16-Normal Clearing But not connecting

Hi,
Gateway: Quintum Tenor AF 8 port

I’m having a problem with ASR.
When I get calls from the carrier, say 6 calls at a time, maximum of 4 calls gets connected all the time.
Other’s disappear with:
“16-Normal Clearing”

Please tell me what I have to do.
I don’t have any bandwidth problem and all my ports are working.
I think my problem is in some setting in Gateway.

Most of the calls just go off with:
“16-Normal Clearing”

Help need ASAP.

Thank you!