From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Carlson Date: Thu, 30 Jun 2005 15:36:29 +0000 Subject: Re: PPP Encapsulated in GRE with IP Precedence headers Message-Id: <17092.4477.875971.589942@gargle.gargle.HOWL> List-Id: References: <20050630051424.GA13477@digitalpath.net> In-Reply-To: <20050630051424.GA13477@digitalpath.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ppp@vger.kernel.org Ray Van Dolson writes: > > If it's just plain IP over PPP, and you're not negotiating any of MP, > > ECP, CCP, VJ Header Compression, or Robust Header Compression, then > > you should be able to get away with this. The above protocols, > > though, generally assume strict ordering (it is point-to-point, > > right?) and will fall apart if that's compromised. > > Unfortunately we are using MPPE, so perhaps this solution is not as viable as > I thought it would be. Thanks for the clarification. I did say "generally." If the actual compressor/encryptor is able to deal with multiple session states for the separate flows that can be scheduled independently, then this could still work. But I don't see that MPPE (in particular) can do that. It has just one 'coherency count' field, and doesn't seem to maintain multiple histories. Unless there's buffering and reordering done at the receiver (which would pretty much nullify any goodness you might hope to get from priority queuing), I think you're sunk. An alternate path that might do the job would be to set up multiple parallel PPP sessions (one for each distinct ordering class), and direct the traffic on entry from IP into PPP based on DSCP. Though it looks feasible from the protocol level, that might take some doing depending on the implementations involved. (In practice, I haven't been any too impressed with prioritization schemes that do more than just make sure that network control traffic has highest priority. And even then there are some interesting failure modes ...) -- James Carlson