Subject: Re: [lemonade] Wireless latencies

From: Randall Gellens <[email-masked]>
Date: Thu, 12 Jun 2003 16:22:49 -0400

At 9:50 AM -0500 6/11/03, Greg M (Greg) Vaudreuil wrote:

>  My earlier message was incorrect.  Below I suggest an average RTT 
> of abount 100 ms, or a simple message submission time using 
> SMTP-submit of about 1 second.  My measured experience using a CDMA 
> data network has an average RTT of 1200 milliseconds (100 samples), 
> or about 10 seconds to send a short message using a separate SMTP 
> connection, or about 1-2 seconds using an existing IMAP connection. 
> There is good bandwidth at that RTT if the app uses it effeciently. 
> This longer RTT is consistent with other literature I have seen on 
> the subject.

The round-trip times can vary considerably, depending on a number of 
factors, including the specific options supported by the 
infrastructure, the service options requested by the handset, the 
packet sizes, the amount of interference, etc.  However, 1200 ms 
seems quite high.  It should be more like 120-140 ms.  (Plus 
processing time by the endpoints, but that shouldn't vary that much 
for wireless versus wireline.)  For example, opening a TCP connection 
(40-byte packets) would be 3*120 or 3*140 ms = 360 to 420 ms.  The 
numbers would be somewhat lower (faster) if certain service options 
are used.  Going to hosts outside the carrier's network will be 
somewhat higher (slower) of course.  In some recent tests, 280 ms 
averages were seen for18 byte pings (18+28byte header = 40 bytes) to 
www.google.com.

-- 
Randall Gellens
Opinions are personal;    facts are suspect;    I speak for myself only
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Every man thinks God is on his side.
The rich and powerful know he is.
                     --Jean Anouilh
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---

From: Mark Crispin <[email-masked]>
Date: Fri, 13 Jun 2003 10:08:20 -0700 (PDT)

On Thu, 12 Jun 2003, Randall Gellens wrote:
> > My measured experience using a CDMA
> > data network has an average RTT of 1200 milliseconds
> seems quite high.  It should be more like 120-140 ms.

I have to agree.  If this is the performance of CDMA data networks, then I
think that I'll stick with CDPD!  :-)

For what it's worth, PC Pine (using full IMAP and SMTP) works quite well
over CDPD.  I use it all the time.  The only time I have a problem is when
the ferry boat makes its turn and I lose the signal...

-- Mark --

http://staff.washington.edu/mrc
Science does not emerge from voting, party politics, or public debate.
Si vis pacem, para bellum.
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