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From Dirk Stöcker <apa...@dstoecker.de>
Subject [users@httpd] Apache Proxy data delay question
Date Wed, 23 Sep 2009 15:38:41 GMT
Hello,

I already tried that question two weeks ago and till now got no answer. 
Either nobody can help me (which would be bad) or it was overlooked, so I 
try once again.

I have a general problem with proxy redirects on one of my servers and I'm 
out of helpful documentation to solve the issue. The described situation 
is no a single setup, but I try to find a general solution for this topic. 
I was one of the authors of NTRIP 2.0 standard and I search a way to say
- "here, that's the way to have secure data transfer", so we don't need to
   extend the standard to do so and
- "use this to allow NTRIP on port 80 where also you webserver is
   running".

Situation:

- There is an NTRIP-Caster (this is a special purpose HTTP server) running
   on port 2101 of the machine.
- On Port 80 (and 443 for HTTPS) is an Apache.

The Apache now should pass request to a virtual domain through to the local 
2101 port and deliver results. It also should do the HTTPS encryption. 
Generally this all works, but the delays are much to high for real-time data.

NTRIP is a system which has usually very low data rates but requires low 
latency.

I use following configuration:

<VirtualHost *:80>
       ServerName xxx
       <Directory proxy:*>
          Order deny,allow
          Allow from all
       </Directory>
       ProxyPass / http://xxx:2101/ flushpackets=on
       ProxyIOBufferSize 128
       ProxyReceiveBufferSize 512
</VirtualHost>
<VirtualHost *:443>
       ServerName xxx
       SSLEngine on
       ...
       <Directory proxy:*>
          Order deny,allow
          Allow from all
       </Directory>
       ProxyPass / http://xxx:2101/ flushpackets=on
       ProxyIOBufferSize 128
       ProxyReceiveBufferSize 512
</VirtualHost>

According docs flushpackets=on should cause immediate flusing and also the 
reduced buffers should help, but still I have several seconds delay in the data 
which is to much. Delays in the range of 1 or 2 seconds would be the maximum I 
can accept.

I can change the source code of the NTRIP-Server, so additional header lines 
speeding up the transfer would be possible. The server sends data in chunked 
transfer mode and sends on TCP-packet for each chunk.

Any helpful hint would be greatly appreciated. Or suggestion where to get 
the help I need when nobody can help me here.

Ciao
-- 
http://www.dstoecker.eu/ (PGP key available)


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