TITRE Adaptive Packet Video Streaming Over IP Networks - LaBRI

3.2.2.1 End-to-End Retransmission
Retransmission is an Automatic Repeat ReQuest (ARQ) scheme for reliable communication.
In this approach, lost packets are requested by the receiver from the sender. In this case, it is
necessary to have a back channel to notify the sender which packets to send. The retransmission
technique has the advantage to uses efficiently the available bandwidth. However, it has the major
disadvantage that led it impracticable. Indeed, retransmission leads to additional delay which
corresponds to the RTT (round trip time) experienced between the sender and the receiver. The
retransmission approach is commonly considered as not useful in case of real-time traffic,
particularly when the network RTT is large. Buffering at the receiver can be used to reduce delay
constraint but it introduces high memory requirement. There exist a new approaches based on
retransmission. For example, lost packets are retransmitted only if they can be playback by the
client. This means that a particular packet must arrive before the deadline time. Many works are
based on this idea [96], [97], [98], [99], and [100]. However, [101] argues that error recovery using
retransmission is not feasible in case of multimedia traffic due to the imposed delay.
3.2.2.2 Forwarding Error Correction
Forwarding Error Correction (FEC) provides a mechanism to rebuilt lost packets by adding
redundant information to the original data stream. The redundant data is derived from the original
data using techniques from coding theory [102]. Many schemes can be applied to implement the
FEC. Parity-based scheme using XOR and Reed Solomon Code are the most important schemes
and are proposed as an RTP payload [103]. These techniques are called media-independent because
the operation of the FEC does not depend on the contents of the packets and the repair is an exact
replacement for a lost packet. In contrary to retransmission approach, FEC-based approach does
not need a back channel. However, sending redundant data consumes additional bandwidth and
can aggrieve the packet losses. Furthermore, it imposes an additional delay and makes the decoder
more difficult for implementation.
FEC can be applied efficiently when knowing the characteristics of the data transmitted. In
case of video, it can be applied unequally, so that important video part are more protected than less
important part, as shown in [104], [105], [106], [107], [108], and [109].
3.2.2.3 Data Interleaving
Data Interleaving is a useful technique for reducing the effects of loss. The sender resequences
the packets before sending them to the receiver, so that originally adjacent packets are
separated by a guaranteed distance. The received packets are returned to their original order at the
receiver. The interleaving disperses the effect of packet losses. This allows avoiding the effect of
burst losses. Thus, error concealment techniques at the receiver will work better on interleaved
packets. The disadvantage of the interleaving is that it increases the latency. This limits the use of
this technique for interactive applications. The key advantage of interleaved is that it does not
increase the bandwidth requirement of a stream.
3.2.2.4 Error Resilience: Application Level Framing and Data Partitioning
We expose, in this approach, two techniques for error resilience (1) Application Level Framing
(ALF) and (2) Data partitioning.
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