A 14-PC Laboratory with a Collapsing Cable Chain
Government Bilingual High School, Molyko, runs a 14-PC computer laboratory for GCE O-Level practical classes. The computers are wired in a single chain: each PC connects to the next through a short cable, and only the first PC links to an 8-port hub that feeds a 4 Mbps ADSL router. Teachers report that with 10 or more students logged in, loading a single web page can take three minutes, and when a chair is pushed against a cable near PC 9, PCs 10–14 lose the network. The lab also sees a neighbour's network named 'Molyko_Free_WiFi' on every machine. Last term a Form 4 student's project file disappeared from an open shared folder, and no one could tell who had deleted it. The PTA has released 250,000 FCFA for improvements. The principal wants a written recommendation before the next Parent–Teacher meeting, and asks whether wireless would be cheaper than cabling.
1. Recommend a network topology and the devices the school should buy with the 250,000 FCFA, justifying each choice against the present arrangement.
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Recommendation: star topology with a switch.
Reasoning from the symptoms:
- The present chain is effectively a linear bus joined by a hub. One disturbed cable splits the chain, which is exactly why PCs 10–14 drop out. In a star, every PC has its own cable to a central switch, so one faulty cable affects one workstation only.
- A hub repeats every frame to all ports, creating collisions and forcing half-duplex sharing. A switch learns MAC addresses, sends frames only to the destination port and allows full-duplex links, so 10 simultaneous logins no longer compete for one collision domain.
Indicative spending (prices vary locally):
- 16-port 10/100/1000 switch: about 60,000 FCFA - one spare port for a staff laptop or future PC.
- One 305 m box of UTP Cat5e: about 45,000 FCFA; RJ45 plugs, crimper and tester: about 20,000 FCFA.
- Plastic trunking, wall sockets and clips: about 45,000 FCFA; installation labour: about 40,000 FCFA.
- Total ≈ 210,000 FCFA, leaving a reserve for two spare patch leads.
Wireless is not automatically cheaper: 14 machines sharing one radio channel suffer interference - the neighbouring 'Molyko_Free_WiFi' already visible proves the band is congested - and practical exams need stable links. A single access point for staff devices can be added later. Note also that the 4 Mbps router remains a bottleneck even after the LAN is fixed.
2. Explain two distinct reasons why web pages still load slowly, showing which one is a LAN problem and which is an internet problem. Give one remedy for each.
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Reason 1 (LAN): hub collisions and a single shared cable path. All frames from all PCs pass through the hub, so machines wait and retransmit; effective throughput falls sharply as users are added. Remedy: replace the hub with a switch and give each PC its own cable run - this removes collisions on the local segment.
Reason 2 (internet): a single 4 Mbps ADSL uplink shared by 14 users. Even with perfect LAN equipment, the router's WAN link is one queue. If one student downloads a video or updates a phone, the remaining bandwidth for everyone else may be a few hundred kilobits per second, so a page with images takes minutes. Remedy: a caching proxy or router-level traffic shaping to limit large downloads, block streaming during lessons, and upgrade the ADSL package if the budget allows.
How to tell them apart: test a page served from a PC on the same LAN (or ping the router). If local access is fast but external pages are slow, the fault is the uplink/ISP, not the cabling. This distinction matters because cabling alone will not make 14 users fast on 4 Mbps, and a bandwidth upgrade alone will not stop the cable-chain outages.
3. Recommend three security measures for the laboratory, explaining the specific risk each one reduces.
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Individual user accounts with folder permissions instead of one open shared folder. Create a standard account per student and teacher, and give write access only to each student's own folder. This directly addresses the deleted project file: file deletion and modification are recorded against a named account, and ordinary users cannot delete other users' work. The administrator account should be used only for installing software.
Router and wireless hardening. Change the router's default administrator password, disable WPS and remote administration, and if an access point is added use WPA2/WPA3 with a long passphrase. This reduces the risk of a student or neighbour reconfiguring the router or joining the network to tamper with shared files. The visible 'Molyko_Free_WiFi' shows that nearby wireless devices exist, so an open or WEP network would be reckless.
Antivirus, updates and a backup routine. Files disappearing can also result from malware or disk failure, not only from a person. Schedule weekly offline backups of the practical work folder (external drive kept locked) and keep antivirus definitions current. A backup turns a lost project into a restore rather than an investigation.
Physical measures - locking the lab, a key register and a visitor rule - support all three, but the decisive change is accountability: named accounts plus permissions plus an audit trail.