Sunday, 20 March 2011


The latency inherent in the use of satellite Internet is often held up as reason why satellites cannot be successfully used for IPTV, but in practice latency is not an important factor for IPTV. An IPTV service does not require real-time transmission, as is the case with telephony or videoconferencing services.

It is the latency of response to requests to change channel, display an EPG, etc. that most affects customers’ perceived quality of service, and these problems affect satellite IPTV no more than terrestrial IPTV. Indeed, command latency problems, faced by terrestrial IPTV networks with insufficient bandwidth as their customer base grows, may be solved by the high capacity of satellite distribution.

Satellite distribution does suffer from latency – the time for the signal to travel up from the hub to the satellite and back down to the user is around 0.25 seconds, and cannot be reduced. However, the effects of this delay are mitigated in real-life systems using data compression, TCP-acceleration, and HTTP pre-fetching.[66]

Satellite latency can be detrimental to especially time-sensitive applications such as on-line gaming (although it only seriously affects the likes of first-person shooters while many MMOGs can operate well over satellite Internet[67]), but IPTV is typically a simplex operation (one-way transmission) and latency is not a critical factor for video transmission.

Existing video transmission systems of both analogue and digital formats already introduce known quantifiable delays. Indeed, existing DVB TV channels that simulcast by both terrestrial and satellite transmissions, experience the same 0.25s delay difference between the two services with no detrimental effect, and it goes unnoticed by viewers.

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