BIND query limit

[Edmund]

Is there any parameter to control the maximum number of
quries per second for a BIND 8.2.1 name server ?  Recently,
I'm setting 100~200 'dig' background job running simultaneusly
to simulate the real situation of Name server answering hundred
of queries at the same time, but I got the

   res_nsend to server  my.name.server:  Connection timed out

error.  When this happen, the name server will not respond to
any queries.  Is there an upper limit on the number of queries
per second for a name server ?????  If there is, how to tune
it up ????