To wit, there are no class C or D HPGs (these only exist as class A and B). But there may still be class C and D ComStar stations. I suggested to Cray these might represent a ComStar presence without HPG that can still receive HPG communication, but would rely on pony express message transfer or a temporarily available "stopgap" mobile HPG to send out messages. Cray was agreeable to the idea. (This was in an open forum discussion iirc, but it may have been a non-public factchecker discussion or even via private messages.)
Campaign Ops says that Class C and D represent HPG "service" via a pony express(Every 3 months for C, and every 6 for D).
However, there would still need to an onplanet secure facility for people to send/receive their messages. From the Comstar Sourcebook, we know that the HPG Compound was a Comstar creation and not every world has one(although you can bet that every 'A Service' world has one by the 3050s).
On most worlds without a Compound, the Comstar facility is likely a giant mall. This could be filled with various terminals, where people wait in line. But it could also be efficiently divided by function based on message type(So a military officer does not have to wait in line with a Grandmother sending a money to her grandchild in college).
But on D-service worlds(and poorer C's), its more like a Post Office in a rural area.
On worlds with No HPG Service,this is where there is no Comstar presence at all(perhaps a few undercover operatives to keep tabs). The world is too poor and not strategically important enough for Comstar to make the commitment. Comstar also has an anti-periphery bias for much of its history. Finally, some worlds simply do not trust Comstar because of its association with the Star League obviously has a negative effect in the Periphery.
The local facilities and personnel required would obviously depend on service level, with an A-Class HPG Compound being the most expensive, and restoring an old one costing less than building a brand new one.
A Battletech Blogger(might have been Skilltao) made a post talking about HPGs and why no one had thought about building multiple HPGs on a single world and you could have near-Realtime communication from one end of the Inner Sphere.
I enjoyed the post, but I immediately realized that someone had and did exactly that.
Katrina Steiner.
After the FedCom Civil War began, Katrina implemented her HPG "Command Circuit" between Tharkad and New Avalon.
Ignoring the politics mollifying OTHER world and regional leaders who would seek a dip in their budgets to put HPGs on planets which already had them.
So Katrina commissioned, new B-Class HPGs(and maybe a few A's on worlds with A's) at incredible cost.
In the "Squaring the Circle" thread, there was discussion about how hard it actually is to defend a planet, so having TWO HPGs would not make things easier. The HPG pair would need to be relatively close for the Realtime Communication link to work.
So what happened to the 2nd HPG on these worlds?
Were some destroyed in the Jihad?
Were others taken offline by Yvonne and Peter to pay for reconstruction of each realm?(maybe breaking down the equipment than 'selling' it to Comstar as a downpayment for a series of reconstruction loans?)
Why didn't Devlin Stone do the same thing for the Republic of the Sphere?