Seamlessly switching from one wifi network to another

[M0RPH]

You would think that this would be seamless. I'm downloading from a file sharing site like Rapidgator, the type of download that doesn't support resuming. I'll be 3/4 done with my download and I need to leave the wifi hotspot, so I figure I'll just turn on my phone's own wifi hotspot and tether to complete the download. Nope, the download breaks as soon as I try to switch wifi connections. Why can we not seamlessly switch wifi connections without having network connections break? Seems like something that should have been built into the wifi protocol.

 

[Mushkins]

Because you're given a brand new IP address from a brand new router (in this case your phone) and you're on a totally different network. It's not something they *could* build into the Wifi protocol, it's a routing issue on top of a TCP/IP issue and there's simply no device-side solution to the problem you described. Its up to the server to manage the session for that connection, Rapidshare would need to design their infrastructure and connectivity to support interrupted sessions and that sort of roaming, essentially giving you some sort of cookie that expires after say, 10 minutes, and regardless of your IP address/network would let you resume your download.

They specifically dont do that because their business model is built around promoting premium accounts with advanced download features (like resuming interrupted downloads) and unlimited downloading. A session cookie system like this would be rampantly abused by people with premium cookies sharing them with people so they dont have to pay for premium accounts. In fact, cookie sharing already goes on quite frequently with people just looking to get free premium access even If you're downloading via bittorrent, for example, and you do that handoff you still lose connectivity for a moment, but the bittorrent client still has that list of IP addresses you were connected to and just reconnects to them because the protocol, the client, and the server (the tracker) were designed with this functionality in mind.

The only way to do a truly seamless WiFi handoff is if your handing it off between two access points on the *same* network, such as in an office building, and only then with higher end access points that are properly configured. We've got a system like this at work, and I can carry my laptop around the whole building and not skip a beat even with a download going. It just hops right to the next AP with the stronger signal when they overlap.

 

[John Connor]

IP address woes... The best way to do that is called network teaming or load balancing. Remove one device and the other will continue the download. There's a program called NAT32 that can do it, but it's complicated to set up and you would have to have both devices on at the same time. You can't just unplug the WIFI and tether. The IP addresses change. Why use that form of P2P. If you used uTorrent than there wouldn't be a problem, the download would finish where it left off.

 

[Kadarin]

The client and server side apps need to both be Multipath TCP capable for this to happen.

 

[imagoon]

The client and server side apps need to both be Multipath TCP capable for this to happen.

TCP/UDP is inherently multipath. Neither protocols care what path they take to a destiniation. The real issue here is the download is interrupted and can't be reestablished. High odds this is because of the source server uses the IP address as part of the session and won't resume to a new IP address because it drops the sessions. However ancient FTP (1985) and slightly less ancient HTTP 1.1 (1999) has supported resume from any IP. FTP didn't even require you to start at the beginning of a file if you didn't want to. You could log in and immediately issue a resume for file you have never downloaded.

The issue here is purely some server side reason / poor programming.

 

[Red Squirrel]

Switching hotspots is equivalent to unplugging an ethernet cable and plugging it into a different internet source. Can't make that seamless.

Now are these two hot spots on the same internet and are they controlled by you? You could look at setting up unifi access points then you will be able to walk around and it will pick whatever one is best and it will be seamless, kinda like a cell will jump towers.