Network Cable Types – UTP, STP, Coax & Fibre

1. Why Cabling Knowledge Matters

Physical cabling is the foundation of every wired network. Choosing the wrong cable category, wrong cable type, or wrong connector results in link failures, speed limitations, or excessive interference — problems that can be invisible in configuration but devastating in practice. CCNA candidates are expected to understand which cable to use in which situation, how copper and fibre behave differently, and how cabling standards define the wiring inside an RJ45 connector. Cabling operates at Layer 1 of the OSI model and forms the physical foundation of every LAN.

Cable Family	Medium	Typical Max Distance	Best Use Case
UTP (Unshielded Twisted Pair)	Copper wire pairs	100 m (Cat5e/Cat6/Cat6a)	LAN access layer, desktop connections, patch panels
STP (Shielded Twisted Pair)	Copper wire pairs + shielding	100 m	High-EMI environments (factories, data centres near heavy machinery)
Coaxial	Central copper conductor + braided shield	Up to 500 m (thick coax) / 185 m (thin coax)	Legacy Ethernet; cable TV; CCTV; some WAN links
Multimode Fibre (MMF)	Glass/plastic core; multiple light paths	Up to 550 m (OM3/OM4 at 10G)	Building backbone; campus fibre; data centre
Single-mode Fibre (SMF)	Glass core; single light path	Up to 40+ km (and further with amplifiers)	WAN, metro, inter-building, service provider links

2. Twisted Pair Cable – UTP and STP

Twisted pair cable is the most common type of network cabling in LAN environments. It consists of pairs of copper wires twisted together to reduce electromagnetic interference (EMI) and crosstalk — the electrical interference between adjacent wire pairs. The twisting causes the interference picked up on each wire to cancel out on its partner wire when the differential signal is decoded at the receiver.

2.1 UTP vs STP

Feature	UTP (Unshielded Twisted Pair)	STP (Shielded Twisted Pair)
Shielding	None — relies entirely on twist rate for noise rejection	Metal foil or braided shield around each pair and/or around the entire cable bundle
EMI resistance	Moderate — suitable for most office environments	High — significantly better rejection of external EMI and RF interference
Cost	Lower — less material, simpler termination	Higher — shielding material adds cost; termination requires proper grounding
Grounding requirement	None	Must be properly grounded at both ends — improper grounding can make interference worse
Flexibility / ease of installation	Very flexible; easy to pull through conduit and terminate	Stiffer and heavier; more difficult to route and terminate
Typical use	Standard office and enterprise LAN; the default choice for most installations	Industrial environments, factories, medical facilities, data centre areas with heavy equipment, or where FCC regulations require shielding

2.2 STP Shielding Types

Designation	Shielding Description	Common Name
U/UTP	Unshielded cable, unshielded pairs — standard UTP	UTP
F/UTP	Foil-shielded cable, unshielded pairs — foil around the entire bundle	FTP (Foil Twisted Pair)
S/FTP	Braided-shield cable, foil-shielded pairs — both a braided outer shield and foil on each pair	SSTP / SFTP (most shielded type)
U/FTP	Unshielded cable, foil-shielded pairs — foil around each individual pair but no outer shield	FTP (individual pair shielding)

3. Copper Cable Categories – Cat5e, Cat6, Cat6a

The TIA/EIA-568 standard defines the performance specifications for twisted pair cabling categories. The category (Cat) number indicates the minimum performance the cable must achieve — higher category cables have tighter twist rates, better shielding, and can handle higher frequencies and data rates.

Category	Max Frequency	Max Data Rate	Max Segment Length	Typical Use	Notes
Cat3	16 MHz	10 Mbps	100 m	Legacy 10BASE-T Ethernet; voice (telephone)	Obsolete for data networking; still found in old installations
Cat5	100 MHz	100 Mbps (Fast Ethernet)	100 m	Legacy Fast Ethernet installations	Superseded by Cat5e — rarely installed new
Cat5e	100 MHz	1 Gbps (Gigabit Ethernet)	100 m	Current standard for office LAN access layer; 1000BASE-T	"e" = enhanced — better crosstalk specs than Cat5; most common installed base
Cat6	250 MHz	1 Gbps at 100 m; 10 Gbps at up to 55 m	100 m (1G); 55 m (10G)	Higher performance LAN; 10GBASE-T over short runs	Spline separator between pairs reduces crosstalk; thicker and less flexible than Cat5e
Cat6a	500 MHz	10 Gbps at full 100 m	100 m (10G)	10GBASE-T at full 100 m; data centre access; PoE++ deployments	"a" = augmented — thicker jacket to reduce alien crosstalk; heavier and more difficult to terminate
Cat7	600 MHz	10 Gbps	100 m	Data centre; industrial	Individual pair shielding + overall shield; not an official TIA standard — uses GG45 or TERA connectors, not standard RJ45
Cat8	2000 MHz	25/40 Gbps	30 m	Data centre ToR (Top of Rack) and server connections	Very short range; shielded only; RJ45 compatible

3.1 Key Rule – 100-metre Copper Limit

All standard Ethernet copper categories share the same maximum segment length: 100 metres. This is the total channel length from wall jack to switch, including patch cables at both ends. The breakdown is:

Segment Component	Max Length
Horizontal run (wall to patch panel)	90 m maximum
Patch cable at the switch end	Up to 5 m
Patch cable at the workstation end	Up to 5 m
Total channel (end to end)	100 m maximum

4. T568A vs T568B – Wiring Standards

The TIA/EIA-568 standard defines two wiring schemes for terminating an RJ45 connector on the end of a twisted pair cable: T568A and T568B. Both are electrically equivalent in performance — they simply assign the wire colours to pins in a different order. The critical rule is: use the same standard on both ends of a cable for a straight-through, and different standards (one A, one B) for a crossover.

4.1 T568A and T568B Pin Assignments

Pin	T568A Wire Colour	T568B Wire Colour	Function (100/1000BASE-T)
1	White/Green	White/Orange	TX+ (transmit positive)
2	Green	Orange	TX− (transmit negative)
3	White/Orange	White/Green	RX+ (receive positive)
4	Blue	Blue	Unused / PoE (in PoE deployments: pair carries power)
5	White/Blue	White/Blue	Unused / PoE
6	Orange	Green	RX− (receive negative)
7	White/Brown	White/Brown	Unused / PoE (in 1000BASE-T: bidirectional pair)
8	Brown	Brown	Unused / PoE (in 1000BASE-T: bidirectional pair)

Which standard to use? T568B is the more common standard in North America for new commercial installations. T568A is preferred by the US government (TIA-568-C). Either is acceptable as long as it is applied consistently throughout the installation. The T568B standard is the default on most patch panels and structured cabling systems.

5. Straight-Through, Crossover, and Rollover Cables

Three types of copper patch cables are defined by the wiring scheme at each end. Understanding which cable connects which devices is a fundamental CCNA topic — although the practical relevance of crossover cables has diminished with Auto-MDIX.

5.1 Straight-Through Cable

Both ends use the same wiring standard (both T568A or both T568B). Pin 1 on one end connects to Pin 1 on the other; Pin 2 to Pin 2; and so on. This is the most common cable type.

Connection Type	Use Straight-Through?	Reason
PC / workstation → Switch	✔ Yes	Different device types — TX pins on PC connect to RX pins on switch (MDI to MDIX)
Router → Switch	✔ Yes	Router port (MDI) to switch port (MDIX) — different types
Switch → Router	✔ Yes	Same as above
Anything → Wall jack (patch)	✔ Yes	Patch cables to structured cabling are always straight-through

5.2 Crossover Cable

One end is wired T568A and the other end T568B. This swaps the transmit and receive pairs — Pin 1 (TX+) on one end connects to Pin 3 (RX+) on the other, and Pin 2 (TX−) connects to Pin 6 (RX−).

Connection Type	Use Crossover?	Reason
Switch → Switch	✔ Yes (without Auto-MDIX)	Both switches have MDIX ports — TX from one must cross over to RX on the other
Router → Router (direct)	✔ Yes (without Auto-MDIX)	Both have MDI ports — TX must cross to RX
PC → PC (direct, no switch)	✔ Yes (without Auto-MDIX)	Both NICs are MDI — need crossover
Hub → Hub	✔ Yes (without Auto-MDIX)	Same-type devices

Auto-MDIX (Automatic Medium-Dependent Interface Crossover) is supported on all modern Cisco switches and most modern NICs. Auto-MDIX automatically detects the cable type and adjusts the TX/RX polarity electronically — meaning either a straight-through or crossover cable will work regardless of which device types are connected. In practice, crossover cables are rarely needed in modern networks, but CCNA still tests this concept.

5.3 Rollover (Console) Cable

A rollover cable (also called a console cable or Cisco flat cable) is used exclusively to connect a PC's serial port (or USB-to-serial adapter) to the console port on a Cisco router or switch for out-of-band management access. It is recognisable by its flat, light-blue colour in Cisco environments. See Console & VTY Line Configuration for how console access is configured once the cable is connected.

The wiring is a complete reversal — Pin 1 connects to Pin 8, Pin 2 to Pin 7, Pin 3 to Pin 6, Pin 4 to Pin 5, and so on. This "rolled" wiring pattern gives the cable its name. It does not carry Ethernet — it carries RS-232 serial signals at 9600 baud (default Cisco console settings: 9600 baud, 8 data bits, no parity, 1 stop bit, no flow control — 9600 8N1).

Cable Type	End A Standard	End B Standard	Carries	Typical Use
Straight-Through	T568B (or T568A)	T568B (same as A)	Ethernet data	PC/router to switch; any unlike device pair
Crossover	T568A	T568B	Ethernet data	Switch to switch; router to router; PC to PC (without Auto-MDIX)
Rollover	Pins fully reversed	Mirror of End A	RS-232 serial (console)	PC COM port to Cisco console port (9600 8N1)

6. Coaxial Cable

Coaxial cable has a central copper conductor surrounded by an insulating dielectric, a braided metal shield, and an outer plastic jacket. The shield provides excellent noise rejection. Coaxial cable was the dominant medium for early Ethernet (10BASE5 and 10BASE2) but has been almost entirely replaced by twisted pair and fibre in modern enterprise LANs. It remains in use for cable TV (CATV), CCTV/video surveillance, and some broadband WAN connections.

Type	Designation	Impedance	Max Distance	Use Case
Thick coax	10BASE5 (RG-8)	50 Ω	500 m per segment	Legacy 10BASE5 Ethernet (Thicknet) — obsolete
Thin coax	10BASE2 (RG-58)	50 Ω	185 m per segment	Legacy 10BASE2 Ethernet (Thinnet) — obsolete for data; still used in some audio applications
Cable TV coax	RG-6	75 Ω	Varies (hundreds of m with amplifiers)	Cable TV (CATV); broadband cable internet (DOCSIS); CCTV video
Serial WAN	Various	75 Ω	Varies	DSL and cable modem connections; some leased line CPE connections

7. Fibre Optic Cable

Fibre optic cable transmits data as pulses of light through a glass or plastic core, surrounded by cladding (lower refractive index glass that reflects light back into the core) and a protective jacket. Fibre is immune to electromagnetic interference, supports much higher bandwidths than copper, and can span far greater distances. It is the standard medium for building backbones, campus networks, WAN connections, and data centre inter-switch links.

Feature	Fibre Optic	Copper UTP
Medium	Light pulses in glass/plastic	Electrical signals in copper
EMI immunity	Complete — light is unaffected by electromagnetic fields	Susceptible — shielding reduces but does not eliminate EMI
Max distance (typical)	Multimode: up to 550 m; Single-mode: 40+ km	100 m maximum
Bandwidth	Very high — terabit-scale possible	Up to 10 Gbps (Cat6a) or 25/40 Gbps (Cat8)
Security	Difficult to tap without detection; no RF emission	Easier to tap; generates EMI that can be detected
Cost	Higher cable and termination cost; SFP transceivers needed	Lower cable cost; RJ45 connectors inexpensive
Fragility	Glass core can crack if bent too sharply (minimum bend radius must be observed)	More robust to physical stress

8. Single-Mode vs Multimode Fibre

The most important distinction within fibre optic cable is between single-mode fibre (SMF) and multimode fibre (MMF). The choice determines the maximum distance, the type of transceiver/SFP required, and the cost of the link.

Feature	Single-Mode Fibre (SMF)	Multimode Fibre (MMF)
Core diameter	8–10 µm (very narrow)	50 µm or 62.5 µm (larger)
Light paths (modes)	Single — only one mode (path) of light propagates through the narrow core	Multiple — light enters at different angles, creating multiple paths through the larger core
Light source	Laser — highly focused, narrow beam; more expensive	LED or VCSEL (Vertical Cavity Surface Emitting Laser) — cheaper, lower power
Dispersion	Very low — single mode means no modal dispersion	Higher — multiple modes arrive at slightly different times (modal dispersion) limiting distance at high data rates
Maximum distance	Up to 40 km (standard) — 80 km and beyond with amplifiers or DWDM	Up to 550 m (OM3/OM4 at 10G); up to 400 m (OM4 at 40/100G)
Wavelength	1310 nm or 1550 nm	850 nm (most common); 1300 nm (some)
Connector colour code	Yellow jacket; blue or green LC/SC connectors	Orange (OM1/OM2) or aqua/turquoise (OM3/OM4) jacket; beige or aqua connectors
Cost	Higher — laser transceivers; precise alignment	Lower — LED/VCSEL sources; less precise tolerances
Typical use	WAN links; inter-building campus; metro Ethernet; service provider backbones — see WAN Overview and MPLS; any link > 550 m	Building backbone; data centre switch-to-switch and server connections; campus core within a building

8.1 Multimode Fibre Categories (OM Classification)

Classification	Core Diameter	Jacket Colour	Max Distance at 10G	Max Distance at 100G	Notes
OM1	62.5 µm	Orange	33 m	Not supported	Legacy; being phased out
OM2	50 µm	Orange	82 m	Not supported	Legacy
OM3	50 µm	Aqua	300 m	100 m	Current minimum for new data centre installs
OM4	50 µm	Aqua (or erika violet)	400 m	150 m	Standard for high-speed data centre links
OM5	50 µm	Lime green	400 m	150 m (and supports SWDM4 for 40G/100G over 2 fibres)	Wideband multimode — supports multiple wavelengths

8.2 Fibre Connectors

Connector	Full Name	Common Use	Notes
LC	Lucent Connector (small form-factor)	SFP and SFP+ transceivers; data centre and enterprise	Most common connector in modern enterprise — small size; push/pull latch; duplex LC is standard for most SFPs
SC	Subscriber Connector / Standard Connector	Legacy equipment; GBIC transceivers; some telco	Larger than LC; square push-pull; duplex SC common on older equipment
ST	Straight Tip	Legacy multimode installations	Bayonet-style twist-lock; largely replaced by LC and SC
MPO/MTP	Multi-fibre Push On	40G/100G QSFP transceivers; data centre trunk cables	Carries 8, 12, or 24 fibres in one connector; requires precise alignment; used for parallel optics

9. When to Use Each Cable Type

Selecting the right cable for each situation is a core design and installation skill. The following table consolidates the key decision-making criteria:

Scenario	Recommended Cable	Reason
Desktop PC to office switch (standard office LAN)	Cat5e UTP straight-through	100 m limit easily met; 1 Gbps sufficient; low cost
Switch to switch (same rack or room, <55 m)	Cat6 UTP (or Cat6a for 10G at <55 m)	Cat6 handles 10G at short distances; Cat6a extends 10G to full 100 m
Switch to switch in the same building, <100 m, 10G required	Cat6a UTP or OM3/OM4 multimode fibre	Cat6a handles 10G at 100 m; fibre avoids alien crosstalk in dense cable runs
Building-to-building connection (50–500 m)	Multimode fibre (OM3 or OM4)	Exceeds copper 100 m limit; EMI immune for outdoor runs; OM3/OM4 supports 10G at these distances
Building-to-building connection (>500 m)	Single-mode fibre	Multimode distance limit exceeded; SMF handles km-range links
WAN / metro Ethernet / service provider link	Single-mode fibre	Long distances (km to hundreds of km) only achievable with SMF
Console / out-of-band management access to Cisco device	Rollover (console) cable RJ45 to DB9/USB	Specifically designed for RS-232 console access; not Ethernet
High-EMI environment (factory floor, near motors)	STP (shielded) UTP or fibre	Shielding or immunity required to prevent data corruption from electromagnetic interference
Data centre server-to-ToR switch (<10 m), 25G/40G	DAC (Direct Attach Copper) twinax cable or OM4 fibre	DAC is lower cost and lower latency for very short runs; OM4 for slightly longer distances
PoE (Power over Ethernet) for IP phones and APs	Cat5e minimum; Cat6 or Cat6a recommended for PoE+ and PoE++	Higher categories have better thermal performance for power delivery; Cat6a specified for PoE++ (IEEE 802.3bt). See Interface Configuration for enabling PoE on switch ports.

10. Cable Testing and Common Faults

After installation, cables must be tested to verify correct wiring, adequate signal level, and compliance with category specifications. For software-side interface troubleshooting, see show interfaces and Troubleshooting Connectivity.

Test / Fault	Description	Tool
Wire map test	Verifies that each pin at one end connects to the correct pin at the other — detects opens, shorts, reversed pairs, and split pairs	Cable tester (e.g., Fluke LinkRunner, Ideal Networks)
Length measurement (TDR)	Time Domain Reflectometry — sends a pulse down the cable and measures the time for a reflection to return; determines cable length and locates breaks	Cable certifier with TDR (e.g., Fluke DTX)
Attenuation (insertion loss)	Signal strength lost over the cable length — must remain below the limit for the category	Cable certifier
NEXT (Near-End Crosstalk)	Interference between pairs measured at the same end as the signal injection — higher value = better	Cable certifier
Alien crosstalk (ANEXT)	Interference from adjacent cables in the same bundle — critical for Cat6a 10G and dense patch panel runs	Cable certifier
Split pair	Wires from different pairs terminated together — appears correct on a simple continuity test but fails crosstalk testing because twisted pairs are broken	Cable certifier (simple testers may miss this)
Optical power meter	Measures light power level at the far end of a fibre link — confirms sufficient power for the transceiver's receiver sensitivity	Optical power meter + light source

11. Cable Types Quick-Reference Summary

Concept	Key Fact
Max copper segment length (all categories)	100 m (90 m horizontal run + 10 m patch cables)
Cat5e max speed	1 Gbps at 100 m (100 MHz)
Cat6 max speed	1 Gbps at 100 m; 10 Gbps at up to 55 m (250 MHz)
Cat6a max speed	10 Gbps at full 100 m (500 MHz)
T568B pin 1 colour	White/Orange
T568A pin 1 colour	White/Green
Straight-through cable ends	Both T568A or both T568B (same standard on both ends)
Crossover cable ends	One end T568A, other end T568B
Rollover (console) cable	Pins fully reversed (1↔8, 2↔7, 3↔6, 4↔5); RS-232 serial; Cisco console access
Auto-MDIX	Modern switches auto-detect cable type — crossover not required in practice
Multimode fibre max distance (OM4 at 10G)	400 m
Single-mode fibre typical max distance	40 km standard; further with amplifiers
SMF core diameter	8–10 µm; yellow jacket; laser light source
MMF core diameter	50 or 62.5 µm; orange or aqua jacket; LED/VCSEL source
Most common fibre connector in enterprise	LC (Lucent Connector) — used in SFP/SFP+ transceivers

Test Your Knowledge – Cable Types Quiz

1. What is the maximum segment length for all standard Ethernet copper twisted pair cables (Cat5e, Cat6, Cat6a), and what makes up this total?

A. 50 m — limited by the Cat5e specification B. 200 m — Cat6a can reach 200 m at 10G C. 100 m total — 90 m for the permanent horizontal run plus up to 10 m for patch cables at both ends D. 100 m for Cat5e; 150 m for Cat6; 200 m for Cat6a

Correct answer is C. All standard Ethernet copper cabling is limited to a 100-metre channel regardless of category. The 100 m is broken into a 90-metre permanent horizontal run (wall jack to patch panel) plus up to 10 metres total for patch cables (typically 5 m at the switch and 5 m at the workstation). The category determines speed within this 100 m limit, not the distance. Exception: Cat6 supports 10 Gbps only at up to 55 m; Cat6a extends 10G to the full 100 m.

2. You need to support 10 Gbps Ethernet over the full 100-metre structured cabling run. Which cable category is the minimum required?

A. Cat5e — it supports 1 Gbps and has headroom for 10G B. Cat6a — the augmented category supports 10 Gbps at the full 100-metre channel; Cat6 only reaches 10G at up to 55 m C. Cat6 — it supports 10G at all distances D. Cat7 — only Cat7 is rated for 10G Ethernet

Correct answer is B. Cat6 supports 10GBASE-T but only up to 55 metres due to alien crosstalk limitations at 250 MHz. Cat6a (augmented Category 6) was specifically designed to support 10 Gbps at the full 100-metre channel by increasing the frequency rating to 500 MHz and using a thicker jacket to reduce alien crosstalk. Cat5e (100 MHz) is limited to 1 Gbps. Cat7 is not a TIA-recognised standard and uses non-standard connectors.

3. Which type of cable would you use to connect two Cisco switches together in a network without Auto-MDIX, and which wiring standard describes it?

A. Straight-through — both ends T568B B. Rollover — pins fully reversed for switch-to-switch connections C. Straight-through — one end T568A, one end T568B D. Crossover — one end T568A and the other T568B; this swaps transmit and receive pairs so the TX pins of one switch connect to the RX pins of the other

Correct answer is D. When connecting two like devices (switch to switch, router to router, PC to PC) with legacy equipment that does not support Auto-MDIX, a crossover cable is required. A crossover cable has T568A on one end and T568B on the other, which physically swaps the transmit pair (pins 1, 2) and the receive pair (pins 3, 6) — so each device's TX connects to the other's RX. Modern Cisco switches with Auto-MDIX support will work with either cable type, but CCNA still tests this concept.

4. A technician needs to access the console port on a Cisco router from a laptop. Which cable type is used, and what is Cisco's default console baud rate?

A. Rollover (console) cable — flat blue cable with RJ45 to DB9/USB adapter; default baud rate is 9600 bps (9600, 8N1) B. Crossover cable — used for direct device management; default baud rate is 115200 bps C. Straight-through Cat5e cable; baud rate is not applicable for Ethernet console connections D. Single-mode fibre with LC connectors; the console port uses light signals

Correct answer is A. The rollover cable (also called a console cable) is the unique cable type used for out-of-band management access to Cisco equipment. It is characterised by its flat profile, light-blue colour, and wiring in which each pin is the mirror image of its counterpart (Pin 1 → Pin 8, Pin 2 → Pin 7, etc.). One end has an RJ45 connector that plugs into the Cisco console port; the other uses a DB9 serial connector (or USB via an adapter). Default Cisco console settings: 9600 baud, 8 data bits, no parity, 1 stop bit, no flow control.

5. What is the primary difference between single-mode fibre (SMF) and multimode fibre (MMF)?

A. SMF uses copper for long distances; MMF uses glass for short distances B. SMF operates at 850 nm wavelength; MMF operates at 1310 nm C. SMF has a very narrow core (8–10 µm) that allows only a single light path — eliminating modal dispersion and enabling distances up to 40+ km. MMF has a larger core (50–62.5 µm) with multiple light paths, limiting it to up to ~550 m. D. SMF uses multicolour CWDM; MMF uses only a single wavelength

Correct answer is C. The fundamental difference is the core diameter. Single-mode fibre has an 8–10 µm core — so narrow that only one mode (propagation path) of light can travel through it. This eliminates modal dispersion and allows very long distances (10–40+ km) using laser light sources (1310/1550 nm). Multimode fibre has a 50 or 62.5 µm core — wide enough for multiple modes. Modal dispersion limits its distance (up to ~550 m for OM3/OM4 at 10G). MMF uses cheaper LED/VCSEL sources at 850 nm.

6. A network engineer sees a fibre cable with an aqua (turquoise) jacket and LC connectors. What type of fibre is this most likely, and what is its typical use?

A. Single-mode fibre — used for WAN links over 40 km B. OM3 or OM4 multimode fibre — aqua jacket is the standard colour for OM3/OM4; used for data centre and campus backbone links up to 550 m at 10G C. OM1 multimode fibre — orange jacket with aqua connectors D. Cat6a UTP — aqua is the standard Cat6a cable jacket colour

Correct answer is B. Cable colour coding is standardised: yellow jacket = single-mode fibre; orange jacket = OM1 or OM2 multimode (legacy); aqua/turquoise jacket = OM3 or OM4 multimode (current standard for enterprise and data centre). OM3/OM4 with LC connectors is the most common fibre type in modern enterprise data centres, supporting 10G up to 300 m (OM3) or 400 m (OM4). LC connectors are the standard for SFP+ transceivers.

7. In the T568B wiring standard, what colour is Pin 1?

A. White/Green B. Blue C. Orange D. White/Orange

Correct answer is D. In T568B: Pin 1 = White/Orange, Pin 2 = Orange, Pin 3 = White/Green, Pin 4 = Blue, Pin 5 = White/Blue, Pin 6 = Green, Pin 7 = White/Brown, Pin 8 = Brown. In T568A, the orange and green pairs are swapped: Pin 1 = White/Green, Pin 2 = Green, Pin 3 = White/Orange. T568B is the more common standard in North American commercial installations. The key difference between A and B is the position of the orange and green pairs.

8. Why does STP (Shielded Twisted Pair) require proper grounding, and what happens if it is not grounded correctly?

A. The shield must be grounded to drain induced electrical noise. Improper grounding (ground loops or only one-end grounding) can cause the shield to act as an antenna, making interference worse than standard UTP B. Grounding is needed to power the shield's active noise-cancellation circuit C. Ungrounded STP causes data to transmit in reverse byte order D. Grounding is optional for STP — it only affects PoE delivery

Correct answer is A. The shield in STP must be connected to a clean earth ground at one or both ends (depending on the installation standard) to provide a path for induced noise currents to flow to ground rather than coupling into the signal wires. If the shield is not grounded, or if there is a ground loop (different ground potential at each end), the shield itself can pick up electrical noise and radiate it into the cable — potentially making the cable perform worse than unshielded UTP. This is why STP is more complex to install correctly than UTP.

9. A cable tester reports a "split pair" fault. What is a split pair, and why does it pass a simple continuity test but still cause problems?

A. A split pair means the cable was cut in half and repaired — it passes continuity but has higher attenuation B. A split pair is when the TX and RX wires are swapped — it fails continuity on a standard tester C. A split pair occurs when wires from two different twisted pairs are terminated together (e.g., white/green with white/orange). It passes pin continuity but the twisted pairs are broken, causing severe crosstalk that is only detected by a certifier D. A split pair is when the cable shield is connected at one end only

Correct answer is C. A split pair is an insidious wiring error where a technician inadvertently pairs wires from different twisted pairs. For example, Pin 1 (White/Green from pair 3) and Pin 2 (White/Orange from pair 2) — these wires are correctly connected end-to-end, so a simple continuity tester shows correct pin mapping. However, each signal pair is now untwisted, destroying the cancellation effect that prevents crosstalk. The result is severe near-end crosstalk (NEXT) that causes errors and poor performance — especially visible at Fast Ethernet and above speeds. Only a cable certifier with NEXT testing detects this fault.

10. You need to run a fibre cable between two buildings that are 800 metres apart on a university campus. Which fibre type should you use, and why?

A. OM4 multimode fibre — it supports 10G and can easily reach 800 m B. Single-mode fibre — OM4 multimode is limited to 400 m at 10G; the 800 m run exceeds multimode distance limits and requires single-mode fibre which can reach 10+ km C. Cat6a UTP — with a signal repeater at the midpoint it can cover 800 m D. OM1 multimode — its 62.5 µm core provides better distance than OM4

Correct answer is B. OM4 multimode fibre supports 10GBASE-SR at up to 400 m — the 800 m run exceeds this limit. Single-mode fibre is the correct choice for distances beyond 550 m. SMF supports 10GBASE-LR at up to 10 km (and further with other standards), making 800 m trivial. The trade-off is slightly higher cost for SMF transceivers (laser-based vs LED/VCSEL), but for a permanent campus installation this is justified. OM1's larger core actually gives it worse bandwidth-distance product than OM4 — a larger core does not mean longer distance.

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