Assam ASSEB HS Skill Telecom cheat sheet

Decibel is a logarithmic ratio: dB = 10 log10(P2/P1) for power; for voltage or current across equal impedance, dB = 20 log10(V2/V1).

Absolute power references: dBm = 10 log10(P/1 mW); 0 dBm = 1 mW, +30 dBm = 1 W, −30 dBm = 1 µW.

Nyquist sampling theorem: a band-limited signal of bandwidth B must be sampled at fs ≥ 2B to be reconstructed without aliasing.

Shannon capacity: C = B log2(1 + S/N) bit/s; doubling bandwidth doubles capacity, but capacity rises only logarithmically with SNR.

SNR in dB = signal level (dBm) − noise level (dBm); noise floor of a receiver is kTB plus noise figure, with kTB ≈ −174 dBm/Hz at 290 K.

Fourier relation: any periodic signal equals a sum of sinusoids at f0 and its harmonics; a sharper pulse edge means wider occupied bandwidth.

Modulation families: AM varies carrier amplitude, FM varies carrier frequency (constant envelope, more noise-immune), and digital schemes (ASK, FSK, PSK, QAM) map bits to symbol states.

Quantisation noise in PCM falls about 6 dB per added bit; a companding law (A-law or µ-law) compresses dynamic range for speech.

Twisted pair categories: Cat5e supports 1 Gbit/s to 100 m; Cat6/6A support 1–10 Gbit/s with tighter crosstalk limits; characteristic impedance is 100 Ω.

Coaxial cable carries broadband signals with low loss and high shielding; characteristic impedance is typically 50 Ω (radio) or 75 Ω (video/broadband).

Optical fibre: single-mode core ≈ 8–10 µm carries one mode over tens of km; multimode core 50 or 62.5 µm is used for short spans.

Network topologies: star is easy to fault-isolate, ring offers path protection, mesh gives highest redundancy, bus is cheapest but a single break kills the segment.

Attenuation is signal loss per unit length (dB/km); dispersion spreads pulses; both limit the maximum reach and bit rate of a link.

OSI reference model has 7 layers: Physical, Data Link, Network, Transport, Session, Presentation, Application; TCP/IP collapses these to 4.

Transmission impairments: attenuation, distortion, noise (thermal, crosstalk, impulse) and interference; crosstalk between pairs is measured as NEXT and FEXT.

Circuit switching reserves a dedicated path for the whole call; packet switching shares links and buffers packets, which suits bursty data traffic.

IPv4 header fields: version, header length, TTL, protocol, source and destination address (32 bits); TTL is decremented per router hop and dropping to 0 discards the packet.

Private IPv4 ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16; these are not routed on the public Internet without NAT.

Subnetting: usable hosts = 2^h − 2 where h is the host-bit count; /24 gives 254 usable hosts, /30 gives 2 (used for point-to-point links).

Routing: static routes are manually configured; dynamic protocols include RIP (distance vector, hop-count metric) and OSPF (link state, cost metric).

Key protocols and ports: DNS 53, DHCP 67/68, HTTP 80, HTTPS 443, SMTP 25, SSH 22, Telnet 23, SNMP 161.

TCP is connection-oriented with a 3-way handshake (SYN, SYN-ACK, ACK) and retransmission; UDP is connectionless with no delivery guarantee.

VLANs segment a switch into separate broadcast domains; trunk links between switches carry tagged frames (IEEE 802.1Q).

Cellular reuse: a cluster of N cells uses the same frequency group; co-channel reuse ratio Q = D/R = √(3N), so larger N means less interference but fewer channels per cell.

GSM uses 200 kHz carrier spacing, 8 time slots per TDMA frame, and a 4.615 ms frame period; uplink is 890–915 MHz and downlink 935–960 MHz in the 900 MHz band.

Handover transfers an active call between cells; roaming lets a subscriber use a visited network through a home-location register and visitor-location register exchange.

Multiple access: FDMA divides frequency, TDMA divides time slots, CDMA separates users by spreading codes, OFDMA assigns subcarriers and is used in LTE and 5G NR.

Free-space path loss rises with the square of distance and frequency: FSPL(dB) = 32.44 + 20 log10(d_km) + 20 log10(f_MHz).

Antenna gain relates to effective area; a half-wave dipole has 2.15 dBi gain, and EIRP = transmitter power (dBm) + antenna gain (dBi) − cable loss (dB).

Link budget rule: received power = EIRP − path loss + receive antenna gain; the link closes only if received power exceeds receiver sensitivity plus margin.

Fibre windows: 850 nm (multimode LAN), 1310 nm (zero dispersion in standard single-mode), 1550 nm (lowest attenuation, ≈0.2 dB/km, used with EDFA amplifiers).

Total internal reflection occurs when light travels from a denser core to a rarer cladding and the incidence angle exceeds the critical angle; numerical aperture sets the acceptance cone.

Splicing: fusion splicing gives the lowest loss (typically 0.05–0.1 dB); mechanical splices and connectors show higher loss, so connectors are kept to a minimum.

FTTH architectures: PON shares one feeder fibre among users via passive splitters; GPON downstream is 2.488 Gbit/s and upstream 1.244 Gbit/s.

xDSL runs over existing copper pairs; ADSL is asymmetric with higher downstream, while VDSL gives higher rates over shorter loops.

OTDR testing sends a light pulse and plots backscatter versus distance, revealing splice loss, connector reflections and fibre breaks.

Broadband access options include FTTH, xDSL, cable (DOCSIS over coaxial/HFC) and fixed wireless; each trades reach, capacity and cost differently.

Structured cabling hierarchy: work area → horizontal cabling (max 90 m) → telecommunications room → backbone → equipment room; patch cords add up to 10 m in the channel.

UTP termination on RJ-45 uses T568A or T568B pinout; both ends of a straight-through cable must use the same standard, while a crossover swaps transmit and receive pairs.

Bend radius rule of thumb: at least 4× cable diameter for UTP and 10× for fibre during installation; exceeding it raises loss and can crack fibre.

Separation from power cabling reduces interference: keep data cable at a safe distance from mains and cross power lines at right angles, never parallel-adjacent.

Earthing and bonding: equipment racks, cable shields and surge protectors must be bonded to a common earth to control potential differences and lightning surge.

Labelling and documentation of every port, patch panel and cable end is required for later fault tracing and maintenance.

Fibre connector types: SC (square, push-pull), LC (small form factor), ST (bayonet); keep connectors and ferrules clean, since dust causes high loss.

Continuity and polarity are checked with a multimeter or cable tester; a wire-map test shows opens, shorts, crossed pairs and split pairs.

Certification tests for copper links measure insertion loss, NEXT, return loss and length against the category limit; a pass requires all parameters within limits.

Optical power meter measures absolute received power (dBm); loss of a link = transmit power − received power, which must stay within the link budget.

OTDR trace interpretation: a downward step indicates splice or bend loss, a spike indicates a reflective connector, and a sudden end indicates a break.

Fault-finding sequence: confirm the symptom, isolate the layer (physical, link, network), substitute known-good components, then verify after repair.

Common faults: loose connectors, water ingress in outdoor cable, corroded joints, damaged drop wire, faulty power supply and misconfigured equipment.

Preventive maintenance includes periodic cleaning, checking earth connections, tightening terminations and logging alarms for trend analysis.

Service categories: voice telephony, broadband data, leased lines, IPTV and value-added services; each has its own SLA parameters for availability and latency.

Customer premises equipment includes ONT/ONU, routers, modems and set-top boxes; the demarcation point separates operator responsibility from customer wiring.

Billing components: monthly rental, usage charges, one-time installation fee, taxes and late-payment charges; itemised bills must show each component separately.

Prepaid billing deducts from a balance in real time; postpaid billing accumulates usage and issues a periodic invoice, so credit control differs.

Tariff structures include flat rate, usage-based, bundled and tiered plans; the tariff must be transparent and published before subscription.

Customer care workflow: log the complaint, assign a ticket number, resolve within the SLA, record the resolution and follow up with the customer.

Churn control relies on service quality, timely fault repair and clear billing, since repeated disputes are a leading cause of customer loss.

Electrical safety: isolate and lock out the circuit before work, verify dead with a tester, and treat all conductors as live until proved otherwise.

Personal protective equipment for telecom work includes helmet, safety shoes, gloves, safety belt for pole or tower work and eye protection for fibre and drilling.

Laser safety: never look into a fibre end or connector; use an optical power meter instead of the eye, and label fibre links as laser sources.

RF/EMF exposure is controlled by limiting power density and time near antennas; keep the public outside the exclusion zone and follow the operator's maximum permissible exposure limits.

Working at height requires a tested safety belt anchored above the worker, a second person at ground level and no work in lightning or high wind.

Regulatory compliance covers licensed spectrum use, type-approved equipment, electromagnetic compatibility limits, and privacy of subscriber data.

Incident reporting: any shock, fall or fibre eye exposure must be recorded and investigated so the cause is corrected, not just the symptom.

A business plan states the service offered, target customers, cost structure, pricing, break-even point and funding requirement.

Break-even quantity = fixed costs ÷ (price per unit − variable cost per unit); below this volume the venture makes a loss.

Cash flow differs from profit: a profitable venture can still fail if cash is tied up in stock or unpaid customer bills.

Market survey before launch identifies demand, competitor tariffs and the local willingness to pay for telecom services.

Employability skills for telecom roles: technical troubleshooting, safety awareness, documentation, teamwork and basic customer handling.

Effective communication: listen fully, confirm understanding by restating, avoid jargon with customers, and record commitments in writing.

Licensing and registration for a small service provider include business registration, tax registration and compliance with telecom equipment and spectrum rules.

Bandwidth is the range of frequencies a channel carries (Hz); bit rate is the number of bits per second; they are related by the modulation's spectral efficiency (bit/s/Hz).

A 3 dB loss halves power; a 10 dB loss reduces power tenfold; a 3 dB gain doubles power, so cascaded gains and losses add in dB.

Noise figure NF = SNR_in(dB) − SNR_out(dB) of an amplifier; lower NF means a quieter receiver front end.

Multipath causes fading and intersymbol interference; equalisation and diversity (space, frequency, time) are the standard countermeasures.

Quantisation error is at most half a step size; more levels per sample reduce error but increase bit rate.

Guided media are copper and fibre; unguided media are radio, microwave, satellite and free-space optical.

Satellite links: GEO is about 35,786 km altitude with roughly 250 ms one-way delay, while LEO is much lower and has lower latency.

Microwave line-of-sight links need a clear Fresnel zone; obstruction causes fading, so antennas must be aligned and the path surveyed.

Fibre advantages over copper: far higher bandwidth, immunity to electromagnetic interference, lower attenuation and no crosstalk.

Network performance metrics: bandwidth, throughput, latency, jitter and packet loss; voice needs low jitter while bulk data tolerates delay.

MAC address is 48 bits written as six hex pairs; the first three bytes identify the vendor (OUI).

ARP resolves an IPv4 address to a MAC address on the local link; a switch forwards frames by learning source MAC addresses into its table.

DHCP assigns IP address, subnet mask, default gateway and DNS server automatically; without it, hosts need static configuration.

NAT translates private addresses to a public address, conserving IPv4 space and hiding internal hosts.

IPv6 uses 128-bit addresses, written as eight hex groups; it removes the need for NAT and has no broadcast, using multicast instead.

Ping uses ICMP echo request/reply to test reachability; traceroute reveals the hop-by-hop path to a destination.

Frequency bands: 900/1800 MHz for GSM, 2100 MHz for 3G, 1800/2300/2500 MHz for LTE, and sub-6 GHz plus mmWave for 5G.

Sectorisation divides a site into 3 sectors of 120°, raising capacity without new spectrum but increasing handover events.

Fading: slow (shadowing) fading varies over metres, fast (Rayleigh) fading varies over fractions of a wavelength; diversity and margin counter it.

Higher-order QAM raises bit rate but needs a better SNR; 64-QAM needs a much cleaner channel than QPSK.

5G features: enhanced mobile broadband, ultra-reliable low-latency communication and massive machine-type communication.

Single-mode fibre has a very small core, so only the fundamental mode propagates, eliminating modal dispersion and allowing long-haul links.

Chromatic dispersion broadens pulses because different wavelengths travel at different speeds; dispersion compensation or coherent receivers mitigate it.

WDM puts multiple wavelengths on one fibre; DWDM spacing is typically 0.4 or 0.8 nm in the C-band.

PON split ratios such as 1:32 or 1:64 share one feeder fibre; higher split ratio lowers per-user bandwidth.

Optical return loss measures reflections at connectors and splices; poor polishing or dirty ferrules raise reflections and degrade the link.

Cable trays and conduits must be sized with spare capacity and supported at regular intervals to avoid sag and mechanical stress.

Outdoor aerial drop wire needs proper tension, clamps and a drip loop at the entry point to keep water out of the premises.

Rack installation: heavy equipment at the bottom, adequate ventilation, cable management at the side and a clear earth bar for bonding.

Fibre splicing requires a clean cleave at 90°, matched fibre types and a splice loss check on the OTDR or power meter afterwards.

Power for telecom equipment uses a UPS or battery bank with a defined backup time; polarity must be verified before connecting DC feeds.

A loopback test returns the transmitted signal to the sender; it isolates whether a fault lies in the local equipment or the line.

Bit error rate (BER) is errored bits divided by total bits sent; a typical target for a good link is below 10^-9.

Signal level too high can also cause faults (receiver saturation), so both weak and excessive levels must be checked.

Intermittent faults are traced by logging time, temperature and traffic conditions, then correlating the pattern with the failure.

Spare-parts and test-equipment calibration records are part of maintenance management and support warranty claims.

Quality of service for voice is judged by call setup success, drop-call rate and mean opinion score; for data by throughput and latency.

A service-level agreement states uptime percentage, fault repair time and compensation for missed targets.

Number portability lets a subscriber keep the number when changing operator; the routing database must be updated after the switch.

Bill dispute handling requires the usage records (call detail records) to be retained and produced as evidence.

Prepaid recharge, voucher and top-up systems must reconcile the balance with the billing system to prevent revenue leakage.

Electric shock severity depends on current path, magnitude and duration; even low currents through the chest can disturb the heart rhythm.

First aid for electric shock: switch off the supply, do not touch the victim until isolated, then call for help and give CPR if trained.

Fire safety: use a CO2 or dry-powder extinguisher on electrical fires, never water; keep escape routes clear.

Antenna sites are marked with warning signs and exclusion distances; RF power must be switched off before climbing near live antennas.

Chemical and battery hazards: lead-acid batteries release hydrogen, so ventilate the room and avoid sparks near them.

Costing for a service business separates fixed costs (rent, salaries) from variable costs (cable, connectors, fuel per job).

Pricing must cover cost plus a margin while staying competitive with local tariffs; undercutting below cost is not sustainable.

A simple book of accounts (receipts, payments, stock) supports tax filing and shows the venture's true position.

Customer retention is cheaper than acquisition, so follow-up calls and warranty service protect repeat business.

A curriculum vitae for a technician role should list certifications, tools handled and safety training, with measurable achievements.

Interview communication: answer the question asked, give a concrete example, and state what you would do differently next time.

For a sinusoid, RMS value = peak/√2; power in a resistive load P = V_rms²/R, so a 6 dB rise in voltage is a 6 dB rise in power across the same R.

Eye diagrams show signal quality: a wide-open eye means good margin, a closing eye means noise, jitter or dispersion.

Intermodulation products fall at sums and differences of input frequencies and cannot be filtered out if they land in-band.

Companding in PCM follows a logarithmic curve so quiet speech gets more levels, improving perceived quality at 8-bit, 8 kHz sampling (64 kbit/s).

Phase noise and jitter degrade high-order modulation more than low-order modulation, limiting the usable constellation size.

Plesiochronous digital hierarchy rates: E1 = 2.048 Mbit/s (32 timeslots of 64 kbit/s); E3 = 34.368 Mbit/s; SDH STM-1 = 155.52 Mbit/s.

SDH multiplexing is synchronous with pointer adjustments, while PDH uses bit stuffing, which is why SDH simplifies drop-and-insert.

Ethernet frame: preamble, destination and source MAC, type/length, payload (46–1500 bytes), and frame check sequence (CRC-32).

Maximum transmission unit of standard Ethernet is 1500 bytes; jumbo frames exceed this and need consistent configuration end to end.

FDM shares a medium by frequency, TDM by time slots; WDM is FDM applied to optical wavelengths.

A /26 subnet has 64 addresses and 62 usable hosts; a /30 has 4 addresses and 2 usable hosts.

Longest-prefix match rule: a router chooses the most specific matching route, regardless of metric.

Spanning Tree Protocol prevents Layer-2 loops by blocking redundant ports; without it, broadcast frames loop endlessly.

OSPF uses hello packets to form adjacencies and link-state advertisements to build a topology database; cost is inversely related to bandwidth.

QoS marking with DSCP lets voice and video traffic be prioritised over bulk downloads during congestion.

Cellular capacity can be raised by more spectrum, smaller cells, sectorisation, or higher spectral efficiency from better modulation and MIMO.

MIMO uses multiple antennas at both ends; spatial multiplexing sends parallel streams while beamforming directs energy at the user.

A link budget margin covers fading and body loss; a typical design margin for indoor coverage is 10–20 dB.

Frequency reuse factor 1 (as in LTE) means every cell uses the same band, relying on interference coordination instead of planning.

Adjacent-channel interference comes from insufficient filtering or frequency spacing; co-channel interference comes from cells reusing the same frequencies.

Link loss budget: total loss = fibre attenuation × length + splice losses + connector losses; this must be less than transmit power minus receiver sensitivity.

Macrobending loss occurs when fibre is bent beyond its minimum radius; microbending comes from mechanical stress on the coating.

Optical amplifiers such as EDFA amplify in the 1550 nm window without electrical regeneration, but add amplified spontaneous emission noise.

GPON downstream uses 1490 nm for data and 1550 nm for video overlay, with 1310 nm upstream.

Fibre-to-the-building and fibre-to-the-curb place the optical termination closer to the user, reducing the copper segment and raising achievable speed.

Power over Ethernet (IEEE 802.3af/at) delivers up to about 15.4 W or 30 W at the source, used for IP phones, cameras and access points.

Shielded cabling needs the shield bonded at one or both ends per design; improper bonding turns the shield into an antenna.

Fibre cable pulling tension and bend radius limits are stricter than copper; exceeding them causes hidden loss that appears later.

Cable testing after installation should include length, wire map, attenuation and NEXT, with results recorded against the port label.

Rack earthing uses a dedicated earth bar bonded to the building earth, with separate earth conductors for equipment and cable shields.

TDR (time-domain reflectometry) locates copper faults by measuring the reflection delay; distance = velocity × time / 2.

A high NEXT reading above the limit indicates excessive crosstalk, often from untwisted pairs at the termination or a crushed cable.

Optical time-domain reflectometer dead zones hide events close to the instrument; use a shorter pulse for near-end detail.

Spectral analysis with a spectrum analyser reveals interference and spurious emissions that a power meter cannot show.

Fault closure requires a root-cause note, the corrective action taken and a re-test result, not just a cleared alarm.

Call detail records capture calling and called number, start time, duration and charge; they are the basis for usage billing and disputes.

Billing mediation collects records from switches, removes duplicates, rates them and passes them to invoicing.

Revenue assurance compares billed usage with network records to detect leakage from unrated or misrated calls.

Customer premises wiring belongs to the customer beyond the demarcation point; faults there may attract a charge.

Broadband fair-use policy limits excessive usage; the threshold and consequence must be stated in the contract.

Maximum permissible exposure limits are frequency dependent; power density limits are stricter for the general public than for trained workers.

Specific absorption rate (SAR) measures RF energy absorbed by body tissue and is regulated for handsets.

Licensed spectrum use requires an authorisation; operating without one is illegal and can cause harmful interference to licensed services.

Electromagnetic compatibility requires equipment to limit emissions and to have adequate immunity to external interference.

Subscriber data protection requires consent for use, secure storage and restricted access to billing and call records.

A cash-flow forecast lists expected receipts and payments per month; a negative month requires a credit line or deferred payment plan.

Return on investment = (gain from investment − cost) ÷ cost, expressed as a percentage.

A service contract should define scope, response time, exclusions and payment terms to avoid disputes.

Team communication uses a clear handover note: what was done, what remains, what is at risk and who owns the next step.

Negotiation basics: know your walk-away point, separate the person from the problem, and trade on interests rather than positions.

Power in dBm can be added directly to gains and losses in dB; never add dBm to dBm, since that is meaningless.

A receiver sensitivity of −100 dBm with a 20 dB margin requires at least −80 dBm at the antenna port under worst-case fading.

Rise time and bandwidth are inversely related: a faster edge needs a wider channel, so bit rate and bandwidth scale together.

Aliasing folds high frequencies to low ones; an anti-aliasing filter before the sampler prevents this.

Impulse noise is short and high-amplitude; it is the main cause of burst errors on copper lines.

A 100 m channel limit includes the horizontal cable plus patch cords; exceeding it causes attenuation and NEXT failures.

Fibre attenuation is quoted in dB/km; a 10 km span at 0.35 dB/km loses 3.5 dB before splices and connectors.

Cable shielding effectiveness depends on coverage and grounding; foil plus braid gives better shielding than foil alone.

Wireless links need line of sight; at 2.4 GHz, Fresnel zone clearance matters more than at lower frequencies.

Network documentation should record cable routes, pair assignments and port labels so a fault can be traced without guesswork.

A default route 0.0.0.0/0 matches any destination not covered by a more specific route and points to the upstream gateway.

A VLAN trunk carries multiple VLANs; an access port carries one VLAN to an end device.

DHCP lease renewal happens at half the lease time; a lost DHCP server leaves hosts with expired addresses.

Ping succeeds but the application fails: check DNS resolution, port blocking and application configuration, not just the link.

A loop between switches causes broadcast storms; enabling STP and checking for duplicate links prevents it.

Antenna downtilt controls coverage: more downtilt shrinks the cell and reduces interference to neighbours.

VSWR measures antenna and feeder match; a high VSWR reflects power back and reduces radiated power.

Site survey records signal strength and interference at candidate locations before installing access points or base stations.

Cell breathing in CDMA means the coverage shrinks as load rises, so capacity and coverage are coupled.

Battery backup at a cell site must be sized for the required holdover time and the site's actual load current.

Before splicing, clean the fibre and cleave at 90°; a poor cleave gives high splice loss or a failed splice.

The optical power meter must be set to the correct wavelength, since detector response differs at 1310 and 1550 nm.

A dirty connector can add several dB of loss; inspect and clean ferrules before every mating.

A PON splitter loss is about 3 dB for 1:2, 10.5 dB for 1:8 and 17 dB for 1:32, so split ratio consumes link budget.

Broadband speed tests should be run wired, with no other traffic, and repeated to separate line limits from Wi-Fi limits.

Terminate UTP pairs with the correct untwisted length kept to a minimum; untwisting more than about 13 mm raises NEXT.

Use the correct punch-down tool for the patch panel; a poor punch causes intermittent opens.

Fibre connectors must be mated with the correct polish type (PC, UPC, APC); mismatched polish causes high loss and reflections.

Test every link after termination and label both ends before closing the cabinet.

Equipment installation follows the manufacturer's clearance and ventilation requirements; blocking vents causes overheating and early failure.

Start from the physical layer: check power, connectors and cable before suspecting software.

Substitute a known-good patch cord or port to localise a fault quickly, then test the suspect item separately.

Record the pre-fault and post-repair test values so the improvement can be demonstrated.

A repeating alarm pattern at the same time of day points to a load or temperature-related cause.

Keep test equipment calibrated and within its calibration date; an out-of-calibration meter invalidates the result.

A customer complaint about slow broadband should be checked from the router outward: line sync, router throughput, then Wi-Fi.

The bill must show the tariff plan, usage period, taxes and any one-time charges separately.

Prepaid balance must be checked before a recharge is accepted to avoid double crediting.

Fault tickets need a unique number and a promised resolution time, both communicated to the customer.

Service activation requires the order, the installation record and the customer's acceptance signature.

Before climbing, inspect the pole, ladder and safety belt; a cracked pole or frayed belt means stop work.

Use a voltage detector on the line before touching it, and treat a metal pole stay as live until tested.

Keep the work area cordoned off so the public stays clear of falling tools and open trenches.

When working near antennas, confirm the transmitter is off and the key is held by the worker.

Report near-misses as well as injuries; near-miss data prevents the next accident.

Quote preparation: list materials, labour hours, travel and contingency, then add the agreed margin.

A simple invoice states the service, date, amount, tax and payment due date, and is numbered for record.

Track receivables and follow up on overdue invoices promptly; unpaid work is the most common cash-flow failure.

In a job interview, describe a fault you diagnosed: situation, action, result, and what you learned.

Written customer communication should be short, specific and free of unexplained technical terms.

Conversion: power ratio dB = 10 log10(P2/P1); voltage ratio dB = 20 log10(V2/V1).

Cascaded stages: total gain (dB) = sum of individual gains minus sum of losses.

Free-space path loss at 2.4 GHz over 1 km ≈ 100 dB; at 5 GHz over the same distance it is about 6 dB higher.

Noise floor for a 20 MHz channel ≈ −174 + 10 log10(20×10^6) ≈ −101 dBm before noise figure.

Shannon example: B = 1 MHz, SNR = 20 dB (100 linear) gives C ≈ 1×10^6 × log2(101) ≈ 6.66 Mbit/s.

Fibre loss budget example: 20 km at 0.25 dB/km = 5 dB, plus 4 splices at 0.1 dB = 0.4 dB, plus 2 connectors at 0.5 dB = 1 dB, total 6.4 dB.

Copper attenuation rises with frequency, so higher-speed DSL uses shorter loops.

TDR distance = (velocity of propagation × round-trip time) ÷ 2.

Throughput = window size ÷ round-trip time for a TCP connection with no loss.

Cable length limit for a 1000BASE-T link is 100 m, of which 90 m is permanent link and 10 m patch cords.

Subnet mask /24 = 255.255.255.0; /25 = 255.255.255.128; /26 = 255.255.255.192; /27 = 255.255.255.224.

Block size = 256 − the interesting mask octet; subnets step by that block size.

Network address has all host bits 0; broadcast address has all host bits 1; neither is assignable to a host.

Two hosts communicate directly only if their address AND mask give the same network address.

A /30 point-to-point link uses two addresses for the routers and wastes two (network and broadcast).

EIRP (dBm) = transmit power (dBm) + antenna gain (dBi) − feeder loss (dB).

Received power (dBm) = EIRP − path loss (dB) + receive antenna gain (dBi) − receive feeder loss (dB).

Link closes when received power ≥ receiver sensitivity + required margin.

Reuse distance D = R√(3N); for N = 7, D ≈ 4.58 R.

Wavelength λ = c/f; at 900 MHz λ ≈ 33 cm, so a quarter-wave antenna is about 8 cm.

Total fibre link loss = (attenuation per km × length) + (splice loss × number of splices) + (connector loss × number of connectors).

Power budget = transmit power − receiver sensitivity; the design must leave a margin for ageing and repairs.

Splitter loss in dB = 10 log10(split ratio); 1:16 gives about 12 dB.

Attenuation in dB/km = (input power dBm − output power dBm) ÷ length in km.

Numerical aperture NA = √(n_core² − n_cladding²); a larger NA accepts a wider cone of light.

Pre-installation checklist: site survey, cable route, power availability, earthing, materials and safety equipment.

Post-installation checklist: continuity, wire map, length, labelling, documentation and customer demonstration.

Fibre checklist: clean connectors, correct polish type, bend radius respected, splice loss recorded, power meter reading within budget.

Rack checklist: earth bonded, ventilation clear, cables dressed and labelled, spare capacity left for expansion.

Handover checklist: as-built drawing, test results, warranty terms and contact details for fault reporting.

No sync on a copper line: check pair continuity, insulation resistance and line card before replacing the modem.

Low optical power: clean connectors first, then re-test; if unchanged, check splice loss and fibre route.

Intermittent Wi-Fi drops: check channel congestion, interference sources and access point placement before replacing hardware.

High packet loss but good signal: suspect upstream congestion or a duplex mismatch rather than the radio link.

After any repair, re-run the original failing test to confirm the fix rather than assuming it.

If the fault is on the customer's side of the demarcation point, the visit may be chargeable; state this before the visit.

If usage exceeds the fair-use threshold, apply the contract's stated action, not an ad hoc restriction.

If a bill is disputed, suspend collection action until the usage records are checked and the outcome recorded.

If the customer requests disconnection, confirm the final bill, equipment return and number portability options.

If a service-level target is missed, apply the agreed compensation automatically and inform the customer.

If a circuit cannot be isolated, do not work on it; use the approved live-work procedure with a second person present.

If measured RF power density exceeds the limit, stop work and reduce power or increase distance before continuing.

If equipment is not type-approved, do not install or connect it to the public network.

If a spectrum authorisation is missing, do not transmit; apply for the licence first.

If a data breach is suspected, contain access, record what happened and notify per the regulatory requirement.

If a job's quoted price is below the calculated cost, decline or re-scope the work rather than accept a loss.

If a customer asks for work outside the contract, issue a variation quote before starting.

If a team member is unsure of a safety step, stop the job and clarify before proceeding.

If a complaint escalates, restate the agreed resolution time and escalate to the responsible owner.

If a payment is overdue, send a written reminder with the invoice number and due date before further action.

Sensitivity is the minimum input power for a specified output quality; it is negative in dBm and lower is better.

Dynamic range is the span between the weakest usable signal and the overload point of a receiver.

Selectivity is a receiver's ability to reject adjacent channels; it depends on filter sharpness.

Linearity means output is proportional to input; non-linearity creates harmonics and intermodulation.

Jitter is timing variation in a digital stream; excessive jitter causes bit errors and lost synchronisation.

Latency is the delay for a packet to travel one way; round-trip time is the two-way delay.

Jitter is variation in latency; real-time voice needs low jitter and buffering to absorb it.

Throughput is the actual achieved data rate, always less than or equal to the link capacity.

Goodput excludes retransmitted and protocol-overhead bytes, so it is lower than throughput.

Availability = uptime ÷ (uptime + downtime), usually quoted as a percentage per year.

Broadcast domain is the set of devices reached by a broadcast frame; a router bounds it, a switch does not by default.

Collision domain is the set of devices sharing one collision path; a switch gives each port its own domain.

Gateway is the router that forwards traffic out of the local subnet.

Metric is the value a routing protocol uses to choose between paths to the same destination.

Encapsulation wraps data with headers at each layer as it moves down the stack; decapsulation removes them on receipt.

Sector is a directional coverage area of a site; a trisector site has three 120° sectors.

Handover is the transfer of an active connection between cells or sectors without dropping the call.

Roaming is using a visited network with the home network's subscription and authentication.

Diversity uses independent signal paths so that a fade on one path does not lose the signal.

Beamforming steers antenna energy toward the user, improving gain and reducing interference.

Numerical aperture is the light-gathering ability of a fibre, determined by core and cladding refractive indices.

Mode field diameter is the effective width of the light spot in single-mode fibre; a mismatch between fibres adds splice loss.

Insertion loss is the loss caused by inserting a component such as a connector or splitter into the link.

Return loss is the ratio of reflected to incident power at a discontinuity; higher return loss means fewer reflections.

PON is a passive optical network in which a single feeder fibre is shared by passive splitters.

Permanent link is the fixed cabling between patch panels and outlets, excluding patch cords.

Channel is the end-to-end path including patch cords and equipment cords.

Patch panel provides a fixed termination point for horizontal cables and a port for patching.

Demarcation point is the boundary between operator network and customer premises wiring.

Cable management keeps bend radius, separation and labelling under control inside racks and trays.

Baseline is the recorded healthy measurement against which later tests are compared.

Symptom is the observable failure; root cause is the underlying reason the failure occurred.

Loopback returns the signal to the sender to test the local equipment independently of the line.

Calibration is the documented adjustment of a meter against a known reference.

Mean time to repair is the average time taken to restore a failed service.

Tariff is the published schedule of charges for a service.

Call detail record is the usage record used for billing and dispute resolution.

Mediation is the process that collects, validates and rates usage records before invoicing.

Revenue assurance detects and prevents billing leakage and unbilled usage.

Fair-use policy defines acceptable usage limits and the action taken if they are exceeded.

Lockout/tagout is the procedure that isolates and marks equipment so it cannot be re-energised during work.

Maximum permissible exposure is the regulatory limit on RF field strength or power density for people.

SAR is the rate of RF energy absorption per unit mass of body tissue.

Electromagnetic compatibility is the ability of equipment to work without causing or suffering harmful interference.

Type approval is the regulator's confirmation that equipment meets the required standards.

Break-even point is the volume at which total revenue equals total cost.

Cash flow is the timing of money in and out, distinct from accounting profit.

Working capital is current assets minus current liabilities, the money available for day-to-day operation.

Service-level agreement defines the measurable service commitments between provider and customer.

Active listening means concentrating, not interrupting, and confirming understanding by restating.