[asterisk-dev] [IAX] ping time calculations

[Yousf Ateya]

One of the ways in which IAX calculates peer ping time is using
POKE/PONG/ACK sequence as follows:

- Peer1 sends POKE (frame timestamp is time of sending)
- Peer2 sends PONG with same time stamp received from POKE.
- Peer1 calculates ping time by doing: pong_reception_time - poke_send_time.

While using a shaky connection, sometimes ping time changes from normal
~100ms to long ping time (~2 seconds, sometimes get TOO LAGGED) for one
ping and returns to normal again.

This happens because of packet loss. Here is what happens:

- Peer1 sends POKE (it mark sending time stamp in channel member `offset`)
- POKE packet is dropped
- After sometime (qualify / 2), POKE is retried.
- Peer2 receives the POKE packet and sends PONG.
- Peer1 receives the PONG packet, and calculates ping time =
pong_receiption_time - first_poke_send_time

So ping time becomes high for short period because of a packet retry, not
because the network is slow.

Is it better to calculate ping time = pong_receiption_time -
last_poke_send_time? So we get **actual** network ping time instead of
network_ping_time + packet_retry_time.
-- 
Yousf Ateya,

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