ches. User-network interfaces (UNI): This is the interface between end systems and the switch. Communication Networks ATM switch ATM router Public interface Network cloud Figure 9.1 ATM network simplified architecture. These interfaces can further be categorized as public or private interfaces where the private interfaces are usually proprietary (not standards based) and used inside private ATM networks, while the public interfaces confirm to standards. Communication between two ATM switches in different networks is handled by a public interface. ATM cells carry connection identifiers (details of path to follow from one end- point to another) in their header as they are transmitted through the virtual channel. These identifiers are local to the switching node and assigned during connection setup. Based on the ATM circuit, the connection identifier can be a VPI (virtual path identifier) or VCI (virtual channel identifier). The operations performed by the ATM switch include Looking up the identifier in a local translation table and finding the outgo- ing ports. Retransmission of the cell though the outgoing link with appropriate con- nection identifiers. From a network management perspective, the basic FCAPS functionality is required in a management system for this network. Unlike a switched virtual connection (SVC) that is automatic configuration, the setting up of a permanent virtual connection (PVC) would require external intervention. The setting up of a PVC in the ATM network using the network management system is an example of specialized configuration management function specific to this network. 9.3 GSM Network GSM stands for global system for mobile communication. It is a cellular (user COV- erage area defined in the shape of cells) communication network. It was developed Fundamentals of EMS, NMS and OSS/BSS Core network Figure 9.2 GSM network simplified architecture. as an attempt to standardize the European mobile telephone network and is now one of the most popular standards for mobile phones in the wor