What does a custom APN profile actually do, and why do I have to re-enter the proxy in my browser when I tether?

Question

I'm currently in Canada and I'm using the 7-Eleven Speakout "unlimited browsing" mobile internet plan. Unlimited browsing means that only HTTP and HTTPS are unblocked, while any services that use other ports probably won't work. In order to use the Speakout internet service, you have to specify custom APN settings, as follows: (according to the official website)

Homepage http://wap:8582/start.wml
Connection security: Off
Active Bearer: GPRS
Connection type: GPRS Attach on Demand
Authentication Type: Normal Access Point Name: goam.com
User Name: wapuser1
Password: wap
Login Type: Automatic
Primary Proxy Server Setting 10.128.1.69
Primary Proxy Server Port: 80

Once I entered these settings into my phone, all my apps worked fine. However, when I first tried to tether my phone to my PC, I couldn't get any websites to load. A helpful tip suggested that I try using 10.128.1.69:80 as a proxy server, and once I dialed those settings into Firefox, everything started working as expected. However, I still have absolutely no idea how the whole system is working under the hood, and this bothers me.

My questions:

1. What do the APN settings on the phone actually do? In regards to the access point name and the primary proxy server, What exactly happens when I tell Safari to load a webpage?
2. Why do I have to enter the proxy server a second time in Firefox? Shouldn't my computer traffic be transparently sent through my phone's mobile internet, exactly the same as Mobile Safari?
3. I never have to enter any proxy settings into Firefox when I'm using normal tethering with my AT&T mobile internet plan. What makes Speakout so different?

Thank you!

Answer 1

What do the APN settings on the phone actually do?

The APN settings contain information required to set up an internet data connection while you are on a mobile network (that is, not connected to wifi).

In regards to the access point name and the primary proxy server, What exactly happens when I tell Safari to load a webpage?

Most of the magic of APN settings happens at a much lower level and is handled on an OS-wide basis, so Safari itself doesn't particularly need to concern itself with these settings.

The HTTP proxy and port are an exception to this - even though the HTTP proxy settings are included within the APN settings they are used by HTTP clients (such as Safari) as a proxy to use for all HTTP requests. When loading a web page in your browser it will consult its HTTP proxy setting to determine whether it should directly connect to a server or go via a proxy.

The intention behind offering this is to allow web access to restricted mobile networks that do not allow direct HTTP communication except through the provider's HTTP proxy. Such setups are comparatively rare these days.

Why do I have to enter the proxy server a second time in Firefox? Shouldn't my computer traffic be transparently sent through my phone's mobile internet, exactly the same as Mobile Safari?

Proxy settings are used by the HTTP client (eg, a web browser). Most operating systems including your phone will communicate a set of default proxy settings to other compliant HTTP clients that run on the same operating system but when tethering you're crossing over to another separate system and the proxy settings would need to be set up there separately.

I never have to enter any proxy settings into Firefox when I'm using normal tethering with my AT&T mobile internet plan. What makes Speakout so different?

Different providers have different requirements. Many providers these days run everything through a transparent proxy at their end so you don't need to set up proxy settings in your client software. It sounds like this provider doesn't do that.

Providers don't need to use proxies at all, but proxies can help them with various things like modifying websites for your device, calculating/indicating whether you're accessing sites within a "free"/"unmetered" zone, blocking access to certain sites, etc.