Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network.
The following sections discuss the types of cables used in networks and other related topics.
- Unshielded
Twisted Pair (UTP) Cable
- Shielded
Twisted Pair (STP) Cable
- Coaxial
Cable
- Fiber
Optic Cable
- Wireless
LANs
- Installing
Cable - Some Guidelines
Unshielded Twisted Pair (UTP) Cable
Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks (See fig. 1).
Fig.1. Unshielded twisted pair
The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated five categories of wire.
Categories
of Unshielded Twisted Pair
Type
|
Use
|
Category 1
|
Voice Only (Telephone Wire)
|
Category 2
|
Data to 4 Mbps (LocalTalk)
|
Category 3
|
Data to 10 Mbps (Ethernet)
|
Category 4
|
Data to 20 Mbps (16 Mbps
Token Ring)
|
Category 5
|
Data to 100 Mbps (Fast
Ethernet)
|
One difference between the different categories of UTP is the tightness of the twisting of the copper pairs. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. Buy the best cable you can afford; most schools purchase Category 3 or Category 5. Category 5 cable is highly recommended.
If you are designing a 10 Mbps Ethernet network and are considering the cost savings of buying Category 3 wire instead of Category 5, remember that the Category 5 cable will provide more "room to grow" as transmission technologies increase. Both category 3 and category 5 UTP have a maximum segment length of 100 meters. In
Unshielded Twisted Pair Connector
The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector (See fig. 2). A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.
Fig.2. RJ-45 connector
Shielded Twisted Pair (STP) Cable
A disadvantage of UTP is that it may be susceptible to radio and electrical frequency interference. Shielded twisted pair (STP) is suitable for environments with electrical interference; however, the extra shielding can make the cables quite bulky. Shielded twisted pair is often used on networks using Token Ring topology.
Coaxial Cable
Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield (See fig. 3). The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers.
Fig.3. Coaxial cable
Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial cabling are: thick coaxial and thin coaxial.
Thin coaxial cable is also referred to as thinnet. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to the approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable is popular in school networks, especially linear bus networks.
Thick coaxial cable is also referred to as thicknet. 10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to the maximum segment length being 500 meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network. One disadvantage of thick coaxial is that it does not bend easily and is difficult to install.
Coaxial Cable Connectors
The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector (See fig. 4). Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather than screw, onto the cable.
Fig.4. BNC connector
Fiber Optic Cable
Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials (See fig. 5). It transmits light rather than electronic signals, eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting.
Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify. 10BaseF refers to the specifications for fiber optic cable carrying Ethernet signals.
Fig.5. Fiber optic cable
Facts about fiber optic cables:
- Outer insulating jacket is made of Teflon or PVC.
- Kevlar fiber helps to strengthen the cable and prevent
breakage.
- A plastic coating is used to cushion the fiber center.
- Center (core) is made of glass or plastic fibers.
Fiber Optic Connector
The most common connector used with fiber optic cable is an ST connector. It is barrel shaped, similar to a BNC connector. A newer connector, the SC, is becoming more popular. It has a squared face and is easier to connect in a confined space.
Ethernet
Cable Summary
Specification
|
Cable Type
|
Maximum length
|
10BaseT
|
Unshielded Twisted
Pair
|
100 meters
|
10Base2
|
Thin Coaxial
|
185 meters
|
10Base5
|
Thick Coaxial
|
500 meters
|
10BaseF
|
Fiber Optic
|
2000 meter
|
Wireless LANs
Not all networks are connected with cabling; some networks are wireless. Wireless LANs use high frequency radio signals or infrared light beams to communicate between the workstations and the file server. Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data. Information is relayed between transceivers as if they were physically connected. For longer distance, wireless communications can also take place through cellular telephone technology or by satellite.
Wireless networks are great for allowing laptop computers or remote computers to connect to the LAN. Wireless networks are also beneficial in older buildings where it may be difficult or impossible to install cables.
Wireless LANs also have some disadvantages. They are very expensive, provide poor security, and are susceptible to electrical interference from lights and radios. They are also slower than LANs using cabling.
Installing Cable - Some Guidelines
When running cable, it is best to follow a few simple rules:
- Always use more cable than
you need. Leave plenty of slack.
- Test every part of a network
as you install it. Even if it is brand new, it may have problems that will
be difficult to isolate later.
- Stay at least 3 feet away
from fluorescent light boxes and other sources of electrical interference.
- If it is necessary to run
cable across the floor, cover the cable with cable protectors.
- Label both ends of each
cable.
- Use cable ties (not tape) to
keep cables in the same location together.
 |
||||||||||||||||||||||||
| 4 pair
cable's color code table. Every pair uses white as a tip color and one of
four (blue, orange, green, brown) ring colors.
Please note that CAT5 cable shown for clarity of the illustrations (tightly twisted conductors). You will see the same color code in a lesser grade cable (CAT3, voice grade) but the conductors of the pair will not be as close together and so they will be marked with small stripes of the opposite color (blue stripes on white, white stripes on blue and so on). This way you can identify the conductors as belonging to the same pair even though they are not close together in the loose bundle of wires you get after stripping the jacket off
|
Categories of twisted pair cabling systems
|
 |
|
  - ANSI/EIA
(American National Standards Institute/Electronic Industries Association)
Standard 568 is one of several standards that specify "categories"
(the singular is commonly referred to as "CAT") of twisted
pair cabling systems (wires, junctions, and connectors) in terms of the
data rates that they can sustain effectively. The specifications describe the
cable material as well as the types of connectors and junction blocks to be
used in order to conform to a category. These categories are:
The CAT 6 specification is now completed and for some time products have been offered that conform to this specification which improves on CAT 5E in terms of near-end crosstalk and other ways. According to IEEE, 70% of new installs in 2004 were CAT 6. A CAT 7 specification exists but is not yet official. |
HOW to make Cables
This document shows how to properly construct a Crossover network cable. This cable can be used to directly connect two computers to each other without the use of a hub or switch. The ends on a crossover cable are different from each other, whereas a normal 'straight through' cable has identical ends. Their uses are shown in the following diagrams.
This document shows how to properly construct a Crossover network cable. This cable can be used to directly connect two computers to each other without the use of a hub or switch. The ends on a crossover cable are different from each other, whereas a normal 'straight through' cable has identical ends. Their uses are shown in the following diagrams.
Crossover cable use
'Straight Through' cable use
Typically the ports on a hub are MDIX ports. This allows the machine at the other end to utilize its
To expand on this a little, when using a hub or switch, the Transmit wires on the workstation need to be connected to the Receive wires on the hub; likewise, the Receive wires on the hub need to be connected to the Transmit wires on the workstation. But if you remember what we stated earlier - cables which are run from PC to Hub are 'straight through' type cables. This is because the hub is providing the required crossover functions internally for you. Thus, when you connect two machines together without the use of a hub or switch, a crossover cable is required - because both 'ends' are essentially the same - a NIC Card. The crossover function must take place somewhere, and since there is no hub or switch to do it for you, the cable must.
Now that we know what a crossover cable is for, let's talk for a few about types of cabling. The two most common unshielded twisted-pair (UTP) network standards are the 10 Mbit (10BASE-T Ethernet) and the 100Mbit (100BASE-TX Fast Ethernet). In order for a cable to properly support 100 Mbit transfers, it must be rated Category 5 (or CAT 5). This type of low loss extended frequency cable will support 10 Base T, 100 Base-T and the newer 100VG-AnyLAN applications. Other types of cabling include Category 3 which supports data rates up to 16 Mbps, and Category 1 which only supports speeds up to 1Mbps. The cable we are about to make is considered Category 5, and will work on both 10 Mbit and 100 Mbit systems, assuming all components used (cables and jacks) are rated for Category 5.
What you need
Cable - Be sure the cable(s) you are using is properly rated for CAT 5. It should state clearly on the jacket of the cable, what it is rated at. One option that you have when selecting your cable is to use a pre-made normal 'straight through' cable, and simply whack off one of the ends, and replace with a new "Crossed Over" end. For the purpose of this article, though, we aren't going to go that route. We are going to make the whole thing from scratch - using bulk CAT 5 cable.
Keep everything within hands reach of you...
Connectors - Crossover cables are terminated with CAT 5 RJ-45 (RJ stands for "Registered Jack") modular plugs. RJ-45 plugs are similar to those you'll see on the end of your telephone cable except they have eight versus four contacts on the end of the plug. Also, make sure the ends you select are rated for CAT 5 wiring. There are also different types of jacks which are used for different types of cabling (such as Solid Core wire). Make sure you buy the correct jacks for your cabling.
Crimper - You will need a modular crimping tool. My advice on what brand to get? Well, I really don't have a preference at this point, but make sure you buy a good one. If you spend about 40 to 50 bucks, you should have one that will last ya a lifetime. Spend 10 to 20 bucks, and you might be able to make a few cables with it if you're lucky. You definitely get what you pay for when it comes to crimpers!
Stripper - No I'm not talking about what Spot had at his bachelor party, I am talking about a tool to strip the ends off the wires you pervert! There are several specialized tools, which can be used to strip the jackets off of cabling. If you do not have access to one of these tools, cautious use of a razor blade or knife should work just fine - but keep in mind if you go the razor blade / knife route, extra special care must be used as to not damage the wires inside the jacket.
Cutters - You need a pair of cutters that will allow you to cut a group of cables in a straight line. It is very important that all the wires are the same lengths, and without proper cutters, this can be a difficult task.
Doing the deed
You now know what crossover cables are used for. You know why you need one. You also know what you need to make one, so I guess we're ready... First thing you will want to do it cut off the appropriate length of cable that you will need. Be sure that it is plenty long enough. If you screw up, and don't cut it long enough, you will have to start all over, and you will not only waste you time, but cable and the RJ-45 ends as well. If you are pulling this cable through a wall, or ceiling, make sure the pulling is completed first. It is much more difficult to pull a cable with the ends already on it. So you have all the parts, you understand the concepts, and you have your cable, lets get started!
Baby steps...
1) - Start by stripping off about 2 inches of the plastic jacket off the end of the cable. Be very careful at this point, as to not nick or cut into the wires, which are inside. Doing so could alter the characteristics of your cable, or even worse render is useless. Check the wires, one more time for nicks or cuts. If there are any, just whack the whole end off, and start over.
1) - Start by stripping off about 2 inches of the plastic jacket off the end of the cable. Be very careful at this point, as to not nick or cut into the wires, which are inside. Doing so could alter the characteristics of your cable, or even worse render is useless. Check the wires, one more time for nicks or cuts. If there are any, just whack the whole end off, and start over.
2) - Spread the wires
apart, but be sure to hold onto the base of the jacket with your other hand.
You do not want the wires to become untwisted down inside the jacket. Category
5 cable must only have 1/2 of an inch of 'untwisted' wire at the end; otherwise
it will be 'out of spec'. At this point, you obviously have ALOT more than 1/2
of an inch of un-twisted wire, but don't worry - well take care of that soon
enough.
3) - Up to this point,
things have been pretty easy. Things will get a little bit tricky here, but
don't worry, we'll get through this together. We are at a point in this article
where a decision needs to be made. You need to decide which end of the cable
you are making at this point in time. If you are making your cable from scratch
like I am doing while writing this article, you have 2 end jacks, which must be
installed on your cable. If you are using a pre-made cable, with one of the
ends whacked off, you only have one end to install - the crossed over end.
Below are two diagrams, which show how you need to arrange the cables for each
type of cable end. Decide at this point which end you are making and examine
the associated picture below.
 |
 |
568a -
standard end
(you will need one of the ends on your cable to look like this) |
Crossed
over end wire pattern
(you will want the other end to look like this) |
Begin to untwist the twisted exposed wires on
your cable. Use caution so that you do not untwist them down inside the jacket.
Once you have all the wires untwisted begin to arrange them in the proper order
based on the pictures above. This stage can be a pain in the ass, especially
some of the middle wires. Once you get all the wired arranged in the proper
order, make sure your wire cutters are within reach then grasp them right at
the point where they enter the jacket. Make sure you keep them in the proper
order! Grab your cutters now. Line them up along your prepared wires about 1/2
inch above the jacket. Be sure at this point that you are both 1/2 inch above
the jacket, and that your cutters are aligned straight across the wires. You
want to make a clean cut here - also make sure you don't let go of that jacket
/ wires!
4) - Don't worry. From this point forward things get a lot easier. Grab your jack, and begin to slide the wires into the jack. Once you get to the point where the jacket begins to enter the jack things might get a little tough, but just have some patience and hold onto those wires. It will fit in there just fine. Once it is in as far as it will go the wires should extend almost to the front of the jack, and about 3/8 of an inch of the jacket will be inside the jack. Like the pictures below.
5) - Grab those crimpers - because not all crimpers are exactly the same your pictures may not match exactly what you see below. Be sure to keep a good grip on that jack and the cable. Insert the jack into the crimper. It should only go in one way, so you don't have a whole lot to worry about inserting it. Begin to compress those crimpers. You will more than likely hear a clicking sound. Keep squeezing. If you try to let go to early, nothing will happen. They will not release. Keep going until they stop clicking / stop moving all together. At this point, you should be able to let go of the jack, and the crimpers. The crimpers should release now leaving you with a crimped jack. If the crimpers do not release, you probably are a wimp and didn't press hard enough. Go ask your mom to help you at this point. She can probably finish what you started.
 |
 |
Insert
the jack into the crimper
|
Crimp
it! Crimp it good!
|
6) - It's time to examine what we have done. If you look at the end of the jack (distal), you should see that the copper connectors should not be pressed down into the wires. Toward the back of the jack (where the jacket meets the jack) it should be crimped securely holding the jacket / cable in the jack. If something has gone wrong, don't worry, its not the end of the world. Grab those cutters, and just whack the whole jack off and start back at step 1 (a pain in the ass I know, but its better to have a cable that works, than to spend hours trouble shooting your PC trying to figure out why you can't see the other machine). If everything is cool, all you have to do now is make the other end of the cable (unless you are using a pre-fab cable and have whacked one of the ends off), so go back to step one, and make the other end now.
In
closing
You should now have a fully functional CAT 5 Crossover cable. It's a good idea to label it as such, especially if you have a lot of other cables lying around. So what are ya waiting for... install the cable and test it out. If it doesn't work, double-check the ends. There is always a possibility that you have overlooked something. If so just whack the bad end and make new one. Remember the more jacks you install, and the more cables you make, the easier it gets. It's really not that hard to do, the first time is definitely the most difficult.
Here are a few other things to keep in mind...
You should now have a fully functional CAT 5 Crossover cable. It's a good idea to label it as such, especially if you have a lot of other cables lying around. So what are ya waiting for... install the cable and test it out. If it doesn't work, double-check the ends. There is always a possibility that you have overlooked something. If so just whack the bad end and make new one. Remember the more jacks you install, and the more cables you make, the easier it gets. It's really not that hard to do, the first time is definitely the most difficult.
Here are a few other things to keep in mind...
- Maximum Cable length for including
connectors is 100 meters (or about 328 feet)
- Do not allow the cable to be
sharply bent, or kinked, at any time. This can cause permanent damage to
the cables' interior
- Do not overtighten cable ties
- Do not use excessive force when
pulling cable through floors, walls or ceilings
- Do not use staples to secure
category-5 cable, use the proper hangers, which can be found at most
hardware stores
- ================================================
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