Comcast: Simulating shitty network connections so you can build better systems

Re:Comcast: Simulating shitty network connections so you can... by api on Wednesday January 28, 2015 @04:30PM (#8962665)

P2P doesn't necessarily mean cooperative relaying or swarm distribution like BitTorrent. I agree that those applications are mobile-unfriendly with current batteries and cell networks. It just means you are talking directly to your peers instead of back-hauling to the cloud. You can have P2P where the only traffic you handle is your own. In that scenario total aggregate bandwidth shouldn't be that different from a cloud-backhauled app -- the only difference you'd see is in how many endpoints you're talking to. So instead of seeing 25mb transferred to/from one IP, you'd see it sprayed across a few dozen IPs.

The big hurdles I see are (in no particular order):

- Connection maintenance and keep alive. Basically this is bad, so you want to be more aggressive about shutting down unnecessary P2P links on mobile than you need to on desktop/server. Keep alive requirements generally suck anyway, and are one way NAT murders kittens.

- Restrictions around background tasks on mobile OSes (iOS is particularly onerous).

- Squelching inbound traffic from badly behaved or broken peers to avoid inbound flooding.

- Battery life and related concerns.

I understand it this way: cellular networks currently have their own "netiquette." It includes things like don't be too chatty, try to coalesce instead of spewing packets at excessively random times, etc. These things are less important on wired networks since they don't have the same resource constraints or bandwidth issues.

I guess a related question is why you would do P2P and not backhaul to the cloud? I can think of many:

- Reduced latency for things like AR and VR where latency matters a lot.

- Reduced bandwidth cost due to lack of back-haul, and back-hauling a pic being sent between two people in the same city 2000 miles to a cloud server is just offensively stupid anyway.

- Privacy and security.

- With P2P you could have a more open app model where apps aren't wedded to proprietary cloud infrastructure. They still work even without someone's cloud, etc.

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Re:Comcast: Simulating shitty network connections so you can... by exelius on Thursday January 29, 2015 @12:47PM (#8967671)

If you're talking about P2P over cellular, I think it's just in general a bad idea. The way cellular networks are operated, you can't do device-to-device connections - they have to go through the tower for a number of (very good) reasons. That's where the latency comes in, and the wireless transmission latency can be an order of magnitude higher than the latency on a cross-country connection. Furthermore, the resource that is constrained is the amount of available spectrum - so we need to optimize for that. Bandwidth is effectively infinite from the tower to the cloud, but bandwidth from the tower to the device is the constraint.

P2P over non-cellular (i.e. Wi-Fi or Bluetooth) where you can actually make a direct device-to-device connection seems like it may have some use cases (messaging apps, etc.) But they're edge cases and by no means a common use case because it just isn't reliable enough.

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