Assam ASSEB HS Skill Telecom common mistakes
Assam ASSEB HS Skill Telecom · Understand the traps and how to avoid them.
Confusing signal power and amplitude relationships, treating a doubling of amplitude as a doubling of power, or misapplying the dB = 10 log10(P2/P1) versus 20 log10(V2/V1) formulas when converting gain or loss.
Candidates memorise the decibel formula without linking it to the physical quantity. Because power scales with the square of voltage or current, the factor 10 versus 20 is a common trap, and exam items that give voltage ratios are answered with the power formula.
What to do instead
Before any dB question, write which quantity is given (power, voltage, current). Use 10 log for power and 20 log for voltage/current ratios. Practise converting a 3 dB loss to a half-power point and a 6 dB loss to a half-voltage point until the mapping is automatic.
Mixing up transmission media characteristics, for example stating that twisted pair has lower attenuation than coaxial cable, or claiming that multimode fibre supports longer distances than single-mode fibre.
Media are studied as a list rather than compared on attenuation, bandwidth, distance, immunity and cost. Candidates recall names but not the trade-off table, so they guess when two options both sound plausible.
What to do instead
Build a single comparison table with rows for twisted pair, coaxial, multimode fibre and single-mode fibre, and columns for bandwidth, attenuation, distance, EMI immunity and cost. For each row, write one sentence on when it is the correct choice. Revise the table, not the textbook chapter.
Assigning the wrong OSI layer to a device or protocol, such as placing a switch at Layer 3, a router at Layer 2, or TCP at the network layer.
Candidates memorise device names without mapping each to the layer where it makes forwarding decisions. Multi-layer switches blur the picture, so the answer becomes a guess instead of a layer-by-layer check.
What to do instead
For every device and protocol, state the layer and the unit of data it handles: hub Layer 1 bits, switch Layer 2 frames, router Layer 3 packets, TCP/UDP Layer 4 segments. When a question mentions a device, first ask what address it reads, MAC or IP, and derive the layer from that.
Confusing circuit switching with packet switching when asked about call setup, resource reservation, or efficiency for bursty data traffic.
The definitions are simple but the consequences are not drilled. Candidates remember that circuit switching reserves a path but cannot explain why that wastes capacity for data or why packet switching needs headers and buffering.
What to do instead
Learn a three-line contrast: circuit switching establishes a dedicated path before data, guarantees bandwidth and delay but wastes capacity; packet switching uses store-and-forward with headers, is efficient for bursty traffic but has variable delay and possible loss. Apply the contrast to one voice example and one data example.
Miscalculating link budget or free-space path loss, for example forgetting to add antenna gains or using the wrong frequency unit in the FSPL formula.
Candidates plug numbers into formulas without tracking units. FSPL depends on frequency in MHz or GHz and distance in km or m, and a unit slip changes the answer by orders of magnitude.
What to do instead
Always write the formula with units beside each symbol before substituting. Use the standard form FSPL(dB) = 32.44 + 20 log10(d in km) + 20 log10(f in MHz). Do a sanity check: doubling distance adds about 6 dB, doubling frequency adds about 6 dB.
Treating optical fibre loss and dispersion as the same impairment, or confusing attenuation-limited distance with dispersion-limited distance.
Both reduce signal quality, so candidates merge them. They do not separate loss (power reduction, fixed by amplifiers or regenerators) from dispersion (pulse spreading, fixed by compensation or narrower linewidth).
What to do instead
Write two separate cause-and-effect chains. Loss: power falls with distance, measured in dB/km, fixed by amplification. Dispersion: pulses spread and overlap, causing ISI, fixed by dispersion compensation or coherent detection. When a question mentions bit rate limits at long distance, check dispersion first.
Skipping the pre-installation survey and labelling steps in cabling answers, giving only the cable-pulling step and ignoring bend radius, separation from power cables, or documentation.
Candidates study cabling as a physical task and forget that exam items test practice standards: minimum bend radius, avoiding EMI from mains wiring, correct termination, and labelling both ends.
What to do instead
Answer cabling questions in a fixed sequence: survey and route planning, separation from power, respect bend radius, terminate and test, label both ends, update documentation. Memorise the sequence and apply it to every installation scenario.
Jumping to a component replacement in fault-diagnosis questions instead of following a structured isolation process from the customer premises inward.
Real troubleshooting is taught as intuition, so candidates pick the most dramatic cause. Exam items reward the methodical path: verify the fault, isolate the section, test at demarcation points, then repair.
What to do instead
Use a fixed diagnostic order: confirm the reported symptom, check the customer end first, test at the demarcation point, then work toward the exchange or node. Eliminate one section at a time. In the answer, state the test and the expected result before naming the faulty component.
Confusing billing concepts such as call detail record, tariff, rental, and usage charge, or ignoring proration and tax lines when computing a sample bill.
Billing is treated as a commercial topic rather than a data-handling one. Candidates cannot map a charge to its source record, so they mislabel line items or omit proration for a mid-cycle change.
What to do instead
Learn the chain: an event generates a CDR, the tariff rates it, the billing system aggregates rental plus usage, then applies proration and taxes. Practise one full sample bill with a mid-cycle plan change so each line item is traceable.
Underestimating EMF exposure rules, for example stating that a rooftop antenna is safe because it is high up, or ignoring the compliance distance and exclusion-zone requirements near transmitting antennas.
Candidates treat EMF as a general safety topic and rely on intuition. They do not recall that exposure limits are frequency-dependent and that power density falls with distance but can still exceed limits in the main beam near the antenna.
What to do instead
Memorise the principle: limits depend on frequency, power density decreases with distance squared, and exclusion zones must be marked and respected. For any scenario, state the compliance distance, the exclusion-zone marking, and the rule that work near live antennas requires shutdown or reduced power.