nuttcp is a network performance measurement tool intended for use
by network and system managers. Its most basic usage is to determine
the raw TCP (or UDP) network layer throughput by transferring memory
buffers from a source system across an interconnecting network to
a destination system, either transferring data for a specified time
interval, or alternatively transferring a specified number of bytes.

nuttcp is based on nttcp, but have several useful  features such
as a server mode, rate limiting, multiple parallel streams, and
timer based usage.

WWW: http://www.lcp.nrl.navy.mil/nuttcp/