Packet Reconstruction in
Free Phone
Lost packets are reconstructed in three different ways:
- Using redundant information to reconstruct (at least part of the)
missing information
- Using the previously received packet (i.e. using packet
duplication)
- Using silence
An example of packet reconstruction is shown in the figure
below. The figure shows a sequence of 8 lost packets starting at packet
i+1 and finishing at packet i+8. Packet i is
duplicated as packet i+1. Packets i+2 and i+3 are
replaced with silence. Packet i+4 is a duplication of packet
i+5. Finally, packets i+5 trough i+8 are
reconstructed using the redundant information contained in packets
i+9 and i+10
We do reconstruction by duplication and silence insertion only after
any redundancy has being taken into account. In Free Phone,
we can control the number of frames duplicated and the number of
silences inserted with the following options:
- /a <dups> The maximal number of packets allowed to be
duplicated at the beginning of the lost sequence (i.e after packet
i). The default value is 1.
- /b <dups> The maximal number of packets allowed to be
duplicated at the end of the lost sequence after redundancy (i.e. before
frame i+5). The default value is 1.
- /n <silences> The maximal number of packets of silence
that can be inserted between the duplications. The default value is 3.
Free Phone attempts to reconstruct lost packets first
using redundancy, then using duplication if no redundant information
is available, then using silence if the maximum number
of duplications has been reached. Note that using these
reconstruction techniques does increase the end-to-end
delay.
Last modified Jun 28, 1996.
Your comments are welcome.