Generic Stream Encapsulation: Difference between revisions

Revision as of 10:45, 20 September 2011

Revision as of 08:50, 12 October 2011

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On [[DVB-S2]], [[DVB-T2]], and [[DVB-C2]] the ACM/VCM modes may cause the Base Band frames to vary in size depending on the transmission conditions. Hence there may be situations where the first fragments of a payloafpayload frame have been sent, but the encapsulator is forced to set aside the current payload frame, and start working on a new one. This may e.g. occur when large fragments have been prepared while transmission conditions were fine, but suddenly the conditions deteriorate, and only small Base Band frames are available.

This is when the '''Fragment ID''' field becomes important. It is a short-term identification of the payload frame. Whenever the encapsulator needs to move on to the next payload frame, without having finished transmitting the previous one, it uses the next available Fragment ID. That way, up to 256 payload frames can be "kept open" at any time. The decapsulator uses the Fragment ID to pick the reassembly buffer in which to store the fragment.