Updating Windows Phone 8.X on slow WiFi

Question

I have a WiFi internet connection through a proxy with several limitations. The connection reaches 70kbps on certain hours of the day, but it is mostly about 20kbps. The proxy is also configured to allow a slow number (5) of concurrent connections per host, and a single connection gets dropped after a certain amount of time.

I've been trying to update my Lumia 920 via Setting > Phone Update, and several things have been going on, leading to unsuccessful update attempts every single time.

1) Since my threads get dropped after some time, I get a lot of udpate errors (e.g. 801882d2), so I have to tap on the "Search updates" very often.

2) After tapping the "Search updates", sometimes the percent returns to where it was, sometimes it starts on a lower number, sometimes it just goes back to zero.

3) I've been doing this for several days, sometimes the percentage resumes the next day, sometimes it doesn't as I explained before. After several days I had the feeling the percent bar was moving faster even when it started from 0%. Then I turned off the phone and then on again for the first time since I started updating, and now I feel it just started from the very beginning, for now I feel the bar is moving as slowly as it was on my first days of trying.

I know this is a very uncommon case, for I have searched on the internet for similar problems and I have found none. I understand that having such a biased connection is very uncommon.

My question bundle is:

What's going on? Is the percentage bar dependable, is it telling me the truth about the volume of data that has been downloaded? Is it really starting to download the update from the beginning every time it goes back to zero? Is there a way to actually update the phone on such a relatively slow, biased WiFi?

Any answer or clue might be helpful, in the worst case I could just stop trying on this slow connection and try in a faster, not biased (but way more expensive) connection.

Thanks in advance.

Answer 1

Here's the answer. Requests from Windows Phone Update timeout after 30 seconds. If connection is slow enough to prevent a full POST to http://statsfe2.update.microsoft.com/ReportingWebService/ReportingWebService.asmx the download won't even start.

After downloading, the update uses partial downloads to speed up the process. Some update files can be significantly big, and most proxied connections through Squid are not trivial to configure so that partial downloads are smartly cached, primarily because Squid itself does not support caching of partial downloads.

When the percent goes back it is because one of the partial downloads has died. If many downloads fail the process starts over again. The only way to overcome this is caching .cab files so that when it restarts it can go up fast.