03 - Network Cabling and Hardware Devices

3.1 Copper Cables and Connectors

Twisted Pair Facts

Stuff to discuss here.

Coaxial Cable Facts

Stuff to discuss here.

Questions/Answers

Stuff to discuss here.

3.2 Fiber Optic Cables and Connectors

Fiber Optic Facts

Stuff to add here

3.3 Wiring Implementation

Twisted-Pair Construction

CrossOver Cables vs Straight Through Cables

Straight through cables have wires that much up with the same pins on the opposite connector. Crossover Cables are used to connect computers together w/o use of switches for communication. Connectors on these cables have to connect between their transmit to the opposite ends' receive.

ie. pair the TIA568A with TIA568B to make a crossover cable.

Straight-Through Cables

• Most twisted pair cables are manufactured as straight-through cables
• Connect computers to a hub or switch with a straight-through cable.
• The pinout order on a computer's network interface card (NIC) is different than the pinout order on the hub or switch port.
• Transmit pins of the NIC map to the receive pins on hub or switch and vice versa.

If a network device such as a hub or switch does not have an uplink port, use a crossover cable when connecting it to another network device.

You can also connect one computer directly to another using a crossover cable. A crossover cable maps the transmit pins on one end of the cable with the receive pins on the other end.

You can easily create a crossover cables as follows:

• Use the T568A standard to attach an RJ45 connector to one end.
• Use the T568B standard to attach an RJ45 to the other end.

RJ45 Wiring Conventions

Pin	TIA568A Order	TIA568B Order
1	Green w/ White	Orange w/ White
2	Green	Orange
3	Orange w/ White	Green w/ White
4	Blue	Blue
5	Blue w/ White	Blue w/ White
6	Orange	Green
7	Brown	Brown w/ White
8	Brown w/ White	Brown

Gigabit Ethernet Cabling

10-Mbps (10BASE-T) and 100-Mbps (100BASE-TX)

You use only 2 pairs of wires in Cat 3, Cat 5, or Cat 5e.

Computer NIC:

• Pin 1: Transmit +
• Pin 2: Transmit -
• Pin 3: Receive +
• Pin 6: Receive -

Pins 4, 5, 7, and 8 are unused.

1000BASE-T or Gigabit Ethernet

Uses all four pairs of wires in Cat 5e and above.

• There are positive (+) and negative (-) pins for each pair of wires.
• Signals go in both directions over each pair of wires, so there are no dedicated transmit and receive pins.
• The T568A and T568B wiring standards are still used.

If Cat 7 cabling is used for 10 Gigabit Ethernet, the cables are terminated with GG45 or TERA connectors.

• GG45 connectors require a special set of tools that are different from the RJ45 crimping tool.
• TERA connectors can be installed without any special tools.

Power over Ethernet Cabling (POE)

Lets you carry power over ethernet like a phone being powered.

• power is through unused pairs of wires in 10/100-Megabit Ethernet
• Power can be done via data wires
• Many network switches can apply PoE
• PoE injection devices can be added to the middle of the cable span

Wiring Distribution

Demarc

The demarcation point is where the line enters the building. Responsibility is determined on which side the point this occurs. ie. inside the building is for the network admin, outside is the ISP.

This is also known as the mininum point of entry (MPOE) or end user point of termination (EU-POT). Sometimes, we may need a Demarc extension in order to extend the line to the IDF where its actually needed.

Distribution Frames (MDF and IDF) and Building Industry Cross-Connect (BIX)

The MDF is the main wiring closet, from there it gets connected to IDFs using vertical cross connects, typically located above the MDF.

MDF: A traditional MDF may exist in a dedicated room or a within rack space in a datacenter. An MDF is usually located on the bottom floor or basement of a building. All internet or WAN demarcation points are normally near or within the MDF.

IDFs: IDFs are typically located on each floor directly above the MDF, although additional IDFs can be added on each floor as necessary. IDFs located above the MDF are connected using a vertical cross connect (VCC) or wire bundles that run vertically between the MDF and an IDF. If a floor has more than one IDF, the IDFs are connected with a horizontal cross connect (HCC).

BIX is certified for Cat 5e composed primarily of 2 parts

Punchdown Blocks

66 block

• 66 block has 25 rows of 4 metal pins, pushing wire into pin pierces plastic sheath
• Connects individual copper wires together
• in the 25-pair block (non-split block) all pins are bonded/electrically connected. this connects a single wire with up to 3 other wires
• 50-pair block (split block), each set of two pins in a row are bonded. we use this to connect a single wire to another. bridge clips connect pins and are used in troubleshooting/testing

When using with data:

• be sure to use blocks rated for cat 5
• when inserting wires, place both wires in a pair through the same slot to preserve the twist

110 Block

• 110 block comes in different sizes (50, 100, 300 pair)
• Has rows of plastic slots, with each slot connecting two wires Place the first wire into the plastic slot on the 110 block. Insert a connecting block over the wire and slot. The connecting block has metal connectors that pierce the plastic cable sheath. Place the second wire into the slot on the connecting block.
• C4 connectors connect 4 pairs of wires; C5 connectors connect 5 pairs
• Connecting Wires should be done in a specific order: White wire with a blue stripe followed by the solid blue wire. White wire with an orange stripe followed by the solid orange wire. White wire with a green stripe followed by the solid green wire. White wire with a brown stripe followed by the solid brown wire.
• 110 is mostly used for telephone applications. Preferred over 66-block, because they introduce less crosstalk

When using with data:

• Use blocks rated for Cat 5, 6, and 6a
• Inserting wires, preserve the twist

Krone is an alternative to the 110 block.

3.4 Troubleshooting Network Media

Troubleshoot Copper Wiring Issues

Interference

EMI

Presence of a foreign electrical signal on a wire. Typically EMI, electromagnetic interference. Absorbed electromagnetic field results in the interference. This can lead to seeing CRC errors on an interface.

EMI can be caused by nearby devices that use electricity. Say near generators, or motors or even fluorescent lights

How to eliminate interference:

• use fiber optic cables
• use STP shielded twisted pair cables. typically uses foil sheathing.
• Use a drain wire, a wire that doesn't have plastic coating. EMI will be absorbed by the drain wire.
• Cat 6 and Cat 7 are typically used since they have STP

To protect against EMI/RFI:

• Use fiber optic instead of copper cables. Fiber optic cables are immune to EMI/RFI.
• Use shielded twisted pair cables. Shielded cables have a metal foil that encloses all the wires. Some cables might also include a drain wire that is a bare wire outside of the foil, but within the cable jacket. The drain wire can be grounded to help absorb EMI/RFI.
• Avoid installing cables near EMI/RFI sources.

Crosstalk

Interference that can result from signal sent on one pair inside the Twisted Pair getting absorbed by another.

Types of Crosstalk:

• Near End Cross Talk (NEXT), signal generated on one wire is measured on the other wires at the same end. It measures crosstalk that occurs at the same connector on different wires
• Far End Cross Talk (FEXT), we measure crosstalk that happens on the opposite end of where the transmission occurs.
• Alien Crostwalk: When a single wire bundle running parallel with another wire bundle picks up signal from the other bundle. This can be amplified if bundling cables together with a tie.

Sources of possible crosstalk:

• Plastic Sheath wearing Down
• Within connectors where twists are removed to add the connector

Preventing Crosstalk:

• Make sure all connectors are properly connected
• Use pre-made certified cables
• Keep wires twisted
• The tighter the twist, the better
• Cat 6 is twisted more tightly than Cat3

Power over Ethernet (PoE)

Power over Ethernet is a networking feature defined by the IEEE 802.3af and 802.3at standards. It describes any of several standard or ad-hoc systems that pass electric power along with data on twisted pair Ethernet cabling. Keep in mind the following: PoE technology is used on twisted-pair Ethernet cabling (CAT 5 or higher). Power is usually supplied by a PoE-enabled Ethernet switch. PoE is commonly used to power network devices that are located where physical access to a power outlet may not be available. For example, a PoE-enabled surveillance camera mounted on a tall pole can be powered via its Ethernet cabling. You can use a PoE injector to add PoE capability to regular non-PoE network links. PoE injectors can be used to upgrade existing LAN installations to PoE and provide a solution where fewer PoE ports are required. To upgrade a network connection to PoE, patch it through the PoE injector. Power injection is controlled and automatic.

Attenuation

Loss of signal strength over distance

Preventing Attenuation:

• Don't exceed the max distance allowed by network architecture
• Ex., Ethernet using copper, usually about 100 meters - this includes the full distance traveled
• As temps rise, it can get worse
• Use Repeaters to receive, regen, and amplify the electrical signal

Impedance Mismatch

Impedance is the measure of resistance within the transmission medium, represented by ohms. Problems can occur when the electricity hits the spot where the impedance changes. Where this occurs, it can reflect it back resulting in an Echo.

• Impedance is measured in ohms (Ω).
• All cables must have the same impedance rating. The impedance rating for the cable must match the impedance of the transmitting device.
• Impedance is mostly a factor in coaxial cables used for networking. Be sure to choose cables with the correct rating (50 or 75 ohm) based on the network type. Never mix cables that have different ratings.
• When signals move from a cable with one impedance rating to a cable with another rating, some of the signal is reflected back to the transmitter, distorting the signal (known as an echo). With video (cable TV) impedance mismatch is manifested as ghosting of the image.
• Cable distance does not affect the impedance of the cable.

Shorts/Open Circuit

When an electrical signal takes a path other than the one intended. Where a signal can hop to another wire. Remember, path of least resistance for electricity.

Open circuits where the wire has a break in it can lead to electrical signals not reaching to where it needs to go.

Miswiring

When wires don't match up correctly within a connector.

Reversal:

• Straight through instead of a crossover cable between two computers.
• Basically one end's transmit is the other's receive.
• This is known as a Reversal, when the connection won't work

Wiremapping:

• Determines whether wires connected to each pin are correct or not.
• When a wire isn't properly placed into the correct or matching pin.

Split Pair:

• Occurs when the pins between two pairs are crossed. When wires are crossed between pin pairs on both ends.
• Problem is when the signals aren't traveling down the correct wires which can lead to cross talk.

Troubleshooting Fiber Optic Wiring

Common Issues:

• Connector Issues
• Cable Issues
• Media Adapter Issues
• Attenuation

Connector Issues

Fiber inside needs to line up with the connector. Keep things clean, using lint-free cloth or specialized cleaning tools

Insertion Loss can occur whenever connector is used. Better the polish, the better light can pass through. We want to reduce Optical Return Loss (ORL).

Polishing Types:

• Physical Contact (PC), ends are polished with a slight curvature so that only the cores touch
• Super Physical Contact (SPC)/Ultra Physical Contact (UPC), used to reduce ORL reflections
• Angled Physical Contact (APC), 8 degree cut that prevents reflected light from traveling back into the fiber. These are colored green to prevent mixing with non-APC connectors.

Several issues can occur when you are working with fiber optic cabling.

Fiber optic cabling is much less forgiving of physical abuse than copper wiring. The fiber core is fragile and can be easily damaged by rough handling. For example, bending a fiber cable at too tight of a radius will break the core. Wavelength mismatch causes serious issues with fiber optic cables. You cannot mix and match types of cable. For example, if you connect single-mode fiber to multi-mode fiber, you will introduce a catastrophic signal loss of up to 99%. Even connecting cables of the same type that have different core diameters can cause a loss of up to 50% of the signal strength.

Signal Loss

This can be contributed to things like cable length, connectors, and splices. Measured in decibels (dB).

Several physical cable attributes can contribute to signal loss:

Cable length - While higher quality cables carry light signals further, the longer the cable, the more signal absorption and the greater the signal loss. Connectors - Every connector causes some level of signal loss, mostly due to reflection. While patch cables at each end of a run are to be expected, minimize any other connections. Splices - There are tools that you can use to splice a cut fiber optic cable. However, the signal loss from a splice is comparable to the signal loss from a connector. Bends - Micro bends in the cable due to things such as temperature change or manufacturing anomalies can cause signal loss. While you have little control over micro bends, even macro bends that can't be detected by the human eye can contribute to signal loss. The straighter the fiber optic cable, the less the signal loss.

Adding average losses of all losses within the cable to give an estimate of the attenuation that can occur is called a loss budget.

Connectors and Splices: 0.3 dB Multi-mode cabling:

• 3 dB loss per 1000 meters when using an 850 nm light source.
• 1 dB loss per 1000 meters when using a 1300 nm light source. Single-mode cabling:
• 0.5 dB loss per 1000 meters when using a 1310 nm light source.
• 0.4 dB loss per 1000 meters when using a 1550 nm light source.

Should be nore more than 3 dB less than the total power at the transmission source. Link loss margin less than 3 dB ensures the cable run will function.

Troubleshooting Tools

Spare Parts

One of the first things is to have spare parts.

• Change the drop cable that connects a computer to the network.
• Replace a NIC with a verified working NIC.
• Move a device from one switch port to another.

Loopback Plugs

Helps test ports to determine network or NIC issues.

If data sent is the same as the one received confirms that the device works.

• There are loopback plugs for both copper and fiber connections.
• A failure in the loopback test indicates a faulty network card.
• A successful loopback test means the problem is in the network cabling or another connectivity device.

You can purchase pre-made loopback plugs, or you can make an inexpensive one by cutting the end of a cable and manually connecting the transmit wires to the receive wires. To do this, connect the wire from pin 1 to the wire at pin 3, and the wire at pin 2 to the wire at pin 6.

Smartjack

A special jack on a WAN link near the demarc point. This tells us if the issue is tied into the service provider or on the site.

• Technicians at the central office can send diagnostic commands to the smartjack to test connectivity and performance between the central office and the demarc.
• When you contact a WAN service provider for assistance, the provider might execute a test using the smartjack.
• A successful test indicates that the problem is within the customer premises equipment (CPE).

Cable Tester

Used to test if cables function. Specifically to verify if the cable can carry a signal from one end to the other and all wires are in their correct positions. Sometimes includes a Timed Domain Reflector (TDR) - which helps measure the signal travel time on a wire run to measure the distance to the fault. An OTDR is used for testing fiber cables.

• High-end cable testers can check for various miswire conditions such as wire mapping, reversals, split pairs, shorts, or open circuits.
• You can use a cable tester to quickly identify a crossover and a straight-through cable.
• Most testers have a single unit that tests both ends of the cable at once.
• Many testers come with a second unit that can be plugged into one end of a long cable run to test the entire cable.

Cable Certifiers

Multi-function tool that validates a cable's specification. Certifier checks the physical compnents. Includes TDR and cable tester.

• A certifier is very important for Cat 6 cable used with bandwidths at or above 1000 Mbps. Slight errors in connectors or wires can cause the network to function at 100 Mbps instead of the desired 1000 Mbps (10 Gbps).
• Certifiers can also validate the bandwidth capabilities of network interface cards and switches. Many can detect the duplex settings of network devices.
• Most certifiers include features of a toner probe, TDR, and cable tester.
• Certifiers are very expensive and are typically used by organizations that specialize in wiring installations.

TDR/OTDR

A time-domain reflectometer is a special device that sends electrical pulses on a wire to discover information about the cable. The TDR measures impedance discontinuities (the echo received on wire in response to a signal on the same wire). The results of this test can be used to identify several variables:

• Estimated wire length.
• Cable impedance.
• The location of splices and connectors on the wire.
• The location of shorts and open circuits.

An optical time-domain reflector performs the same function as a TDR, but is used for fiber optic cables. An OTDR sends light pulses into the fiber cable and measures the light that is scattered or reflected back to the device. The information is then used to identify specifics about the cable:

• The location of a break.
• Estimated cable length.
• Signal attenuation (loss) over the length of the cable.

Tone Generator and Probe

Emits a tone along the wire where it gets picked up by the probe.

Multimeter

Helps measure electrical point difference across two points in an electronic circuit. A multimeter can measure several parameters:

• AC and DC voltage
• Current (amps)
• Resistance (ohms)
• Capacitance
• Frequency

Wiring Tools

• Wire Strippers

  • Wire strippers are rated to specific gauge (cable width) ranges.
  • Most wire strippers are combination tools. They can strip, cut, and crimp cables.
  • Almost all wire strippers have multiple holes or can be adjusted for specific cable sizes.

• Wire Cutters

• Wire Crimpers

Speed Test Sites

Transfers ICMP packets between a computer on the network and a speed test server to measure bandwidth. Helps Measure:

• Connection latency (ping)
• Download speed
• Upload speed