Branch network for a community library service
A community library service in Namibia has five branches and one central library. Each branch has 6 staff computers, 10 public computers, and a Wi-Fi access point for visitors; the central library has 20 staff computers and 30 public computers. The catalogue is hosted by a company on the internet and is updated continuously. The central library has an 8 Mbps ADSL line with a 60 GB monthly cap; each branch has a 2 Mbps line with a 25 GB cap. Staff report that catalogue searches freeze for 20–30 seconds at peak times, branches lose the internet three or four times a day, and staff then copy borrower records onto USB drives and take them to the central library. Last month two members were registered twice and 47 books were recorded as returned at the wrong branch. The service cannot afford fibre at every branch this year.
1. Recommend a network topology and connection arrangement for the five branches and central library. Justify your choice against the constraints, including cost, single points of failure, and the USB copying problem.
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Use a star topology at two levels: each library's LAN is a star with a switch connected to staff PCs, public PCs and the Wi-Fi access point; each branch connects to the central library through one WAN link, making the central library the hub of a star of five branches. A full mesh between all six sites would need 15 links and would be far too expensive at 2–8 Mbps. The star is cheaper, easier to manage and matches the central catalogue. Its weakness is that the central library and each branch's single link are single points of failure. Mitigate this with a local cache or replica server at each branch, a second inexpensive backup link at the central library if possible, and UPSs at branch switches. Keep the public Wi-Fi on a separate VLAN from staff and catalogue traffic. The USB copying should stop: branches need an offline mode that stores transactions locally and synchronises automatically when the link returns, not a manual file transfer.
2. Explain why the current cloud-only catalogue and USB copying cause the duplicate registrations and wrong-branch returns. Propose a hybrid approach that reduces these errors without requiring fibre at every branch.
Read the worked answer
The cloud catalogue is continuously updated, but a branch with no link sees only a stale page. Staff work around this by copying borrower records to USB. Each USB copy is a separate version of the truth. When the files are merged at the central library, there is no unique member number check, no timestamp and no record of which branch created a row, so the same person can be inserted twice. A return recorded on a USB file may be keyed under the wrong branch because the file does not carry the branch context, producing the 47 wrong-branch returns. A hybrid approach: each branch runs a small local database with the same member and item keys. It enforces a unique member ID and records every loan and return with branch code, timestamp and transaction ID. When online, it sends only new transactions to the central server, which rejects duplicates and resolves conflicts by timestamp. The catalogue can be a read-only local copy refreshed in batches, while borrower transactions are queued. This gives offline operation without USB merging.
3. The monthly cap is 25 GB per branch. Suggest three practical ways to reduce WAN traffic while keeping the catalogue usable.
Read the worked answer
Three practical measures: (1) Cache the catalogue and web proxy at each branch so repeated searches and cover images do not cross the WAN; refresh only changed records overnight. (2) Reduce content: store catalogue text and small thumbnails, not large cover images or videos, and block streaming and large downloads on public Wi-Fi. (3) Schedule and compress: run catalogue replication and backups outside opening hours, use delta updates rather than full copies, and set per-user quotas or time limits. Also separate staff and public traffic so a few public users cannot consume the whole 25 GB cap. These measures keep the catalogue usable while the service saves for fibre.