Network interfaces A network interface is a device that connects a client computer, server, printer or other component to your network. Most often, a network interface consists of a small electronic circuit board that is inserted into a slot inside a computer or printer. Alternatively, some computers, printers, or other devices include network interfaces as part of their main circuit boards (motherboards). In either case, the network interface provides two important services—it connects your computer physically to your network, and it converts information on your computer to and from electrical signals for your network
Hubs On 10BaseT and 100BaseTX Ethernet networks larger than two computers, each computer or printer (or other networked device) is connected to a hub. The hub is a small box that gathers the signals from each individual device, optionally amplifies each signal, and then sends the signal out to all other connected devices. Amplification helps to ensure that devices on the network receive reliable information. You can think of an Ethernet hub like the hub of a wheel, at the center of the spokes that connect each individual computer or printer. Hubs are also called concentrators or repeaters. Hubs come in various sizes, the most common being 12-port or 24- port (meaning they can connect to 12 or 24 computers/printers/hubs).
Switches Like a hub, an Ethernet switch is a device that gathers the signals from devices that are connected to it, and then regenerates a new copy of each signal. You can see a picture of a switch at: http://www.asante.com/products/p_sw6.html .
Like a hub, a switch is a device that connects individual devices on an Ethernet network so that they can communicate with one another. But a switch also has an additional capability; it momentarily connects the sending and receiving devices so that they can use the entire bandwidth of the network without interference. If you use switches properly, they can improve the performance of your network by reducing network interference. Switches have two benefits: (1) they provide each pair of communicating devices with a fast connection; and (2) they segregate the communication so that it does not enter other portions of the network. (Hubs, in contrast, broadcast all data on the network to every other device on the network.)
Bridges A bridge is a device that connects two or more local area networks, or two or more segments of the same network. For example, suppose that your network includes both 10BaseT Ethernet and LocalTalk connections. You can use a bridge to connect these two networks so that they can share information with each other. In addition to connecting networks, bridges perform an additional, important function. They filter information so that network traffic intended for one portion of the network does not congest the rest of the network. (You may remember from the previous section that switches also perform
Routers Like bridges, routers are devices whose primary purpose is to connect two or more networks and to filter network signals so that only desired information travels between them. For example, routers are often used to regulate the flow of information between school networks and the Internet. However, routers can inspect a good deal more information than bridges, and they therefore can regulate network traffic more precisely. They also have another important capability: they are aware of many possible paths across the network and can choose the best one for each data packet to travel. Routers operate primarily by examining incoming data for its network routing and transport information—for example, information carried within the TCP/IP, IPX/SPX, or AppleTalk portions of the network signal. This information includes the source and destination network routing addresses. (Remember that every client, server, and peripheral on the network maintains multiple addresses, including both a data link and network routing addresses. The two addresses are used for different purposes. Among other things, the network routing address provides information on which routers base traffic management decisions.) However, most routers also include the same functionality as bridges. That is, they can inspect the data link level portions of the network signals for such information as the Ethernet or LocalTalk destination address.
Firewalls and proxy servers A firewall is a device that prevents unauthorized electronic access to your network. The term firewall is generic, and includes many different kinds of protective hardware and software devices. Routers, discussed in the previous section, comprise one kind of firewall. A different kind of firewall might be created by installing software on a network server that is dedicated to the task of monitoring network activity. Yet another firewall consists of a standalone box (that is, a computer with no keyboard or monitor) which watches all the traffic on your network. All firewalls have one thing in common: they guard your network, examining information inside every network packet. Based on a list of restrictions which you provide, the firewall allows or disables each packet from traveling any further.
Proxy servers. Proxy servers (also called application-level gateways) operate by examining incoming or outgoing packets not only for their source or destination addresses but also for information carried within the data area (as opposed to the address area) of each network packet. The data area contains information written by the application program that created the packet— for example, your Web browser, FTP, or TELNET program. Because the proxy server knows how to examine this application-specific portion of the packet, you can permit or restrict the behavior of individual programs. For example, you can configure your proxy server to allow Web browsing but to deny requests from FTP programs such as Fetch or WS_FTP. Alternatively, you can configure your proxy to permit FTP requests, but only if they read (not write) information. As a third example, proxies can deny Web browsers access to unauthorized Web sites.
Local area network information for schools:
• A Guide to Networking a K-12 School District http://www.ncsa.uiuc.edu/edu/nie/overview/handbook/handbook.html
• Smart Valley Technical Guidebook for Schools http://www.svi.org/netday/info/guidebook.html
• The Virginia Department of Education’s K-12 Technology Handbook (especially the link to The Technical Side of Networking): http://www.pen.k12.va.us/go/techbook/toc.shtml Network primers from manufacturers:
• Tips for education networks from Asante: http://www.asante.com/solutions/s_edu_c1.html
• The Educator's Guide from Asante: http://www.asante.com/solutions/pdf/edu_guide.pdf • Networking: A Primer from Bay Networks: http://www.baynetworks.com/products/Papers/wp-primer.html
• Network Essentials for Small Businesses from Cisco: http://www.cisco.com/warp/public/779/smbiz/netguide/index.html Advanced technical information:
• Network Computing magazine (series on networking technologies): http://www.networkcomputing.com/netdesign/series.htm
• Network Magazine (white papers on network technologies) http://www.networkmagazine.com/
• techguide.com (white papers on communications and internet technologies) http://www.techguide.com/
What is Network?
• A network consists of two or more computers that are linked in order to share resources (such as printers and CDs), exchange files, or allow electronic communications.
• The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams. Different Types of Networks
• Depending upon the geographical area covered by a network, it is classified as: – Local Area Network (LAN) – Metropolitan Area Network (MAN) – Wide Area Network (WAN) – Personal Area Network (PAN)
• A LAN is a network that is used for communicating among computer devices, usually within an office building or home.
• LAN’s enable the sharing of resources such as files or hardware devices that may be needed by multiple users
• Is limited in size, typically spanning a few hundred meters, and no more than a mile • Is fast, with speeds from 10 Mbps to 10 Gbps
• Requires little wiring, typically a single cable connecting to each device
• Has lower cost compared to MAN’s or WAN’s Local Area Network (LAN) Local Area Network (LAN) •
LAN’s can be either wired or wireless. Twisted pair, coax or fibre optic cable can be used in wired LAN’s.
• Every LAN uses a protocol – a set of rules that governs how packets are configured and transmitted.
• Nodes in a LAN are linked together with a certain topology. These topologies include: – Bus – Ring – Star
• LANs are capable of very high transmission rates (100s Mb/s to G b/s). Local Area Network (LAN) Advantages of LAN
• Speed •
• Resource Sharing Disadvantages of LAN
• Expensive To Install •
Requires Administrative Time
• File Server May Fail
• Cables May Break Metropolitan Area Network (MAN)
• A metropolitan area network (MAN) is a large computer network that usually spans a city or a large campus.
• A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities.
• A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. Metropolitan Area Network (MAN)
• A MAN often acts as a high speed network to allow sharing of regional resources.
• A MAN typically covers an area of between 5 and 50 km diameter.
• Examples of MAN: Telephone company network that provides a high speed DSL to customers and cable TV network. Metropolitan Area Network (MAN) Wide Area Network (WAN)
• WAN covers a large geographic area such as country, continent or even whole of the world.
•A WAN is two or more LANs connected together. The LANs can be many miles apart.
• To cover great distances, WANs may transmit data over leased high-speed phone lines or wireless links such as satellites. Wide Area Network (WAN)
• Multiple LANs can be connected together using devices such as bridges, routers, or gateways, which enable them to share data.
• The world's most popular WAN is the Internet. Wide Area Network (WAN) Personal Area Network (PAN)
• A PAN is a network that is used for communicating among computers and computer devices (including telephones) in close proximity of around a few meters within a room
• It can be used for communicating between the devices themselves, or for connecting to a larger network such as the internet.
• PAN’s can be wired or wireless Personal Area Network (PAN)
• A personal area network (PAN) is a computer network used for communication among computer devices, including telephones and personal digital assistants, in proximity to an individual's body.
• The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. Personal Area Network (PAN)