What is rport parameter in IP Phone setting page?

There is a parameter “rport” on web page of the sip user agent(i mean ip phone).
There is a checkbox like “enable rport”. If i check this box so what does it mean? if i dont sign this box so what does at mean?
Is it about signalling ?
When it must be"yes"? when it must be “no”?
Why we need like this parameter?

I’d ask the author of your GUI. However it probably has something to do with https://www.ietf.org/rfc/rfc3581.txt and one of Asterisk’s nat= options, i.e. to do with having the remote party reply to the source port, rather than the one in the Via, of forcing the local system to pretend that it hat been told to do that.

rport parameter must be supported in client side and server side?
i mean:

Sip Client Support rport ,Sip Server support rport,Rport works for specified client
No ,No,No

What problem are you really trying to solve?

i just want to learn.

rport has to be supported by the server, but whether you have to turn it on or not is up to the server… in the case of Asterisk the option controls whether we force it on (even if the client did not ask for it).

Thanks friend. You give the valuable answers.