Tao Qian, a research assistant at RENCI and a PhD student of Professor Frank Mueller at the Computer Science Department, NC State University, has built a software module that allows latency emulation of IP packets per interface in Linux VMs. There is an Ubuntu image pre-loaded with this module available from the ExoGeni image proxy:
- nsdelay IP delay
- nsdelay $Node0.IP(“Link0”) 100
To remove the delay, use
- nsdelay IP 0
which will setup the link with a FIFO queue without delay.
- The latency is purely emulated on the virtual interfaces of the VMs, which means that the physical transportation latency on the virtual links in your virtual topologies is not counted, which you may need to take into consideration when conducting experimentation.
- If delays are changed in high frequency, excessive packet drop may occur.