and QoS Parameters, KPIs, and Measurements Table 7.6 Popular types of OTT applications and quality parameters. Data application/ Importance of KPI for data applications/services service type (Very low, Low, Medium, or High) Data transmission Delay speed (bit/s) Delay variation Packet loss Downlink Uplink Browsing (text) Medium Very low Medium Very low Browsing (media) Very low Medium File download Very low Very low File upload Very low Very low Transactions Very low Very low Medium Very low Streaming media Very low Very low Voice over IP (VoIP) Video telephony Gaming UDP on the transport layer. For real-time services such as VoIP or streaming media (e.g. video streaming with accompanied audio streams), the bitrate in downstream is the most important KPI because video streaming requires high bitrates (which is dependent upon the picture resolution used for the given video stream). Delay and delay variation (i.e. jit- ter) are less important KPIs for streaming media because they can be compensated (and with that eliminated) by the playout buffering at the receiving media player (one should note that the receiving device that plays the video should have enough capabilities to play the video stream on the screen, such as processing power for real-time decoding of media streams and enough memory for buffering the media in order to have smooth reproduction without the picture freezing or lost media data). What can be defined as the main KPIs for data services? The availability of broadband IAS is the most influential KPI for data services (that is percentage of time the broadband/ultra-broadband access to Internet is available to the user). Although the availability of PSTN over fixed networks has reached availability of 99.999% of the time, availability of services in mobile networks for voice is in the range 98-99%, and the availability of data services tends to be in the same ranges. However, availability of Internet connectivity depends also on the functionalities and performances of DHCP and DNS functions, which a