Schematic display of the network.
The Hirogen communications network was a large array of stations which spanned the Delta Quadrant, and reached into Alpha and Beta Quadrants as well. It was first encountered in 2374 by the USS Voyager. One of the arrays encountered by Voyager was powered by an artificial quantum singularity, generating almost four terawatts of energy, and was found to be over 100,000 years old.
Using the relay network, Voyager was able to locate the USS Prometheus, a Starfleet vessel on the edge of the Alpha Quadrant, and attempted to communicate with it. However, the message quickly became degraded, and bounced back to Voyager. It was determined that a holographic data stream would not suffer degradation to the same extent, and so, The Doctor, Voyager's EMH, was transferred to the Prometheus to make contact.
When the Hirogen, operators and controllers of the network, discovered Voyager's use of their technology, they attempted to cut off the ship's connection with the network. When negotiating failed, Seven of Nine sent a feedback surge along the communications link, incapacitating the Hirogen commander.
The Doctor was successful in making contact with Starfleet Command, and was returned through the network to relay their message back to Voyager. (VOY: "Message in a Bottle")
Several weeks later, Starfleet attempted to use the network to contact Voyager directly. However, the same problems with communications caused a large portion of the data transfer, containing messages and letters from the crew's families, to become lodged in a relay station near to Voyager's position. Whilst attempting to retrieve the data, Voyager came under attack from a Hirogen hunting party, and was forced to use an antithoron burst against the relay station, causing the quantum singularity within to be exposed, destroying the Hirogen vessel, along with the remaining messages. The energy released in the process spread to every relay in the network, disabling them, and rendering the network inert. (VOY: "Hunters")