webdispatcher external server communication

Hi,

Our webdispatcher communicates to backend ERP and portal systems via
message server http port.In addition to this we defined a non-sap
system using the following webdispatcher parameter.The following
definition of the wdisp/system parameter works fine

wdisp/system_2 =
SID=EXT,EXTSRV=http://localhost.xx.com:8080,SRCSRV=*:443,SRCURL=/xyz

But when using the below url the webdispatcher does not establish
communication to the external server eventhough the port 8090 is open.
Are there any additional parameters that need to go for HTTPS
communication for external server communication..

wdisp/system_2 =
SID=EXT,EXTSRV=https://localhost.xx.com:8090,SRCSRV=*:443,SRCURL=/archive

Please advise.

thanks,
Lanke