IPTV services should use an IP multicast solution for a network bandwidth efficient delivery of the media contents. PIM-SM is the most commonly used IP multicast routing protocol in IPTV systems. A short introduction to the operation of PIM-SM is given. Its fault tolerance is examined by experimenting on a mesh topology multicast test network built up by XORP routers in a virtualizcd environment. Different fault scenarios are played and different parameters of PIM-SM and OSPF are examined if they influence and how they influence the outage time of an IPTV service. A formal model is given for the service outage time of the IPTV service on the basis of the results of the experiments.