How to find transmission speed?

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http://unix.stackexchange.com – Two host machine's one as a client and other as a server, i am testing udp load-test in these two machines.Machine Ethernet speed is 100 Mbps but i want to send 30000 packets each of 512 bytes at 1 Mbps speed how to do? Is their any Linux command to set Ethernet speed at 1 Mbps? (HowTos)