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| Whitepapers/The VideoBridge concept Chapter 4 of 8 TV over IP - parameters to watch When considering transfer of time sensitive data such as real-time video across IP there are a number of quality-of-service parameters that should be monitored. These are:
Table 1 - Typical quality parameters of global Tier-1 IP network infrastructures available today. Note that when carrying MPEG-2 video in UDP frames any packet loss and packet reordering events will affect the video quality. In triple-play networks used for carrying video traffic these parameters should therefore ideally be zero. Forwarding outages is the time it takes for the network to automatically restore service after a fibre cut event. If re-routing is performed at the IP layer using OSPF, ISIS, BGP or another routing protocol then a maximum value of 3 seconds is considered very good. Packet loss is the percentage of IP packets lost when transferring data from any given point on the network to any other given point on the network. Packet reordering is the percentage of IP packets that arrive out of order compared to the order in which they were sent into the network. IP packet jitter is the variation in arrival time of the IP packet compared to its ideal arrival time. IP packet jitter is thus a measure of how uniformly the network is switching packets from source to destination. IP packet jitter will occur when the IP frames traverse IP routers and switches in the network. IP packet jitter will be affected by how well the network traffic engineering has been carried out and also by the queuing algorithms in the switches and routers. By monitoring packet drops at the MPEG-2 Transport Stream layer ('continuity errors') and also the packet jitter of each IP frame it is possible to conclude whether the signal is healthy or not. The two most important parameters to continuously monitor at strategic points in the network are therefore:
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