CISSE Advanced Level

Networking and Telecommunications flashcards

Read the question, say the answer to yourself, then turn the card to check. The first 10 of 61 cards are free; the rest come with the subject.

Card 1 of 61

Jump to a card

Complete Flashcard Reference

Review every card in this deck. Open any card to reveal its answer. The first 10 are free; the other 51 come with the subject.

What are the five blocks of the telecommunication model, in order?

Source, transmitter, transmission medium or channel, receiver, destination. The transmitter converts the message into a signal suited to the medium, the medium carries it and is where noise is introduced, and the receiver converts it back for the destination.

State the Shannon-Hartley formula for channel capacity, and work it for B = 4,000 Hz and S/N = 255.

C = B log2(1 + S/N), with S/N as a plain power ratio, not decibels. C = 4,000 x log2(256) = 4,000 x 8 = 32,000 bits per second. Unlike the Nyquist bound, it accounts for noise as well as bandwidth.

How does the FFT relate to the DFT, and what does it save?

The FFT computes exactly the same result as the DFT; it is a faster algorithm, not a different transform. It cuts the work from N² to N log N operations. For N = 1,024: 1,048,576 against 1,024 x 10 = 10,240, roughly 102 times fewer.

Which carrier parameter does each analogue modulation technique vary, and what is its trade-off?

AM varies amplitude: simple, but vulnerable to noise. FM varies frequency: resists amplitude-based noise, but needs more bandwidth. PM varies phase: closely related to FM, and the basis of digital PSK. Each holds the other two parameters constant.

How do FDM, TDM and WDM each divide a shared medium?

FDM: each signal gets its own frequency band, all travelling at once. TDM: each signal gets its own repeating time slot, with the full medium for its turn. WDM: the fibre version of FDM, each signal on its own wavelength of light.

Name the seven OSI layers from the top down, with the job of each.

7 Application: network services to the user's application (HTTP, email). 6 Presentation: translation, encryption, compression. 5 Session: sets up, manages and ends sessions. 4 Transport: end-to-end delivery, reliability, flow control (TCP). 3 Network: logical addressing and routing between networks (IP). 2 Data Link: framing and Media Access Control on one local network. 1 Physical: raw bits over the medium.

Single-mode or multi-mode fibre: how do they differ, and when is each used?

Single-mode: very narrow core, a single light path, travels much further with less loss. Long-distance and backbone links. Multi-mode: wider core, several light paths, cheaper but more dispersion over distance. Shorter runs within a building or data centre.

How do circuit switching and packet switching differ in their use of bandwidth?

Circuit switching reserves a dedicated path for the whole call, even when idle, with a set-up delay first. It suits continuous real-time traffic such as traditional voice. Packet switching uses bandwidth only when there is data to send. It suits bursty data traffic.

Rank WEP, WPA2 and WPA3 for securing a wireless network today.

WEP: broken, cracked in minutes with freely available tools. Never recommend it. WPA2 (AES encryption): the practical minimum. WPA3: preferred where the equipment supports it, with stronger protection against offline password guessing.

In a VoIP call, what does SIP do and what does RTP do?

SIP (Session Initiation Protocol): signalling, setting up, modifying and ending the session. RTP (Real-time Transport Protocol): carries the encoded voice media once the session exists, with timestamps to help playback despite jitter. A call that will not connect points to SIP; poor audio on a connected call points to RTP or the network's QoS.

Distinguish simplex, half-duplex and full-duplex transmission, with an example of each.