As noted in the preceding section, four new interfaces have been introduced with UMTS/UTRAN. With the new interfaces came a huge set of protocol layers for mobile communication networks. Dealing with these new protocols presents a demanding challenge to manufacturers, operators, and measurement equipment suppliers.

Tektronix Measurement Approaches
The following will present a case study of Tektronix's measurement approaches. Nearly all measurement situations can be considered in three categories with related approaches. Even though there are situations where two or more approaches could be applied to the same interface, the first steps in protocol testing should always be to determine the characteristics of the system under test and the test objectives.

• Do you have a living network that you should not, or are not allowed, to disturb?Use the nonintrusive monitoring approach.
• Do you have a dead node or system that needs to be externally stimulated?Use the simulation/emulation approach.
• Do you need to verify compatibility with standards or with other equipment?Use the conformance approach.

Monitoring [see also CCITT 880 and GSM 12.04]
Monitoring is the process of collecting data from the interface. The main reason for operators and manufacturers to collect data is to retrieve the necessary information for decision-making in relation to a specified objective. The item under investigation can be an individual network element, parts of the PLMN, or even the whole PLMN. The major objectives for monitoring data collections include the following:

• To get an overall view of the actual performance level
• To determine a possible need for an improvement
• To discover the differences between specified and predicted characteristics and its actual performance
• To improve predictions of behavior and potential problems

Interface monitoring can collect data and present results in two ways:

• Measurement result collection—Use of cumulative counters to capture the number of occurrences of an event and/or discrete event registers to capture and trace specified results such as overload situations and failures
• Data review for evaluation—The storage of measured data for subsequent review and analysis; the amount of data is normally reduced through the filtering of specified events (such as abnormal call termination), the use of statistical methods or the selection of specific conditions (tracing data at a defined address, tracing a call setup, etc.)

Simulation
Simulation is the representation or imitation of a process or system by another device. In a test environment, a simulator can be used in place of a network element or a part of the network to produce desired conditions. For instance, when testing an RNC, the test equipment can simulate the CN behavior, keeping the RNC independent of the network. Simulators are used to do the following:

• To get information about the dependability of a network element (NE); normal and abnormal situations are specified and simulated, and the NE’s ability to cope with the simulated environment allows the operator to predict how well the NE will perform in the field; simulations are also used for conformance testing where standardized conditions are applied to the NE.
• To substitute missing network elements or parts of a network during the development process; simulation creates a realistic operating environment for the item under development.
• To save development and installation costs; the strong and weak points of an item can be discovered in the development process, before introducing it to an operating network.

Emulation
Emulation is a higher form of simulation where the behaviors of selected layers of communication protocols are simulated automatically and in conformance with standards. For instance, the simulation of the Iu RANAP is based on an emulation of the corresponding lower layers. While the lower layers are defined to act as specified, the simulated layer can be used to deliberately add faults to test an element’s ability to handle them.

Figure 16. Simulation and Emulation

Conformance Testing [ETSI ETR 021]
Standards allow different manufacturers to develop systems that can interoperate and exchange and handle information. A system or an implementation is declared conformant when its capabilities and external behavior meet those defined in the referenced standards. Conformance testing is the verification process that determines whether a system or an implementation is conformant. While specific conformance tests are defined in UMTS for the air interface (see 3G TS 34.xxx series), conformance tests of the remaining UTRAN interfaces are still dependent upon mutual agreement between manufacturers, operators, and measurement suppliers.