Monday, November 17, 2008

A Delay-Tolerant Network Architecture for Challenged Internets

This paper begins with the statement mostly-disconnected networks cannot participate directly in most internet protocols because those protocols were not designed for this regime. The paper then proposes a dramatic architectural shift which leaves no layer untouched. The architectural idea is that each network in a challenged regime has already been optimized with naming and configuration mechanisms designed for the particular space developed. Thus [it is claimed] what is necessary is a new layer of glue consisting of a new generalized naming layer and set of gateways to bridge between these challenged networks like military ad-hoc networks or sensor networks and other, more reliable networks like the internet. This paper proposes a lot in eight pages.

Without going further, I think it's worth bringing up what I think is the central architectural fallacy of this paper: a new naming layer is necessary to support these protocols. The reason this is a fallacy is that we already have such a layer which is incredibly general and imposes none of the semantics which this paper seems to view as problematical. It's called IP. While I agree that below IP the link layers differ, within IP routing differs, and above IP transport cannot remain the same, the fact is that IP presents a naming mechanism which seems no worse then what is proposed here. We already have a name for "DTN Gateways": routers.

The paper does have a number of bright spots. They do consider SMTP as valuable prior work, although noting that static mail relays will never work in a mobile environment. It also correctly discards application layer gateways as blemishes on a network architecture as they spread application code throughout the network.

If you examine the set of tasks presented in section 4 like path selection, custody transfer, and security, the issues sound no different then what would be expected for bringing the internet to a new network layer, and so I would concluded that the paper doesn't really succeed in making the case for a wholesale architectural shift; as is noted in the conclusion, an evolutionary approach of better link technologies and more adaptive internet protocols seem likely to solve the problem this paper addresses.

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