Unified Performance Tool (or uperf for short) is a network
performance tool that supports modelling and replay of various
networking patterns.  It represents a new kind of benchmarking tool
(like filebench) where instead of running a fixed benchmark or
workload, a description (or model) of the workload is provided and
the tool generates the load according to the model.  By distilling
the benchmark or workload into a model, you can now do various
things like change the scale of the workload, change different
parameters, change protocols, etc and analyse the effect of these
changes on your model.

Some of the questions you could answer using uperf are:
 * Bandwidth and latency (unidirectional and bi-directional) with different
   protocols like TCP, UDP, SCTP, SSL
 * Connection setup and teardown scalability for different protocols
 * Effect of noise on ongoing network connections
 * Does it matter if I use processes instead of threads to do network
   communication?
 * What is the L2 cache miss rate for connection setup?
 * Is sendfilev(3EXT) (with one file) equivalent to sendfilev(3EXT)?
 * Understand TCP, UDP, SCTP, SSL performance under a variety of conditions
 * Test various TCP Congestion control algorithms

WWW: http://uperf.org/