The LSS and IS use HTTP or HTTPS traffic to communicate. The HTTP payload of the HTTP request contains all the needed traffic for the IS and the LSS to exchange information, instruct the LSS to add scans, send the results back to the IS for report generation, etc
In either case, either port 80 (HTTP) or port 443 (HTTPS) is used.
If required, the LSS can use a Proxy (authenticated, or anonymous) server.
The role of who initiates the connection can be switched, either the LSS initiates the connection, or the IS initiates the connection.
On large deployments we suggest that the LSS initiates the connection.