GBR
Guaranteed Bit Rate: a QoS flow type that has dedicated network resources guaranteeing a minimum bit rate, used for real-time services like voice and video.
A GBR flow comes with a promise: the network reserves resources so it can deliver at least a guaranteed bit rate whenever the application is sending. That reservation is the whole point and the whole cost — it means admission control has to run, because the network can only make so many of these promises before it runs out of capacity, and a new GBR flow it can't honour gets refused rather than admitted on a hope.
This is what you want for real-time, rate-sensitive media — conversational voice and video, where falling below a certain rate breaks the experience rather than just slowing it. Each GBR flow is bracketed by a GFBR (the guaranteed floor) and an MFBR (the burst ceiling), set independently per direction. Contrast with non-GBR flows, which get no such reservation and simply share whatever capacity is left. On the air interface, GBR flows also get tighter scheduling treatment so their delay budget is respected.
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