Sam Stickland wrote: > > Ted Hardie wrote: >> Fred Baker writes: >> >> >>> Hence, moving a file into a campus doesn't mean that the campus has >>> the file and will stop bothering you. I'm pushing an agenda in the >>> open source world to add some concept of locality, with the purpose >>> of moving traffic off ISP networks when I can. I think the user >>> will be just as happy or happier, and folks pushing large optics >>> will certainly be. >>> >> >> As I mentioned to Fred in a bar once, there is at least one case >> where you have >> to be a bit careful with how you push locality. In the wired campus >> case, he's certainly >> right: if you have the file topologically close to other potentially >> interested users, >> delivering it from that "nearer" source is a win for pretty much >> everyone. >> This is partly the case because the local wired network is unlikely >> to be resource >> constrained, especially in comparison to the upstream network links. >> >> In some wireless cases, though, it can be a bad thing. Imagine for a >> moment that >> Fred and I are using a p2p protocol while stuck in an airport. We're >> both looking >> for the same file. The p2p network pushes it first to Fred and then >> directs me to get >> it from him. If he and I are doing this while we're both connected >> to the same resource-constrained base station, we may actually be >> worse off, as the >> same base station has to allocate data channels for two high data >> traffic >> flows while it passes from him to me. If I/the second user gets the >> file from outside the pool of devices connected to that base >> station, in other words, the base station , I, and its other users >> may well be better off. >> > A similar (and far more common) issue exists in the UK where ISPs are > buying their DSL 'last mile' connectivity via a BT central pipe. > Essentially in this setup BT owns all the exchange equipment and the > connectivity back to a central hand-off location - implemented as a > L2TP VPDN. When the DSL customers connects, their realm is used to > route their connection over the VPDN to the ISP. The physical hand-off > point between BT and the ISP is what BT term a BT Central Pipe, which > is many orders of magnitude more expensive than IP transit. > > In this scenario it's more expensive for the ISP to have a customer > retrieve the file from another customer on their network, then it is > to go off net for the file. > > (LLU (where the ISP has installed their own equipment in the exchange) > changes this dynamic obviously). > > S
Also bear in mind that many wireless systems have constrained uplink capacity and anything P2P can quite happily kill a wireless network by using up too much uplink resource. -- Leigh Porter
