Portal Server aggregates content from external sources. If external content providers cannot sustain the necessary bandwidth for Portal Server to operate at full speed, Portal Desktop rendering and throughput request times will not be optimum. The Portal Desktop waits until all channels are completed (or timed out) before it returns the request response to the browser.
Plan your back-end infrastructure carefully when you use channels that:
Scrape their content from external sources
Access corporate databases, which typically have slow response times
Provide email content
Provide calendar content