TCP Performance

Blake Dunlap ikiris at gmail.com
Tue Aug 27 14:32:23 UTC 2013


You didn't indicate this, but do you understand how TCP windowing works?
This conversation can go two very different ways depending on the answer.

To me, it looks like this is what you'd expect, and you need to fix your
packet loss issues, which possibly might be QoS settings related (but it's
hard to tell based on the information given).

-Blake


On Mon, Aug 26, 2013 at 2:07 PM, Nick Olsen <nick at flhsi.com> wrote:

> Greetings all, I've got an issue I was hoping to put a few more eyes on.
>  Here's the scenario. Downloading a file at our Border is multiple orders
> of magnitude faster then a few hops out. Using the same 128MB test file, I
> tested at two different locations. As well as between them. Using multiple
> connections improves throughput, However it's the single stream issue we're
> looking at right now. All testing servers in question are Centos Linux.
>  Orlando Datapath: Cogent>Orlando Border Router (Mikrotik)>HP Procurve
> Switch> Server Results: 2013-08-29 05:04:09 (52.6 MB/s) - `128mbfile.tgz'
> saved [127926272/127926272]
>  Cocoa NOC Datapath: Cogent>Orlando Border Router (Mikrotik)>Licensed
> Microwave Link (300+Mb/s Capacity)>East Orange Router (Mikrotik)> Licensed
> Microwave Link (300+Mb/s Capacity)>Cocoa Router (Mikrotik)>Licensed
> Microwave Link (300+Mb/s Capacity)>Colo Router (Mikrotik)>NOC Router
> (Mikrotik)>HP Procurve Switch>Server Results: 2013-08-26 13:42:25 (398
> KB/s) - `128mbfile.tgz' saved [127926272/127926272]
>  Orlando-Cocoa NOC Datapath: Orlando Server>HP Procurve Switch>Orlando
> Border Router (Mikrotik)>Licensed Microwave Link (300+Mb/s Capacity)>East
> Orange Router (Mikrotik)> Licensed Microwave Link (300+Mb/s Capacity)>Cocoa
> Router (Mikrotik)>Licensed Microwave Link (300+Mb/s Capacity)>Colo Router
> (Mikrotik)>NOC Router(Mikrotik)>HP Procurve Switch>ServerResults:
> 2013-08-26 13:56:25 (3.31 MB/s) - `128mbfile.tgz' saved
> [134217728/134217728]
>  Now, For the fun of it. I ran Iperf single TCP between our Cocoa and
> Orlando POP's. Just like the HTTP test above. (Server has a 100Mb/s port).
> It maxes out the port, Unlike the HTTP test.
>  [root at ded01 ~]# iperf -c
> 208.90.219.18
> ------------------------------------------------------------Cli
> ent connecting to 208.90.219.18, TCP port 5001TCP window size: 16.0 KByte
> (default)------------------------------------------------------------[  3]
> local 206.208.56.130 port 47281 connected with 208.90.219.18 port 5001[
> ID]
> Interval       Transfer     Bandwidth[  3]  0.0-10.0 sec   114 MBytes  95.7
> Mbits/sec
>
> Here's associated packet captures for each transfer. As well as full wget
> output and traceroutes for each test. As you can see, The tests crossing
> the wireless links show about 3x more TCP re-transmits/dup ACK's. But I'm
> not sure I'm sold this could show such a huge drop in throughput. Other
> then that, nothing really stands out to me as to why these transfers are so
> much slower. Intra-network iperf testing shows full throughput the whole
> way with single connection. As well as UDP testing. One thing to note is
> the Iperf testing has far less TCP re-transmit/dup acks then any of the
> HTTP testing, Crossing the same Microwave Links and routers.
> http://cdn.141networks.com/files/captures.zip
> I appreciate any insight anyone might have. Thanks!
>  Nick Olsen
> Network Operations (855) FLSPEED  x106
>
>
>


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