olerable loss rates may be higher depending on degree and quality of set-top box loss suppression. For QoS provisioning, IPTV streams are differentiated from IP traffic originating from other applications which have different performance requirements. Table 6.3 Requirements for satisfactory QoE for IPTV over DSL. Maximum IPTV stream duration Corresponding Average video bitrate Latency Jitter of a single loss period in stream packet (Mbit/s) error (ms) IP packets Loss distance loss rate 4 IP packets 1 error event per hour <6.68E-06 5 IP packets 1 error event per hour <7.31E-06 5 IP packets 1 error event per hour <5.85E-06 6 IP packets 1 error event per hour <5.85E-06 14 IP packets 1 error event per 4h <1.28E-06 17 IP packets 1 error event per 4h <1.24E-06 20 IP packets 1 error event per 4h <1.22E-06 6 Services in Fixed and Mobile Ultra-Broadband The QoE of IPTV can also be expressed via MOS, similar to QoE for voice. There are three main types of issues that can impact IPTV QoE: Degraded IPTV service. It appears when some amount of the IPTV stream is unavail- able to the set-top box at the playout time. This happens due to packet loss at some network segment, but also can be due to certain content encoding issues in the case of bigger jitter at the set-top box. IPTV service unavailable. This is the case when no IP packets arrive at the set-top box (no picture is shown on the screen), which may be caused by broadband IP access interruption, an IPTV delivery problem (network congestion or link failure), an IPTV platform problem (e.g. failure of streaming servers), or interruption of the input TV channel (e.g. digital TV from satellite or terrestrial broadcast systems) to the IPTV encoders (at the service provider's domain). Insufficiently responsive service. This could happen due to long channel change times for IPTV or delay in responsiveness of video on demand commands (play, stop, pause, etc.). So, the major influence on the IPTV QoE has packet loss that cannot be recovered. In practice, IPTV typically uses RTP/U