Most civilized worlds (meaning those in the Inner Sphere and major Periphery nations) will have some form of HPG service. HPG services are always provided by ComStar, and take the form of a ComStar compound (major worlds can have multiple compounds) built around one or more HPG generators.

The most visible part of a HPG generator is the transceiver array, which looks pretty much like a huge radio dish (or multiple dishes for larger compounds). There is more to it than that of course, but everything else is hidden below ground or behind thick concrete – and a wall of silence from the ComStar personnel that operate it.

HPGs do not operate continuously. They require enormous amounts of power, and are often run at night to minimize the load on the local power grid. Major compounds may have their own power generators (big fusion plants), and sometimes even sell energy to surrounding areas when there is a surplus (don’t forget that ComStar, for all their “monastic” posturing, is a business).

HPGs have about 50 ly range (by comparison a jumpship has 30 ly range), which is why there has to be a chain of them to reach far away worlds. To send or receive, the dish must be very precisely pointed towards the target world, which requires a great deal of calculation and fine tuning. To make it simpler, HPG relays mostly operate according to a very specific predetermined schedule. This schedule is decided and overseen by the main office on Terra.

Assuming you have access to an A-class facility, ComStar guarantees that your messages will reach any A-class facility within 24 hours (usually less). If there is a B-class facility, the estimate is 1-3 days to reach an A-class world, longer to reach B or C class. C-class facilities provide 1-7 days to an A-class, longer to reach B or C class. Those are the times ComStar guarantees. If alignments schedules match, it can go a lot faster.

There is also a system for priority messages for those in a hurry. There is no use just pointing the dish at any given world as the target needs to be actively listening in the right direction. Instead every HPG station will know the alignment of every other HPG station, and therefore where it can transmit/receive at any given moment. Based on the final destination a “path” is then calculated, the dish is moved to the correct alignment, and the message sent. Sometimes a priority message will have to be bounced back and forth quite a bit before it reaches its destination. Depending on the number of relay points, and the number of dishes that have to be realigned out of schedule, the base price can range from very high to astronomical.

Messages can be transmitted as text (common), images (also common), sound and live capture (costlier, but common enough), and data files (price varies with size). Live communication between adjacent systems is possible is the relays are at least B-class. Typically, this is sound only, or very low res images. It is very expensive.

It is technically possible to set up a real-time conversation across vast distances if arrays can be lined up all the way from one speaker to the next (you could even make a conference call between multiple star systems). This requires scheduling beforehand to align the various arrays. Every system involved has to be an A-class, except the terminus systems, which need only be B-class). Needless to say the cost of such a venture puts it beyond that reach of even wealthy people.

In a few places orbital arrays and deep space relays do exist, but they are very, very rare. They have no major benefits over planet bound relays, except they are less constrained by planetary interference. This is outweighed by the complexity and cost of building and maintaining such deep space relays. It also seems that ComStar just has a preference for building on planets. Maybe it’s a policy thing.

During the heyday of the Star League, some fleet flagships were fitted with HPGs, but it was seen as problematic because the mass of the HPG and its power requirements reduced the military value of the warship. There were also built a few fleet communication ships, but these were both vulnerable to attack and weakly armed. All of this is now lostech.