a baseline for NMM development. This standard defines the following measurements for a given carrier frequency: Received Signal Strength Search for any cells (within range) that are transmitting Read (decode) the PBCH Read (decode) the System Information Block 1 Read (decode) remainder Broadcast Channel information blocks. Operation can be supported for in-band (only on the channel that this cell is operating at) or out-of-band (also on other channels) operation. Operation can also happen either only at boot time or also during run-time, and either whilst base station operation is ongoing or only in when idling from normal user operation. As long as requirements are simple, NMM 206 Open Radio Access Network (O-RAN) Systems Architecture and Design can be implemented in hardware that is also used for communication operation or with ded- icated hardware: the NMM unit. Dedicated hardware allows for more advanced modes such as out-of-band operation, nonboot-time operation, and SO on. Security aspects For commercial and private networks both, security aspects are important but often over- looked. Telecommunications equipment is seen as critical infrastructure and thus needs to be protected against intruders. Given the software centric nature of modern telecommunica- tion equipment, we can treat it as any web-connected application. O-RAN and other net- working equipment is often installed (like any other networking equipment) on private or semipublic networks and subject to similar attack vectors, both from the Core Network side where the networking equipment is connected to the Internet as well as from the client side where the network is accessed over the wireless air interface which makes all local applica- tions subject to attack from any malicious user within the wireless network range. In this chapter, we discuss some common attack scenarios and appropriate protection mechanisms against them, in the form of a checklist of best practices. We discuss them in the sequence in which they are commonly executed, focusing