Ethernet/category 5 Network Cabling Guide

Transcript

Ethernet/Category 5 Network Cabling Guide Prepared by SJ Wilkinson (August 2002) Based on Steve DeRose’s Guide to CAT5 Network Wiring (See later Web Reference) Networks A Local Area Network (LAN) can be as simple as two computers, each having a network interface card (NIC) or network adapter and running network software, connected together with a crossover cable. Here the crossover cable would have a plug at either end to connect into the NIC socket at the back of each computer. The next step up would be a network consisting of three or more computers and a hub. Each of the computers is plugged into the hub with a straight-thru cable (the crossover function is performed by the hub). For a small network the straight-thru cables would have plugs at either end – one to connect to the computer and one to the hub. For larger networks wall cabling, wall sockets and patch cables are used. A CAT5 "patch panel" is used at the hub end where all your wires come together and provides a group of sockets for further cables. Straight-thru patch cables connect computers to sockets (jacks). Straight-thru wall cables connect sockets to the patch panel. Straight-thru patch cables connect the patch panel to the hub. Patch panels often make network cabling neater but are not essential as (a) wiring a plug is no harder than wiring a panel; (b) you still need cables to go from the panel to the hub; and (c) it adds extra connections, so lowers reliability. 1 Planning your Network Pick a location for your hub, preferably centred to keep cable runs shorter. For larger network it may save you a lot of wiring if you use different hubs in different location: weigh your time and the cost of wire, versus the cost of an extra hub(s). Map out your wiring plan and decide how many wires go to each place. You may want to pull cable TV, phone, audio, intercom, etc. at the same time. You may want to install flexible conduit and/or leave a string in to pull more wires if you anticipate adding wires later. Plan wire placements to avoid anything that puts out much of a magnetic field. Stay at least 6" from electrical wires if running parallel to them. Make a materials list and then order materials. Plan to leave a couple extra feet at each end of each wire run. Buy at least 10% more of everything (especially wire) than you think you'll need. If you're new to this, practice cutting and stripping until you can cut the outer insulation without nicking the inner insulation. Practice fitting connectors and keystones on scrap cable. Learn how to use any network testers you have. Try your made-up patch cables in a working network to make sure they support 100Mbps speeds. What you need Make sure every part you use is at least CAT5 rated. Lots of CAT3 parts look about the same, but won't handle higher data rates. • CAT5 wire or better. Much cheaper by the 1000-foot reel. • CAT5 RJ45 sockets for the equipment end of your wires. These normally come in two or three parts – a backplate, a cover (or faceplate) and a keystone (or insert). • CAT5 modular plugs/connectors for the hub end of your wires and for the patch cables to connect computer to socket • An Ethernet hub to plug all those plugs into • A RJ-45 568A or 568B (preferably both) patch panel • A modular RJ-45 plug crimp tool. Phone ones won't do it. You don't need a lot of bells and whistles, just a tool that will securely crimp RJ-45 connectors. • A stripping tool. These make a much neater cut than the old pliers-type. • Diagonal wire cutters ("4 to 6"). It is easier to use diagonal cutters to cut the cable off at the reel and to fine-tune the cable ends during assembly. • If you are installing a patch-panel you will also need a 110 Punch-Down tool to push the wires into the back. • A RJ-45 CAT5 cable tester. Wire an Ethernet plug to some alligator clips and you can use the tester for lots of other things too (but don't try it on live power circuits!). • Cable ties or a cable staple gun (must be designed for CAT5). • Cable-labelling tape. • Typical stuff like screwdrivers, pliers, sledgehammers, etc. • Safety glasses, dust mask, gloves, and other safety equipment as appropriate. • An inductive signal tracer is also a really good investment if you are adding to a network: you clip the tester on one end of a wire, and the tracer lets you follow the wire even hidden behind walls, or obscured in bundles. Don't forget Ethernet cards for your devices (most new machines have them off-the-shelf, as Macs have for years), and short Ethernet cables to go from outlets to devices. 2 Cable Ethernet networks are generally used for connecting machines, printers, etc. in a single building. Older Ethernets ran on coax cables ("10base-2") a little like the cable used for TV aerials. Newer networks use phone-like "twisted pairs": "10base-t" can carry 10 Megabits (not Megabytes!) per second, and "100base-t" can carry 100 Mbps.. Ease of use and lower cost has given twisted-pair cables the advantage over the older thinwire, coaxial cables. Category 5 (CAT5) cabling is one type of twisted-pair cable and is used for most modern networking CAT5 wiring will happily work at either 10Mbps or 100Mbps, with just about any machine; so you can run a slow net now, and upgrade later without rewiring. One snag is that your network must be arranged in a "star". That is, every device must have a separate wire back to the hub. CAT 5 cable has four twisted pairs of wire for a total of eight individually insulated wires. Each pair is colour coded with one wire having a solid colour (blue, orange, green, or brown) twisted around a second wire with a white background and a stripe of the same colour. The solid colours may have a white stripe in some cables. Cable colours are commonly described using the background colour followed by the colour of the stripe; e.g., white-orange is a cable with a white background and an orange stripe. CAT5 wire is typically 24AWG solid copper with each pair twisted about 3 times per inch (actually, each pair is twisted at a different rate). You can get it with or without a foil shield, and in various outer insulation materials. Commercial cable is often made with stranded instead of solid wire to enable easier bending without breaking. This type of cable apparently has lower high-frequency performance, so keeping patch cables as short as possible seems like a very good idea. Wiring Schemes There are many, many different ways to connect the eight wires of a CAT5 cable to the eight wires of another CAT5 cable. Luckily for network engineers three standard wiring schemes exist for CAT5, called T568A, T568B, and USOC. USOC is traditionally found in telecommunications systems and has a sequence of: brown/white, green/white, orange/white, blue, blue/white, orange, green, brown. T568A and T568B are classed as standard for Ethernet networks and so the rest of this document will refer only to these two schemes. 3 As can be seen in the diagram the only difference between the two schemes is the interchanging of the 2nd and 3rd pairs (white/orange and white/green, respectively). There is no difference between the two wiring schemes in connectivity or performance when connecting two modular devices so long as they are both wired for the same scheme. The only time when one scheme has an advantage is when one end of a segment is to be connected to a punch block. In this case the 568A has the advantage of having a more natural progression of pairs. Even though the 568A scheme is preferred for new installations, both wiring methods exist within the 568A Standard. The reason for this is that a great deal of cabling plants has already been installed to the B standard (formerly known as WECO or AT&T 258A). Today the most popular wiring method remains 568B. However the existence of both methods does nothing but cause errors and confusion. Originally, patch panels and jacks were manufactured either A or B and were often not labelled as such. Most suppliers stocked only the B wired products. Luckily, today, almost all jacks and patch panels show diagrams for both A and B. Of course it makes no functional difference which standard you use for a straight-thru cable. A 568A patch cable will work in a network with 568B wiring and 568B patch cable will work in a 568A network. The electrons couldn't care less. However, such a mixture of schemes can cause confusion when adding crossover cabling and/or troubleshooting. So which method to choose? The answer, is that it does not matter at all, unless you are terminating one end onto a punch block, in which case, the A method has an advantage. The main thing is that you choose one method, and stick with it. If adding wiring to an existing installation check what scheme has been adopted and use that. Crossover Cables CAT5 signals are "balanced": the striped and solid wires in a pair carry the same information negated, so their magnetic fields tend to cancel. Unlike phone wires, CAT5 wires do not cross over; the same wires go to the same pin numbers at all connectors. This works because hubs all have internal crossovers. 4 2-computer networks with no hub, hub-to-hub and hub-to-router interconnects all need a special crossover cable. Basically, a crossover cable swaps pairs 2 and 3 (not the wires within each pair); pairs 1 and 4 go straight through. This means one end is T568A and the other is T568B. You can start a crossover cable with either standard as long as the other end is the other standard. So a crossover cable looks like: Noise and Crosstalk Ethernets consist of two transmission lines. Each transmission line is a pair of twisted wires. One pair receives data signals and the other pair transmits data signals. A balanced line driver or transmitter is at one end of one of these lines and a line receiver is at the other end. With only two transmission lines, Ethernet only needs 4 wires of the 8 inside CAT5 cable. Only pair 3 (green, on pins 1 and 2), and pair 2 (orange, on pins 3 and 6) are actually used. You can split out the 8 into two sets of 4, and put 2 devices at the end of any wire (there are even handy adapters for this, like a one-to-two phone line adaptor; sadly they're not easy to find, but you can make one with a plug and two sockets). Or you may be able to use the other pairs for phone lines. However, the formal CAT5 definition reserves the remaining wires, so this is technically not allowed. Pulses of energy travel down the transmission line at about the speed of light (186,000 miles/second). This energy can also be considered as residing in the magnetic field that surrounds the wires and the electric field between the wires. In other words, an electromagnetic wave that is guided by, and travels down the wires. The main concern is the transient magnetic fields which surrounds the wires and the magnetic fields generated externally by the other transmission lines in the cable, other network cables, electric motors, fluorescent lights, telephone and electric lines, lightning, etc. This is known as noise or cross-talk (the term cross-talk came from the ability to overhear conversations on other lines on your phone) . This noise may slow or completely bury the Ethernet pulses, the conveyor of the information being sent down the line. The primary means of reducing noise between the pairs in the cable, is the double helix configuration produced by twisting the wires together. This configuration produces symmetrical (identical) noise signals in each wire. Ideally, their difference, as detected at the receiver, is zero. In actuality it is much reduced. 5 Cabling Tips • • • • • • • • • • • • • • • • • • • Plan your network carefully before you begin. Decide where you network sockets now and in the future. Choose either 568A or 568B wiring standard, before you begin your project. Run all cables in a "Star" configuration. Keep all cable runs to a maximum of 295 feet (for each run). If you need to cross an open area, install proper cable supports, spaced no more than 5 feet apart. Keep CAT 5 cables as far away as possible from potential sources of electromagnetic noise as possible. This may include copy machines, electric heaters, speakers, printers, TV sets, fluo rescent lights, copiers, welding machines, microwave ovens, telephones, fans, elevators, motors, electric ovens, dryers, washing machines, and shop equipment. Try to avoid running cables parallel to power cables or tying cables to electrical conduits. Do not run UTP cable outside of a building. It presents a very dangerous lightning hazard! Start with the longest runs first: that way if you do damage a wire, you have a chance of cutting out the damage and having enough for a short run later. Start by getting wires in place. Dress the cables neatly with cable ties to support long runs and to ensure gradual rather than sharp curves. Allowing the cable to be sharply bent, or kinked can cause permanent damage to the cables' interior. Don’t over tighten cable ties on single or groups of cables. Don’t use a stapler that crimps the cable tightly. It's best to finish each cable and test it before going on to the next. Maintain the twists of the pairs all the way to the point of termination, or no more than 0.5" untwisted. Don’t skin off more than 1" of jacket when terminating. Never install taut cables. A good installation should have the cables loose, but never sagging. Don’t use excessive force when pulling cable. Use cable pulling lubricant for cable runs that may otherwise require great force to install. Don’t use oil, or any other lubricant, not specifically designed for cable pulling. These can infiltrate the cable, causing damage to the insulation. Treat the cable with care. Do not stomp on it, crimp it, bend, fold, spindle, or otherwise mutilate. You can easily make the wire no good for 100MB with no visible sign of damage. If you put a staple through it, plan on replacing the run. Always label every termination point with a unique number. This helps to make changes and troubleshooting as simple as possible. Always install jacks in such a way as to prevent dust and other contaminants from settling on the contacts. The contacts of the jack should face up on flush mounted plates, or left, right, or down on surface mounted boxes. Do not splice or bridge CAT5 cable at any point. Always test every installed segment with a cable tester. Always leave extra slack on the cables, neatly coiled up in the nearest concealed place. Always obey all local, and national, fire and building codes. Always use grommets to protect the cable where passing through metal studs or anything that can possibly cause damage to them. Be sure to "firestop" all cables that penetrate a firewall. Use plenum rated cable where it is mandated. Do not install cable that is supported only by ceiling tiles or other potentially weak supports. 6 Sockets and Keystones CAT5 RJ-45 network sockets are made up of three main parts: the backplate (or backbox), the cover (or faceplate) and the keystone (or insert). The backplate (backbox) fits onto (into) the wall. The keystone is connected to the wall cable and provides the socket for the RJ-45 plug on the end of the patch cable. The cover (faceplate) makes the whole assembly look pretty. To assemble the socket you need to: 1. Attach the backplate to the wall (or sink the backbox into the wall). 2. Pass the network cable through the backplate or backbox. It is often easier to wire the sockets first so that you can have as much cable as you need – then pull it through towards the hub afterwards. Make sure that you have at least 4” to work with. 3. Strip the Cable. Trim the jacket of the cable back approximately 1 inch. Don't strip the wires. Remove only as much outer cover as you need to do the connections. Do not damage the conductors. If you nick them, cut the cable off and start again. Fan out all four twisted pairs. 4. Align The Wires In the Slots. Following the instruction of the colour-coded wire positions printed on the keystone, lay the conductors into the punch down slots. Untwist each pair just enough to get the wire ends all even. Keep pairs twisted as close to the punch down slots as possible. They must be twisted within ½” to conform to Cat 5 specifications. 5. Terminate The Wires In The Slots. Make sure that the wires are in the proper slot. Double-check which wire is which. Most RJ-45 keystones are self-terminating with a plastic header cover that snaps down or hinges down over the connector and provides a secure connection. 6. Trim the ends. Don't let copper hang beyond the ends of the keystone, it can easily bend a little and short out the cable. 7. Insert keystone into cover or faceplate. Keystones normally only fit one way into the socket cover or faceplate. Make sure you don’t force it or it will break the socket. 8. Attach cover/faceplate to backplate/backbox. 9. Test the connection. The hub end is likely to be without a plug to insert into a network tester so use crocodile clips, add a plug, or wire it into a patch panel so that you can test your new wall cable. 10. If the cable doesn’t work don’t immediately blame the keystone/socket. Check the plug or patch panel connections first – they are more likely to have errors. Plugs and Patch Cables The straight thru and crossover patch cables are terminated with CAT5 RJ-45 modular plugs. (RJ means “Registered Jack”). RJ-45 plugs are similar to those you’ll see on the end of your telephone cable except they have eight versus four or six contacts on the end of the plug and they are about twice as big. You can physically plug a 6-pin plug into an 8-pin socket, but it may damage pins 1 and 8 of the socket. Make sure that all connectors you buy are rated for CAT 5 wiring. There are some connectors designed for both solid core wire and stranded wire. Others are designed 7 specifically for one kind of wire or the other. Be sure you buy connectors appropriate for the wire you are going to use. To make up a patch cable with a plug on either end you need to: 1. Cut the cable to the desired length. If you are pulling cables through walls, a hole in the floor, etc., it easier to attach the RJ-45 plugs after the cable is pulled. The total length of wire segments between a PC and a hub or between two PC's cannot exceed 100 Meters (328 feet or about the length of a football field) for 100BASE-TX (and 10BASE-T). 2. Strip one end of the cable with the stripper. Place the cable in the groove on the blade (left) side of the stripper and turn the stripper about one turn or so. If you turn it much more, you will probably nick the wires. The idea is to score the outer jacket, but not go all the way through. Once scored, you should be able to twist the end of the jacket loose and pull it off with one hand while holding the rest of the cable with the other. 3. Inspect the wires for nicks. Cut off the end and start over if you see any. 4. Spread the pairs roughly in the order of the desired cable end. 5. Untwist the pairs and arrange the wires in the correct order. Flatten the ends between your thumb and forefinger. There should be little or no space between the wires. Trim the ends so they are even with one another. Make sure that the untwisted end is slightly less than ½” long. If it is longer it will be susceptible to crosstalk and if it is a lot less than ½” it will not be properly clinched when crimped. One trick is to strip a little more than you need, sort the wires into the right order, then trim them off evenly to the right length. 6. Insert the wire firmly into the plug whilst holding it with the clip facing down or away from you. The most common error at this point is putting the plug on upside down, which will swap the wire order and not work. Inspect it before crimping and wasting the plug! Looking through the bottom of the plug, the wire on the far left side will have a white background. The wires should alternate light and dark from left to right. The furthest right wire is brown. The wires should all end evenly at the front of the plug. The jacket should end just about where you see it in the diagram - right on the line. 7. Crimp the plug firmly after inserting it into the crimper Iit only goes in one way). The crimper pushes two plungers down on the RJ-45 plug. One forces a cleverly designed plastic plug/wedge onto the cable jacket and very firmly clinches it. The other seats the "pins," each with two teeth at its end, through the insulation and into the conductors of their respective wires. 8. Test the crimp. If done properly you should not easily be able to pull the plug off the cable with your bare hands. But, don't pull that hard on the plug. It could stretch the cable and change its characteristics. 9. Do it again so that the other end of the cable has the desired end and crimp. 10. Test the cable with a network tester. If both ends of the cable are within reach, hold them next to each other and look through the bottom of the plugs to check they are identical. But note that the most testers do not stress-test cables at high bit rates; it just tests that you've got all the connections right so Test the cable again by copying some large files over it as part of an operational network, if you have one. 11. If the cable doesn't work, inspect the ends again and make sure you have the right cable and that it is plugged into the correct units for the type of cable. If applicable try power-cycling (cold booting) the involved computers. 12. If the cable still doesn’t work, and the ends look good, try again with a different piece of cable – the previous piece may have been damaged. 8 Definitions Category 5 Cable (UTP) (Unshielded Twisted Pair) A multipair (usually 4 pair) high performance cable that consists of twisted pair conductors, used mainly for data transmission. Category-5 UTP cabling systems are by far, the most common (compared to SCTP) in the United States. Category 5 cable is typically used for Ethernet networks running at 10 or 100 Mbps. Category 5 E Cable (enhanced) Same as CAT5, except that it is made to somewhat more stringent standards. The CAT5E standard is now officially part of the 568A standard and is recommended for all new installations. It is designed for transmission speeds of up to 1 gigabit per second (1000Mbps). Category 6 Same as CAT5E, except that it is made to a higher standard. The CAT6 standard is not yet part of the 568A standard (at time of writing). Category 7 Same as CAT6, except that it is made to a higher standard. The CAT6 standard is not yet part of the 568A standard (at time of writing). CAT7 cable has all 4 pairs individually shielded, and an overall shield enwraps all four pairs. CAT7 will use an entirely new connector (i.e. not the familiar RJ45). Category 5 Cable (SCTP) (Screened Twisted Pair) Same as CAT5 above, except that the twisted pairs are given additional protection from interference by an overall shield. There remains disagreement over whether SCTP or UTP is better. CAT5 SCTP cabling systems require all components to maintain the shield, and are used almost exclusively in European countries. Category 5, RJ45 jack (Work Area Outlet) An 8 conductor, compact, modular, female jack that is used to terminate CAT5 cable at the user (or other) location. The jack is engineered to maintain the performance of CAT5 cabling. Category 5 Patch Panel A CAT5 Patch Panel is basically just a series of many CAT5 jacks, condensed onto a single panel of 12, 24, 48, and 96 ports. Patch panels are typically used where all of the horizontal cable sections meet, and are used to connect the segments to the Network Hub. Category 5 Patch Cable A CAT5 Patch Cable consists a length of CAT5 cable with a RJ-45 male connector, crimped onto each end. EIA/TIA 568A Standard This standard was published in July of 1991 and set the minimum requirements for CAT5 cable and hardware. The 568 "standard" is not to be confused with 568A or 568B wiring schemes which are part of the "568A standard". Prior to the adoption of this standard, many "proprietary" incompatible cabling systems existed. The 568A or 568B wiring scheme which dictates the pin assignments to the pairs of CAT5 cable in a jack, connector or patch-panel. There is no 568A and 568B difference between the two wiring schemes in connectivity or performance Wiring when used to connect two modular devices so long as both devices are wired for the same scheme. The only time when one scheme has an Schemes advantage over the other is when wiring to a punch block in which case 568A has the advantage of having a more natural progression of pairs. Four Pairs Pair 1: White / Blue Pair 3: White / Green Pair 2: White / Orange Pair 4: White / Brown Wiremap This is the most basic test that can be performed on a CAT5 segment. Wiremap tests for the basic continuity and absence of shorts, grounding, 9 and external voltage between two devises. All eight pins of each device should be wired straight through (1 to 1, 2 to 2, 3 to 3, etc.). Crosstalk Crosstalk is the "bleeding" of signals carried by one pair, onto another pair through the electrical process of induction (wires need not make contact, signals transferred magnetically). This is an unwanted effect that can cause slow transfer, or completely inhibit the transfer of data signals over the cable segment. Two types are NEXT (Near End Crosstalk), and FEXT (Far End Crosstalk). The purpose of the wire twists in CAT5 cable is to significantly reduce the crosstalk. Fibre Optic cable is the only medium that is 100% immune to the effects of crosstalk. Ambient Noise or Similar to crosstalk, in that it is an unwanted signal that is induced into the Electromagnetic cable. The difference is that ambient noise (or EMI) is typically induced Interference from a source that is external to the cable. (EMI) Attenuation Attenuation is the loss of signal in a cable segment due to the resistance of the wire plus other electrical factors that cause additional resistance (Impedance and Capacitance for example). A longer cable length, poor connections, bad insulation, a high level of crosstalk, or ambient noise, will all increase the total level of attenuation. Web References Steve DeRose's guide to CAT5 computer network wiring http://www.stg.brown.edu/~sjd/wiring/CAT5-wiring.html Category 5 Tutorial and FAQ's http://www.atcomservices.com/highlights/cat5notes.htm How To Make Your Own Cat 5 Twisted-Pair Network Cables http://duxcw.com/digest/Howto/network/cable/cable1.htm How To Terminate & Assemble Keystone Jacks http://www.9thtee.com/networkingts.htm 10