G.1 Interleaving for Tune-in Time Reduction of FEC protected MBMS Services

26.3463GPPMultimedia Broadcast/Multicast Service (MBMS)Protocols and codecsRelease 17TS

Interleaving may be applied to source blocks before FEC encoding to re-arrange the order of transmission of the UDP packets. The target of the interleaving is to provide high priority and correctly decodable media units in a way that maximizes the resulting media duration at the receivers that tune in at that specific source block. The interleaver may operate at two different levels:

– Inter-stream interleaving: prioritize the media streams and arrange their transmission order according to the ascending order of priorities. In other words high priority data, e.g. audio data, is transmitted towards the end of the source block.

– Intra-stream interleaving: high priority media data units such as Random Access Points of a video stream are transmitted towards the end of a source block.

The interleaving procedure enables receivers to reliably decode and present media data that has been received from a fraction of the tune-in source block.

Interleaving is transparent to legacy receivers.

G.1.1 Timestamp Offsets

The timestamp offset field may be used to signal a timestamp offset for the received media units in the FEC block as specified in clause 8.2.3.2.

The timestamp offsets may be used to reconstruct the presentation time line at the UE. They may also be used to reduce the out time caused by the reception of a partially received interleaved FEC source block as shown in figure G.1.

Figure G.1: Early tune-in using variable timestamps

G.1.2 Early Playout

A UE that desires to make use of the interleaving to reduce the tune-in time may start the playout earlier than dictated by the min-buffer-time value.

Instead, the UE may schedule the first media unit of the succeeding source block to be played out after the min-buffer-time. It may then estimate the appropriate time for starting early playout based on the amount of media duration that was received from the current block, the playout time of the earliest media unit of the next source block, and the highest presentation time of the media units of the current source block.

The early playout behavior is depicted by the following figure.

Figure G.2: Early play out of interleaved media data of a FEC protected MBMS service