Dear Brian;
On Aug 6, 2008, at 6:28 PM, Brian E Carpenter wrote:
On 2008-08-07 08:45, Spencer Dawkins wrote:
This got skipped over ... but since you asked ...
Real-time traffic, including online games, VoIP, videoconferencing,
relies
heavily on UDP, if only to avoid TCP head-of-line blocking.
Huh? Head of line blocking?
TCP provides a reliable, stream-oriented service - so if you drop a
packet, none of the packets that follow the dropped packet can be
delivered to the application until the dropped packet is
retransmitted
and received. So, the sequence number gap blocks all subsequent
delivery
until that happens.
Which is the fundamental weirdness about using TCP to deliver media
streams,
since codecs generally prefer to forget about a dropped packet ASAP
and
just get on with the next packet.
Streaming media (as opposed to video conferencing or VOIP)
typically use large (multi-second) buffers, so they can use even
fairly late packets.
The tcp streaming generally cannot recover from a timeout of the TCP
session, though.
Regards
Marshall
Brian
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