Traffic outbound is larger than traffic inbound at SBC

Hi Acme !

I'm using SBC Net-net 4500, image version nnSCX610m11p5.xz, and use the PBRB model.

I graphed the traffic on the SBC 's interface which has public IP, and I monitor for a long time.

I see the outbound traffic (from SBC to internet) is usually larger the inbound traffic (from internet to SBC), sometimes up to 10% difference between the inbound and outbound traffic.

My partner complained about this, too. The inbound traffic from my SBC's public IP address to their deivice is usually larger the outbound traffic from their device to my SBC, especically on the time high trafffic or peak time, in the peak time, their inbound traffic is about 12MB and their outbound traffic is about 10MB.