Hi Ravi,
Zero connection timeout is nothing but port opening from your portal to ECC system.
In your case if you have firewall between portal and ECC then you can tell the network team to open the SAP ports(3600,3201,3301,8100) between the same. SO firewall wont inspect the traffic on those ports and there wont by any drop of packets.
If you want to verify with out doing that, just note down the time when the error comes and check the gateway/ICM logs in ECC side or ICM logs in portal side. Also you can the network team to check if any packet loss was there at that time.
Regards
Ankit