Hello,
As mentioned earlier, the GUP technology has been designed for local networks only. Even the Explicit GUP configuration is meant for single sites with multiple subnets.
Having clients over WAN links use a GUP has several implications, the most important one that there is no bandwidth control and you can clog up the remote link.
Keep also in mind, that clients waiting for the GUP to download content updates from the SEPM go into an accelerated heartbeat. So if for example you have 20 remote machines with 30 min heartbeat and the content download takes 30 min. you will have to expect 20 machines basically trying to download the updates at once.
Also mixing LAN and remote site use for a GUP and limiting simply the number of connections might most probably cause other unwanted side effects such as a slow content update speed also for the LAN due to remote clients using up most or all allowed connections, releasing them only hours later...
I would really advise not to use GUP over WAN connections - I have never seen a customer who did not run into trouble with such a setup at least at some point in time.
If you want to reduce the remote sites bandwidth use you have several other possibilities (certainly not as elegant as GUP, but still worth a try):
1. Use a longer heartbeat interval and random to spread out the content downloads over a broader window reducing the impact of content updates. I have seen 2 or 3 hour heartbeats with 1 or 2 h randomization. Don't exagerate, otherwise you will have some other unwanted side effects... Don't forget to keep a long history of content updates on the SEPM servers - even though it takes space on disk (currently count with about 200-250 GB for 80-90 revisions) it will reduce the number of full downloads.
2. LU: Use LiveUpdate Administrator to create LiveUpdate Distribution Centers at strategic places such as data centers. Configure then the clients on those remote sites to update content updates against the LiveUpdate Distribution Centers only at specific times of the day where downloads won't impact business processes. Using LU has also the advantage that clients will only download incremental updates for up to 1 year.
I would also suggest: Make sure that you deploy on sites with sensitive bandwidth always clients with pre-updated content updates so that initial content updates are small and successful...
Hope this helps.
Best regards
Pierre