Huge uplink data rate on idirect X1 Outdoor

Dears

I have been using idirect X1 modem outdoor unit for gsm backhauling. anyway one of our modems is directly connected to GSM BTS, but we realized huge uplink datarate (using imonitor). even more than the maximum configured. Maximum configured for uplink is 170 kbps, but from imonitor I can see that it can reach 900 kbps which is the maximum datarate could be reached with the return carrier.
During that, ping to the BTS reach till 2000 msec which is huge and make the BTS disconnect from BSC. From imonitor I realized that this traffic is UDP traffic and it does not appear on IP traffic tap so, I am not sure if it is coming from the BTS or not.
When I shutdown the BTS, this behavior disappear.

So, my question is why this modem could reach this datarate while it is Maximum information rate is 170 Kbps?

could it be the problem is from the BTS?


Regards