Date: Wed, 17 Jan 1996 11:08:27 -0700 From: Nate Williams <nate@sri.MT.net> To: kline@tera.com (Gary Kline) Cc: questions@FreeBSD.ORG Subject: Re: delays in ppp solved Message-ID: <199601171808.LAA08626@rocky.sri.MT.net> In-Reply-To: <9601171721.AA01331@tera.com> References: <199601171517.IAA00439@intele.net> <9601171721.AA01331@tera.com>
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[ Assertion that modem compression is a 'bad-thing' ] > So, what's the bottom line, Gentlemen? Should > I disable compression with my user-ppp; and how? > > A few days back I ftp'd back a *.zip file and my USR 28.8 > gave me a comparitively good 3.2Kbps rate. The ``CS'' LED > flashed on the modem. (I don't know why... ) I tested > the transfer rate with the same file compressed with gzip. > The CS light was steady and the transfer rate fell to 2.9K. > > To me this could mean that the EEPROM in the modem recognized > the *.zip compression and let it through. And it wasn't > intelligent enough to recognize the *.gz compression. > > Or?? Or other data was going on. I don't have the 'bottom' line, but I will give the experiences of SRI-Montana. We have USR-Sportster 28.8K modems at both ends of our link, if that matter. We ran w/out modem compression for the first 6 months last year, and with compression on for the last 6 months of last year. After doing both, we are leaving modem compression on. For most of last year we were using MorningStar PPP on a SunOS4 box, but moved to a FreeBSD box after our ISP switched to a Livingston Portmaster. Having used both, I found that the latency increased *slightly* (~15ms or about 10%) and throughput for most traffic was about 25-35% better. Since most of the traffic is sent through uncompressed (we have a full-time link, and get lots of email *grin*), we decided that the extra latency was worth the extra throughput. However, the link to SRI-CA is about 300ms on a good day (a little under half of that is from our PPP link), so adding a couple percentage more latency didn't seem to effect our work. Your milage may vary, but it depends on what's important to you. I also use compression on both modems on my link at home, and I don't notice the latency at all and I *really* appreciate the extra throughput when doing non-compressed transfers, and don't notice the little extra delay with compressed files. If you have a mix of compressed/non-compressed data going over your lines, I suspect enabling modem compression is a good thing. At least I think so. :) Nate
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