I think you are talking about IPC. There are good examples based on events in samples... Have a look at them... Specifiacally, PortletA, PortletB in the samples events package.
I think you should consider the second page to be the same portlet
or you should make a menu "link to the other portlet"
In the first case it is the same portlet.
In the second case it works as the menu system works. (Only difference your link comes from another portlet .. not the menu)
A third case could be called IPC Inter portlet communication. The best design is to avoid this.
The basic idea behind portlets in JSR 168 is independence. It does not specify IPC.
You can ask. Was the JSR 168 team sleeping ... doing a bad job?
I think No. I think the JSR 168 team did a fair job.
You should think about portlets as independent units.
At the wildest linked together like a menu...
By such a perception I believe you will end up being happier...
The benefit from portlets for you shoud be the power of combining portlets into a portal.
The benefit should not be another way of combining components.
Components are much better combined in frameworks like JSF