[Ti] A real world comparison

[Dennis Fazio]

--On June 10, 2005 01:05:19 PM -0500 Shawn King <shawn at yourmaclife.com> wrote:

>  No one seems to know what the hell UDP is or why the hell Apple
> defaults back to it.

UDP (User Datagram Protocol) is the alternative transport to TCP 
(Transmission Control Protocol). They both run on top of IP (TCP/IP or 
UDP/IP).

TCP allows flow control via receiver/sender feedback and error recovery 
(packets that fail to show up are resent). The vast majority of Interent 
traffic is TCP/IP. UDP is a simple stream; packets are sent off in a stream 
with the expectation that they will just get there.

UDP is the preferred protocol for streaming and broadcasting for video and 
voice, because the acknowledgements and retransmits can interfere with 
isochronous (time-critical) packet streams.

HTTP is a higher level protocol than runs on top of TCP/IP to mostly serve 
web content, so it's a little puzzling to me how it can be described as an 
"alternative" to UDP. They are at different levels of the protocol stack. My 
guess is that HTTP selects HTTP on TCP/IP, which turns on the flow 
control/resend ability of TCP plus the upper layer communication intelligence 
of HTTP. Thus if there are a lot of dropped packets from a poor or congested 
connection, the  more complex sender/receiver communication and packet 
resends likely allow the Quicktime player to get its act together better to 
determine the proper flow of video information, process it and display it. 
But that's just my guess without any real research.

-- 
Dennis Fazio, TIES
Director, Technical Services
651-999-6201
-- 
Dennis Fazio
dfz at mac.com