On 03/07/07, Brian Butterworth <[EMAIL PROTECTED]> wrote:
The whole point of using peer-to-peer networks is that after the first copy is grabbed from the initial seeder, all other clients grab their "blocks" from other peers, not the initial seed. The clients are designed to collect the least-available blocks from the network first, which causes them to no longer be the least available.
But the problem is that in practice, demand for a file is very high initially and tails off quickly - which means that the original seeder is flooded with a lot of requests at the same time. A case in point is the way that Blizzard uses P2P to release patches for World of Warcraft. Because the number of seeders initially (when there is highest demand) is very low, there is a huge demand from everyone trying to download around the same time. As anyone who's played WoW will tell you, the best way to get anything on patch day is for one person to download it, and everyone else download it directly from them, ignoring P2P completely. Given that iPlayer compresses demand into a seven-day window, I'd imagine that situation is actually going to be replicated very widely for popular programmes.
Of course. One advantage of peer-to-peer networks of this type is that the clients can grab files from the clients that appear "closest" on the network, which means the communications are often local, metropolitan, national well before they go onto the slower international links.
Actually, the international links are often faster, thanks to the vast cross-Atlantic bandwidth. It's more often local links which are slow. Grabbing a file from someone in New York on an academic server (with a nice fat pipe) is going to be a lot faster than getting something from someone down the road using a 2Mb down/256Kb up broadband connection. TCP/IP is specifically designed to share bandwidth, and that's what it will
do.
TCP/IP on its own is actually incredibly inefficient at sharing bandwidth. Because all TCP/IP packets are created equally, it doesn't know the difference between a packet containing voice data (which needs to get to its destination promptly) and one containing email data (which can be delayed by a few seconds without any meaningful damage). If you were designing a protocol from scratch for bandwidth efficiency and considering quality of service, it would look very different from TCP/IP. That's why solutions like MPLS are used, effectively enclosing TCP/IP packets which additional information describing what the packet contains and how routers should treat it. The job of your ISP is to provide you with bandwidth - that is their job.
Remember just because you have some crappy copper providing slow ADSL to your home, the backbone fiber network has an unlimited speed and capacity (in theory).
Unfortunately, backbones don't have unlimited bandwidth even in theory - and, in practice, the demands on them are growing faster than additional bandwidth can be added. That's why providers run their own backbones are utilizing Next Generation Networks based on MPLS, so they can categorize traffic and ensure quality of service for all their users.
Thus everyone moaning about the iPlayer!!!! If we are paying for distribution, the BBC's restrictions are offensive!
No, they're not. In fact, here's a better deal: No iPlayer at all, and in five years time you can pay Sky for the privilege of watching TV over the internet. I assure you that they'll charge you a whole lot more.
