Re: Asymmetric TCP/ATM throughputs between client and server

Alain Kaminski (Alain.Kaminski@bbl.be)
Fri, 27 Mar 1998 13:11:39 +0000

At 04:47 27/03/98 -0500, you wrote:
>Hi,
> I wonder if anyone has encountered a similar problem before. I have
>obtained different throughput readings when transferring data between a
>client and a server from both directions. I am talking about a different
>of about 50 times in magnitude. This happens when I use the TCP/IP over
>ATM and the default ATM MTU of 9188 on two Sun's running Solaris. When I
>set the ATM MTU to 65535, the problem goes away.
>
> I suspect there is some kind of deadlock and time out ocurring. Some
>papers discuss a throughput deadlock situation which could happen in
>TCP/IP over ATM environments. I'm not sure if this is the case because it
>cannot explain why it occurs in one direction only.
>
> To help understanding the problem more, I measured the time taken for
>each individual read or write call in both directions. 10 chunks of 8KB
>data were sent in each case.
>
>Client -> Server
>----------------
> (server read) (client write)
>1 0.000867 0.000739
>2 0.000634 0.000471
>3 0.000759 0.000387
>4 0.002860 0.001939
>5 0.000863 0.000356
>6 0.000697 0.003460
>7 0.001868 0.000968
>8 0.000612 0.000403
>9 0.001159 0.002203
>10 0.000922 0.000489
> ----------------
> Total: 0.011424 second
>
>Server -> Client
>----------------
> (server write) (client read)
>1 0.000707 0.052361
>2 0.000948 0.043168
>3 0.000406 0.050055
>4 0.092609 0.050401
>5 0.000859 0.049735
>6 0.099258 0.049865
>7 0.000422 0.049974
>8 0.099437 0.050011
>9 0.000362 0.049966
>10 0.099599 0.050677
> ----------------
> Total: 0.496438 second
>
>As far as I know, the throughput deadlock is a result of the presence of
>the delay acknowledgement at 200ms time intervals, which does not seem to
>relate to my case. I hope someone may know something about this.
>
>Thanks in advance,
>Edwin.
>
>
>

Hi Edwin,

Can you also tell us more about the ATM traffic class and parameter values
you are currently using during your test for both directions.

I've been doing ATM measurements myself with NTs and I never measured such
unbalanced performances.

Alain.

_______________________________________
Alain KAMINSKI - Bank Brussels Lambert
ASO-TEL/NCS (Telelift 23)
60 Cours Saint Michel
1040 Brussels
BELGIUM
Phone (direct) : + 32 2 738 29 99
E-mail : alain.kaminski@bbl.be