Live webcam video becomes choppy after 600 connections per stream

Hi!

Server conf:

2 x Intel(R) Xeon(R) CPU           L5410  @ 2.33GHz

16Gb RAM

2 Gbit ethernet channel

OS - Linux CentOS 5.5 x86_64

FMS4 Interactive

Live stream parameters:

320х240
qua_=87
bw_=200000
kf_=5
fps_=18

So, after approximately 600 connections to one stream video becomes choppy (periodically freeze, slow motions). CPU-usage at this time is 100-120% (maximum is 800%, 100% per each core), network usage is 500 Mbit/sec.

But second live stream(with few connections) at this server looks fine simultaneously with 600 connections at first stream.

Experiments with recommendation in "Configuring performance features" documentation chapter(enabling/disabling  aggregate messages and configure the size of stream chunks) do not help.

Please, help me to find bottleneck!

Thanks for answers.

Apologisw my english.