(Changing subject again, since this has strayed from the baseline thread) On 02/26/11 19:47, Bernard Aboba wrote:
Silvia Pfeiffer said:
"I doubt both of these statements about HTTP are true any longer."
[BA] In fact, they haven't been true for quite a while.
Every day users participate in interactive sessions over HTTP, largely in circumstances where use of UDP media is not possible. Because of the prevalence of highly restrictive enterprise firewalls that do not permit passing of UDP, the ability to support realtime communications over HTTP is now considered a practical requirement for business-oriented services, such as web conferencing.
Although realtime communications over HTTP is largely used as a fallback, measurements show surprisingly high audio quality in the majority of sessions, probably because many sessions take place over well-provisioned enterprise networks.
The Google Talk numbers I've seen published elsewhere are that ~5-10% of sessions run over TCP, relayed through a server, because UDP doesn't get there. The reasons to prefer point-to-point UDP if possible include: - Much lower delay when the endpoints are close to each other, network-wise - Much cheaper provisioning for the service provider The lower delay is the factor with the largest impact on comfort of conversation, I think; as long as we don't encounter congestion, the audio quality shouldn't be that much different. When we encounter congestion, audio-over-TCP will experience this as jitter, while audio-over-UDP will experience this as packet loss, so the experience may be different. There are many tricks available for lessening the impact of both.