From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jar Date: Sun, 16 Nov 2008 16:20:31 +0000 Subject: Re: ppp0 and it's txqueuelen with HSDPA gsm modems Message-Id: <4920484F.4060100@pcuf.fi> List-Id: References: <48FE2309.3060907@pcuf.fi> In-Reply-To: <48FE2309.3060907@pcuf.fi> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ppp@vger.kernel.org Lie Arne wrote: >> What would be "optimal" value for ppp0 device's txqueuelen, >> when it is used with HSDPA gsm modem for link which downlink >> speed is 1Mbit/s and uplink speed is 384kbit/s and ping >> ~80..100 ms? Is the default value 3 just OK? >> >> -- >> Best Regards, Jar > > I would suggest using normal TCP calculation, i.e. that you dimension > the txqueue size after the "BDP rule": bandwidth x delay product. Using > your outbound numbers this is: > 1,000,000 x 0.1 = 100,000 bits = 12,500 bytes. Assuming 1500 byte > packets, this is txqueue = 12,500 / 1500 = 8.3 packets. So you could try > txqueue size in the region 8-10, this should prevent queue starvation at > packet drop events caused by traffic overload, even if you only have one > single TCP flow. OK, thanks. But is txqueuelen for transmit data only and then the downlink value (384kbit/s) should be used in the calculation? With 384kbit/s the txqueuelen would be 3.2 which is quite same as ppp0 default 3. -- Best Regards, Jar