Date: Fri, 19 Mar 2010 16:59:27 +0100 (CET) From: Harti Brandt <hartmut.brandt@dlr.de> To: Atis <the.kfx@gmail.com> Cc: FreeBSD-hackers@freebsd.org Subject: Re: Google Summer of Code 2010 ideas Message-ID: <20100319165409.Y37887@beagle.kn.op.dlr.de> In-Reply-To: <7f9bf5711003190850i6052ab2i1273754d207003f0@mail.gmail.com> References: <7f9bf5711003190636k1aab3r2adce891e9acaad@mail.gmail.com> <20100319152014.T37887@beagle.kn.op.dlr.de> <7f9bf5711003190850i6052ab2i1273754d207003f0@mail.gmail.com>
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On Fri, 19 Mar 2010, Atis wrote: A>On Fri, Mar 19, 2010 at 4:25 PM, Harti Brandt <hartmut.brandt@dlr.de> wrote: A>> Hi, A>> A>> On Fri, 19 Mar 2010, Atis wrote: A>> A>> A>2) SCPS, Space Communication Protocol Standards A>> A>This is probably my first project choice if all goes well. Space A>> A>protocols - this sounds very cool :) and is related to my research A>> A>interests (IP protocols over lossy networks). The first question is - A>> A>do these protocols also have some practical value? This is not-so-new A>> A>family of protocols, but it seems that very few implementations exist. A>> A>On the one hand, this could be a good thing, because now there a A>> A>chance for FreeBSD to be the first OS with open source SCPS A>> A>implementation. On the other hand - lack of use seems to imply lack of A>> A>importance and usefulness. The second question - is complete A>> A>implementation of all the protocols supposed? At first glance it seem A>> A>that e.g. SCPS Security Protocol simply duplicates the functionality A>> A>already present in IPSec. Still, support for all protocols may be A>> A>needed for interoperability and completeness of the implementation. A>> A>Also, the amount of work required for this project is very unclear at A>> A>the moment. A>> A>> Acctually the definition of these protocols has been taken over by CCSDS A>> (ccsds.org). I think they are now in some of the green or blue books A>> (cannot remember the color). There is some heavy push in the satellite A>> community on moving towards CCSDS protocols so, for sure, there is A>> practical value in the corresponding communities. I cannot answer the A>> question to what extend an implementation is required. I know that we have A>> some activity in the lower layers and that the upper layers are also used A>> (file transfer, for example). Don't know about networking and security, A>> though. A>> A>> harti A>> A> A>Thanks for the reply. Looks like I will cross this project out from my list. A>I have found that there is even a reference implementation of SCPS protocols: A>http://www.openchannelsoftware.com/projects/SCPS. A>It's usable from FreeBSD too, because they have implemented everything A>in userspace, probably to achieve portability. I wonder whether it A>would make sense to rewrite it or some parts of it (TCP "performace A>enchancing proxy" is the interesting one) for kernel mode. A>Theoretically, that should mean better latency, and no data copy A>overheads, right? But then again, satellite link bandwidths probably A>are too small to make such improvements important. PEPs are a big issue for the satellite people. With DVB-S2 over a 40MHz transponder you can get 60-80MBit/s if you have good whether. With a RTT of 600ms or more getting TCP to an acceptable speed gets quite tricky. Of course not all people can afford a full transponder, but even a shared link DVB-S2 + RCS requires tuning... I don't know what bitrate you can get in a Docsis system, but I would assume that it is comparable. There are also a lot of commercial users of different VSAT systems, but I have no idea what the share of FreeBSD is in these systems. harti
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