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CompTIA A+ Core 1 (220-1201) · chapter 3 of 15

Week 3: Cables in the ceiling

In this chapter Objectives 3.2, 2.8

  1. Network cables
  2. Peripheral, video and drive cables
  3. Connector types
  4. Network tools
  5. Practice questions
  6. Chapter recap

Objective 3.2

Network cables

Twisted pair: UTP, STP and categories

Ethernet copper has 4 twisted pairs; the twists cancel interference. UTP (unshielded) is standard in offices. STP (shielded) adds foil/braid for noisy places (motors, machinery) and must be grounded. Copper Ethernet runs up to 100 m.

Cat    Speed       Max length
Cat 5e 1 Gbps      100 m
Cat 6  10 Gbps     37-55 m
       (1 Gbps)    100 m
Cat 6a 10 Gbps     100 m
Cat 8  25/40 Gbps  30 m (data center)
Cross-sections of two Ethernet cables. UTP: an outer jacket around four twisted pairs, orange, green, blue and brown, each paired with a white-striped wire, and no shielding. STP: the same four pairs wrapped in a foil or braided shield, plus a drain wire to ground it. Below, a twisted pair drawn from the side shows how the twists cancel interference.
STP adds a grounded shield around the same four twisted pairs.

Exam tip 10 Gbps over a full 100 m run? Cat 6a, not Cat 6.

Direct burial and plenum-rated

Direct burial cable (UTP or STP) has a tough, water-resistant jacket so it can be buried in the ground without conduit, e.g. to a gate camera. Plenum-rated cable has a fire-resistant, low-smoke jacket for plenum spaces (air-handling areas above drop ceilings or under raised floors). Normal PVC gives off toxic smoke that the air system would spread.

Exam tip Above a drop ceiling used for air return? Fire code says plenum-rated.

T568A and T568B

Two wiring standards for RJ45 pin order. They swap the orange and green pairs. Use the same standard on both ends for a straight-through cable (B is most common). A on one end and B on the other makes a crossover cable (old PC-to-PC links; modern ports auto-detect with Auto-MDI-X).

Pin  T568A         T568B
1    white/green   white/orange
2    green         orange
3    white/orange  white/green
4    blue          blue
5    white/blue    white/blue
6    orange        green
7    white/brown   white/brown
8    brown         brown
Two RJ45 plugs seen from the front with the latch down and the gold contacts up, pin 1 on the left. T568A wires, pins 1 to 8: white-green, green, white-orange, blue, white-blue, orange, white-brown, brown. T568B wires, pins 1 to 8: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown. Only the orange and green pairs swap places; blue and brown stay put.
T568A and T568B swap the orange and green pairs; blue and brown never move.

Exam tip Blue and brown never move. Only orange and green trade places.

Coaxial

Coax has one center conductor, insulation, a braided shield and a jacket. RG-6 is used for cable TV and cable internet (cable modems), with F-type screw-on connectors. RG-59 is an older, thinner type for short video runs.

Left: a coaxial cable cut across, showing four rings from the center out: the copper center conductor, white insulation (dielectric), a braided shield, and the outer jacket. Right: an F-type connector from the side, with a hex screw-on nut and the center wire sticking out as the pin. Labels say RG-6 is used for cable TV and cable modems; RG-59 is older and thinner.
Cable modems use RG-6 coax with a screw-on F-type connector.

Exam tip Cable modem input = RG-6 coax with an F-type connector.

Fiber: single-mode vs. multimode

Optical fiber carries light, so it ignores electrical interference and is hard to tap. Single-mode has a tiny core (~9 micron), uses lasers, and runs many kilometers: building-to-building and ISP links. Multimode has a wider core (50/62.5 micron), cheaper LED/VCSEL light, and runs hundreds of meters: inside a building or data center.

Two fiber cables cut open lengthwise. Top: single-mode fiber with a very thin core about 9 micron wide; one straight laser beam travels down the middle; label says lasers, kilometers. Bottom: multimode fiber with a wider 50 or 62.5 micron core; several light rays bounce off the core walls at different angles; label says LED or VCSEL light, hundreds of meters. Both have cladding around the core.
Single-mode: thin core, one path, long distance. Multimode: wide core, many paths, shorter runs.

Exam tip Longest distance = single-mode. "Multi" mode bounces many light paths, which limits distance.

Check yourself 1Dev needs to link the HQ building to the warehouse 4 km away. Which cable should he use?

  1. Cat 6a shielded twisted pair
  2. Multimode fiber
  3. RG-6 coax
  4. Single-mode fiber
Show the answer

Answer: D. Single-mode fiber

Single-mode fiber uses a laser and a tiny core, so it runs many kilometers. That makes it the choice for building-to-building and ISP links.

Objective 3.2

Peripheral, video and drive cables

USB 2.0, USB 3.0 and Thunderbolt

USB 2.0 (High-Speed) = 480 Mbps, up to 5 m. USB 3.0 (SuperSpeed, now called USB 3.2 Gen 1) = 5 Gbps, about 3 m, blue inserts on Type-A. Later: 10 Gbps (Gen 2), 20 Gbps (Gen 2x2), 40 Gbps (USB4). Thunderbolt joins PCIe data, DisplayPort video and power: TB 1/2 used the Mini DisplayPort plug (10/20 Gbps); TB 3 and 4 use USB-C at 40 Gbps and can daisy-chain devices.

Two USB Type-A ports side by side. USB 2.0 has a black or white tongue with 4 contacts. USB 3.x has a blue tongue with 9 contacts. Below, a speed ladder: USB 2.0 480 Mbps; USB 3.0, now USB 3.2 Gen 1, 5 Gbps; USB 3.2 Gen 2 10 Gbps; Gen 2x2 20 Gbps; USB4 and Thunderbolt 3 and 4 40 Gbps over the USB-C plug.
Blue tongue = USB 3.x. The same USB-C plug can be anything from USB 2.0 to Thunderbolt 4.

Exam tip Same USB-C plug can be USB 2.0 or Thunderbolt 4. Look for the lightning-bolt logo.

Serial (RS-232)

Serial ports send one bit at a time over RS-232, using a 9-pin DB9 (technically DE-9) connector. Still found on network gear console ports, label printers, barcode scanners and lab equipment. Modern laptops use a USB-to-serial adapter.

A 9-pin serial connector seen face on: a D-shaped metal shell, wider at the top, with 5 pins in the top row and 4 in the bottom row, and a screw post on each side. Labels say it is RS-232 serial, called DB9 (properly DE-9), found on console ports, label printers and lab gear, and modern laptops use a USB-to-serial adapter.
DB9 (DE-9) = RS-232 serial: one bit at a time.

Exam tip Configure a switch through its console port: serial (DB9 or RJ45-style console cable).

Video cables

HDMI: digital video plus audio, TVs/projectors/monitors (2.0 = 18 Gbps, 2.1 = 48 Gbps). DisplayPort: digital video + audio, PC monitors, supports daisy-chaining (MST); latches. DVI: digital (DVI-D), analog (DVI-A) or both (DVI-I); no audio. VGA: analog only, blue 15-pin 3-row DE-15 connector, image gets fuzzy at high resolutions. USB-C carries video via DisplayPort Alt Mode or Thunderbolt.

Five video connectors face on, each with notes. HDMI: a wide trapezoid with the bottom corners angled; digital video plus audio. DisplayPort: a rectangle with one corner cut off; digital video plus audio, latches, can daisy-chain. DVI: a wide connector with a grid of pins and a flat blade; digital or analog, no audio. VGA: a blue three-row, 15-pin D-shaped connector; analog only. USB-C: a small oval carrying video through DisplayPort Alt Mode or Thunderbolt.
HDMI and DisplayPort carry audio; DVI and VGA do not; VGA is the only analog-only one.

Exam tip No sound on the monitor speakers? VGA and DVI carry no audio. HDMI and DisplayPort do.

Hard drive cables: SATA and eSATA

Internal SATA drives use a thin 7-pin data cable (SATA III = 6 Gbps) plus a separate 15-pin SATA power cable. eSATA is external SATA with a shielded, sturdier connector (up to 2 m). It carries no power (except the rare eSATAp combo port) and is largely replaced by USB 3.x and Thunderbolt.

The back edge of a 2.5-inch SATA drive showing two L-shaped connectors side by side: the wide 15-pin SATA power connector and the narrow 7-pin SATA data connector. Labels: SATA power carries 3.3, 5 and 12 volts; SATA III data runs at 6 Gbps. Below, an eSATA port: a straight, shielded connector with no L-shape and no power pins.
Every SATA drive takes two cables: wide 15-pin power and narrow 7-pin data.

Exam tip eSATA drive needs its own power supply; plain eSATA has no power pins.

Adapters

Adapters convert one connector or signal to another: USB-C to HDMI, DisplayPort to HDMI, DVI-to-HDMI (both digital, passive), USB-to-Ethernet, USB-to-serial, Lightning to 3.5 mm. Digital-to-analog (e.g. HDMI to VGA) needs an active converter with a chip, not a simple adapter.

Exam tip Laptop has only USB-C, projector only HDMI? A USB-C to HDMI adapter (DP Alt Mode).

Check yourself 2The boardroom's old projector has only a VGA input. The new laptop has only HDMI. What do you need to connect them?

  1. An active HDMI-to-VGA converter
  2. A simple pin-to-pin HDMI-to-VGA cable
  3. A DVI-to-HDMI adapter
  4. A USB-to-serial adapter
Show the answer

Answer: A. An active HDMI-to-VGA converter

HDMI is digital and VGA is analog. Going from digital to analog needs an active converter with a chip, not a simple passive adapter.

Objective 3.2

Connector types

Copper network connectors

RJ45 (8P8C): Ethernet, 8 pins. RJ11 (6P2C, up to 4 used): phone lines and DSL, smaller than RJ45. F-type: screw-on coax connector for cable modems/TV. A punchdown block is where wires terminate in a closet or patch panel: 66 blocks (older phone) and 110 blocks (data, Cat 5e and up).

Front views of two modular plugs side by side. RJ45 is wider with 8 gold contacts, used for Ethernet. RJ11 is narrower with 6 positions where only the middle 2 or 4 have contacts, used for phone lines and DSL. Each has a latch tab underneath.
RJ45 (8 pins) is wider than RJ11 (6 positions, 2 or 4 wired).

Exam tip Phone/DSL = RJ11 (2 or 4 wires). Ethernet = RJ45 (8 wires). RJ11 fits loosely in an RJ45 jack, not the reverse.

Fiber connectors: ST, SC, LC

ST (straight tip): round, bayonet twist-lock. SC (subscriber/standard connector): square, push-pull snap. LC (Lucent/little connector): small form factor, often duplex pairs, common on modern switches and SFP modules.

Three fiber optic connectors drawn from the side. ST: a round body with a bayonet collar and a long ferrule, pushed in and twisted. SC: a square push-pull body that snaps in. LC: a small duplex pair of connectors with latch levers, like a tiny RJ45 clip.
ST twists, SC clicks, LC is the little one with a latch.

Exam tip Memory: ST = "stick and twist", SC = "stick and click", LC = "little connector".

Device connectors

USB-C: reversible 24-pin, current standard for phones, laptops and docks. MicroUSB: small, one-way, older Android phones. MiniUSB: bigger than micro, older cameras and controllers. Lightning: Apple 8-pin reversible. Molex: 4-pin peripheral power from the PSU (+12 V and +5 V) for old drives, fans and adapters.

Exam tip Molex is a power connector, not a data connector.

Check yourself 3A switch's SFP module takes a small fiber connector that snaps in, usually as a duplex pair. Which connector is it MOST likely?

  1. ST
  2. SC
  3. LC
  4. F-type
Show the answer

Answer: C. LC

LC (little connector) is the small form factor fiber connector, often in duplex pairs. It is the common choice on modern switches and SFP modules.

Objective 2.8

Network tools

Making a cable: stripper and crimper

A cable stripper removes the outer jacket without nicking the pairs. Untwist, arrange in T568B order, trim flat, slide into the RJ45 plug fully. The crimper presses the plug pins into the wires and locks the jacket strain relief.

Exam tip Crimper = puts connectors ON the cable end. Punchdown tool = pushes wires INTO a block or keystone jack.

Punchdown tool

A punchdown tool seats each wire into the IDC (insulation-displacement) slots of a 110 block, 66 block, patch panel or keystone jack, and trims the extra wire. Use the right blade for the block type.

A punchdown tool pressing a wire down into a slot on a 110 block. The wire sits across the insulation-displacement slot; the tool pushes it in, the slot cuts through the insulation to make contact, and the blade trims the extra wire. A note compares tools: a crimper puts an RJ45 plug on a cable end, a punchdown tool seats wires into a block, patch panel or keystone jack.
Punchdown tool: wires go INTO a block or jack. Crimper: a plug goes ON the cable end.

Exam tip Patch panel back side = punched down. Front side = RJ45 patch cords.

Testing: cable tester and loopback plug

A cable tester checks each wire: continuity, opens, shorts, miswires, split pairs (wiremap). Advanced certifiers also measure length and crosstalk. A loopback plug sends a port's transmit back into its own receive so you can test a NIC, switch port or serial port without another device.

Exam tip Testing the port itself? Loopback plug. Testing the cable run? Cable tester.

Finding and watching: toner probe, tap, Wi-Fi analyzer

A toner probe (tone generator + inductive probe) traces an unlabeled cable: clip the tone onto one end, listen for it at the patch panel. A network tap sits inline and copies all traffic to a monitoring tool. A Wi-Fi analyzer shows nearby networks, signal strength (dBm), channels and overlap so you can pick clear channels and find dead spots.

SSID            CH   BAND   SIGNAL
Kibble-Staff     6   2.4    -48 dBm
Neighbor-Guest   6   2.4    -55 dBm
Cafe-Free        7   2.4    -62 dBm
Kibble-Staff    44   5      -57 dBm

Exam tip Signal: -30 dBm excellent, -67 dBm fine for voice/video, -80 dBm barely usable. Closer to 0 is stronger.

Check yourself 4You are terminating new Cat 6 runs on the back of a patch panel in the packing room closet. Which tool do you need?

  1. Crimper
  2. Punchdown tool
  3. Toner probe
  4. Loopback plug
Show the answer

Answer: B. Punchdown tool

Patch panels and keystone jacks use IDC slots. The punchdown tool seats and trims each wire.

Practice questions

Answer in your head, then open the answer. Ranger's Help Desk has 436 questions like these for A+ Core 1, with mock exams.

Question 1A technician has cut a length of Cat 6 cable and arranged the wires in T568B order. Which tool attaches the RJ45 connector?

  1. Punchdown tool
  2. Toner probe
  3. Loopback plug
  4. Crimper
Show the answer

Answer: D. Crimper

A crimper presses the RJ45 connector's pins into the wires and locks the connector onto the cable jacket.

Question 2Before terminating a cable, a technician needs to remove the outer jacket without nicking the twisted pairs inside. Which tool should be used?

  1. Punchdown tool
  2. Cable stripper
  3. Cable tester
  4. Network tap
Show the answer

Answer: B. Cable stripper

A cable stripper cuts and removes the jacket to a set depth so the conductors inside are not damaged.

Question 3None of the cables at a patch panel are labeled, and a technician needs to find which one runs to wall jack 214. Which tool should the technician use?

  1. Loopback plug
  2. Wi-Fi analyzer
  3. Crimper
  4. Toner probe
Show the answer

Answer: D. Toner probe

A toner puts a tone on the cable at the wall jack, and the probe finds that cable at the patch panel by sound.

Question 4A technician is terminating a new cable run on the back of a patch panel with 110-style IDC connectors. Which tool seats the wires and trims the excess?

  1. Crimper
  2. Punchdown tool
  3. Cable tester
  4. Toner probe
Show the answer

Answer: B. Punchdown tool

A punchdown tool pushes each wire into the IDC slot of a 110 block, patch panel, or keystone jack and cuts off the extra.

Question 5A technician wants to confirm that a NIC port on a workstation is working, without connecting it to the network. Which tool should be used?

  1. Toner probe
  2. Network tap
  3. Loopback plug
  4. Cable stripper
Show the answer

Answer: C. Loopback plug

A loopback plug routes the port's transmit pins back to its receive pins, so a diagnostic can check that the port works.

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