What is the importance of installing DHCP in computer system servicing?

CONFIGURE COMPUTER SYSTEM AND NETWORK
System Configuration is the way a system is set up, it is the collection of components that make up the system. Configuration can refer to either hardware or software, or the combination of both. For instance, a typical configuration for a PC consists of 32MB (megabytes) main memory, a floppy drive, a hard disk, a modem, a CD-ROM drive, a VGA monitor, and the Windows Operating System.

Many software products require that the computer has a certain minimum configuration. For example, the software might require a graphics display monitor and a video adapter, a particular microprocessor, and a minimum amount of main memory capacity.

When you install a new device or program, you sometimes need to configure it, which means that you need to set various switches and jumpers (for hardware) and to define values of parameters (for software). For example, the device or program may need to know what type of video adapter you have and what type of printer is connected to the computer. Thanks to technological advancements, such as plug-and-play, much of this configuration is now performed automatically.

SAFETY PRECAUTIONS RELATED TO NETWORKS
Installing network cables, whether copper or fiber-optic, can be dangerous. Often, cables must be pulled through ceilings and walls where there are obstacles or toxic materials. You should wear clothing such as long pants, a long-sleeved shirt, sturdy shoes that cover your feet, and gloves to protect you from those toxic materials. Most importantly, wear safety glasses. If possible, ask building management, or someone responsible for the building, if there are any dangerous materials or obstacles that you need to be aware of before entering the ceiling area.

SAFETY PRECAUTIONS WHEN USING A LADDER:

• Read the labels on the ladder, and follow any safety instructions written on it.
• Never stand on the top rung of the ladder. You could easily lose your balance and fall.
• Make sure that people in the area know you will be working there.
• Cordon off the area with caution tape or safety cones.
• When you are using a ladder that leans up against a wall, follow the instructions written on the ladder, and have someone hold the ladder to help keep it steady.

SAFETY RULES WHEN WORKING WITH CABLES
The tools required to install copper and fiber-optic cable may cause danger through improper use. When working with cables, strictly follow these safety rules:

• Make sure that the tools you are using are in good working condition.
• Watch what you are doing, and take your time. Make sure that you do not cut yourself or place anyone in danger.
• Always wear safety glasses when cutting, stripping, or splicing cables of any kind. Tiny fragments can injure your eyes.
• Wear gloves whenever possible, and dispose of any waste properly.

Use common sense when installing cables and fixing network problems. Call for assistance for tasks that you cannot do on your own.

FIBER-OPTIC SAFETY
Fiber-optic cables are useful for communications, but they have certain hazards:

• Dangerous chemicals
• Tools with sharp edges
• Light which you cannot see that can burn your eyes
• Glass shards produced by cutting fiber-optic cable that can cause bodily harm.

Specific types of tools and chemicals are used when working with fiber-optic cable. These materials must be handled with care.

CHEMICALS
The solvents and glues used with fiber optics are dangerous. You should handle them with extreme care. Read the instructions on the label, and follow them carefully. Also, read the material safety data sheet (MSDS) that accompanies the chemicals to know how to treat someone in case of emergency.

TOOLS
When working with any tool, safety should always be your first priority. Any compromise in safety could result in serious injury or even death.

The tools used for working with fiber optics have sharp cutting surfaces that are used to scribe glass. Other tools pinch cables with high pressure to fasten connectors to them. These tools can produce shards of glass that can splinter and fly into the air.

GLASS SHARDS

• The process of cutting and trimming the strands of fiber-optic cables can produce tiny fragments of glass or plastic that can penetrate your eyes or skin and cause severe irritation. The fibers can be extremely difficult to see on your skin because they are clear and small.
• When you work with fiber-optic cabling, the working surface should be a dark mat so that you can see the tiny glass or plastic fragments. The mat should also be resistant to chemical spills.
• You should keep the work area clean and neat.
• Never pick up fiber-optic fragments with your fingers.
• Use tape to pick up small fragments, and dispose of them properly.
• Use a disposable container, such as a plastic bottle with a screw-on lid, to store fiber fragments.
• Close the lid tightly before disposing of the container.

HARMFUL LIGHT

• Protect your eyes from the harmful light that may be in the fiber-optic strands. The light is a color that humans cannot see. It can damage your eyes before you can feel it.
• When you use a magnifier to inspect fiber-optic cable and connectors, the light emitted from the fiber could be directed into your eyes.
• When working with fiber, be sure to disconnect the light source. Use special detectors to help you tell if a fiber is energized.

NETWORKING DEVICES, MEDIA AND CONNECTOR
To make data transmission more extensible and efficient than a simple peer-to-peer network, network designers use specialized network devices such as hubs, switches, routers, and wireless access points to send data between devices.

COMMON NETWORK CABLES
Cables were the only medium used to connect devices on networks. A wide variety of networking cables are available. COAXIAL and TWISTED-PAIR CABLES use copper to transmit data. FIBER-OPTIC CABLES use glass or plastic to transmit data.

TWISTED PAIR
Twisted pair is a type of copper cabling that is used for telephone communications and most Ethernet networks. A pair of wires forms a circuit that transmits data. The pair is twisted to provide protection against crosstalk, the noise generated by adjacent pairs of wires in the cable. Pairs of copper wires are encased in color-coded plastic insulation and are twisted together. An outer jacket protects the bundles of twisted pairs.

UTP vs STP

Shielded Twisted Pair (STP)

• STP cables are best used in industrial settings with high amounts of electromagnetic interference, such as a factory with large electronic equipment, where they can be properly installed and maintained.

Unshielded Twisted Pair (UTP)

• UTP cables are the most commonly used cables for ethernet connections and have a number of advantages.

UNSHIELDED TWISTED PAIR (UTP)
UTP is the cable that has two or four pairs of wires. This type of cable relies solely on the cancellation effect produced by the twisted-wire pairs that limit signal degradation caused by the electromagnetic interface (EMI) and radio frequency interference (RFI).

SHIELDED TWISTED PAIR (STP)
Each pair of STP wire is wrapped in metallic foil to better shield the wires from noise. Four pairs of wires are then wrapped in an overall metallic braid or foil. STP reduces electrical noise from within the cable.

CATEGORY RATING
UTP comes in several categories that are based on two factors:

• The number of wires in the cable
• The number of twists in those wires

1. Category 3 is the wiring used for telephone systems and Ethernet LAN at 10 Megabyte per second (Mbps).
2. Category 3 has four pairs of wires.
3. Category 5 and Category 5e have four pairs of wires with a transmission rate of 100 Mbps.
4. Category 5 and Category 5e is the most common network cables used.

5. Category 5e has more twists per foot than Category 5 wiring.

Some Category 6 cables use a plastic divider to separate the pairs of wires, which prevents interference.

COAXIAL CABLE
Coaxial Cable is a copper-cored cable surrounded by a heavy shielding. Coaxial cable is used to connect the computers to the rest of the network.

SEVERAL TYPES OF COAXIAL CABLE EXIST:

• Thicknet (10BASE5) is a coaxial cable used in networks operating at 10 Mbps, with a maximum length of 500 meters.
• Thinnet (10BASE2) is a coaxial cable used in networks operating at 10 Mbps, with a maximum length of 185 meters.
• RG-59 is most commonly used for cable television in the U.S.
• RG-6 is higher-quality cable than RG-59, with more bandwidth and less susceptibility to interference.

FIBER OPTIC CABLE
An optical fiber is a glass or plastic conductor that transmits information using light. Fiber optic cable has one or more optical fibers enclosed in a sheath or jacket. Because it is made of glass, fiber-optic cable is not affected by EMI or RFI. All signals are converted to light pulses to enter the cable and are converted back into electrical signals when they leave it. This means that fiber-optic cable can deliver signals that are clearer, and can go farther, without compromising the clarity of signals.

Fiber-optic cable can reach distances of several miles or kilometers before the signal needs to be regenerated. Fiber-optic cable usually is more expensive to use than copper cable, and the connectors are more costly and harder to assemble. Common connectors for fiber-optic networks are SC, ST, and LC. These three types of fiber-optic connectors are half-duplex, which allows data to flow in only one direction. Therefore, the two cables are needed.

These are the two types of glass fiber-optic cable:

• Multimode is the cable that has a thicker core than single-mode cable. It is easier to make, can use simpler light sources such as Light Emitting Diodes (LEDs), and works well over distances of a few kilometers or less.
• Single-mode is the cable that has a very thin core. It is harder to make, uses lasers as a light source, and can transmit signals dozens of kilometers with ease.

CREATING AN ETHERNET CABLE
Ethernet cabling has been the standard in networking installation for years. It is the fastest way of connecting PC to a peer or to your router or a central switch.

FABRICATING AN ETHERNET CROSS-OVER AND STRAIGHT-THROUGH CABLE
In an Ethernet networking environment – like in a home or an office with multiple PCs that are wired – the computers need to be connected to a central router to allow data transfer. The router takes all the bits being sent out by the computers and relays them onto the other devices on the network.

The STRAIGHT-THROUGH ETHERNET CABLE is used in local area network to connect a PC to a network hub and router. This is the standard cable used for almost all purposes.

A CROSS-OVER CABLE, on the other hand, can be used to connect two network devices directly, without the need for a router in the middle. It simply reverses some of the pins so that the output on one computer is being sent to the input of another.

The following items are the materials and tools used for making Ethernet cables:

• Ethernet Cable Category 5e or Cat5e- standard wire for cabling;
• RJ45 crimpable connectors for Cat5e;
• RJ45 Crimping tool;
• Wire cutter, stripper or pliers; and
• Ethernet cable tester.

CABLE FABRICATION PROCEDURES

1. Cut into the plastic sheath 1 inch from the end of the cut cable. The crimping tool has a razor blade that will do the trick with practice.

2. Unwind and pair the similar colors.
3. Pinch the wires between your fingers and straighten them out as shown. The color order is important to do this correctly.
4. Use wire cutter to make a straight cut across the wires 1/2 inch from the cut sleeve to the end of the wires.
5. Push the wires into the connector. Each wire fits into a slot in the RJ45 connector. Note the position of the blue plastic shielding. Also, note how the wires go all the way to the end.
6. Take a view from the top. Make sure the wires are all the way in. There should be no short wires.
7. Crimping the Cable – carefully place the connector into the Ethernet Crimper and cinch down on the handles tightly. The copper splicing tabs on the connector will pierce into each of the eight wires. There is also a locking tab that holds the blue plastic sleeve in place for a tight compression fit. When you remove the cable from the crimper, that end is ready to use.
8. For a standard “Straight-Through” cable, repeat all steps and wire color order on the other end of the cable. For a cross-over cable – the other end will have a different color order.
9. Make sure to test the cables before installing them. An inexpensive Ethernet cable tester does this quite well.

INTERNET PROTOCOLS
Internet protocols are sets of rules governing communication within and between computers on a network. Protocol specifications define the format of the messages to be exchanged. Timing is crucial to network operation. Protocols require messages to arrive within a certain amount of time so that computers do not wait indefinitely for messages that may have been lost.

Therefore, systems maintain one or more times during transmission of data. Protocols also initiate alternative actions if the network does not meet the timing rules. Many protocols consist of a suite of other protocols that are stacked in layers. These layers depend on the operation of the other layers in the suite to function properly.

THE MAIN FUNCTIONS OF PROTOCOLS

• Identifying errors
• Compressing the data
• Deciding how the data should be sent
• Addressing the data
• Deciding how to announce sent and received data

TCP/IP
The Transmission Control Protocol /Internet Protocol (TCP/IP) suite of protocols has become the dominant standard for internetworking. TCP/IP represents a set of public standards that specify how packets of information are exchanged between computers over one or more networks.

IPX/SPX
Internetwork Packet Exchange/Sequenced Packet Exchange is the protocol suite originally employed by Novell Corporation’s network operating system, NetWare. It delivers functions similar to those included in TCP/IP. Novell in its current releases supports the TCP/IP suite. A large installed base of NetWare networks continues to use IPX/SPX.

NetBEUI
NetBIOS Extended User Interface is a protocol used primarily on small Windows NT networks. NetBEUI cannot be routed or used by routers to talk to each other on a large network. NetBEUI is suitable for small peer-to-peer networks, involving a few computers directly connected to each other. It can be used in conjunction with another routable protocol such as TCP/IP. This gives the network administrator the advantages of the high performance of NetBEUI within the local network and the ability to communicate beyond the LAN over TCP/IP.

AppleTalk
AppleTalk is a protocol suite used to network Macintosh computers. It is composed of a comprehensive set of protocols that span the seven layers of the Open Systems Interconnection (OSI) reference model. The AppleTalk protocol was designed to run over LocalTalk, which is the Apple LAN physical topology. This protocol is also designed to run over major LAN types, notably Ethernet and Token Ring.

HTTP
Hypertext Transfer Protocol governs how files such as text, graphics, sound, and video are exchanged on the World Wide Web (WWW). The Internet Engineering Task Force (IETF) developed the standards for HTTP.

FTP
File Transfer Protocol provides services for file transfer and manipulation. FTP allows multiple simultaneous connections to remote file systems.

SSH
Secure Shell is used to securely connect to a remote computer.

Telnet
It is an application used to connect to a remote computer that lacks security features.

POP3
Post Office Protocol is used to download e-mail from a remote mail server.

IMAP
Internet Message Access Protocol is also used to download e-mail from a remote mail server.

SMTP
Simple Mail Transfer Protocol is used to send e-mail to a remote e-mail server.

PROTOCOL PORTS

IP Addressing
An IP address   Each device on a network must have a unique IP address to communicate with other network devices. Network devices are those that move data across the network, including hubs, switches, and routers. On a LAN, each host (device that sends or receives information on the network) and network device must have an IP address within the same network to be able to communicate with each other.

A person’s name and fingerprints usually do not change. They provide a label or address for the person’s physical aspect—the body. A person’s mailing address, on the other hand, relates to where the person lives or picks up mail. This address can change. On a host, the Media Access Control (MAC) address is assigned to the host Network Interface Card (NIC) and is known as the physical address. The physical address remains the same regardless of where the host is placed on the network in the same way that fingerprints remain with someone regardless of where he or she goes.

An IP address consists of a series of 32 binary bits (1s and 0s). It is very difficult for humans to read a binary IP address. For this reason, the 32 bits are grouped into four 8-bit bytes called octets. An IP address, even in this grouped format, is hard for humans to read, write, and remember. Therefore, each octet is presented as its decimal value, separated by a decimal point or period. This format is called dotted-decimal notation. When a host is configured with an IP address, it is entered as a dotted-decimal number, such as 192.168.1.5.

Five Classes of IP Address

Subnet Mask
The subnet mask indicates the network portion of an IP address. Like the IP address, the subnet mask is a dotted-decimal number. Usually all hosts within a LAN use the same subnet mask.

Default subnet masks for usable IP addresses

• 255.0.0.0: Class A, which indicates that the first octet of the IP address is the network portion
• 255.255.0.0: Class B, which indicates that the first two octets of the IP address are the network portion
• 255.255.255.0: Class C, which indicates that the first three octets of the IP address are the network portion

IPCONFIG
Ipconfig is a command used to find out the IP address of a certain network you are connected to.

How to use the ipconfig command?

1. Click on Start Button, then type cmd (command prompt) on the search box.

2. A black screen will appear.

3. Type ipconfig and press enter. The figure below shows the IP configuration window using the ipconfig command. The information from this window will be useful because it shows the IP address, subnet mask and default gateway of a network you are connected to.

Assigning a STATIC IP Address
In a home network with several computers and devices, it is ideal to assign each of them a specific address. This is for the purpose of avoiding problems when you do troubleshooting which requires figuring out the IP address of each of them. It is also a means to prevent address conflicts between the devices. You can also manage them with ease if you have assigned their own addresses.

1. Click the Start button and type ncpa.cpl.
2. Open the icon representing your computer’s network connection.
3. Click the Properties button in the Status dialog box.

4. From the list of items, choose Internet Protocol (TCP/IP).

5. Click the Properties button. The Internet Protocol (TCP/IP) Properties dialog box appears.
6. Type the IP address for your computer. Enter the appropriate IP Address in the IP address section.

7. Type a subnet mask. The value used on a local network is commonly 255.255.255.0, but it can be different, such as 255.255.255.127.

8. Type the default gateway address. The default gateway is the router, so type the router’s address.
9. Type the address for the preferred DNS server. The address should be obtained from your Internet Service Protocol. It is used to help your computer find web pages and other addresses on the internet.
10. Type the address for the alternate DNS server. The alternate Domain Name System (DNS) server’s IP address is something that your ISP provides.
11. Click OK to confirm the settings.

12. Close all other open dialog boxes and windows.

Dynamic Host Configuration Protocol (DHCP)
Dynamic Host Configuration Protocol (DHCP) is a software utility used to dynamically assign IP addresses to network devices. This dynamic process eliminates the need to manually assign IP addresses. A DHCP server can be set up and the hosts can be configured to automatically obtain an IP address.

Dynamic Host Configuration Protocol (DHCP) is a software utility used to dynamically assign IP addresses to network devices. This dynamic process eliminates the need to manually assign IP addresses. A DHCP server can be set up and the hosts can be configured to automatically obtain an IP address.

When a computer is set to obtain an IP address automatically, the other entire IP addressing configuration boxes are dimmed or disabled. The server maintains a list of IP addresses to assign, and it manages the process so that every device on the network receives a unique IP address. Each address is held for a predetermined amount of time. When the time expires, the DHCP server can use this address for any computer that joins the network.

These are the IP address information that a DHCP server can assign to hosts:

• IP address
• Subnet mask
• Default gateway
• Optional values, such as a Domain Name System (DNS) server address

The DHCP server receives a request from a host. The server then selects IP address information from a set of predefined addresses that are stored in a database. After the IP address information is selected, the DHCP server offers these values to the requesting host on the network. If the host accepts the offer, the DHCP server leases the IP address for a specific period of time.

Using a DHCP server simplifies the administration of a network because the software keeps track of IP addresses. Automatically configuring TCP/IP also reduces the possibility of assigning duplicate or invalid IP addresses. Before a computer on the network can take advantage of the DHCP server services, the computer must be able to identify the server on the local network. You can configure a computer to accept an IP address from a DHCP server by clicking the Obtain an IP address automatically option in the NIC configuration window.

If your computer cannot communicate with the DHCP server to obtain an IP address, the Windows operating system automatically assigns a private IP address. If your computer is assigned an IP address in the range of 169.254.0.0 to 169.254.255.255, it can communicate with only other computers in the same range.

An example of when these private addresses would be useful is in a classroom lab where you want to prevent access outside to your network. This operating system feature is called Automatic Private IP Addressing (APIPA). APIPA continually requests an IP address from a DHCP server for your computer.

PING
The ping is a Command Prompt command used to test the ability of the source computer to reach a specified destination computer. The ping command is usually used as a simple way to verify that a computer can communicate over the network with another computer or network device.

The ping command operates by sending Internet Control Message Protocol (ICMP) Echo Request messages to the destination computer and waiting for a response. How many of those responses are returned, and how long it takes for them to return, are the two major pieces of information that the ping command provides.

PING COMMAND SYNTAX

Using the PING Command
Ping is one of your most important tools in troubleshooting Internet problems. It shows you whether the Domain Name Server is working, whether the computer you are trying to talk to is reachable, and how long it takes to get there. It does this at a very low level — only the most basic Internet functions have to be up and running.

1. Click on Start Button, then type cmd.
2. A black screen will appear.
3. Type ping followed by the IP address you desire to verify.

This output shows several things:

• Decoding names to network addresses — A domain name server (DNS) resolves machine names to numeric addresses. A single machine can have many names, all of which resolve to the same Internet address. In the example just given, the name //www.google.com resolves to the Internet address 122.2.152.23.

• Round-trip response time — The parts of the replies that say things like time=105ms show you how long it took from the time the client machine sent out the ping message until a reply came back (1 ms is 1 millisecond or one-thousandth of a second). The variability in the times you see reflects that networks do not always respond identically. Differing amounts of traffic on the communication lines or differing loads on the server are common causes.

• Routing hop count — The part of the replies that say TTL=50 tells you about the route the message took from one point to another. The acronym TTL stands for Time to Live, which is a measure of how many rerouting from one point to another the packet has to go through before IP declares it undeliverable. The number following TTL (called the hop count) is a number that usually starts at 255 and counts down by one every time the message gets rerouted through an intermediary computer.