The concept of NGN [ITU-T Y.2001] is an evolutionary tendency in public telecommunication networks development. All stages of NGN evolution could be divided into networks which are realized by PES architecture@ which employs interworking between CS and PS networks and networks whose architecture is based on IMS platform with a wide range of services and different types of content. Independent from the evolutionary state of the networks@ network providers need to implement a network monitoring system which can manage the quality of network operations and prevent faults. The NGN monitoring system (NMS) has to be built in accordance with the NGN functional model and has to control all protocols implemented by it. For example@ the control protocol list may include: services layer (SIP@ H.323@ H.248@ MGCP@ etc.)@ transport layer (MPLS@ BGP@ EGP@ Diffserv@ etc.)@ and application layer (Diameter@ SIP@ AAA@ Parlay@ etc.). Also in accordance with NGN evolution@ the NMS could include protocols implemented by CS networks (SS7@ DSS1@ etc.). NMS could be also used as part of the OSS systems and take part in fault management and in performance management systems [b-ITU-T M.3060]. The monitored parameters form the fundamental data about the different layers (LLA) of the OSS architecture [b-ITU-T M.3060]. NMS could control and compare different parameters of protocols and operational interfaces and@ in accordance with [ITU-T M.3010] could control all network elements and services. NMS allows the control of not only stand-alone elements@ but also of different types of NGN call scenarios and maintenance parameters@ which could be useful for QoS testing. As a result@ NMS is an important and a basic measurement instrument which must be provided in the NGN network. NMS must be used in the model network in accordance with [ITU-T Q.3900] and is a basic requirement for testing of NGN technical means. This Recommendation describes the basic requirements of an NGN monitoring system and allows to understand what parameters have to be controlled by the NMS.