Circuit switching, packet switching — practice questions

1. Jitter: Because the network uses packet switching, each voice data packet is routed independently. Due to varying levels of congestion at different routers, packets may take different paths or experience different queuing delays. This results in variable arrival times at the destination, a phenomenon known as jitter. For a voice call, this can cause the audio to sound choppy or distorted as the receiving device struggles to play the audio smoothly. [1 mark for identifying jitter, 1 mark for explanation linked to packet switching principles].
2. Packet Loss: During periods of high network congestion, routers may become overwhelmed with more packets than they can process. When a router's internal buffer (queue) is full, it may be forced to drop incoming packets. If voice packets are lost, there will be gaps in the audio stream, leading to words or syllables being missed by the listener, severely degrading call quality. [1 mark for identifying packet loss, 1 mark for explanation linked to congestion].

First, convert the file size to bytes: 1.2 MB = 1.2 * 1,000,000 = 1,200,000 bytes.

(i) Number of packets: Number of packets = Total file size / Payload size per packet = 1,200,000 / 1500 = 800 packets. [1 mark]

(ii) Total size of headers: Total header size = Number of packets * Header size per packet = 800 * 40 bytes = 32,000 bytes (or 32 KB). [1 mark]

(iii) Total data transmitted: Total data = Original file size + Total header size = 1,200,000 bytes + 32,000 bytes = 1,232,000 bytes (or 1.232 MB). [1 mark]

(iv) Transmission efficiency: Efficiency = (Useful data / Total data transmitted) * 100 = (1,200,000 / 1,232,000) * 100 = 0.9740 * 100 ≈ 97.4%. [1 mark for correct calculation and answer]