January 15, 2004

What is wrong with NATs?

Martin Geddes has an entry regarding NATs and its impact on end-to-end application. His final three sentences are jarring: “The market has spoken. Get used to it. Move on.” I would like to review some of the points he makes in his entry, a paper by Andrew Odlyzko that he refers and a paper by Blumenthal and Clark that Odlyzko refers. The question is has the market really spoken, if so what is its message and finally are the service providers hoodwinking the consumers into an architecture that is contrary to everybody’s expectations.

Martin notes that consumers like to use NAT because “it just works” for those users who use only web browsing and email. Others who want to avoid NAT just have to pay extra to get additional public IP addresses. This is analogous to business class customers paying extra unlike economy class passengers in an airline. As far as VoIP is concerned, SBC is a proven way to address the NAT traversal problem. Even though Skype does not say it openly, its solution is effectively based on SBC; except that the SBC function is implemented in fellow members’ (who happen to be in the public Internet) computers. So there are no insurmountable problems with customer owned NATs.

Now consider the case where the ISP is deploying NATs, meaning the subscribers “get a pre-NATted private IP address”. Andrew suggests that historically there are incentives for ISPs to move towards “price discriminate”. Blumenthal and Clark agree as well. The motivation seems to be the pot of gold called voice (is that why it used to be called “POTS”?). If this happens, then Skype’s solution will be in trouble because there are not enough members in the public internet to support the vast number of “NATted” members. In my reading this is the problem anticipated by Speak Freely.

Those ISPs who provide only private IP addresses to their subscribers are breaking the end-to-end model. Tough luck? No way. The service providers would like to keep the Internet unregulated because the technology fosters competition. But isn’t this an anticompetitive behavior? Aren’t they behaving like traditional telecom providers in the sense that they are artificially keeping their resources (IP addresses) scarce? This is the reason ISP based NATs are bad; not because it is ideologically incorrect. My appeal is that we have to ensure end-to-end nature is not hindered by the service provider, because this is the aspect that makes Internet competitive.

Posted by aswath at January 15, 2004 01:23 AM
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