WebSphere Portal uses a very large number of GET requests to satisfy a page render request. It is not uncommon for it to take 50-70 GETs. This large number of GET requests would be untenable from a performance perspective if each of these GETs required a round trip to the Portal server for each render.
Luckily, for each HREF in the base Portal page triggering a GET, the response back is typically invariant over short intervals of time. Stated in a more technical way, the "cache-control" headers of a vast number of the GET requests when rendering a Portal page indicate that the contents of the responses are invariant.
That is one of the reasons that the Portal tuning guide recommends setting up your IHS (Apache) server's httpd.conf file to use mod_disk_cache. This off loads the serving of these invariant files from the Portal server to the IHS (Apache) server where cycles are generally much cheaper and the responses much faster.
Use of a CDN (Content Delivery Network) can further improve the response time for Portal pages by insuring that the server that actually calculates the response for a GET request is "network close" to the origin. This is due to the fact that a lot of the round trip delay in the network can be avoided. The blog entry here discusses this possibility.
If your Portal resides in Bluemix (IBM's SaaS Portal offering), you can associate your IHS server which front-ends Portal to easily use a CDN with Portal. Check out the details here and here. If you augment your DXC Portal with a CDN as mentioned, you will improve your Portal's response time to your customers.
Note the one caveat that the initial Portal base page is not cachable as it is generated as a result of access control, personalization and other factors which dictate that the page be (generally) not cachable. Therefore, the initial Portal page always has to be responded to by the Portal server itself. However, with a CDN, overall response times above and beyond that initial page will be much better regardless of the client browser's location in the world. It is worth noting, however, there for a small number of Portals whose initial page is both anonymous and invariant, that it could be cached and would be applicable on a CDN. Consult this page if you are interesting in making such a cachable Portal page.