 3.5 GHz spectrum and a cell bandwidth of 100 MHz; obviously the data flow 7.6 MAC Layer Initial BWP Maximum bandwidth Smaller BWPs Frequency Figure 7.12 BWP example. only requires a small fraction of the allocated spectrum. With BWP, the UE does not have to monitor the full channel bandwidth and can therefore reduce its power consumption. Several BWPs can be configured by RRC, but only one is active at a time (the active BWP). The configured BWPs can differ in width (to save power in periods of low activ- ity), in location within the frequency domain (to increase scheduling flexibility), and in the subcarrier spacing offered (to allow different services). Switching between config- ured BWPs for a UE can be triggered by RRC signaling, physical layer signaling (DCI), or by the MAC sublayer itself when an inactivity timer expires, or upon initiating a random access procedure. We distinguish between two kinds of BWPs: the initial one and the default one. The initial BWP is the BWP selected by the MAC sublayer when performing a random access, or configured by the network for an SCell in CA. The default BWP is the BWP associated with the inactivity timer by the network: when an inactivity timer is config- ured, the expiry of the timer switches the active BWP to the default BWP. An example of BWP operation is depicted in Figure 7.12. Note that BWP also impacts system infor- mation reception (see Section 7.7.2) as well as the UE measurement operations. 7.6.11 BFD and Recovery BFD relies on the same principles as RLF: the physical layer notifies the upper layers of failure events and once too many such events are detected (as measured on the Beam Failure Detection Reference Signal for the beams in questions), the UE initiates beam failure recovery with a random access procedure: it starts with beam selection, and upon completion of the random access procedure, beam failure recovery is considered suc- cessful. Note that the random access procedure can be contention free when random access resources were provided by the gN