[ns] ParePool/ProxyTrace Server Problem and effect on Average Client Latency

[Anino Reyes]

Here is my topology below:

Clients   Single Web Cache        Outer Router   Servers
CCC============E=======================O============SSS
  100mbps 1ms       10 mbps 100 ms       100mbps 1ms 

*All links are duplex.


I have 72 client computers (CCC) connected to a single cache server (E)

for { set i 0} { $i <72 } { incr i }{
 $client($i) connect $cache
}

I also connect the cache (C) to N servers (SSS)

for { set i 0} { $i < $N } { incr i }{
 $cache connect $server($i)
}


and start each client to connect to all N servers using a nested for loop

 $client($i) start-connection $cache $server($j)

Then, I use PagePool/ProxyTrace and a proxy trace file to simulate actual request from our proxy server. I also defined client num as 72, but there is no way to define how many servers are needed.

The problem is that in my simulation, the more servers I add, the lesser the average latency of the client request. It seems there is a bottleneck somewhere in the simulation that I can't seem to find. The 10 mbps link is not congested so the bottleneck is not in the network topology. I looked at the source code for the HTTP/Cient , Http/Server and HTTP/Cache and it does not limit the number of connections per server per client.

Here is a table regarding the average latency during a 1 hour test period with varying number of Servers.

============================================================
Servers	Ave. Latency	Max Latency	Size of max latency
============================================================ 
1	44.273616178936	194.75787848001	63958 bytes
2	19.054615947881	76.160913280016	27259 bytes
3	6.8249151116920	43.515350479991	1958 bytes
5	2.6904748712405	40.750138319997	2026007 bytes
10	1.4624603352714	41.162682479988	2026007 bytes
25	1.1519090774774	40.951985199996	2026007 bytes
50	1.0554587133410	41.318702239997	2026007 bytes
72	1.0247390695315	41.328403759997	2026007 bytes
100	0.9999169117431	41.315464239997	2026007 bytes
500	0.9304826117915	41.332590639997	2026007 bytes
1000	0.9044198998673	39.927294799988	2026007 bytes

Is there a limit to the number of request in a single TCP connection/wrapper when a client connects to a Server?

How can I simulate N number of servers into a single server node using Pagepool/ProxyTrace without affecting latency? It is cumbersome and unrealistic to simulate all Servers in the Internet this way. 

Thank you for your time and consideration.


Richard Reyes
Instructor