The School Network Bottleneck
A school computer lab has 30 computers connected to a single 100 Mbps switch. The switch connects to the internet through a 20 Mbps router. During a digital exam, all 30 students simultaneously download a 50 MB file from the internet. The network administrator observes that the download takes much longer than expected. He suspects the bottleneck is either the switch or the router. He also notices that the switch's uplink port is running at 100 Mbps but the router's LAN port is only 100 Mbps. The school has a budget to upgrade either the router or the switch, but not both.
1. Calculate the theoretical minimum time to download one 50 MB file if the router is the bottleneck, and explain your reasoning.
Read the worked answer
The router's internet connection is 20 Mbps. 50 MB = 50 × 8 = 400 megabits. Time = 400 / 20 = 20 seconds per file if only one computer downloads. However, with 30 computers sharing the 20 Mbps connection, the total data is 30 × 400 = 12,000 megabits. Time = 12,000 / 20 = 600 seconds = 10 minutes. The switch's 100 Mbps capacity is not the bottleneck because the router limits the internet speed to 20 Mbps. Therefore, the router is the bottleneck.
2. Recommend which device to upgrade and justify your answer with reference to the data.
Read the worked answer
The router should be upgraded because the internet connection speed (20 Mbps) is the limiting factor. The switch's 100 Mbps capacity is sufficient for the local network, but the router's 20 Mbps connection cannot handle 30 simultaneous downloads. Upgrading the router to a higher speed (e.g., 100 Mbps) would increase the internet bandwidth and reduce download time. Upgrading the switch would not help because the bottleneck is the router's connection to the internet. The administrator should also consider whether the school's internet service provider can support a higher speed.