Latency and speed related to ocserv config

[Xianjin YE]

Hi dear list,

After I connect my client to the ocserv, the rtt(round trip time, client to the ocserv server) is about 100ms. There are some packet loss between my local machine and the ocserv server.
Whenever I start to download data through the vpn route, the rtt increases to about 1s and drops back to normal 100ms if the download stops. 
The download is a simple wget file, and I have noticed the download speed is about to reach my local machine's bandwidth. 
However I tried different output-buffer settings in the ocserv config, bigger buffer size do lead to faster speed. The rrt increases during downloading regardless the buffer size.

is this behavior normal? If not, how can I get a decent download speed without interfering the rtt. I am using ocserv 0.8.1 with Cisco Anyconnect client.