Question 7 of 7: Technical Terminology

Question 7: Technical Terminology (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

1. Full duplex. A transmission mode in which both ends of a link can send and receive data simultaneously (as opposed to half duplex, where the two directions must take turns on the same channel). Modern switched Ethernet links and telephone circuits are full duplex.
2. QPSK (Quadrature Phase Shift Keying). A digital modulation scheme that encodes 2 bits per symbol by shifting the carrier's phase to one of four equally-spaced values ($45^{\circ}, 135^{\circ}, 225^{\circ}, 315^{\circ}$); compared with binary PSK (1 bit/symbol), QPSK doubles the bit rate within the same bandwidth (or halves the bandwidth for the same bit rate) at the cost of needing a higher SNR to distinguish the four phases reliably.
3. SMTP (Simple Mail Transfer Protocol). The application-layer protocol used to transfer e-mail from a sender's mail client/server to a recipient's mail server, using a simple command/response text dialogue (HELO, MAIL FROM, RCPT TO, DATA) over TCP port 25; retrieval by the end recipient is normally handled by a separate protocol (POP3/IMAP), not SMTP.
4. Codec (coder-decoder). A device or algorithm that converts an analog signal (e.g. voice) into a digital bit stream for transmission/storage (coding) and reverses the process at the far end (decoding); e.g. a PCM codec used in digital telephony samples, quantizes, and encodes speech into 64 kbps digital channels.
5. Crosstalk. Unwanted coupling of a signal from one circuit or cable pair into an adjacent one, caused by electromagnetic (inductive/capacitive) coupling between conductors run close together; it is one of the impairments (with attenuation, delay distortion, and noise) that limits achievable data rate, and is mitigated by twisting wire pairs, shielding, and physical separation.
6. CSMA/CD (Carrier Sense Multiple Access with Collision Detection). The classic Ethernet medium-access method: a station listens before transmitting (carrier sense), and if two stations transmit at once anyway, both detect the resulting collision, stop, and each backs off a random time before retrying (using the binary exponential backoff algorithm) — used on shared (half-duplex/coaxial or hub-based) Ethernet segments; switched full-duplex Ethernet has no collisions and does not need it.
7. FFT (Fast Fourier Transform). An efficient $O(N\log N)$ algorithm for computing the Discrete Fourier Transform of a length-$N$ sequence (versus $O(N^2)$ for a direct DFT computation); in communications it is used to move signals between the time and frequency domains, e.g. for spectral analysis and as the core operation of OFDM modulation/demodulation.
8. UDP (User Datagram Protocol). A connectionless, unreliable transport-layer protocol: it sends independent datagrams with only a minimal header (source/destination port, length, checksum) and no handshaking, acknowledgment, retransmission, or ordering guarantee — trading reliability for low overhead and low latency, which suits real-time traffic (VoIP, streaming, DNS queries) where a late retransmission is worse than an occasional dropped packet.
9. TCP/IP. The Transmission Control Protocol / Internet Protocol suite that underlies the Internet: IP (network layer) provides best-effort, connectionless addressing and routing of packets between hosts, while TCP (transport layer) layered above it adds a reliable, connection-oriented, ordered, flow- and congestion-controlled byte stream on top of IP's unreliable delivery.
10. Packet. A formatted unit of data transmitted across a packet-switched network, consisting of a header (source/destination address, sequencing/control information) and a payload; large messages are broken into multiple packets, each routed independently (potentially over different paths) and reassembled at the destination.