## 5 The PON Network Availability Evaluator  
The PON Network Availability Evaluator is a simulation program that allows comparing various traffic protection schemes utilized in passive optical networks from a viewpoint of the network availability. In [20], a performance analysis of TDM-PON protection schemes is presented. For this contribution, the PON Network Availability Evaluator must be modified and extended for obtaining relevant results available for advanced protection schemes. The realized simulation program evaluates real scenarios of the WDM-PON protection schemes based on various specific technical specifications--a protection scheme, a restoration time, values of MTTR and MTBF parameters for utilized optical components. The PON Network Availability Evaluator is created in the Microsoft Excel program environment by means of ActiveX control elements and by utilization of the Visual Basic for Applications (VBA) code. The simulation program allows for configuring specific parameters of traffic protection schemes considered for the WDM-PON networks. The client can intuitively control a program interface and arrange values of requested specific parameters according to real network implementations. The simulation program is oriented on both-P2 MP and RING-WDM-PON protection schemes. For each protection scheme, various presumptive scenarios are considered. A calculation of the WDM-PON network availability is realized by using of values network presented in Table 3 for each network component. Basic parameters are divided according to the topology, whereby the fiber length is corresponding to the WDM-PON protection scheme. Table 3 summarizes some data related to the network unavailability as a consequence of failures of WDM-PON network components [7]. The simulation program utilizes values of MTTR and MTBF parameters for particular optical components and directly presents a resultant value of the network availability for a selected WDM-PON protection scheme. Each component is changing independently and/or simultaneously with other components depending on the selected protection scheme. Therefore, values of considered specific parameters for the OLT terminal, ONU units, AWG and OS elements, FF and DF fibers can be changed according to the [7] or specific network operator's data, if available. Figure 3: The comparison of power budget requirements for RING WDM-PON protection schemes. The Main Screen of the PON Network Availability Evaluator  
First, the main screen is presented with default parameters of the P2 MP WDM-PON protection scheme for the unprotected network scenario (Figure 4). On the left side, the P2 MP topology can be selected and subsequently related protection scenarios are offered. For all protection scenarios, the expected restoration time is necessary to select. The button CALCULATE starts a process for calculating the network availability in [%]. For better understanding, a value of the Mean Down Time (MDT) in [min/year] related to the network unavailability is depicted. In the middle of the screen, two graphs related to the selected protection scheme are presented. The upper graph charts the network unavailability of components, and the lower graph presents a comparison of the network availability for all protection scenarios offered for the selected network topology. Immediately after selecting the protection scenario and setting options, resultant values of the network availability and unavailability are shown. On the right side, a WDM-PON network architecture corresponding to the selected P2 MP protection scenario is then pictured. For better understanding, an explanation of active working and protection elements and redundant parts in different architectures is embedded. Next, the main screen with modified parameters of the RING WDM-PON protection scheme for the protected metro-access network scenario--a ring topology, a protected  
Figure 4: The main screen’s part for the unprotected P2 MP WDM-PON network.