Hyerpsace is a domain of subspace coexisting physically with normal space but within a different layer or level of subspace. The region is largely devoid of matter mostly consisting of swirling red-hued energy eddies and currents in all directions. These currents pull or push vessels along them requiring ships to maintain their course through continuous use of maneuvering thrusters. Since there are no stellar bodies within hyperspace this makes navigation very difficult as it is impossible to tell, without a point of reference, the relative course, speed, and location of a vessel. There is no "magnetic north" within hyperspace to base navigation on.
Relation to Normal Space
Hyperspace is coupled to normal space as with any subspace domain but the correspondence is not 1:1, rather distance in hyperspace is smaller than the relative distance in real space, or rather hyperspace is compressed space. Depending on the precise conditions, one kilometer travelled in hyperspace can be many hundreds of times more kilometers distance travelled in real space. As such a vessel traveling at conventional sub-light speeds in hyperspace can achieve relative FTL travel in real space without ever going faster than light.
Sensing / Communicating
Although transmissions can breech the subspace boundaries, such as with the beacon network, sensors cannot. It is impossible to sense real space from within hyperspace or vise versa. Since the coexist in the same 3 dimensional realm but at different layers there is a direct correspondence of a location in real space to every location in hyperspace. Only a tachyon beam transmission can penetrate the divide between normal space and hyperspace.
The rim of known space is roughly defined as the edge at which a vessel in hyperspace can still detect the navigational beacons within hyperspace. Beyond this barrier vessels have no way to navigate back to known jump gates. The Rim is essentially the boundary of known space as detectable from within hyperspace.
Automated probes are currently being used by the Vulcan Science Academy to attempt to derive weather patterns in hyperspace and map out the real state of the currents of energy which push and pull at vessels in hyperspace. These probes are also attempting to plot the conditions by which distance in hyperspace relates to distance in real space through the use of short-range tachyon beams and vessels within real space.
So far the project has had only limited results.
Jump Gates / Jump Points
Transit into hyperspace is only possible from a jump gate or a jump point capable vessel. Vessels capable of forming a jump point create a temporary vortex which allows entry into hyperspace, due to the size and power requirements, they are rarely used as it takes more power to create a jump point than it does to use warp drive and the two technologies are incompatible to be used at the same time. A warp drive system would be required to generate the power to create a jump point where as it would have to be shut down prior entering the jump point.
To allow for navigation specially designed subspace beacons in normal-space broadcast within hyperspace. These signals use tachyon beams between beacons jump gates and the coordination of tachyon beams / beacons allows vessels to navigate through hyperspace safely through the beacon network.
Without these beacons a vessel within hyperspace would be unable to navigate.
To aid in navigation many beacons on non-jump gates exist at planetary facilities, space stations, and even very large vessels to assist in navigation.
Due to potential mental issues from long exposure to hyerspace conditions, it is illegal for anyone to be forced to stay in hyperspace for extended periods of time against their will. Additionally, any combat, for any reason except for self defense against an aggressor who has already broken this law, is illegal.