On Mar 18, 2009, at 6:06 PM, Robin Whittle wrote:
End-to-end transparency (the packet received is identical to that sent, including its source and destination addresses, but not including hop limit etc.) is a major component of the Internet's flexible and open-ended nature.
I'm actually of a slightly different opinion. I think it is important that one application instance be able to select another application instance, or a set of them, and send packets to all of those applications, one of them, or a specific one as it requires. That doesn't mean that the process knows anything about what is happening below the application layer; in fact, that would be about naming those application instances, and the fact that it can name and exchange sessions with sets of applications that it is authorized access to implies nothing further than that.
I also think it is important that one transport endpoint be able to select another transport endpoint, or a set of them, and send packets to all of those transport endpoints, one of them, or a specific one as it requires. That doesn't mean that the transport endpoint knows anything about what is happening below the transport layer beyond a string of bits that it uses to identify the far end; in fact, that would be about addressing those transport endpoints, and the fact that it can address and exchange datagrams with sets of transport endpoints that it is authorized access to implies nothing further than that.
The fact that a system, and by extension the applications and transports on it, can identify other systems by name or address is the critical bit, not that every system in the network uses the same name or address. If that were not true, multi-named systems and multihomed systems would be a problem, as would multicast and anycast.
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