Communication Protocols

• Flow Control Demo
• Error Detection Schemes Demo
• IPv4 Address Quiz
• IPv4 Address Assignment Demo
• Protocol Layers Demo
• Routeing Demo
• Sliding Windows Demo
• Switching Techniques Comparison Demo
• Token Bucket Algorithm Demo

Flow Control Demo

Not completely bug-free this one yet, but since I’ve started using this myself I thought I should put it up here. Hopefully what it does is reasonably self-explanatory, however note that the “Satellite” checkbox slows down the second link to simulate what happens on a satellite link. Proxies have infinite buffer space, routers have buffer space defined by the program.

Error Detection Schemes Demo

Illustrates the operation of parity, checksum, Internet-style checksums and the CRC. I like to use this one to demonstrate the effectiveness of the Internet checksum, and they challenge the students to work how much better they could do; then change to the CRC scheme, and just let them watch it carry on for minutes not suffering from any undetected errors at all. That gets their attention; and they get curious to wonder how CRCs work – and they need some motivation before they start on that bit of maths.

IPv4 Address Quiz

Demo to provide some fun in lectures, and some practice outside.
Mostly obvious – but note you can use the right and left mouse buttons to copy an IP address from either the question or a possible answer into the hexadecimal to binary convertors at the bottom of the screen. You can also edit the numbers in the hexadecimal and binary blocks and the other box will be updated automatically.

IPv4 Address Assignment Demo

Demo to provide some practice in assignment blocks of IPv4 addresses, and to check answers that students have come up with to tutorial problems. Check one of the checkboxes next to the buttons to turn on a new subnet; then you can drag the block of addresses around. Each row of space is 256 addresses (a /24 block).
If you double-click on the subnet’s button, you can enter the number of addresses required for that subnet, and then the program will warn you if there isn’t enough space assigned.

Protocol Layers Demo

Mostly obvious, but there’s a bit more going on under the hood that might be immediately obvious. Firstly – right click on any packet and it will stop, left click and it will disappear. Reliable layers also re-order packets, and have a window size of seven packets. Also, when paused you can put the mouse over a header and get a description of what it is.

Routeing Demo

This is a slightly more advanced version of one of the original VB demos about routeing. Originally just for demonstrating the operation of the Bellman-Ford algorithm, I’ve also added reverse path forwarding so I can use it for multicasting as well. Note the colours on the packets: in order from the front to the back they are MAC destination, MAC source, IP destination, IP source, data type (routeing packets are pink, broadcast packets are white).

Sliding Windows Demo

Another one with rather more going on under the hood than might be obvious at first sight. It can do some basic TCP congestion control stuff as well, implementing slow-start, delayed acknowledgements and fast re-transmit. Put the mouse over a pane in the window for more details; and you can kill packets by double-clicking on them, and pause and re-start them with a single click.

Switching Comparison Demo

Demonstrates the difference between message, circuit and packet switching, and shows the situations in which each of the them is the best choice. Quite basic this one, and needs a bit of description while it’s running.

Token Bucket Algorithm Demo

Demonstrates the token bucket algorithm. This is very much a work in progress, since it occurs to me that with not much modification this one could be used to demonstrate a lot of effects in queueing theory, and I’m due to start teaching that subject again next year. Watch this space for updates.