Path: utzoo!attcan!uunet!seismo!ukma!uflorida!uakari.primate.wisc.edu!gem.mps.ohio-state.edu!tut.cis.ohio-state.edu!ucbvax!MIRSA.INRIA.FR!Christian.Huitema From: Christian.Huitema@MIRSA.INRIA.FR (Christian Huitema) Newsgroups: comp.protocols.iso Subject: Re: TP0-4 question (novice level) Message-ID: <8910180850.AA05969@jerry.inria.fr> Date: 18 Oct 89 08:49:59 GMT References: Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 26 Juha, you tend to speak too fast, with a bit of a bias against European PTT, and other European bodies in general. It is true that their main argument for not using TP-4 is historical: they specified TP-0 for the TELETEX service back in 1980 and want to "maintain compatibility". Given the failure of the TELETEX service to gain any significant market share (users bought faxes instead), this is a very weak argument. It is also true that their second argument, that of simplicity (TP-0 means 50 times less code than TP-4), does not hold water, as TP-4 codes are already available and just need to be copied. But the real difference is not between TP4 and TP0, it is between CONS and CLNS. In practice, TP-4 codes are distributed in a CLNS environment -- assuming a stateless, fully connected, network. The difference between CONS and CLNS is indeed largely political, as one could very well carry isograms over X.25 virtual circuits. But this will have a cost, i.e. the volume charges of carrying 50 extra bytes of headers per packet, and also paying for extra acknowledge packets: TP ACK are carried as data, and charged for, while X.25 RRs are not accounted. To give an order of magnitude, we have observed that running TCP over IP over X.25 involves approximately 25% of overhead compared to running the application straight over X.25; as our X.25 bill runs here to approx 500,000FF per year, that would mean spending an extra 125,000FF (16000 ECUs, 20000 US$) per year. We would rather not. And the solution for not paying any overhead is called TP-0, not TP-4. Christian Huitema