Hello Akhas
This is an excellent question, and it really highlights all of the parameters that are involved in an end to end communication that can affect the throughput of data.
Things that can affect this particular communication include:
- The application being used to transfer the files. Remember that when sending data using the SMB or FTP protocols, TCP is being used. This means that the receiver can regulate the flow of data using TCP flow control mechanisms. If the receiver can’t handle the speed (due to application, bandwidth, or hardware limitations) it will request that the sender slow down sending, which will ultimately reduce the throughput. This is also highly dependant on the operating system being used and how it manages the various TCP sessions.
- QoS policing and shaping parameters that are configured at various parts of your and the ISP’s network.
- Other traffic that may be on the network at the time.
- Overhead from tunnelling protocols.
- Method of measurement used by solar winds (are you sure it’s 49 Mbps and not 49 MBps?)
Now I know that you have taken many of these into consideration, as you mention in your post, but I am mentioning them here for completeness.
In order to remove such factors from the equation, my suggestion would be to use an IP SLA traffic generator as you mention in your post. More info can be found here:
Configure the generator on a device as close as possible to the ISP edge (possibly your edge router) and the responder also as close as possible to the network edge of your DR site. This way you eliminate the passage of traffic on your internal network which may also affect the result.
Next make sure to use UDP for the transmission so that you don’t involve any flow control that may limit the transmission.
Finally, use several measuring techniques, including both your solar winds monitoring system as well as using a policy map on the network devices using an access list as described in the above linked lesson. That way you can verify (or not) the measurements being taken by the monitoring system.
I hope this has been helpful!
Laz