| A network is a group of computers, printers, and | | | | method of accessing the physical network allows |
| other devices that are connected together with | | | | multiple protocols to peacefully coexist over the |
| cables. The sharing of data and resources. | | | | network media, and allows the builder of a |
| Information travels over the cables, allowing | | | | network to use common hardware for a variety |
| network users to exchange documents & data | | | | of protocols. This concept is known as "protocol |
| with each other, print to the same printers, and | | | | independence," which means that devices that are |
| generally share any hardware or software that is | | | | compatible at the physical and data link layers |
| connected to the network. Each computer, | | | | allow the user to run many different protocols |
| printer, or other peripheral device that is | | | | over the same medium. |
| connected to the network is called a node. | | | | Topologies |
| Networks can have tens, thousands, or even | | | | A network topology is the geometric |
| millions of nodes. | | | | arrangement of nodes and cable links in a LAN, |
| Cabling: | | | | and is used in two general configurations: bus and |
| The two most popular types of network cabling | | | | star. These two topologies define how nodes are |
| are twisted-pair (also known as 10BaseT) and thin | | | | connected to one another. A node is an active |
| coax (also known as 10Base2). 10BaseT cabling | | | | device connected to the network, such as a |
| looks like ordinary telephone wire, except that it | | | | computer or a printer. A node can also be a piece |
| has 8 wires inside instead of 4. Thin coax looks | | | | of networking equipment such as a hub, switch or |
| like the copper coaxial cabling that's often used to | | | | a router. A bus topology consists of nodes linked |
| connect a VCR to a TV set. | | | | together in a series with each node connected to |
| Network Adapter: | | | | a long cable or bus. Many nodes can tap into the |
| A network computer is connected to the | | | | bus and begin communication with all other nodes |
| network cabling with a network interface card, | | | | on that cable segment. A break anywhere in the |
| (also called a "NIC", "nick", or network adapter). | | | | cable will usually cause the entire segment to be |
| Some NICs are installed inside of a computer: the | | | | inoperable until the break is repaired. Examples of |
| PC is opened up and a network card is plugged | | | | bus topology include 10BASE2 and 10BASE5. |
| directly into one of the computer's internal | | | | 10BASE-T Ethernet and Fast Ethernet use a star |
| expansion slots. 286, 386, and many 486 | | | | topology, in which access is controlled by a central |
| computers have 16-bit slots, so a 16-bit NIC is | | | | computer. Generally a computer is located at one |
| needed. Faster computers, like high-speed 486s | | | | end of the segment, and the other end is |
| and Pentiums, , often have 32-bit, or PCI slots. | | | | terminated in central location with a hub. Because |
| These PCs require 32-bit NICs to achieve the | | | | UTP is often run in conjunction with telephone |
| fastest networking speeds possible for | | | | cabling, this central location can be a telephone |
| speed-critical applications like desktop video, | | | | closet or other area where it is convenient to |
| multimedia, publishing, and databases. And if a | | | | connect the UTP segment to a backbone. The |
| computer is going to be used with a Fast | | | | primary advantage of this type of network is |
| Ethernet network, it will need a network adapter | | | | reliability, for if one of these 'point-to-point' |
| that supports 100Mbps data speeds as well. | | | | segments has a break, it will only affect the two |
| Hubs | | | | nodes on that link. Other computer users on the |
| The last piece of the networking puzzle is called a | | | | network continue to operate as if that segment |
| hub. A hub is a box that is used to gather groups | | | | were nonexistent. |
| of PCs together at a central location with | | | | Peer-to-Peer Networks |
| 10BaseT cabling. If you're networking a small | | | | A peer-to-peer network allows two or more PCs |
| group of computers together, you may be able | | | | to pool their resources together. Individual |
| to get by with a hub, some 10BaseT cables, and | | | | resources like disk drives, CD-ROM drives, and |
| a handful of network adapters. Larger networks | | | | even printers are transformed into shared, |
| often use a thin coax "backbone" that connects a | | | | collective resources that are accessible from |
| row of 10BaseT hubs together. Each hub, in turn, | | | | every PC. |
| may connect a handful of computer together | | | | Unlike client-server networks, where network |
| using 10BaseT cabling, which allows you to build | | | | information is stored on a centralized file server |
| networks of tens, hundreds, or thousands of | | | | PC and made available to tens, hundreds, or |
| nodes. Like network cards, hubs are available in | | | | thousands client PCs, the information stored |
| both standard (10Mbps) and Fast Ethernet | | | | across peer-to-peer networks is uniquely |
| (100Mbps) versions. | | | | decentralized. Because peer-to-peer PCs have |
| LANs (Local Area Networks) | | | | their own hard disk drives that are accessible by |
| A network is any collection of independent | | | | all computers, each PC acts as both a client |
| computers that communicate with one another | | | | (information requestor) and a server (information |
| over a shared network medium. LANs are | | | | provider). A peer-to-peer network can be built |
| networks usually confined to a geographic area, | | | | with either 10BaseT cabling and a hub or with a |
| such as a single building or a college campus. LANs | | | | thin coax backbone. 10BaseT is best for small |
| can be small, linking as few as three computers, | | | | workgroups of 16 or fewer users that don't span |
| but often link hundreds of computers used by | | | | long distances, or for workgroups that have one |
| thousands of people. The development of | | | | or more portable computers that may be |
| standard networking protocols and media has | | | | disconnected from the network from time to |
| resulted in worldwide proliferation of LANs | | | | time. |
| throughout business and educational organizations. | | | | After the networking hardware has been installed, |
| WANs (Wide Area Networks) | | | | a peer-to-peer network software package must |
| Often a network is located in multiple physical | | | | be installed onto all of the PCs. Such a package |
| places. Wide area networking combines multiple | | | | allows information to be transferred back and |
| LANs that are geographically separate. This is | | | | forth between the PCs, hard disks, and other |
| accomplished by connecting the different LANs | | | | devices when users request it. Popular |
| using services such as dedicated leased phone | | | | peer-to-peer NOS software includes Most NOSs |
| lines, dial-up phone lines (both synchronous and | | | | allow each peer-to-peer user to determine which |
| asynchronous), satellite links, and data packet | | | | resources will be available for use by other users. |
| carrier services. Wide area networking can be as | | | | Specific hard & floppy disk drives, directories or |
| simple as a modem and remote access server | | | | files, printers, and other resources can be |
| for employees to dial into, or it can be as | | | | attached or detached from the network via |
| complex as hundreds of branch offices globally | | | | software. When one user's disk has been |
| linked using special routing protocols and filters to | | | | configured so that it is "sharable", it will usually |
| minimize the expense of sending data sent over | | | | appear as a new drive to the other users. In |
| vast distances. | | | | other words, if user A has an A and C drive on |
| Internet | | | | his computer, and user B configures his entire C |
| The Internet is a system of linked networks that | | | | drive as sharable, user A will suddenly have an A, |
| are worldwide in scope and facilitate data | | | | C, and D drive (user A's D drive is actually user |
| communication services such as remote login, file | | | | B's C drive). Directories work in a similar fashion. If |
| transfer, electronic mail, the World Wide Web and | | | | user A has an A & C drive, and user B configures |
| newsgroups. With the meteoric rise in demand for | | | | his "C:WINDOWS" and "C:DOS" directories as |
| connectivity, the Internet has become a | | | | sharable, user A may suddenly have an A, C, D, |
| communications highway for millions of users. The | | | | and E drive (user A's D is user B's C:WINDOWS, |
| Internet was initially restricted to military and | | | | and E is user B's C:DOS). Did you get all of that? |
| academic institutions, but now it is a full-fledged | | | | Because drives can be easily shared between |
| conduit for any and all forms of information and | | | | peer-to-peer PCs, applications only need to be |
| commerce. Internet websites now provide | | | | installed on one computer--not two or three. If |
| personal, educational, political and economic | | | | users have one copy of Microsoft Word, for |
| resources to every corner of the planet. | | | | example, it can be installed on user A's |
| Intranet | | | | computer--and still used by user B. |
| With the advancements made in browser-based | | | | The advantages of peer-to-peer over |
| software for the Internet, many private | | | | client-server NOSs include: � No need for |
| organizations are implementing intranets. An | | | | a network administrator � Network is |
| intranet is a private network utilizing Internet-type | | | | fast/inexpensive to setup & maintain � |
| tools, but available only within that organization. | | | | Each PC can make backup copies of its data to |
| For large organizations, an intranet provides an | | | | other PCs for security. By far the easiest type of |
| easy access mode to corporate information for | | | | network to build, peer-to-peer is perfect for both |
| employees. | | | | home and office use. |
| Ethernet | | | | Client-Server Networks |
| Ethernet is the most popular physical layer LAN | | | | In a client-server environment like Windows NT or |
| technology in use today. Other LAN types include | | | | Novell NetWare, files are stored on a centralized, |
| Token Ring, Fast Ethernet, Fiber Distributed Data | | | | high speed file server PC that is made available to |
| Interface (FDDI), Asynchronous Transfer Mode | | | | client PCs. Network access speeds are usually |
| (ATM) and LocalTalk. Ethernet is popular because | | | | faster than those found on peer-to-peer |
| it strikes a good balance between speed, cost and | | | | networks, which is reasonable given the vast |
| ease of installation. These benefits, combined with | | | | numbers of clients that this architecture can |
| wide acceptance in the computer marketplace | | | | support. Nearly all network services like printing |
| and the ability to support virtually all popular | | | | and electronic mail are routed through the file |
| network protocols, make Ethernet an ideal | | | | server, which allows networking tasks to be |
| networking technology for most computer users | | | | tracked. Inefficient network segments can be |
| today. The Institute for Electrical and Electronic | | | | reworked to make them faster, and users' |
| Engineers (IEEE) defines the Ethernet standard as | | | | activities can be closely monitored. Public data and |
| IEEE Standard 802.3. This standard defines rules | | | | applications are stored on the file server, where |
| for configuring an Ethernet network as well as | | | | they are run from client PCs' locations, which |
| specifying how elements in an Ethernet network | | | | makes upgrading software a simple task--network |
| interact with one another. By adhering to the IEEE | | | | administrators can simply upgrade the applications |
| standard, network equipment and network | | | | stored on the file server, rather than having to |
| protocols can communicate efficiently. | | | | physically upgrade each client PC. |
| Protocols | | | | In the client-server diagram below, the client PCs |
| Network protocols are standards that allow | | | | are shown to be separate and subordinate to the |
| computers to communicate. A protocol defines | | | | file server. The clients' primary applications and |
| how computers identify one another on a | | | | files are stored in a common location. File servers |
| network, the form that the data should take in | | | | are often set up so that each user on the |
| transit, and how this information is processed | | | | network has access to his or her "own" directory, |
| once it reaches its final destination. Protocols also | | | | along with a range of "public" directories where |
| define procedures for handling lost or damaged | | | | applications are stored. If the two clients below |
| transmissions or "packets." TCP/IP (for UNIX, | | | | want to communicate with each other, they must |
| Windows NT, Windows 95 and other platforms), | | | | go through the file server to do it. A message |
| IPX (for Novell NetWare), DECnet (for networking | | | | from one client to another is first sent to the file |
| Digital Equipment Corp. computers), AppleTalk (for | | | | server, where it is then routed to its destination. |
| Macintosh computers), and NetBIOS/NetBEUI (for | | | | With tens or hundreds of client PCs, a file server |
| LAN Manager and Windows NT networks) are the | | | | is the only way to manage the often complex |
| main types of network protocols in use today. | | | | and simultaneous operations that large networks |
| Although each network protocol is different, they | | | | require. |
| all share the same physical cabling. This common | | | | |