IIS configuration for number of concurrent connection
Open an administrator command prompt at %windir%\System32\inetsrv\
Run the command below to update the appConcurrentRequestLimit attribute to a suitable number (5000 is the default in IIS7+)
Example
1
appcmd.exe set config /section:system.webserver/serverRuntime /appConcurrentRequestLimit:100000
You can find more details from the following link.
https://github.com/SignalR/SignalR/wiki/Performance