Network hardware


Published on

  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Network hardware

  1. 1. 3 - 1 L E S S O N 3 Network hardware Lesson objectives To understand the hardware components of a computer network, you will: a Become familiar with the components of a simple network. b Become familiar with transmission media and connectors. c Become familiar with interface devices. d Become familiar with internetworking devices.
  2. 2. Understanding Network Fundamentals (Second Edition) 3 - 2 aa Network hardware components Components of a generic network Concepts > A computer network is made up of many different components, but the general operation is basically the same. The user must enter the data, the computer must process the data, and output the result to a user. We will start by looking at a simple network and build on to it to see how data is transmitted and stored on a network. A basic network client server sever client transmission media Figure 3-1: A simple network. In the client-server environment there are essentially three parts: the client, the transmission media, and the server. A client is what is used to run programs, enter data, and make requests for network services. Clients are also called workstations. The client station usually contains a processor, memory, and storage capacity. A client can also be another network device such as a server. Computers that perform a service on behalf of other network devices are called servers. Servers are used to distribute the load of processing or management of the network. The use of servers can be considered distributed computing. Types of servers There are several types of servers. Each type can increase efficiency and provides services to multiple clients. For example, a computer that provides other network nodes with access to network storage devices is called a file server. Print servers provide other network nodes access to a printer. Other types of servers include: message servers, application servers, fax servers, SQL servers, and database servers. In this type of distributed computing, clients send requests for a service to the servers and the servers provide the service. For example, a user wants data from a database stored on a network server. The user enters a request for the data by using some type of front-end software interface. The request is sent through a transmission media to the server that can fulfill the request. The server locates the data needed and sends a copy of it to the user.
  3. 3. Lesson 3: Network hardware 3 - 3 Type of server Example of services provided File File transfer, security control to the network files, version control of software, backup of data Print Queue print jobs to network printer, provide access to printer for multiple users, faxing Message Electronic mail, object linking, routing delivery Application Network versions of applications, coordination of upgrades Database Database storage and retrieval, divides and optimizes requests and provision of data
  4. 4. Understanding Network Fundamentals (Second Edition) 3 - 4 bb Transmission media Concepts > For computers to communicate, they need to be connected. Data-transmission medium is the channel or conduit through which data are transmitted. Computers can be connected by using many different kinds of data-transmission media. This topic introduces those most commonly used, including twisted-pair cable, coaxial cable, fiber optic cable, and unbounded media. Although many networks use a single transmission medium exclusively, networks increasingly use a combination of different media. You should be aware of the characteristics of each medium when deciding on the best one for your network needs. There are physical limits with each type of media. For example, attenuation, or weakening of a signal over distance, is a factor in many types of cable. The amount of data that can be carried on any particular transmission medium is referred to as bandwidth. Bandwidth is measured in hertz (cycles per second) or bits per second (BPS). Although there are other considerations in a network's performance, the general rule is that greater the bandwidth, the greater the amount of data that can be transmitted. How fast the data moves within the medium is referred to as the data rate and it is also measured in BPS. Do not confuse bandwidth with data rate. One way to think of it is: bandwidth can be compared to the number of lanes on a highway and the data rate is the speed limit for that highway. Large bandwith Slow data rate Small bandwith High data rate Speed limit 45 Speed limit 65 Figure 3-2: Bandwidth versus data rate.
  5. 5. Lesson 3: Network hardware 3 - 5 Comparing media types The data-transmission medium (or media) that a network uses determines many of the characteristics and limitations of the network. Following are some of the things that you should consider when you are comparing transmission media: • Susceptibility to electromagnetic interference (EMI). EMI can come from a variety of sources, including power supplies and transformers, high-voltage equipment such as arc welders, and components of other communications systems such as radio transmitters. EMI can severely hinder data communications. • Security. Not only are many types of data-transmission media susceptible to EMI - many emit EMI as well. This can create a problem in crowded wiring closets, where cables can interfere with each other, and it can also create a security problem. A nearby receiver could pick up electromagnetic signals emanating from a cable. With the proper equipment, those signals could be decoded and interpreted. • Bandwidth, or the transmission capacity of the medium. Typically, bandwidth is measured in BPS. Although there are other considerations in a network's performance, the general rule is: the greater the bandwidth, the greater the amount of data that can be transmitted. For this reason, in casual discussions about network performance, bandwidth refers to the maximum amount of data that can be transferred over a network. • Cost to purchase and maintain. Although the initial cost might be low for certain media, you should also consider other expenses that you will experience over the life of the medium, such as maintenance and upgrade costs. Also, certain products are more durable than others and might hold up to the ravages of time, use, and the environment better than others. • Compatibility with other products in your network. If possible, you should purchase products that adhere to established standards. It is more likely that future networking products will be compatible with standard media than with non-standard media. Bounded media Bounded media transmits signals by sending electricity or light over a cable. Some of the common types of cable are below.
  6. 6. Understanding Network Fundamentals (Second Edition) 3 - 6 Twisted-pair cable Insulation Conductors Adapter for connecting Macintoshes to LocalTalk shielded twisted pair wiring. The IBM Data Connector, used in Token Ring networks, contains connections for two sets of shielded twisted pair wiring. DB connectors are sometimes used with twisted pair cable. Common types are DB-25 which can have up to 25 connections; and DB-9, which can have up to 9. LocalTalk connector RJ-11 connector for twisted or untwisted pair Figure 3-3: Twisted-pair cable. Concepts > Twisted-pair (or TP) cable contains two insulated, copper wires that are twisted around each other to reduce EMI. This type of EMI is also referred to as crosstalk. Most twisted-pair cable is relatively inexpensive. Twisted-pair cable has been used for years in the telephone industry, so the technology and standards for this type of cable are well established. However, many standard telephone cables are not twisted pair and are inadequate for most network applications. Although twisted-pair cable is often unshielded (that is, it is not encased in a sheath of foil or braided wire mesh), some products (such as Apple LocalTalk and IBM) use shielding to increase the cable's immunity to EMI. When a distinction must be made, twisted-pair cable is sometimes called UTP (unshielded twisted pair) or STP (shielded twisted pair). STP has slightly reduced EMI as compared to UTP and is more resistant to outside interference. STP is capable of handling more data with greater speed. Twisted-pair cable is susceptible to eavesdropping, however STP is less susceptible than UTP.
  7. 7. Lesson 3: Network hardware 3 - 7 Coaxial cable Braided-wire shield Conductor Insulation RG-58 coaxial cable with BNC connector Figure 3-4: Coaxial cable. Coaxial cable contains a single, solid or stranded wire inner conductor surrounded by an outer conductor and shield of braided wire mesh or foil. The conductor and the shield are separated from each other by a layer of insulation, and the entire cable is wrapped in another layer of insulating material. Because the conductor and the shield share the same axis, the medium is called coaxial cable, or coax for short. Coaxial cable generally provides better protection from EMI than does twisted-pair cabling, but it is still susceptible to EMI. Some standards are compatible with more than one type of cable. Ethernet, for example, can use thick or thin coaxial cable. The thicker cable, which is sometimes called "thick Ethernet," can reliably carry signals over greater distances than "thin Ethernet." However, thick Ethernet cable is more expensive and more difficult to install than thin Ethernet cable. Fiber optic cable Outer cover Optical fiber Glass casing Optical fiber connector Figure 3-5: Fiber optic cable.
  8. 8. Understanding Network Fundamentals (Second Edition) 3 - 8 Optical fiber transmits signals of light through a very fine strand (single-mode) of plastic or glass (optical fiber), which is encased in a tube that is made of glass called cladding, surrounded by a tough outer sheath. The cladding is designed to reflect light back into the optical fiber. Light "bounces" from side to side as it moves through the optical fiber. In some cases, several optical fibers are grouped in the center (multimode) in a ribbon-cable formation to provide several communication channels within a single component. The size and pureness of the core is related to the amount of light that can be transmitted. The outer sheath provides a protective covering for the optical fiber. Advantages of optical fiber include: • Optical fiber is secure; it is nearly impossible to tap. • It does not produce, and is not affected by, EMI. • It has a high capacity for carrying data. • It is lightweight. • It has very little signal attenuation. • It uses less energy to operate than other media. The disadvantage of fiber optic cable is that it is relatively expensive and more complex to install than other cables. However, the price keeps dropping as this technology becomes more available. Task B-1: Matching the medium with its properties q Objective: To identify the corresponding description of twisted-pair cable, coaxial cable, and fiber optic cable. What you do Comments/Prompts 1. Very secure and unaffected by EMI ________________________________________ 2. Single conductor within a shield of mesh or foil ________________________________________ 3. Inexpensive and well established ________________________________________ Unbounded media Concepts > Unbounded (or unguided) media transmits signals without the benefit of a conduit. Unbounded media might transmit data through the open air, water, or a vacuum. In addition to various forms of radio, unbounded media includes links based on laser, infrared, and other light forms. Unbounded media, such as infrared, can be used to connect workstations to a network without a cable. Other unbounded media, such as microwave, can be used to connect networks over very long distances. Unbounded media are typically more prone to eavesdropping and interference than are bounded media.
  9. 9. Lesson 3: Network hardware 3 - 9 An advantage of using unbounded media is that they are useful for portable networks and other environments in which cabling is impractical. However, in many cases, they are highly susceptible to electromagnetic and atmospheric (such as rain and fog) interference and they are generally susceptible to eavesdropping. Radio Although the term "radio” can refer to a large portion of the electromagnetic spectrum, we will refer to the range of frequencies that includes FM radio, television (VHF and UHF), and computer networks. Transmissions in this range are limited by distance because they do not "bounce" off the ionosphere. Transmissions in this range are not as affected by atmospheric conditions as are microwave transmissions. For these reasons, radio is suitable for data communications. However, the signals are constrained by objects and data rates, for radio transmissions tend to be lower than those for microwave transmissions. You must have a license to use radio as a network medium and it is susceptible to EMI and eavesdropping. Cellular phone service, which is widely available, can provide an efficient portable network connection. Terrestrial microwave Buffalo Rochester Figure 3-6: Terrestrial microwave can provide high-speed links over short distances, such as between nearby cities. Concepts > Terrestrial microwave is commonly used for long-distance voice and video transmissions and for short-distance high-speed links between buildings. A common type of microwave antenna is a parabolic dish about 10 feet in diameter. In an area of rough terrain, microwave technology is often less expensive than cabling. Microwave, in fact, is quite similar to radio. A major difference between microwave and radio is that radio broadcasts tend to be omnidirectional (broadcast in all directions), while microwave transmissions are focused in one direction (to the other dish). For this reason, microwave antennas must be aligned precisely for successful transmission.
  10. 10. Understanding Network Fundamentals (Second Edition) 3 - 10 High frequencies generally correspond to a high capacity for carrying data, so very high capacities are available within the high end of the microwave range. However, higher frequencies are also more susceptible to interference such as fog or rain. Furthermore, microwave transmissions can be obstructed by buildings, motor vehicles, mountains, and other solid objects. A license is required and microwaves are susceptible to eavesdropping. Transmissions from far beyond the horizon cannot be picked up. Interestingly, the atmosphere "bends" microwave signals toward the earth somewhat, extending the limit of microwave transmissions beyond the line of sight, although not enough to follow the earth's curvature perfectly. As you can see in the following table, the distance between points can be extended by elevating the antennas above the ground. Elevation of antennas Maximum distance between points 1. meters (32 feet) 26.07 kilometers (16 miles) 2. meters (328 feet) 82.45 kilometers (51 miles) 3. meters (1,640 feet) 184.35 kilometers (114 miles) • The measurements in feet and miles are approximate. Satellite microwave Figure 3-7: Satellite microwave can traverse farther distances than terrestrial microwave. To enable networks to traverse distances greater than those provided by terrestrial microwave, communications satellites high above the earth's surface can relay signals between ground stations. When a ground station transmits a signal to the communications satellite (a process called uplinking), the satellite relays the signal to another ground station (a process called downlinking). The satellite repeats the signal, regenerating digital signals or amplifying analog signals. The ground station can be mobile. However, this technology is expensive, requires a license, is susceptible to eavesdropping, and is affected by weather conditions.
  11. 11. Lesson 3: Network hardware 3 - 11 Typical communications satellites are in a geosynchronous orbit—their path follows the spin of the earth, enabling them to remain in the same location above the earth. The physics involved dictate that communications satellites must be 22,300 miles above earth. Microwave signals (like most other data-transmission media) move data at the speed of light. Even at this high speed, the great distance (more than 44,600 miles by the time a signal returns to earth) involved in a satellite microwave transmission means that there is a significant delay between the time data are sent and the time they are received. When combined with the time it takes for the satellite to repeat the signal, the delay is typically 240 to 300 milliseconds. Sometimes you can notice this delay in long-distance telephone conversations that use satellite microwave transmissions; the echo of your own voice is slightly delayed. For some networking applications, this delay can introduce problems. Laser Concepts > A laser transmitter uses a highly focused beam of light pulses to transmit data. The receiver uses a photoelectronic (light-sensitive) device to convert the laser back into the original data. Like optical fiber, laser uses light, which occurs at a higher frequency than the frequencies used in microwave and various forms of radio. Because of this, laser is capable of very high data rates. However, laser is also susceptible to attenuation (loss of power) and interference. Laser is often synonymous with point-to point infrared. Although the interface devices are expensive, they are resistant to eavesdropping, and capable of high transmission rates. However, laser transmissions are affected by atmospheric conditions, susceptible to high intensity light, and require line of site positioning. Infrared light wireless hub infrared light Figure 3-8: Infrared light can carry digital data throughout an office without cabling.
  12. 12. Understanding Network Fundamentals (Second Edition) 3 - 12 Infrared transmitters are fairly common devices used in many homes—typical remote controllers for televisions, videocassette recorders, and stereos use infrared light to transmit signals. A common networking application of infrared is the wireless hub. Wireless hubs enable workstations to connect to LANs without using cable. This can be an ideal way to set up LANs in locations where the installation of cable is difficult or prohibited, as in historic buildings, or buildings that contain asbestos insulation. Wireless hubs (wiring center) can be installed quickly, and can provide a cost-effective way to set up temporary LANs. To "connect" to a wireless hub, a workstation typically has a small transceiver that attaches to a cubicle wall or some other location above the desk. The transceiver can be aimed directly at the wireless hub, or the signal can be reflected off a mirror or a wall. The wireless hub conveys data between wireless nodes, and it can connect a wireless LAN to a cabled or wireless internetwork. Like laser, infrared can support high data rates, but its distance is limited by attenuation and interference. Broadcast infrared systems do not require such a focused beam. The beam is more dispersed, and hence is called broadcast. This system is easier to line up the transceivers, because of the broadcast of light. A comparison of media types Susceptibilit y to EMI High Moderate Not susceptible Radio: high Other forms: moderate to low Task B-2: Considering the characteristics of transmission media What you do Comments/Prompts Of twisted-pair cable, coaxial cable, fiber optic cable, and unbounded media, identify which type of data-transmission media is: 1. Typically used for standard telephone cable ________________________________________ 2. Bounded medium that is generally most susceptible to EMI and eavesdropping ________________________________________ 3. Includes radio and microwave ________________________________________ 4. Thin or thick Ethernet ________________________________________ 5. Generally least expensive ________________________________________ 6. Conducts signals of light ________________________________________
  13. 13. Lesson 3: Network hardware 3 - 13 7. Surrounds the inner conductor with shielding to reduce EMI ________________________________________ 8. Not susceptible to EMI ________________________________________ Task B-3: Determining the type of medium to use What you do Comments/Prompts For each of the following situations, indicate the medium you would use, and explain why: 1. Your offices are located in a historic 19th-century building. You do not want unsightly cables running across the floor, but you are not allowed to run cables through the walls, floors, or ceiling. ________________________________________ 2. You need to provide a high- speed connection between two offices that overlook the same courtyard. The offices are in different buildings. ________________________________________ 3. You need a high-speed connection between graphic workstations that are in the same office. You have no restrictions except the need for speed. ________________________________________ 4. You need to run a connection through a tunnel connecting two buildings. The tunnel contains many high-voltage lines and large electric motors. You are concerned about security. ________________________________________
  14. 14. Understanding Network Fundamentals (Second Edition) 3 - 14 cc Interface devices 4 6 RJ11 RJ45 50 ohm terminator BNC D-shell fiberoptic Apple T connector Figure 3-9: Connectors. Concepts > Each type of bounded transmission media uses a particular type of connector. The connector attaches the media and the transceiver device so the signal can be transmitted properly. Here is a list of some basic connectors: Unshielded twisted pair cable (10-BASE-T) generally uses RJ 11 or RJ 45 connectors. The RJ connectors look like the modular plug used for telephones. A Bayonet Nut Connector (BNC) is usually used for coaxial cable (10-BASE-2). The connector fits into a coupling and is twisted to lock it into place. A BNC T connector (T-junction or T-connector) provides three-way connection, two connections for the network and one connection for the transceiver device. The D Shell connector is often seen on serial cables (for example, printer cables) and monitor cables. The connector pins on a male connector are protected by a D-shaped collar that is narrow on one end and wider on the other. The female connector has the shape of a “D.“ Often D Shell connectors have thumbscrews used to lock the connector into the device. This connector name usually begins with DB and includes a number. The number refers to the number of pins. For example, the DB-9 connector has 9 pins. Apple connectors are used with Apple and Macintosh devices. The outside of these connectors often have one flat side with an embossed symbol representing the type of device the cable is used for. Fiber optic connectors are used for fiber optic cable. SMA connectors have a threaded nut that is twisted to lock it into place. ST connectors use a bayonet locking system.
  15. 15. Lesson 3: Network hardware 3 - 15 A vampire tap is a connection made in a thick Ethernet cable (10-BASE-5) to a transceiver. Every few feet of cable is marked to indicate where a new connection can be made. The tool to make the connection is a metal spike that pierces the cable and a special connector is then screwed into the thick coaxial cable. Small Computer Systems Interface (SCSI, pronounced “scuzzy”) connectors are used for peripheral devices such as hard disk drives and laser printers. The connectors usually have 50 or 68 pins. At the end of a length of cable you will often see terminators. A terminator is a resistor attached to the end of the cable to absorb energy from the signal and prevent the signal from reflecting back through the cable. Each type of cable has a specific type of terminator. Buses Within a computer, data needs to be shuttled back and forth from installed devices to memory and on to the central processing unit (CPU). The internal pathway that connects the microprocessor to random access memory (RAM) is called a bus. The measurement of a bus is the number of bits that can be transferred at a time. The bus type controls the rate that data can be moved inside the computer. The larger the number of bits that are transferred at a time, the faster the bus is. The bus speed, the microprocessor speed, and the overall design of the computer also affect the speed. The type of bus in the computer determines which type of interface card must be used to connect to the network. There are several types of buses: Bus abbreviation Bus architecture Description ISA Industry Standard Architecture 16-bit system developed in 1983; a majority of computers use this design; compatible with older 8-bit systems, less expensive than EISA EISA Extended Industry Standard Architecture 32-bit design, compatible with ISA standard, compatible with older 8-bit systems MCA MicroChannel Architecture IBM proprietary 32- bit design; a very fast architecture NuBus Macintosh NuBus Apple's 32- bit design; used only on Macintoshes VESA Video Electronics Standards Association 32-bit design; developed to accelerate video displays PCI Peripheral Component Interconnect A more comprehensive 32-bit design that is the first to offer Plug and Play setup
  16. 16. Understanding Network Fundamentals (Second Edition) 3 - 16 Network interface cards Figure 3-10: The network interface card. Concepts > Network interface cards (NICs) installed on a computer receive data from and send data to the network. They are also called network adapters, LAN cards, and interface cards. The NIC fits into a slot in the computer and is attached to the network cable with a connector. NICs are built to work with the specific type of bus the computer uses. You must have a NIC that uses that same architecture. Each NIC on a network has a unique address, or number, that identifies that workstation. PCMCIA card external drive Figure 3-11: The PCMCIA card. The Personal Computer Memory Card International Association cards (PCMCIA cards) are integrated circuits that enable a notebook computer to interface with several different devices with one port. The PCMCIA cards are about the size of a credit card and fit into a slot in a mobile computer. The thickness of the card varies. A PCMCIA card can be used to connect a laptop computer to a fax modem, a network, memory cards, or an external storage drive. The cards are made to be non-vendor specific, and work with most models of computers. One advantage of PCMCIA cards is that they can be changed without restarting the computer (a process called a hot swap).
  17. 17. Lesson 3: Network hardware 3 - 17 HUB Figure 3-12: A hub in a simple network. A hub is a component that connects many cables in one device. When LANs were first developed, all computers were connected to one cable that was strung from office to office. Not only was it difficult to add new computers to the LAN, but if there was a break in the cable, the whole LAN was disabled. Hubs are used to break up the LAN into small point-to-point segments, all connected within the hub’s circuitry. If any one segment has trouble, only computers on that segment are affected. Hubs also allow the network structure to change without restringing cable. All the wiring changes can be made at the hub. In a way, a hub can be seen as a train station. Many train tracks come in to one location and trains can be routed to many destinations. Hubs are used either to amplify a signal and transmit it (active hub) or to just pass the signal along (passive hub). Intelligent hubs have switching and management capabilities and can make a choice as to which network path will be used to transmit the signal. Switching hubs are a newer technology. Switching hubs can increase the number of terminals and computers connected to a LAN by breaking down the LAN into more manageable virtual segments. Enterprise switches use Asynchronous Transfer Mode (ATM) which segments data into 53-byte cells. These cells can be switched at high speeds.
  18. 18. Understanding Network Fundamentals (Second Edition) 3 - 18 dd Internetworking devices Concepts > Devices such as repeaters, bridges, and routers enable you to extend the reach of your network by connecting network segments, subnetworks, and networks. These devices not only extend the distance signals can be transmitted, but also synchronize the signals. The transmission of data needs to be synchronized so that the sender transmits the data at a rate that the receiver expects. Synchronous transmission sends the data at a fixed rate. Asynchronous transmission is controlled by start and stop bits and the time between characters can vary in length. Repeaters ABCDefghijk ABCDE client repeater server repeater server Figure 3-13: A repeater is used to extend the reach of a network. Because of attenuation (loss of signal strength), each of the various types of communication media used in networks has a maximum suggested length. To extend the network beyond this distance, you can use a repeater. Repeaters are not simply amplifiers. If repeaters just amplified a signal, they would amplify any EMI noise on the communication medium, as well as the signal. Instead, repeaters deal with the problem of attenuation by receiving the data (much like any network node) and then immediately transmitting a "clean" copy of the signal on the next span (called a segment) of network cable. Although the number of repeaters that you can use is limited, you can use repeaters to extend the span of a LAN well beyond the normal limitations of the communication medium. Network segments connected by a repeater must be identical (for example, Ethernet to Ethernet, Token Ring to Token Ring). Advantages of repeaters: • Repeaters are inexpensive. • Repeaters extend the reach of the network. • Because repeaters perform little or no processing, they are very fast. • Repeaters can connect different types of media, such as coaxial cable to optical fiber.
  19. 19. Lesson 3: Network hardware 3 - 19 Disadvantages of repeaters: • Repeaters cannot control network traffic. Repeaters cannot filter problems or traffic congestion that comes from other segments. • After network traffic is passed through a number of repeaters, eventually synchronization is lost. Summary of repeaters Function Connects LAN segments, and regenerates signals that it moves between segments. Characteristics Typically easy to install. When to use When you need to extend LAN cabling beyond its normal limitations. Bridges bridge Only data with addresses on “the other side of the bridge” are allowed to pass. Ethernet Token Ring Figure 3-14: A bridge redirects traffic in a LAN. Concepts > Bridges are devices that manage traffic among segments of a LAN. Bridges examine the source and destination address of a data transmission. They use this information to determine which transmissions should be allowed to pass to another network segment. Traffic whose destination is on the same segment as the sender is confined to only that segment; internetwork traffic is allowed to pass through the bridge. This ability can be useful when you need to restrict traffic across network segments.
  20. 20. Understanding Network Fundamentals (Second Edition) 3 - 20 node Segment 2 node node node Segment 1 node node Forward data only to segment on which destination node is located. BRIDGE The bridge examines the destination address of data and forwards it opnly to the segment on which the destination node is located. Figure 3-15: A bridge reroutes local traffic. Using Figure 3-16 as an example, you might find that most network communication occurs among those on the same segment. Bill and Chris communicate often, and Nick and LuAnne communicate often, but Bill and Chris only occasionally use the network to communicate with Nick or LuAnne. With a repeater connecting their two segments, Segment 1 and Segment 2 always carry all traffic, even when the transmission is strictly between Bill and Chris or between Nick and LuAnne. When you use a bridge to filter out traffic according to network addresses, traffic that is initiated on segment 1 is sent to segment 2 only when it is intended for Nick or LuAnne. This eliminates unnecessary traffic on each segment, increasing the overall performance of the network. Bridges know which nodes are on which segments by referring to a filtering database. Some bridges require a system administrator to manually enter address information into the workstation database. Most modern bridges are learning bridges: they build their own routing tables by examining network traffic and figuring out which segment a particular node is attached to. If the bridge must forward a data packet to a node whose address it has not yet learned, it forwards the message to all segments until the node replies, at which point it learns the node's address. Advantages of bridges: • Bridges can restrict the flow of unnecessary traffic across segments. • Bridges can resynchronize signals. Disadvantages of bridges: • Bridges are more complex than repeaters; they are also typically more expensive than repeaters. • Because they examine all network traffic, bridges are generally much slower than repeaters and might be a potential bottleneck.
  21. 21. Lesson 3: Network hardware 3 - 21 Summary of bridges Function Functions like a repeater, except that a bridge can examine a transmission's source and destination address to determine if the data should be transferred between segments. Characteristics Usually do not connect networks with different MAC and signaling protocols (for example, CSMA bus to Token Ring). Can, however, connect different media types (such as coaxial cable to optical fiber). Typically easy to install. When to use Use to increase network performance by localizing traffic. Use to create a single logical network from several segments. Routers router Figure 3-16: Routers reroute traffic between networks. Concepts > Routers do not simply forward data packets as bridges do; instead they extract data from the packets and use addressing information in the packet to move data through the best path to their destination. Because routers know the data's network address, they can be "intelligent" about routing data to its destination. Often the destination is another logically separate network. While bridges forward data if the receiving node is not on the same segment as the sender, routers forward data only if they know that it is intended for a node on a remote network. Routers can relay data transmissions between similar or dissimilar network topologies (for example, Ethernet to Token Ring). Routers can translate between Ethernet, Token Ring, and other signaling and media-access schemes.
  22. 22. Understanding Network Fundamentals (Second Edition) 3 - 22 However, routers are not transparent as bridges are. This can be an advantage in protecting other subnetworks from problems that might occur on a single subnetwork. Because routers enable only properly addressed data packets to move from one network to another, routers can be used to prevent problems on one network from reaching other segments. Advantages of routers: • Routers can choose the best path through the network when there are multiple paths to a destination, making best use of expensive connections. • Routers can protect problems on one network from reaching other networks. • Routers can connect networks that use different media-access methods, such as Token Ring to Ethernet. Disadvantages of routers: • Routers are a potential bottleneck in the internetwork. • Routers are generally more complex and expensive than bridges or repeaters. • Some protocols are not routable. Summary of routers Function Connects networks, determining the best path for traffic. Characteristics Can connect networks with different MAC and signaling protocols (for example, CSMA bus to Token Ring). Cannot connect networks that use different protocols (for example, IP to XNS) unless you use a multiple-protocol router. Because of the complexity of processing involved, routers are generally slower than bridges and repeaters. More difficult to install than bridges or repeaters. When to use When you need to connect various networks. Brouters Concepts > Brouters function like routers, relaying data transmissions between networks. When a brouter encounters a data packet that uses a protocol with which it is unfamiliar, the brouter works like a bridge and does not perform routing functions. Because of this ability, brouters are appropriate for networks on which there is mixed-protocol traffic, but only specific traffic needs routing. Advantage of brouters: • Brouters combine the data-handling capabilities of a router with the protocol transparency of a bridge. Disadvantage of brouters: • Brouters are generally more complex and expensive than other internetworking devices.
  23. 23. Lesson 3: Network hardware 3 - 23 Summary of bridge/routers Function Combination of bridge and router functions. Functions as router for packets that use network-layer protocols that it knows; functions as bridge for packets that use unknown protocols. Characteristics More difficult to install than bridges or repeaters. When to use When you need to provide and control mixed-protocol traffic between network segments. Gateways gateway mail server network server mini computer mainframe Figure 3-17: A gateway relays messages between dissimilar networks. A gateway relays messages between dissimilar network architectures. Gateways are often aimed at a particular application, such as electronic mail or file transfer. Unlike routers, gateways can change the format of data, enabling data to be transferred between systems with different encoding schemes (for example, EBCDIC and ASCII). A typical application of a gateway is connecting personal computers to mainframes. An advantage of gateways: • Gateways provide relatively inexpensive connections between drastically different kinds of networks. Disadvantages of gateways: • Gateways sometimes do not provide perfect connectivity, and are often specialized to specific tasks, such as electronic mail or file transfer. • Gateways can be a network bottleneck because of time for translation between protocols.
  24. 24. Understanding Network Fundamentals (Second Edition) 3 - 24 Summary of gateways Function Translate between incompatible protocols. Characteristics Dependent on applications software. When to use When you need to connect systems that use different architectures. Task D-1: Applying repeaters, bridges, routers, brouters, and gateways What you do Comments/Prompts Of repeaters, bridges, routers, brouters, and gateways, determine which of the network devices would provide the services needed in each of the following scenarios: 1. Prescott Advertising needs to provide occasional communication between segments. Although network traffic is high, most communication is between nodes on the same segment. ________________________________________ 2. Rossi Corp., a company whose offices occupy two floors of a small building, needs to extend the length of its Ethernet cable system to connect the first and second floors. There are no standard network "traffic patterns." ________________________________________ 3. Lighthouse Insurance needs to connect their Macintosh computers to IBM mainframes and DEC VAX minicomputers. These computers use incompatible protocols. ________________________________________ 4. Vision Office Products needs to connect several networks that use the same protocols. They want to use devices that will provide the most efficient path between networks. ________________________________________
  25. 25. Lesson 3: Network hardware 3 - 25 )) Wrap-up for Lesson 3 aa What are some advantages of using servers on a network? bb List some types of transmission media. List some reasons why there are different transmission media. cc What is a major feature that determines the kind of NIC used to connect a workstation to the network cable? dd Describe the differences between a bridge and a router.
  26. 26. 4 - 1 L E S S O N 4 Network software Lesson objectives Software is necessary if want to communicate over a network and to use network services. In this lesson you will: a Become familiar with the uses of network operating systems. b Become familiar with different types of network applications and the implications of using networked applications.
  27. 27. Understanding Network Fundamentals (Second Edition) 4 - 2 aa Network operating systems Concepts > To connect to a network your computer needs network hardware such as cables and network interface cards (NICs). However, a physical connection to the network is not enough. To access network services, such as printers and remote databases, your computer also needs network software. A network operating system (NOS) is software that usually runs on servers, and that enables workstations to establish and maintain the connections between multiple servers and even workstations. The NOS manages how data is transmitted and received on network media. The NOS can provide services such as a menu-driven network management interface, backup of file server software, security restrictions, central storage of applications and databases. It can also enable remote log in and sharing of hardware (such as printers). Network operating systems were developed to resolve problems associated with security of files, data integrity, and requests for access to shared storage devices and peripherals from multiple clients. The network provides services that are transparent to the user and client. The user does not need to know exactly where or how data is stored. In a NOS, the user is given access to certain data; and there are limits to what the user can do. These limits, or rights, are set by the network administrator. For example, the network administrator might grant all users access to a database, but not the ability to delete files in that database. There are two types of network operating systems: peer-to-peer network operating systems and client/server network operating systems. All network operating systems can provide some level of security, network management, shared resources, printing services, and electronic mail. Peer-to-peer network operating systems Peer-to-peer networks generally enable workstations to share resources and files with each other and might not have a central file server. Often these network operating systems can work with different platforms (DOS, Macintosh, OS/2, UNIX) and with different topologies. Examples of peer-to-peer network operating systems include: Artisoft's LANtastic, AppleTalk, Microsoft's Windows for Workgroups, and Windows 95. • Artisoft's LANtastic is a popular LAN operating system for DOS, Windows, OS/2 and Macintosh. It enables peer-to-peer and client/server operation. The Macintosh version can be used as a dedicated gateway between Macintosh workstations and a LANtastic network. • AppleTalk is a group of network protocols for Apple Macintosh computers that enables data to be transmitted over proprietary, Ethernet, and Token Ring network topologies. LocalTalk is the built-in network interface in all Macintosh computers. • Microsoft's Windows for Workgroups is a peer-to-peer NOS with a graphical user interface (GUI). Windows for Workgroups enables users to share resources, chat, send electronic mail, and schedule meetings with other users. Basic security is also built in, which enables files stored on a network drive or a workstation to be used by all or a select group of users. • Windows 95 is Microsoft’s 32-bit local operating system. It provides for peer connectivity with other Windows 95 peers or Windows for Workgroups peers. As with Windows for Workgroups, basic security is built in, which enables files stored on the network drive or workstation to be used by all or a select group of users.
  28. 28. Lesson 4: Network software 4 - 3 Client/server network operating systems A client/server NOS enables client software to interoperate with server software. The client workstation runs software that provides an interface that sends requests for network services and receives data from servers. The servers run software that performs functions such as database management and print queue management. Client/server network operating systems (NOSs) are usually for medium to large companies that need to connect hundreds of users. Examples of client/server NOSs include: Novell's NetWare, Banyan's VINES, and Windows NT. • Novell NetWare is a NOS that does not require vendor specific network hardware. Unlike other NOSs, NetWare servers can be one of a variety of computers. NetWare is used with IBM compatible machines and can support Apple and ARCnet hardware products. NetWare can run on different topologies including star, Token Ring, and bus. The NetWare requestor is installed on each workstation. When a client requests data from a server, DOS will try to satisfy the request locally. If DOS cannot satisfy the request, it redirects the request to its own built-in “REDIR” function. Novell’s NetWare DOS Requestor is designed to accept requests from DOS’s REDIR. The NetWare DOS Requestor passes the request on to the server. • Banyan VINES was designed for large networks. VINES stands for Virtual Networking System. VINES is composed of a set of applications that run over a special version of UNIX. It can provide internetworking connectivity, transparent operation of gateways, multitasking, and security. Add-on products are available for electronic mail and network management. VINES supports DOS, Windows, OS/2, Macintosh, and Windows NT. • Windows NT is a 32-bit NOS. It comes in client and server versions. Windows NT allows long file names (up to 256 characters), true multitasking (simultaneous processing of more than one instruction), and transaction tracking (if the system crashes, the data is rolled back to its previous state). Windows NT includes peer-to-peer software to enable users to share files and applications.
  29. 29. Understanding Network Fundamentals (Second Edition) 4 - 4 bb Network applications Concepts > In many networks, shared resources typically appear to workstations as an extension of local resources. To the workstation's operating system, for example, network storage is made to appear as another disk drive, and network printers are made to appear directly connected to a printer port. For this reason, most applications that were written for non-network computers can also run on a network. Some applications, however, are written particularly for use on a network. This topic examines the types of applications used on networks. Network-only applications Some applications have been designed specifically for use on networks, and therefore will run properly only on computers that are connected to a network. Such applications are called network-only applications or pure network applications. Examples of network-only applications include electronic mail, groupware, and terminal emulation software. Electronic mail (e-mail) is one application that needs a network to be productive. E-mail applications enable users to send and receive electronic messages, text, and reports. Some applications enable users to also send files and data embedded or attached to a message. E-mail uses a store-and-forward method of transmission. The recipient does not need to be present when the mail message is delivered. The message is stored in an electronic version of a mail box. When the recipient logs onto the mail system, the message is forwarded to the workstation. Public e-mail services are now available, such as CompuServe and America On- line (AOL). Users connect to the service by using communication software and a modem. When public e-mail services first started, both the sender and recipient needed access to the same public service. Now with access to the Internet, messages can be sent between different public services and from a private network to a public network. Groupware applications enable users to work together. There are several types of software that can be categorized as groupware. Although groupware works well with word processing applications, it can be used with a variety of applications. One important feature of groupware is the ability to share information across different platforms that might include several network operating systems. Some software programs enable shared databases of information and e-mail capability, such as in Lotus Notes. These databases can contain information that all employees need access to, such as telephone lists, company policies, or forms that need input from several users. Personal information managers (also called PIMs) installed on a network enable users to maintain a personal calendar. Software such as Microsoft Schedule+ enables users to make their personal calendars public, as well as check other users’ calendars, and schedule appointments with others.
  30. 30. Lesson 4: Network software 4 - 5 Workflow applications assist the user in managing and sharing work with others. It is also referred to as team computing or collaborative computing. These applications enable users to route information, share files, work on files together, and view others’ changes and additions. Examples of workgroup applications include Lotus WordPro, and Lotus Notes. Terminal emulation programs are a type of communication program that transforms the client workstation into a terminal for a particular on-line service. The terminal emulation program configures the workstation so that it communicates with the on-line service as a specific type of terminal would. Examples of the types of terminals are: TTY, DEC VT52, and DEC VT 100. Stand-alone applications running on a network Stand-alone applications were designed for non-networked computers, and therefore do not require network interaction. Familiar examples include word processors, such as WordPerfect, and Word, electronic spreadsheets, such as 1-2- 3, and Excel, and database-management software, such as dBASE, and Paradox. Metered software keeps a count of how many workstations are using the application. Only a certain number of workstations can use the software at the same time. Because the software is not installed on workstations, many different people can use the software and the company does not need to buy a license for each workstation. Network versions of stand-alone applications Although some stand-alone applications can run from a network, network versions of many stand-alone applications have been developed to ensure network compatibility and to take advantage of network resources. Some networks provide features that work in conjunction with the workstation's operating system to enable stand-alone applications to work with network files and printers. When applications are run on a network, a license for multiple users will need to be obtained to avoid violating copyright laws. File- and record-locking Concepts > On networks, applications must deal with problems that do not exist on non- networked computers. For example, because files can be shared on networks, there is a possibility that two users might access a data file at the same time. When the users save changes in the file, one user's modifications might undo changes made by the other user. To avoid this, some network applications use file-locking or record-locking. With file-locking, the application or operating system locks a file after a user opens it, so that only one user can modify the file at any given time. Record-locking is similar, except that only the portion of the file that the user is accessing is locked. Other users can modify other parts of the file.
  31. 31. Understanding Network Fundamentals (Second Edition) 4 - 6 Task B-1: Network application scenarios What you do Comments/Prompts 1. For each of the following scenarios, identify which of the items listed at the right best meets the need described. Stand-alone application Pure network application Network version of stand-alone application Rossi Corp. is an international company that spans many time zones. Memos, company policies, product lists, and schedules need to be accessible to all users at all times. ________________________________________ Employees of Prescott Advertising need to use the same graphics program but most people work at home on laptops. ________________________________________ Vision Office Products wants a consistent look for all word processing documents. All employees have desk top machines. ________________________________________ Several employees have access to a network document. Each needs to be able to change it and save their changes. ________________________________________ Task B-2: Identifying advantages and disadvantages of using network applications ü Before you begin: Answers to the following questions can be found in the table on the following pages. What you do Comments/Prompts 1. Identify at least two advantages of using network applications Be prepared to share your answers with the class. ____________________________________________ ____________________________________________ ____________________________________________ ____________________________________________
  32. 32. Lesson 4: Network software 4 - 7 2. Identify at least two disadvantages of using network applications ____________________________________________ ____________________________________________ ____________________________________________ ____________________________________________ Using network applications Concepts > Running network applications can have some advantages, but can also present certain challenges. The following table highlights some of the advantages and disadvantages of using network applications: Advantages Disadvantages Ease of installation. Software is installed on one file server, rather than on individual client workstations. Users must have access to the network and be logged into the network to use the application. Upgrading software is easier, as it needs to be installed only on the file-server. This ensures that all users are working with the same version of the software A large number of users of the application can cause a burden on the server, which can slow down everyone on the network. Network applications are typically less expensive, as you can usually buy site licenses for one software package, rather than buying individual software packages for each workstation. In some cases, a license might limit the number of users running the application at one time. By installing software on one file server, hard disk space is conserved on individual workstations. If the network goes down, or becomes inoperable, no one can use the application. Users can easily share files. Shared files or database records need a locking method to prevent loss of data. Because everyone is working with the same software version, shared files will be compatible among users. Documents can be set up to have a consistent appearance, regardless of who has created or edited them.
  33. 33. Understanding Network Fundamentals (Second Edition) 4 - 8 )) Wrap-up for Lesson 4 Why is network software necessary? aa List two types of network operating systems. bb What feature enables only one user to modify a file at a time? What feature locks only the portion of a file that another user is accessing?
  34. 34. 5 - 1 L E S S O N 5 Standards and protocols Lesson objectives To learn more about the rules that were developed in order to communicate or exchange information over networks where many hardware and software components are used, you will: a Identify standards that we typically see, and apply the concept of standards to networking. b Define protocols and examine some of the common networking protocols available. c Examine some of the differences between standards, protocols, and protocol implementations.
  35. 35. Understanding Network Fundamentals (Second Edition) 5 - 2 aa Network standards What are standards? Concepts > Standards can be defined as a common set of rules. For many of the procedures that we perform every day, we follow standards. For example: • Touch typists can type without searching for keys because keyboards are arranged in the standard QWERTY format. • We drive our vehicles on the right side of the road. The brake pedal is in the center of the floor, and the accelerator is on the right. If the car has a clutch, that pedal is on the left. Manufacturers follow standards when making products for consumers. For example: • In the United States, most plugs on electronic equipment will fit into a standard wall outlet. • When we buy a lamp, we can assume that a standard light bulb will fit into the lamp’s socket. The history of networking standards In the early 1970s, Trudy Ruesser, who was working for an insurance company, was trying to collect data from other insurance companies by computer. The problem was that other insurance agencies used computers of every make, type, and size. Because disparate computers systems were not able to talk to each other or exchange information over networks, Ruesser thought standards could be defined and developed to permit the exchange of information between different computer hardware and software components. While exploring the possibility of standards for open-system computing, Ruesser found that none existed and that no one was working on such standards. She was asked to chair a committee, and did so until 1973. This committee developed a six-layer reference model for communications that became the basis for the International Standardization Committee (ISO). The ISO was formed in 1978, and it added a seventh layer that is the OSI Reference Model we use today. Figure 5-1: Without standards, making even the simplest of connections would be difficult.
  36. 36. Lesson 5: Standards and protocols 5 - 3 Task A-1: Defining standards ü Before you begin: Be prepared to discuss your answers with the class. What you do Comments/Prompts 1. In the space to the right, list at least one existing standard ________________________________________ ________________________________________ 2. Describe what the consequences would be if this standard did not exist ________________________________________ De facto versus de jure standards Concepts > De facto standards (also referred to as industry standards) are established by general acceptance in the industry or by the consumer. They become standards by actual use and public recognition, not by legal or official recognition. For example, when Beta and VHS competed in the marketplace, VHS won and became an industry standard simply by consumer demand. De jure standards are those established “according to the law.” For example, infant car seats must meet certain safety standards. The law dictates that these standards must be met or else the product will not be certified and cannot be sold to the consumer. Task A-2: Identifying standards What you do Comments/Prompts 1. For each of the standards below, indicate what type of standard it is: (De facto or de jure.) Speed limits on the road ________________________________________ Compact disks (versus record albums) ________________________________________ 3.5” diskettes (versus the older 5.25” floppies) ________________________________________ Food & Drug Administration (FDA) regulations ________________________________________ 2. List at least two more de jure standards: 1.__________________________________________ 2. __________________________________________ 3. List at least two more de facto standards: 1.__________________________________________ 2. __________________________________________
  37. 37. Understanding Network Fundamentals (Second Edition) 5 - 4 Open versus closed standards Concepts > Standards organizations benefit consumers by developing open standards, which are available to all developers. Closed standards are owned by a particular company or organization. In the early days of networking, when most networks existed to connect mainframes computers to terminals, closed standards were prevalent. If you purchased one company’s network, you could not easily connect another company’s devices to that network. Although open standards now exist that will encourage connectivity and interoperability, many networks have already been developed and installed by using closed standards. Many network owners and developers have a large investment in those networks. As soon as open systems become available and closed systems “open up,” as do most systems today, networks will provide universal connectivity and interoperability, and more networking options will exist.
  38. 38. Lesson 5: Standards and protocols 5 - 5 bb Network protocols Concepts > Some standards define protocols. Protocols are the rules required to help entities communicate and understand each other. For example, you speak only English and you meet someone who speaks both English and German. If both of you agree that you will communicate in English, you have established a communication standard. If both of you agree that all future communications will be in English, you’ve established a communication protocol. In networking, a protocol is also a set of rules and regulations that govern a specific aspect of data communications. A network protocol generally defines how communication should begin and end properly, and the sequence of events that should occur during transmission. Protocols are typically created by vendors and networking standards organizations. Once established, hardware and software vendors implement the protocols into their products. Protocol suites A set of protocols that are typically used together is called a protocol suite. Many network operating system vendors, such as Novell, provide their own protocol suites, but enable you to use other protocols as well. When interoperability is required, selecting protocols is an important and sometimes complex task. The network operating system you use determines which protocol suites are available. Some networks enable you to run multiple protocols; some networks support only one protocol suite. A protocol stack is a suite that is ordered in a logical hierarchy. The Internet protocol suite The Internet protocol suite was developed in the late 1970s to enable dissimilar computers to connect in a network that would include government, universities, and other research institutions. A popular network that uses this protocol suite today is the Internet. Although the Internet protocol suite includes hundreds of protocols, it is often referred to as TCP/IP, mentioning just two of them (TCP, the Transmission Control Protocol, and IP, the Internet Protocol). To connect different types of systems, the TCP/IP protocols are perhaps the most widely accepted and versatile protocol suite available today. Many networks, even those that are not connected to the Internet, use TCP/IP because of its ability to connect dissimilar computers. OSI protocols Like TCP/IP, the OSI protocols cover a variety of networking needs. Furthermore, the OSI protocols were, like TCP/IP, designed to enable different computers to share data. You should use the OSI protocols when you need to ensure compatibility with other OSI-based networks. OSI lower-layers (referring to the OSI seven-layer model) protocols are already in place and well supported. Novell NetWare protocols The term “NetWare” describes Novell’s protocol suite, as well as many of Novell’s products. NetWare products are typically for client/server environments. Portions of NetWare were based on Xerox Network Systems (XNS) network protocols.
  39. 39. Understanding Network Fundamentals (Second Edition) 5 - 6 The Internetwork Packet Exchange (IPX) protocol is similar to the Internet protocol (IP). The Sequenced Packet Exchange (SPX) protocol is similar to the Internet protocol TCP. Early versions of NetWare required separate network boards for every protocol suite used by a workstation. As a result, the Open Data-link Interface, or ODI, was developed. With ODI, a single network board can support multiple protocols. AppleTalk protocols Apple has developed a network architecture (AppleTalk) that offers a set of layered protocols consistent with the OSI seven-layer model. This has provided some assurance that its Macintosh-based networks will be able to communicate with any IBM PC-based networks. IBM has also moved toward compatibility with the OSI model. If both of these major companies continue to provide OSI- based networks, these networks can be interconnected because they will both use “open” standards. Protocol implementation Protocol implementation is the way in which a company decides to implement and produce a product based on a protocol. For example, in the automobile industry, the protocol is the blueprint. It describes, in detail, the size of the vehicle, the number of doors, the number of seats, and so on. The protocol implementation is the way the designer decides to implement and produce the vehicle, based on the blueprint (protocol). All of the cars built will have the same design, but different interiors, paint schemes, etc. Each designer creates an individual implementation that conforms to the original specification.
  40. 40. Lesson 5: Standards and protocols 5 - 7 cc Differences between standards, protocols, and protocol implementations Concepts > The most effective way to show the difference between standards and protocols is to use an example or an analogy. In this example, we will use the construction industry to illustrate standards, protocols, and protocol implementations. When building a house, standards have been established that describe the type of electrical wiring, plumbing, and building materials that are required to build the house. In this example, these standards are typically de jure standards, or regulated by the law. The protocol in this example, is the blueprint of the house. This protocol describes, in detail, the number of rooms, the dimensions of each room, the number of doors and windows, and so on. The protocol implementation is the way the builder decides to build each house, based on the blueprint (protocol). Although all of the houses built will have the same dimensions and layout, each one will have different fixtures, carpeting, paint schemes, landscaping, and so on. Task C-1: Identifying an analogy for a standard, protocol, and protocol implementation What you do Comments/Prompts 1. Identify an analogy for a standard (not necessarily a network standard) ________________________________________ ________________________________________ ________________________________________ ________________________________________ ________________________________________ 2. Identify an analogy for a protocol ________________________________________ 3. Identify an analogy for a protocol implementation ________________________________________ ________________________________________ ________________________________________
  41. 41. Understanding Network Fundamentals (Second Edition) 5 - 8 (( Practice Unit for Lesson 5 In this activity, you will use the clues below to complete the crossword puzzle. Clues across: 1. Open standards encourage __________. 5. The OSI reference model consists of a __________-layer model that describes how data is handled during transmission. 6. TCP/IP is also called the __________ protocol suite. 8. __________ (or proprietary) standards are owned by a particular company or organization. 9. __________ standards are established “according to the law.” 12. The OSI model ensures efficient __________ within a LAN and among different networks. Clues down: 2. The __________ Packet Exchange protocol is similar to the Internet protocol TCP. 3. Open standards encourage connectivity and __________. 4. De facto standards are sometimes called __________ standards. 7. The Open Data-link Interface (ODI) was developed to enable a single workstation to support __________ protocols. 10. A set of protocols that are typically used together is called a protocol __________. 11. A network __________ is a set of rules that govern data communications.
  42. 42. Lesson 5: Standards and protocols 5 - 9 1. 4. 6. 7. 8. 9. 5. 10. 12. 2. 3. 11.
  43. 43. Understanding Network Fundamentals (Second Edition) 5 - 10 )) Wrap-up for Lesson 5 Why are standards and protocols necessary? aa What type of standards are owned by a particular company or organization? bb What is a protocol suite? cc What is a protocol implementation?