10gb to 1gb over-utilization

Hello,

I have been troubleshooting a file transfer issue for quite some time, which I wont go into full detail, but I found something interesting. The circuit is a 1gb ELINE between datacenters. I have found that if transfer from site A to site B using a laptop with a 1gb NIC, I transfer at 112MBps (full gig). when I transfer from a device with a 10gb nice, I get about 2-5MB. Also, if I am transferring from a 1gb NIC and then start a transfer from another 1gb NIC, they will crash to about 10MB each.

At site B I only have 10Gb devices, and when I transfer back from site B to any devices in Site-A I get 2-5MB.

I can see in captures that there is an issue with TCP windowing, but I am not seeing any errors on any interfaces. The theory fits that the 10gb devices are trying to send at 10gb into a 1gb circuit, the buffer is overflowing and causing the TCP windowing to take a dump, but I would think that the link speed would be taken into consideration during TCP handshake.

I have other 1gb point-to-points that I can transfer from 10gb to 10gb with no problem, so I am perplexed why I am having this issue on this one specific circuit.