Forerunner entanglement dish
From Halopedia, the Halo wiki
A Forerunner entanglement dish is a piece of Forerunner communications technology. Utilising quantum entanglement, the dish allows operators to communicate across vast distances, including make effectively instantaneous communications from outside of the Milky Way galaxy from installations such as The Ark into the galaxy itself. 
By 2552, at least one such device had been recovered by the Covenant and was present on High Charity during its fall. The device was later recovered from the Flood hive during the Outbreak on Installation 00 in a salvage effort led by Pavium and Voridus - the recovery of which being all which saved the errant brothers from execution by Atriox. The recovered dish was only semi-functional, and ultimately took a few weeks of tinkering by Voridus to become working for a short time. The Banished war chief was able to use the entanglement dish to send a brief message to Escharum and his forces back in the Milky Way, organizing them to rally at Reach and dig up the Menachite portal complex to allow Atriox to return from the Second Ark Conflict back into the galaxy.
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