You may try configuring QoS on the firewall. The primary goal of QoS in the security appliance is to provide rate limiting on selected network traffic for both individual flow or VPN tunnel flow to ensue that all traffic gets its fair share of limited bandwidth. A flow can be defined in a number of ways. In the security appliance, QoS can apply to a combination of source and destination IP addresses, source and destination port number, and the Type of Service (ToS) byte of the IP header.