • Terminals can save on the cost of purchasing workstations. • They are also useful in situations with limited need for a workstation, such as a public computer in a library.

7. Components of a Network • In a large network, a workstation is also called a node by the people who take care of the network. • A node is anything connected to the network—a workstation, a printer, a fax, or any other piece of equipment. • Each node is connected to one or more file servers—high speed computers with large hard drives that are used to store large amounts of data. • Each node on the network that has been granted appropriate rights by the network administrator can access the data on the file servers.

8. Components cont. • Collecting and centralizing data on a network file server provides two important benefits: • It gives users access to the most up-to-date data • It eliminates the problem of the same data being duplicated on each user’s computer, which not only wastes storage space, but also increases the likelihood of people using outdated data.

9. Components cont. • All of the nodes and files servers on a network are connected by physical media—the cables or wireless connections that transmit the data on a network. • Many different types of physical media can be used in computer networks.

10. Types of Physical Media

11. Components cont. • You connect a computer to a network cable through a network interface card (NIC). • Most NICs are designed to connect to a particular type of cable, although some work with more than one type. • The NIC is responsible for controlling the flow of data between the computer’s RAM and the network cable.

12. Network Topology • Network topology is the physical arrangement of computers on a network. • The topology of a network determines how the flow of data is handled when two computers try to transmit data across the network at the same time. • The three most common LAN topologies are bus topology, start topology, and ring topology.

13. Network Topology cont. • The simplest topology is a bus topology, in which a single cable runs the length of the network. • Each node (computer or peripheral device) connects to this one cable. • This is an inexpensive network arrangement, but a break in the cable may cause the entire network to “crash”. • This type of network employs special data management techniques to handle the flow of data when two computers transmit data simultaneously.

14. Network Topology cont. • With a star topology, each node connects to a hub through which data travels to the file server and/or other computers. • Star topologies use more cable than a bus topology, but a single broken cable will not “crash” the network. • A star topology also employs special data management techniques to handle the flow of data when two computers transmit data simultaneously.

15. Network Topology cont. • In a ring topology, each node connects to the next in a circular arrangement. • A special set of data, called a token, travels from one computer to the next around the circle. • If a computer needs to send or receive data, it must wait until the token gets to it. • This configuration eliminates the problem of two computers transmitting data at the same time. • However, a single break in the ring can ruin the network.

16. Network Protocols • Once a network is created, the computers and other connected equipment can communicate with one another. • However, there is more involved than just hooking up the network’s physical components. • The communication on a network is called network traffic. • Network traffic is the electronic pulses of information sent by the network cards to carry data through the network wires to its destination.

17. Network Protocols cont. • Computers communicate with languages called protocols. • A protocol sets the rules for how data is formatted and transmitted. • It is the language computers use to “speak” to one another on a network. • There are many different protocols available to use on networks. • For computers to speak with one another, they must use the same protocol. • A network’s protocol is determined by the network’s purpose.

18. Kinds of Protocols • There are two protocol categories: • open • proprietary • An open protocol is available for anyone to use. • The most common open protocol is the Transmission Control Protocol/Internet Protocol. (TCP/IP)

19. Kinds of Protocols cont. • A proprietary protocol, is not open to everyone. • Only people who buy certain equipment, services, or computers can use it. • Some personal digital assistants, digital cameras, and even dial-up Internet services use proprietary protocols. • Open protocols are more common.

20. Kinds of Protocols cont. • The protocols networks use to communicate are often called a protocol suite. • A protocol suite is the stack, or collection, of individual protocols that determines how the network operates. • For example, TCP/IP is not just one network language, but many smaller ones. • Each small protocol in this suite has a specific job to do in a specific order.

21. Kinds of Protocols cont. • The data is transmitted through layers from a sending computer before it actually reaches the physical media. • On the other end it travels through layers from the physical media before it can reach the receiving computer. • Each layer performs a specific function and has its own set of protocols that define exactly how data must pass from one layer to the next.

22. User R e c e I v I n g User S e n d I n g Protocol Layer Physical Media Physical Media

23. Benefits of Networks • Computer networks provide hardware benefits because they let people share hardware. • Networks also provide software benefits because they let people share programs and data. • Physical media connect the network and protocols make sure that the links among hardware, software, and people actually work.

24. Local Area Networks • A LAN is a network in which all the workstations and other equipment are in the same geographical area. • LANs connect computers within a home, an office, or a building. • They can also connect computers in separate buildings that are physically close together. • A LAN can have just a few or several hundred users. • There are three ways to share information: sharing files, using collaborative software, and sharing peripherals.

25. LANs cont. • Sharing Files—through a computer’s operating system people connected to a LAN can participate in file sharing. • File sharing is making files available to more than one user on the network. • Using Collaborative Software—collaborative software enables the network to help people work together more closely. • With collaborative software, users can share calendars, work on a document together, or even hold meetings through the network. • Collaborative software is also called groupware.

26. LANS cont. • Sharing Peripherals—In addition to sharing files and software, a LAN allows users to share peripherals, such as printers, fax machines, or any other equipment. • LANs also offer a number of benefits. • lowering costs • sharing applications • building information resources • connecting people

27. LANs cont. • Lowering Costs—If connected to a network, many computers can share expensive equipment, such as printers, scanners, fax machines, etc. • Sharing Applications—Networks can make use of network versions of software applications. Workers at several workstations can use the applications at the same time. • Building Information Resources—Information can be added to files from any workstation. • Connecting People—People can work together closely. Even if their offices are on different floors, they can easily consult with one another and work on the same files.

28. Organizing LANs • LANs can be set up in one of two ways. • Peer-to-Peer Network • Client/Server Network • In a peer-to-peer network (P2PN), all the workstations are equal and connected to each other through a network cable or a wireless signal. • This network is usually made up of two to ten computers. • The network cable can be connected to a central device called a hub.

29. Organizing LANs cont. • The hub handles the flow of traffic from computer to computer. • A P2PN allows workstations to share files and to access files on other workstations. • Users are responsible for securing their own resources and granting access to other users. • A P2PN is an easy network to create, since all of the workstations are equals. • The operating system of each computer typically has built-in file-sharing abilities.

30. Organizing LANs cont. • A peer-to-peer network is ideal for small offices and homes. • In a large business peer-to-peer networking has some drawbacks: • Security problems can arise. • Data can be hard to back up. • With many users, file sharing can become difficult. • Finding shared files can be difficult. • Managing resources can be complicated. • These problems arise because resources are scattered across many computers. • If one computer fails or is turned off, its resources are no longer available to the network.

31. Organizing LANs cont. • Large businesses usually use a client/server network. • With this system, one powerful computer provides information and management services to the workstation computers, the clients. • In a client/server network, each workstation is a client connected to a central computer called a file server or just server. • A client/server network centralizes all network resources and controls what users can do with files. • Accessing and backing up files is faster and easier than using a peer-to-peer network or no network at all.

32. Organizing LANs cont. • A client/server network is managed and secured by a network operating system, or NOS. • It manages and secures the entire network. • It controls access, permissions, and all aspects of network use. • Only those who provide a username and a password can use the network. • It is far more secure than a P2PN.

33. Organizing LANs cont. • For a large office, file servers are better than peer-to-peer networks, for several reasons: • They offer a central location for files. • Data is easy to back up and easy to recover. • Servers are faster than workstations. • Servers usually are powered on. • Security is easier to maintain.

34. LAN Standards • All of the various network elements; network interface cards, physical media, protocols and topologies are usually viewed together as a set of LAN standards. • One of the most widely implemented LAN standards is Ethernet. • Ethernet is used with bus and start topologies, twisted-pair or fiber optic cables, and an Ethernet-compatible network interface card (NIC). • Ethernet can transmit data at 10 Mbps (10 million bits per second). • A newer standard called Fast Ethernet can support data transfer rates of up to 100 Mbps (1oo million bits per second).

35. LAN Standards cont. • The second most widely used LAN standard is the Token Ring. • This standard uses a ring topology and transfers data at either 4 or 16 Mbps. • The simplest LAN standard is LocalTalk, the system that Macintosh uses. • Ordinary phone cables are arranged in a bus topology. • However, the data transfer rate on a LocalTalk network is only 230 Kbps, or 230 thousand bits per second—which is much slower than the transfer rate on an Ethernet or Token Ring network.

36. Working with Intranets • A growing number of organizations are setting up their LANs—and sometimes their wider networks—as intranets. • An intranet is a private network that uses the same TCP/IP protocol as the Internet. • Firewall software prevents outsiders from accessing the intranet. • Intranets offer the following benefits: • ease and range of uses • cost and time savings

37. Intranets cont. • An intranet looks and functions like the Internet. • Most people have no trouble learning to use it. • Companies use an intranet to distribute all sorts of internal documents: • employee lists • training materials • standard forms • Other intranets allow employees to connect to company databases or hold electronic conferences. • Some companies use their intranet as an employee gateway to the Internet. • Some allow customers or other outsiders to access part of their intranet through the Web. • Intranets generally cost less to set up than other systems. • They also save paper and printing costs.

38. Wide Area Networks • A wide area network connects computers and other resources that are miles or even continents apart. • A business with offices in many places can use a WAN to link its LANs in different cities. • Users from any of the locations can, with the proper permissions, access the network. • Each user can access files, printers, and other resources as if they were local. • Once a WAN is created, users may not even realize the files they are sharing are remote.

39. WANs cont. • How is a WAN Controlled? Like a client/server LAN, a WAN is controlled by a network operating system. • A NOS is helpful on a WAN because there are so many users and resources to manage. • The NOS also helps network administrators secure the resources throughout the network.

40. WANs cont. • Most networks use packet-switching technology. • The sending computer divides information into tiny segments called packets. Each packet is marked with a delivery address, so packet transfers are quick and accurate. • When you transfer a file, send an e-mail, or even browse a Web site, you’re sending and receiving packets. • Some WANs use circuit-switching technology to transmit messages. • Circuit-switching happens on a real, end-to-end connection between the sending computer and the receiving computer, which make up the circuit.

41. WANs cont. • There’s no delay on circuit-switching networks, so they are ideal for sending voice messages and for teleconferencing. • A telephone network uses circuit-switching. • Routers are network devices or programs that choose the best pathway for each packet. • If there is congestion, or too much traffic, on the network, the router can delay some of the packets. • The receiving computer puts the packets back together in the right order.

42. WANs cont. • A WAN needs to connect the resources together physically, and it needs to provide a way to access the connection. • Backbones are the high-speed lines, wired or wireless, that carry data through a network. • Long-distance telecommunications companies carry some of the data traffic. • Government and privately owned lines connect other WANs. • Throughout the world, WAN providers offer local connections for users. • This connection is called a point of presence (POP). • The most common example of a POP is an Internet connection.

43. WANs cont. • How do organizations get to the POP? • ISDN and DSL • leased lines • T1 lines • permanent virtual circuits • ISDN and DSL—these technologies use ordinary telephone lines to attach to the backbone. • Special adapters or modems provide ways to deal with digital data. • Leased lines—some companies rent a private end-to-end connection, called a leased line, from a telecommunications company. • Leased lines allow data to be sent at 56,000 bps.

44. WANs cont. • T1 lines—larger companies and many school districts lease T1 lines. • T1 lines can be either copper or fiber optic, and they allow data to be sent at more than 1.5 million bps. • Permanent Virtual Circuits—a permanent virtual circuit (PVC) allows multiple users’ data to travel the line at once. • They are cheaper than private lines. • Most PVCs use a technology called frame relay. • Frame relay allows voice, data, and video to travel on the same line and at the same time.

45. Types of WANs • A public data network (PDN) allows many different companies to set up their own networks. • Telecommunications companies own the PDNs and charge fees for the use of the network. • Private Data Network—some companies set up a private data network that cannot be accessed by outsiders. • Having a private data network costs more than using a public data network. • A virtual private network (VPN) is a private network set up through a public network. • VPN users connect to an Internet service provider (ISP) to access the network.

46. Comparing WANs and the Internet • A WAN and the Internet are very similar. • The Internet is, in fact, a WAN, though it is not usually called that. • There are three key differences between the Internet and other WANs: • kind of access • degree of security • types of information

47. WANS and the Internet cont. • The Internet is public, while WANs are typically private. • When you connect to the Internet, you are invited as a member of the public to view published information. • Information on a WAN is set up for the internal use of the organization that owns it.

48. WANs and the Internet cont. • While the Internet is becoming more secure, it is still not as secure as a private WAN connection. • As data travels through the Internet, snoops and eavesdroppers on the public networks through which the data moves sometimes try to access it. • A private WAN is more secure because it is more likely that only the organization that owns it has access to it.

49. WANs and the Internet cont. • On the Internet, information is transmitted in the form of Web pages and other types of files. • A WAN is used for more than just browsing Web pages. • It provides access to network resources, such as printers, files servers, and databases.