Packet Flow and End-to-End Delay: Interactive Network Simulation

About this simulator

Every router a packet crosses adds a nodal delay made of four parts: processing, queuing, transmission and propagation. This simulation moves packets across a chain of routers so you can see them waiting in queues, being transmitted and travelling along links, and read off the end-to-end delay.

How it works

1. At each router a packet is processed, waits if the output link is busy, is transmitted bit by bit and then propagates to the next node.
2. Packets sent back to back queue behind each other at the first link; later links rarely queue if all rates are equal.
3. End-to-end delay of one packet $= \sum$ over hops of $(d_{\text{proc}} + d_{\text{queue}} + d_{\text{trans}} + d_{\text{prop}})$.

Formulas used

• $d_{\text{nodal}} = d_{\text{proc}} + d_{\text{queue}} + d_{\text{trans}} + d_{\text{prop}}$
• $d_{\text{end-to-end}} = \sum d_{\text{nodal}}$ over every hop

When to use it

• Practising end-to-end delay questions with several hops.
• Seeing exactly where queues form when packets are sent back to back.
• Explaining how spacing out packets removes queuing delay.

Frequently asked questions