RBSE SS Voc Telecom flashcards

36 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's law

The current through a conductor is directly proportional to voltage and inversely proportional to resistance: I = V/R. It underpins every DC circuit calculation in telecom power and loop analysis.

Power formula

Electrical power P = V × I, also written P = I²R or P = V²/R. Used to size fuses, rectifiers and cable ratings in exchange power plants.

Parallel resistance

In a parallel circuit the reciprocal of total resistance equals the sum of reciprocals of branch resistances, and voltage is equal across all branches.

RMS voltage

The effective value of an AC sine wave, equal to peak voltage divided by the square root of two (about 0.707 × peak). Mains and AC measurements are quoted in RMS.

Capacitive reactance

Opposition of a capacitor to AC, X_C = 1/(2πfC). It decreases as frequency rises, so capacitors block DC and pass high frequencies in coupling and filter circuits.

Decibel

A logarithmic ratio: 10 log(P1/P2) for power or 20 log(V1/V2) for voltage. +3 dB doubles power, +10 dB is ten times power, and −3 dB halves power.

Nyquist sampling rule

To reconstruct a signal, the sampling rate must be at least twice its highest frequency. Voice limited to 4 kHz is therefore sampled 8000 times per second in PCM.

PCM voice channel

Pulse code modulation with 8-bit companded samples at 8000 per second gives 64 kbit/s per voice channel, the DS0 building block of digital transmission hierarchies.

E1 frame

A 2.048 Mbit/s European digital hierarchy level carrying 32 timeslots of 64 kbit/s: 30 voice channels plus one framing and one signalling channel.

Twisted pair crosstalk

Unwanted signal coupling between adjacent pairs. Twisting the pairs cancels much of the coupling; NEXT is measured at the near end and FEXT at the far end.

DTMF signalling

Dual-tone multi-frequency dialling sends two simultaneous tones per digit, one from a low group and one from a high group, so exchanges can decode each key uniquely.

Local exchange

The telephone exchange to which subscriber lines connect directly. It provides dial tone, battery feed, digit collection and routes calls toward tandem or trunk exchanges.

Grade of Service

The probability that a call attempt is blocked during the busy hour, determined by offered traffic in erlangs and the number of trunks, using Erlang B tables.

Alternate routing

A routing rule that sends a call over a second trunk group when the primary route is congested, improving successful call completion at the cost of longer paths.

Common channel signalling

Signalling carried on a separate packet link rather than within the voice channel. SS7/CCS7 enables fast call setup, database queries and intelligent network services.

OSI model layers

Seven layers: physical, data link, network, transport, session, presentation and application. Each layer provides services to the layer above and communicates with its peer.

Private IP ranges

Non-routable IPv4 blocks 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. They are reused inside customer networks and translated to public addresses by NAT.

TCP versus UDP

TCP is connection-oriented with acknowledgements, retransmission and ordering. UDP is connectionless with no delivery guarantee, favoured for real-time voice, video and DNS queries.

GPON rates

A passive optical network using splitters with 2.488 Gbit/s downstream and 1.244 Gbit/s upstream, sharing one feeder fiber among many FTTH customers.

DHCP and DNS

DHCP automatically supplies IP address, mask, gateway and DNS server to clients. DNS resolves human-readable domain names into IP addresses for connection setup.

Frequency reuse

The core cellular principle: the same radio channels are reused in cells far enough apart that co-channel interference stays acceptable, multiplying network capacity.

Handover

Transfer of an active call or data session from one cell or sector to another as the subscriber moves, keeping the connection alive without user intervention.

Antenna gain

The increase in radiated power in a preferred direction compared with a reference antenna, expressed in dBi (isotropic) or dBd, where dBd equals dBi minus 2.15.

VSWR

Voltage standing wave ratio measures impedance match between transmitter, feeder and antenna. A value below about 1.5:1 is good; higher values mean reflected power and faults.

FDD versus TDD

Frequency division duplex uses separate uplink and downlink bands simultaneously. Time division duplex shares one band, alternating uplink and downlink in time slots.

Single-mode fiber

Fiber with a core around 9 micrometres carrying one propagation mode, used at 1310 and 1550 nm for long-haul links with low loss and almost no modal dispersion.

Fusion splicing

Joining two fibers by an electric arc that melts and fuses their cleaved ends, producing a permanent low-loss joint, typically under 0.1 dB, inside a splice protector.

OTDR testing

An optical time-domain reflectometer sends pulses and plots backscatter versus distance, locating breaks, splices and connectors and measuring loss along a fiber link.

APC connector

A fiber connector with an angled (about 8 degree) polished end face that reduces back-reflection compared with flat PC/UPC ferrules, used in high-performance links.

Telecom earth resistance

The resistance of the earth electrode system measured with an earth tester. A low value, commonly 5 ohms or less for telecom installations, protects people and equipment.

ONT receive power

The optical power arriving at a customer ONT, read in dBm. It must lie within the vendor's specified window; too low causes loss of signal, too high can damage the receiver.

Demarcation point

The boundary between operator network and customer premises wiring. Testing dial tone or line sync there separates a network fault from a customer-side fault.

Tower fall protection

A full-body harness with double lanyard, inspected anchors and three-point contact, plus weather and RF checks, are required before any work at height on a mast.

Fiber eye hazard

Laser light exiting a fiber or connector is often invisible and can permanently damage the retina. Never look into an end face; use test equipment and caps instead.

Break-even point

The sales volume at which total revenue equals total cost, calculated as fixed cost divided by contribution per unit (price minus variable cost per unit).

TRAI role

The Telecom Regulatory Authority of India regulates tariffs, interconnection, quality of service and consumer protection, while the Department of Telecommunications issues licences and policy.