Worksheet

F10.4 Network topologies

Networks · GCSE · OCR J277 1.3.1, Edexcel 1CP2 4.1.8 · about 20 min

What this lesson is about

Star, bus, ring and mesh, and routing around a failure in a mesh of robots.

• Four topologies
• Routes through a mesh

Questions 6 marks in all

1. [1 mark]In a star topology, what happens if the central switch fails?

   1. ANo device can communicate
   2. BOnly one device is affected
   3. CData takes another route
   4. DNothing, the devices connect directly

2. [1 mark]Why is a mesh network very reliable?

   1. AThere are many routes, so data can go around a failed link
   2. BIt has a single central switch
   3. CIt uses less cable
   4. DData travels in one direction

3. [1 mark]How many connections does a full mesh of 5 devices need?

4. [1 mark]In a bus topology, what happens if the backbone cable breaks?

   1. AThe whole network fails
   2. BOnly one device is affected
   3. CData goes the other way round
   4. DThe switch reroutes it

5. [1 mark]In a ring topology, how does data travel?

   1. AFrom device to device around the loop, in one direction
   2. BThrough a central switch
   3. CAlong one shared cable to every device at once
   4. DDirectly between every pair of devices

6. [1 mark]What does this program print?

   links = {"A": ["B"], "B": ["A", "C"], "C": ["B"]}
   seen = ["A"]
   for robot in seen:
       for n in links[robot]:
           if n not in seen:
               seen.append(n)
   print(seen)

The task: route around a failure

Write route(links, start, end) that returns the shortest route as a list of robots, using a breadth-first search. Print route: A-B-D-F style for the route from A to F, joining the names with -, and send the same text by radio. Then the link between D and F fails: remove it from both robots' lists, find the route again, and print after D-F fails: <route>.

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

links = {"A": ["B", "C"], "B": ["A", "D"], "C": ["A", "D", "E"], "D": ["B", "C", "F"], "E": ["C", "F"], "F": ["D", "E"]}

Plan your program here, then type it in and press Run.

Do it on the robot
www.bugbotlab.com/learn/f10-4-network-topologies/
The simulator checks it and tells you when it passes. Nothing to install, no account.

Challenges

1. How many links does a full mesh of 6 robots need? Check with a loop.
2. Make C fail completely. Is there still a route from A to F?
3. Change the network into a star with a switch in the middle. What happens to every route if the switch fails?