Module 5 Flashcards
Learning Unit 2 (36 cards)
1
Q
Frequency, Bandwidth, and Throughput
A
- Frequency:
Measured in MHz/GHz. Indicates how often a signal changes state per second. Wired signals don’t need to be tightly confined within a spectrum, unlike wireless. Affects data transfer speed—higher frequency = more data potential.
E.g., 100 MHz = 100 million state changes/sec. - Bandwidth (Two Definitions):
1. Frequency-related: Range of frequencies a cable can carry (in MHz/GHz).
2. Data-related: Theoretical max data transmission rate (in Mbps/Gbps). Like freeway lanes—more lanes = higher potential flow.
Influenced by frequency, cable quality, and SNR. - Throughput:
Actual data received per second (Mbps/Gbps). Lower than bandwidth due to real-world inefficiencies (delays, noise, errors).
Think of it as actual traffic flow reaching the destination, not theoretical capacity. - Important Distinctions:
o Bandwidth = possible data rate
o Throughput = actual data received
o Bandwidth (MHz) ≠ Bandwidth (Mbps)
Modern tech (modulation/encoding) can boost Mbps even if MHz stays constant.
2
Q
Transmission Analogy (Freeway Model)
A
- Frequency: Number of green lights per minute = signal state changes/sec.
- Bandwidth (Mbps): Number of freeway lanes = possible data volume.
- Throughput: Number of passengers actually reaching the destination = real data delivered.
- Modulation/Encoding: Like using buses instead of cars—pack more data into the same space.
3
Q
Data Rate Prefixes and Units
A
Quantity Prefix Abbreviation
1 bit/sec – 1 bps
1000 bits/sec kilo 1 Kbps
1,000,000 bits/sec mega 1 Mbps
1,000,000,000 bits/sec giga 1 Gbps
1,000,000,000,000 bits/sec tera 1 Tbps
4
Q
Transmission Flaws Overview
A
Three key flaws reduce throughput:
1. Noise
2. Attenuation
3. Latency
All reduce efficiency despite high theoretical bandwidth.
5
Q
Noise (Interference)
A
- Definition: Unwanted electrical signals that distort or weaken the transmitted signal. Measured in dB loss.
o 3 dB loss = 50% power loss (e.g., 10 W → 5 W).
o 6 dB loss = 75% loss (e.g., 1000 W → 250 W). - Sources:
o EMI (Electromagnetic Interference): From motors, lights, microwaves, etc.
o RFI (Radio Frequency Interference): Subset of EMI caused by radio signals. - Crosstalk (Signal bleed between wires):
o NEXT (Near-End Crosstalk): At transmission point.
o FEXT (Far-End Crosstalk): At receiving end.
o Alien Crosstalk: Between adjacent cables. - Mitigation: Proper cable design, strong signals vs. noise, and shielding.
6
Q
Attenuation
A
- Definition: Signal weakening over distance, like a fading voice.
- Solution: Use repeaters to regenerate signal.
o Switches = multiport repeaters (each port refreshes the signal). - Result: Clearer digital signals with reduced noise over long distances.
7
Q
Latency
A
- Definition: Delay between sending and receiving data. Measured as RTT (Round Trip Time) in milliseconds.
- Causes:
o Cable length
o Number/type of devices (modems > switches)
o Processing (e.g., firewalls, DNS lookup)
o Media conversions (e.g., wired → wireless)
o Congestion and collisions - Impact: Especially problematic for real-time services like voice, video, or gaming.
More devices = more delay. Modems increase latency more than switches.
8
Q
Transmission Modes (Simplex, Half-Duplex, Full-Duplex)
A
- Full-Duplex (Duplex): Signals travel in both directions simultaneously (e.g. telephone). Modern NICs default to full-duplex.
- Half-Duplex: Signals travel in both directions but only one direction at a time (e.g. intercom systems).
- Simplex: Signals travel in only one direction (e.g. broadcast radio, garage door openers).
- NIC settings for duplex can be configured via Windows Device Manager: options include Full Duplex, Half Duplex, or Auto Negotiation.
- Mismatched speed/duplex settings with neighboring devices can cause slow or failed transmissions.
9
Q
Multiplexing Concepts
A
- Multiplexing: Allows multiple signals to travel over one medium simultaneously by splitting the channel into subchannels. Increases data throughput over given bandwidth.
- Multiplexer (mux): Combines multiple signals at transmitting end.
- Demultiplexer (demux): Separates signals at receiving end.
- Type of multiplexing depends on medium and equipment capabilities.
10
Q
Multiplexing on Copper Lines
A
- TDM (Time Division Multiplexing): Divides channel into time slots reserved for specific nodes regardless of use. Can be inefficient if nodes are idle.
- STDM (Statistical TDM): Similar to TDM but assigns slots dynamically based on node priority/need. Maximizes bandwidth usage by avoiding empty slots.
- FDM (Frequency Division Multiplexing): Divides channel into multiple frequency bands for simultaneous signal transmission. Each signal modulated onto a separate frequency. Used in legacy phone systems and residential last-mile links.
11
Q
Multiplexing on Fiber-Optic Cable
A
- WDM (Wavelength Division Multiplexing): Uses different light wavelengths (colors) to transmit multiple signals over a single fiber. Original version supported 2 channels in one direction.
- Bidirectional WDM: Supports full-duplex transmission (signals in both directions).
- DWDM (Dense WDM): Enhances WDM by supporting 80–320 channels. Can be amplified en route. Used for high-bandwidth or long-distance WAN links (e.g. ISP to NSP).
- CWDM (Coarse WDM): Lower cost version with wider spaced frequencies, allowing cheaper transceivers. Supports fewer channels (e.g. 4, 8, 16, 18). Limited distance due to lack of amplification.
12
Q
Types of Coaxial Cables
A
- Coaxial cable (coax): Older Ethernet tech, still used for cable TV/Internet and some multimedia. Core = copper; surrounded by insulator, metal shielding, and sheath. Shielding = noise protection + grounding.
- RG Specifications: Defined by shielding/conducting materials, affecting attenuation, throughput, and impedance.
o AWG: Higher number = thinner core wire.
o Impedance:
50 ohms: Best for signal transmission (e.g., CB/ham radios, some computer networks)
75 ohms: Best for receiving (e.g., cable TV, satellite, home theater) - Common Types:
o RG-59: 20–22 AWG braided copper core, 50/75 ohms. Used for short-range video signal distribution. Cheaper but more attenuation.
o RG-6: 18 AWG solid copper core, 50/75 ohms. Used for broadband cable Internet/TV and AV systems. - Connectors:
o F-Connector: Threads like nut/bolt; core extends into connector. Common with RG-6.
o BNC (Bayonet Neill-Concelman): Twist-lock, has its own conducting pin. Used with RG-59, less common with RG-6.
13
Q
Twinaxial Cable (Twinax)
A
- Looks like coax but with two conductors for half-duplex transmission.
- Can have multiple conductor pairs for higher throughput.
- Best for short-distance high-speed connections (e.g., switch to router/server).
- Known as DAC (Direct Attach Copper). Supports up to 100 Gbps.
- More resistant to interference, cheaper, and easier to install than fiber. Made with 26 or 28 AWG copper.
- Distance limitations:
o Passive Twinax: No electrical components. <5–7 meters.
o Active Twinax: Has electrical components. Up to 10 meters. - Factory-terminated with modular transceivers. Higher data rates = shorter range.
14
Q
Twisted-Pair Cabling Basics
A
- Contains color-coded pairs of insulated copper wires (0.4–0.8 mm).
- 4 wire pairs used in Ethernet:
o 100 Mbps (Fast Ethernet): 2 pairs (1 send, 1 receive).
o 1 Gbps+ (Gigabit & beyond): All 4 pairs for send/receive. - Standardized by TIA/EIA-568. Modern LANs use Cat 5e or higher.
- Classifications:
o UTP (Unshielded Twisted Pair)
o STP (Shielded Twisted Pair)
15
Q
Twisted-Pair Cable Standards
A
- Cat 3: 10 Mbps, 16 MHz. For phones only—not used in networks.
- Cat 5: 100 Mbps (Fast Ethernet), 100 MHz. Basic data networks.
- Cat 5e: 1 Gbps, 350 MHz. Improved twist ratio + less crosstalk.
- Cat 6: 1 Gbps (or 10 Gbps short), 250 MHz. Plastic core + foil insulation.
- Cat 6a: 10 Gbps, 500 MHz. Reduces crosstalk/attenuation, backward-compatible with Cat 5/5e/6.
- Cat 7: Up to 10 Gbps (or 100 Gbps short), 600 MHz. Each pair shielded + overall shielding. Needs GG45 or TERA connectors. Thick and inflexible.
- Cat 7a: 40–100 Gbps (very short), 1000 MHz. Needs specialty connectors.
- Cat 8:
o Class I (8.1): 25–40 Gbps, up to 30m, 2 GHz. Uses Cat 5e/6 compatible connectors.
o Class II (8.2): Same bandwidth, uses Cat 7/7a compatible connectors.
o Highly shielded, rivals fiber in short-distance backbone setups.
16
Q
Types of Twisted-Pair Copper Cables: STP vs UTP
A
- STP (Shielded Twisted Pair): Twisted-pair wires with individual insulation and metallic shielding (foil or braided copper) that prevents external EM interference and contains internal signal energy. Must be grounded. Effectiveness depends on environmental noise, shielding material/thickness, grounding, and consistency. Cat 8 is a modern STP with advanced shielding and high bandwidth, suitable for short distances.
- UTP (Unshielded Twisted Pair): One or more twisted wire pairs encased in plastic without shielding. Cheaper but less noise-resistant. Variants include:
o PVC-grade (toxic when burned)
o Plenum-grade (flame-resistant)
o Cat 5e, Cat 6 with plastic core. - Key Differences:
o Throughput: Both support 10 Mbps to 10 Gbps; only STP can exceed 10 Gbps.
o Cost: STP is pricier due to materials and grounding; high-grade UTP can also be costly.
o Connectors: Both use RJ-45 (larger than RJ-11 used in phones).
o Noise immunity: STP better by default; UTP requires filtering/balancing.
o Length: Max 100 meters for both at ≤10 Gbps; STP may need shorter lengths.
17
Q
Cable Pinouts and Standards
A
- RJ-45 Termination Standards:
o TIA/EIA-568A (T568A) and TIA/EIA-568B (T568B) are wiring standards.
o Difference is in the position of orange and green wire pairs (Tx/Rx reversed).
o Federal contracts require T568A; T568B is more common in homes/businesses. - Fast Ethernet: Uses 2 pairs (orange & green).
- Gigabit Ethernet: Uses all 4 wire pairs for bidirectional data.
- Straight-through Cable (Patch Cable): Same standard on both ends. Used for:
o PC → Switch
o Switch → Router - Port Types:
o MDI (Medium Dependent Interface): On computers/routers.
o MDI-X: On switches (auto-adjusts Tx/Rx pairs). - Auto-MDI-X: Modern devices auto-detect cable type and adjust Tx/Rx; reduces reliance on correct cables.
18
Q
Crossover and Rollover Cables
A
- Crossover Cable:
o Reverses Tx and Rx wire pairs.
o Used to connect like devices (e.g., PC↔PC, Switch↔Switch).
o Fast Ethernet crossover: Reverses 2 pairs (orange & green).
o Gigabit Ethernet crossover: Reverses all 4 pairs (rarely needed today).
o Obsolete due to Auto-MDI-X. - Rollover Cable (Console Cable):
o Reverses all wires, not just pairs.
o Used to connect a PC to a router’s console port (for configuration).
o Console ports differ from Ethernet ports (used for LAN).
19
Q
Power over Ethernet (PoE)
A
PoE allows power to be delivered over Ethernet cables (twisted-pair copper), defined by IEEE 802.3af (2003).
* Standard PoE (802.3af): 15.4 watts
* PoE+ (802.3at): 25.5 watts
* Useful for: IP phones, WAPs, security cameras far from outlets
* Requires Cat 5 or better cable
* Power can travel over unused or data-carrying wire pairs—must be consistent across devices
PoE Devices:
* PSE (Power Sourcing Equipment): Supplies power (e.g., PoE-capable switch)
* PD (Powered Device): Receives power (e.g., IP camera, phone)
* PSE checks if the PD is PoE-capable before supplying power
PoE Equipment Options:
* PoE-capable switch/router: Provides power directly
* Injector/Midspan: Adds power to network from a non-PoE switch
* Splitter: Allows non-PoE device to receive PoE power
* Switches must support PoE; PDs must be PoE-compatible
* Consistent pair usage across devices is necessary
20
Q
Ethernet Standards for Twisted-Pair Cabling
A
Each Ethernet standard defines max speed, distance, required cable category, and wire pairs used.
Standard Speed (Mbps) Max Distance (m) Cable Wire Pairs Used
10BASE-T 10 100 Cat 3+ 2
100BASE-T 100 100 Cat 5+ 2
100BASE-TX 100 100 Cat 6+ 2
1000BASE-T 1000 100 Cat 5e+ 4
10GBASE-T 10,000 100 Cat 6a/7 4
40GBASE-T 40,000 30 Cat 8 4
* 100GBASE-T exists but is rare; matches fiber-optic speed but limited to 100 m
* Used in high-demand LANs for video/voice (not for WAN due to range limits)
21
Q
Fiber-Optic Cable Structure
A
- Core: Glass or plastic strands transmit data via pulsing light from either a laser (long distance, high throughput) or LED (shorter connections).
- Cladding: Reflects light back into the core to maintain signal integrity even around bends (subject to bend radius limits).
- Buffer: Opaque plastic surrounding cladding to absorb stray light.
- Kevlar: Prevents stretching and adds durability.
- Outer Sheath: Plastic protective cover.
- Simplex transmission is common—two strands needed for full-duplex unless using BiDi (WDM) transceivers, which allow bidirectional communication over one strand.
- Available as bulk fiber bundles (up to 1000 strands) or small, pliable patch cables.
- Zipcord cables: Two strands side-by-side in one jacket for full-duplex connections over short distances.
22
Q
Fiber-Optic Benefits & Drawbacks
A
Benefits:
* Extremely high throughput (up to 100 Gbps/channel; up to 1 billion laser pulses/sec)
* Highly resistant to noise (immune to EMI)
* Excellent signal integrity over long distances
* Secure transmission medium
Drawbacks:
* High cost (cable, equipment, and installation)
* Expensive and time-consuming to repair (requires special splicing equipment)
* Skilled labor needed
* Optical loss increases over distance and with dirty or misaligned connections
23
Q
Single Mode vs Multimode Fiber
A
Single Mode Fiber (SMF):
* 8–10 micron core
* Laser light travels in a single path (minimal dispersion)
* Best for long distances and highest bandwidth
* Used in Internet backbone
* Expensive; rarely used for short links
Multimode Fiber (MMF):
* 50 or 62.5 micron core
* Light travels in multiple angles (increased attenuation)
* Cheaper and easier to install
* Ideal for shorter distances (few km max)
* Common for LAN backbones, router/switch/server links
24
Q
Fiber Distribution & Splicing
A
- FDP (Fiber Distribution Panel): Convergence point for fiber connections and equipment
- Splicing types:
o Fusion splice: Permanent, melted fiber ends
o Connectors: Reusable, used for flexible setups
25
Fiber Connectors Overview
* Connectors vary by fiber type (SMF or MMF) and ferrule size/polish.
* Ferrule: Tip of connector that contacts the port
* Polish types:
o UPC (Ultra Physical Contact): Rounded surface, reduced reflection, worsens over time
o APC (Angled Physical Contact): Angled surface (8°), minimizes reflection, stable over time
26
Common Fiber Connectors
Connector Fiber Type Polish Ferrule Full-Duplex Notes
LC (Local Connector) SMF or MMF UPC, APC 1.25 mm Yes Small, high-density, most common SMF connector
ST (Straight Tip) SMF UPC 2.5 mm No Older type, twist-lock
SC (Subscriber/Standard) SMF UPC, APC 2.5 mm Can be Push-pull, used in older networks
MT-RJ (Mechanical Transfer - RJ) MMF N/A 2 fibers Yes Two strands in one ferrule, compact, most common MMF connector
27
Media Converters
Hardware that interconnects copper and fiber segments by converting electrical signals (from copper) into light signals (for fiber), and vice versa. Must match:
* Fiber types: SMF↔Copper, MMF↔Copper, or SMF↔MMF.
* Connector types used in network segments.
28
Fiber Transceivers
Modular, hot-swappable interfaces for connectivity devices like switches or NICs. Allow upgrades without network downtime. Types:
* GBIC (obsolete) – For Gigabit Ethernet; supports RJ-45 or SC connectors.
* SFP (Small Form-Factor Pluggable) – 1 Gbps, compact, aka mini-GBIC.
* XFP – Up to 10 Gbps, larger than SFP but uses less power than SFP+.
* SFP+ – Up to 16 Gbps, same size as SFP, widely used today.
* QSFP – 4 channels, up to 40 Gbps (4×10 Gbps).
* QSFP+ – 40+ Gbps; QSFP56-DD reaches 400 Gbps (8×50 Gbps).
* CFP – 100 Gbps (centum = 100); later models (CFP2/4/8) smaller & more efficient.
Important Notes:
* Must match transceiver type, speed, protocol, and connector (usually LC or RJ-45).
* Insert before attaching cables; remove cables before extraction.
* Some transceivers have management interfaces (e.g., IP config via Telnet).
* Hot-swappable with keyed alignment to prevent incorrect insertion.
29
Ethernet Standards Using Fiber
IEEE fiber standards by speed and cable type:
Standard Speed (Mbps) Max Distance Fiber Type Notes
100BASE-SX 100 Up to 300 m MMF 850nm wavelength; short-range, cost-effective; distance depends on modal bandwidth.
100BASE-FX 100 Up to 2000 m MMF 1300nm wavelength; Fast Ethernet standard.
1000BASE-SX 1000 Up to 550 m MMF 850nm; for short links like data center to closet.
1000BASE-LX 1000 550 m (MMF), 5 km (SMF) MMF or SMF 1300nm; used for long MAN backbones or ISP connections.
10GBASE-SR 10,000 Up to 300–400 m MMF 850nm; “Short Range”; distance varies by cable quality.
10GBASE-LR 10,000 Up to 10 km SMF 1310nm; “Long Range”; uses laser light.
Notes:
* MMF distance affected by modal bandwidth (MHz-km).
* Modal bandwidth = highest signal frequency fiber can carry at specific distance.
* Only one repeater allowed between segments.
30
Common Fiber Cable Problems
* Fiber Type Mismatch: SMF↔MMF or mismatched core sizes (e.g., 50μm vs 62.5μm) causes transmission issues.
* Wavelength Mismatch: Using incorrect light wavelength for cable type (e.g., 1300nm signal over cable optimized for 850nm).
* Dirty Connectors: Dust/contaminants degrade signal; always keep connectors/jacks covered when not in use.
* Link Loss: Caused by distance, splices, poor connections, or multiplexing.
o Optical Link Budget: Measures signal loss in dB across a link.
o Must be high enough for signal to reach destination with integrity.
o Low budget = reduced efficiency, potential downtime.
31
Cable Troubleshooting Overview
Cabling problems may present as occasional packet loss or total disconnection. Begin troubleshooting by checking network port LEDs:
* Steady light = connectivity
* Blinking light = activity
* Red/amber = possible fault
If NICs and connections are intact, specialized tools can isolate issues in cable media. Tools range from basic continuity testers to advanced performance analyzers.
32
Toner and Probe Kit
Used to trace the termination point of a wire in disorganized setups.
* Tone Generator: Sends a signal through one end of the wire
* Tone Locator/Probe: Emits an audible tone when it detects the signal
Limitations: Cannot detect defects, length issues, or electrical quality. Only identifies where a wire ends.
Usage: Trial-and-error scanning of terminations until the correct one is located.
33
Multimeter
Measures voltage, resistance, and impedance. Useful for both AC and DC circuits.
* Impedance (in ohms): Indicates opposition to current; key for identifying cable faults
* Use cases:
o Verify voltage continuity
o Detect noise (extraneous voltage)
o Identify short circuits (unwanted connections)
o Identify open circuits (broken paths or disconnected wires)
High or low impedance may signal damage or improper termination.
34
Cable Continuity Tester
Battery-operated device with base and remote unit to check signal flow from end to end.
* Verifies basic cable function (pass/fail lights or tones)
* Some testers verify TIA/EIA 568 pinouts and pairing (wire map test):
o Reversed pair: wires in a pair swapped
o Crossed pair: entire pairs swapped
o Split pair: one wire from two pairs swapped—hard to detect, can pass basic test
* Supports copper or fiber:
o Copper: voltage signal
o Fiber: light pulse test
* Portable, lightweight, usually 9V battery
* Price: ~$10–$300
* Brands: Belkin, Fluke, Greenlee
35
Cable Performance Tester (aka Line Tester / Certifier / Network Tester)
Performs continuity tests plus in-depth cable analysis:
* Measures:
o Cable length to device/fault
o Attenuation
o NEXT (near-end crosstalk)
o Alien crosstalk
o Impedance & termination resistance
* Pass/fail ratings for cabling categories
* Results: Saved, printed, or exported to databases
* Graphical output: Shows attenuation/crosstalk along cable
* Includes TDR (Time Domain Reflectometer):
o Sends signal, measures reflection changes
o Detects crimps, bends, shorts, mismatches, bad connectors
* Fiber version uses OTDR (Optical Time Domain Reflectometer):
o Sends light pulses of varying wavelengths
o Measures:
Fiber length
Location of splices, breaks, bends
Attenuation
* Cost: Basic units = few hundred $, advanced = $50,000+
36
Optical Power Meter (OPM)
Also called a fiber light meter. Measures the amount of light transmitted over a fiber line.
* Must be calibrated to NIST standards
* Accuracy affected by:
o Room temperature
o Connector quality
o Technician skill
* Used post-installation to ensure fiber meets power and quality specs
* More advanced models offer higher precision at higher prices
