Bài giảng Network - Chapter 17

Chapter Overview Identifying Network ComponentsTroubleshooting a Network 1Locating Ports The ports on a typical computer are located either on the motherboard or on expansion cards that plug into the system bus. If the same type of port can have more than one function, you can sometimes tell what a port does by where it is located.The locations of the motherboard ports vary, depending on the design of the computer. 2The Back Panel of an Older Computer 3The Back Panel of a Newer Computer 4DB-9 Serial Ports 5DB-9 and DB-25 Serial Ports on an Older Computer 6The Female DB-25 Connector Used by a Parallel Port 7A 15-Pin VGA Connector 8Six-Pin Mini-DIN Connectors 9A Five-Pin DIN Connector 10Universal Serial Bus (USB) Ports The USB is a relatively recent innovation that is replacing many of the ports on computers, such as the serial, parallel, keyboard, and mouse ports. The USB is a multipurpose bus that Runs at up to 12 megabits per second (Mbps) Supports a wide range of devices through the same interface Computers today typically have two USB ports, which use rectangular, female, four-conductor connectors. 11USB A-Connectors 12SCSI Ports The Small Computer System Interface (SCSI) is a mass storage interface that supports many different internal and external devices at speeds up to 160 Mbps. SCSI implementations typically involve a host adapter card that plugs into the computer's expansion bus. A few computers have a SCSI adapter integrated into the motherboard. A SCSI host adapter usually has both internal and external connectors.Internally, SCSI uses ribbon connectors that attach to hard drives and other devices. External SCSI cables are thick and relatively inflexible because of their heavy shielding and the tight bundling of wires contained inside. 13SCSI Connectors 14A Combination Ethernet NIC 15A BNC Connector with a T Attached 16An Ethernet NIC with an RJ-45 Jack 17A Token Ring Media Filter 18The Back of a 10Base-T/100Base-TX Ethernet Hub 19Hubs A hub can be either a stand-alone box or a unit that mounts into a standard 19-inch-wide rack used for large network installations. Hubs can support any one of several data-link layer protocols, including Ethernet, Fiber Distributed Data Interface (FDDI), and Token Ring. A hub can have as few as 4 ports or as many as 24. The basic identifying feature of a hub is one or more rows of female connectors.In most cases, a hub has rows of light-emitting diode (LED) lamps that correspond to the network cable ports. 20The LED Display on a 10Base-T/100Base-TX Ethernet Hub 21Switches Switches look like hubs.The difference between a hub and a switch is in the internal manipulation of incoming data. Switches are available in most of the same configurations as hubs, ranging from small units intended for home or small business networks to large rack-mounted devices. Some switches include an additional nine-pin serial port that connects the device to a computer with a null modem cable. 22A Patch Panel 23A Typical Stand-Alone Router 24A Router Frame with Modules Installed 25Internal and External Print Servers 26Uninterruptible Power Supplies (UPSs) 27The Back Panel of a UPS 28Network Troubleshooting Procedure 1. Establish the symptoms. 2. Identify the affected area. 3. Establish what has changed. 4. Select the most probable cause. 5. Implement a solution. 6. Test the result. 7. Recognize the potential effects of the solution. 8. Document the solution. 29Establish the Symptoms Determine exactly what is going wrong, and note the effect of the problem on the network. Assign a priority to the problem. In a large network environment, it is essential to establish a system of priorities that dictate which calls get addressed first. Most often, the severity of the problem determines who gets attention first. 30Rules for Establishing Priorities Shared resources take precedence over individual resources.  Network-wide problems take precedence over workgroup or departmental problems.  Departmental issues should be rated according to the function of the department. System-wide problems take precedence over application problems.   31Identify the Affected Area See if the problem can be duplicated. Network problems that you can easily duplicate are far easier to fix, primarily because you can easily test to see if your solution was successful. Having the user reproduce the problem can sometimes lead to the solution. If the problem can be duplicated, you can start determining the actual source of the problem. Eliminate the elements that are not the cause, in a logical and methodical manner. 32Establish What Has Changed When a computer or other network component that used to work properly now does not work, some change has probably occurred. Major changes, such as the installation of new hardware or software, are obvious possible causes of the problem. Tracking down the source of a networking problem can often be a form of detective work, and learning to "interrogate" your "suspects" properly can be an important part of the troubleshooting process. 33Select the Most Probable Cause Follow this axiom: when you hear hoofbeats, think horses, not zebras. When you look for possible causes of a problem, start with the obvious first. Work methodically and document everything you check so that you do not duplicate your efforts. 34Implement a Solution After you have isolated the problem, determine if it is caused by hardware or software. If it is a hardware problem, you might replace the faulty unit or use an alternate. Example: for a communication problem, you might replace network cables until you find one that is faulty. Example: if the problem is in a server, you can replace components until you find the culprit. If it is a software problem, you might Use a different computer to run the application or store the dataReinstall the software on the offending system 35Test the Results After you resolve the problem, you should return to the beginning of the process and repeat the task that originally caused the problem. If the problem no longer occurs, you should test the other functions related to the changes you made to ensure that fixing one problem has not created another. Repeat the procedures you used to duplicate the problem exactly, to ensure that the problem the user originally experienced has been completely eliminated and is not just temporarily masked. If the problem was intermittent, it might take some time to ascertain if your solution worked. Check with the user several times to make sure that the problem is not recurring. 36Document the Solution Begin documenting your actions as soon as the user calls for help. A well-organized support organization uses a system to register each problem call as a trouble ticket that eventually contains A complete record of the problem The steps taken to isolate and resolve the problem A support organization often operates by using tiers. Calls come in to the first tier. If the problem is complex or the first-tier technician cannot resolve it, the call is escalated to the second tier, which is composed of senior technicians. If all technicians document their activities, there should be no problem when one technician hands off the trouble ticket to another. Keeping careful notes prevents duplication of effort. 37Chapter Summary Identifying network components Computers have a variety of ports, some of which are implemented by the motherboard and others by expansion cards. Computers use many different types of connectors fortheir various interfaces, and in some cases the same connector type can provide different functions. SCSI host adapters can use any one of several types of connectors, which are not interchangeable. Troubleshooting a network The network troubleshooting procedure involves several steps, including identifying, duplicating, isolating, resolving, and documenting the problem. Isolating a network problem is a matter of eliminating hardware and software components as possible causes. Maintaining documentation and following a methodical troubleshooting procedure are essential parts of maintaining a network. 38