Cabling two of three buildings
A rural health centre has three buildings: an administration block, a clinic, and a laboratory 80 metres away as the cable would run. There are 38 devices: 6 desktop computers in administration, 4 in the laboratory, 12 tablet computers carried between buildings by nurses, 8 networked printers and 8 IP telephones used for calls to the district hospital. Patient records currently travel between buildings on USB flash drives carried by the clerk, and each building keeps its own stand-alone copy of the records. The centre has a 20 Mbps ADSL link to the internet with a 60 GB monthly cap, and it pays for calls to the district hospital by the minute. The buildings have reinforced concrete walls with steel mesh. Management wants to replace the USB routine, add Wi-Fi for the tablets and cut telephone costs, but the budget stretches to cabling only two of the three buildings this year.
1. Explain the risks of the present USB routine and why a client-server network with one shared database is a better arrangement. Give three distinct risks, and name one new risk that the network introduces.
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First, three separate copies will diverge. Two staff can update the same patient on different machines, and whichever USB drive arrives last silently overwrites the other, so nobody can say which record is correct. Second, there is no access control or audit trail: anyone who picks up a flash drive can read or alter every patient record, and afterwards there is no way to show who did it. Third, removable media carried between buildings is easily lost or stolen and is a well-known route for malware, which can spread to every machine the drive touches. There is also the plain delay: a patient's notes cannot be in two buildings at once.
A client-server LAN with one database on a server fixes the substance of these: a single source of truth, record locking so two people cannot overwrite each other, per-user accounts with permissions, an audit log, and one central backup.
The new risk is that the network itself must be defended: the server becomes a single point of failure and a single attractive target, so it needs authentication, encryption of patient data in transit, a UPS and tested backups, or the centre trades one set of problems for a worse one.
2. Given the budget, which two buildings should be cabled and how should the third be connected? How should the tablets be covered? Justify using the physical details in the scenario.
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Cable the administration block and the clinic. That is where the fixed desktops, most printers and the telephones cluster, where the server would sit, and where the records are created; it also keeps the server on a stable wired link rather than on radio.
The laboratory is 80 metres away along the cable route. That is inside the 100 metre limit for twisted-pair copper, but the margin is thin if the route has to go up, around the steel mesh and through ducting, so the cable must be measured along its actual path, not point to point. If the measured run exceeds about 90 metres, or if the cable would run alongside mains or through damp ground, use fibre instead, or a directional point-to-point wireless bridge aimed at the laboratory, with a small switch inside the laboratory for its four desktops.
For the tablets, one access point per building, positioned in the room where nurses actually work. Steel mesh in the walls will attenuate 2.4 GHz heavily, so a single central access point would give dead spots; use non-overlapping channels 1, 6 and 11, WPA2 or better, and Power over Ethernet so each access point needs one cable, not a cable and a mains socket.
3. Management also wants the 8 IP telephones to call the district hospital over the 20 Mbps internet link to cut call charges. Assess whether this is sensible, with a calculation.
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The arithmetic is favourable. At roughly 80 kbps per call in each direction, 8 simultaneous calls need 8 x 80 = 640 kbps, well under 20 Mbps. Over an hour, 640 kbps x 3 600 s = 2 304 000 kb, about 288 MB, so an hour in which all eight lines are busy consumes under 0.3 GB of the 60 GB monthly cap; the cap would allow roughly 200 such hours. For comparison, pushing a 2 GB offsite backup over the link takes 2 x 1 024 x 8 = 16 384 Mb divided by 20 Mbps, about 14 minutes and about 3 per cent of the cap.
Two cautions decide the judgement. First, an ADSL service is usually asymmetric: the 20 Mbps figure is the download speed, and the upload speed, which carries the callers' voices, may be 1 Mbps or less, so the calculation must be redone on the upload figure. Second, voice cannot tolerate delay and jitter, so quality-of-service rules must give voice priority over file transfers and tablet traffic, and backup jobs must be scheduled outside clinic hours. Keep one ordinary telephone line for power cuts and emergencies, and put the router and switch on a UPS.