Android – multiple active APNs

I am using an Android device that supports volte. When the device is connected to LTE, it will automatically obtain a PDN connection to apn1, which is used for Internet access. Then, the device requests a PDN connection to IMS APN (apn2). After this process is completed, the device connects to two different APNs at the same time. The two APNs have different IP addresses, and can send traffic on the two "connections" at the same time

Q: I want to know how Android (4.1.2 in my case) actually implements this (?)

I assume that these are two different interfaces, but netcfg (ADB shell) only displays one interface, the one for apn1. Apn2, which is nowhere to be found. However, it is active and working because the device is sending IMS signaling on it (I am 100% sure). Therefore, I cannot capture traffic (tcpdump) or add routing rules to Ping a specific IP address through apn2

Any tips will be appreciated

thank you

resolvent:

I think the reason why you can't view and access IMS connection from Android application may be clear, but it may not be the mechanism that prevents you from seeing it

The reason why the operator does not want you to access the IMS connection is that it is used to establish call and session connections and conduct them in the IMS network. Allowing untrusted users to access directly will open the door to many interesting and uncontrolled behaviors, which may seriously endanger the operator network (such as denial of service attack)

The visibility of how Android keeps you away from this connection is not so obvious. I think the best way is to treat Android devices supporting LTE as composed of two main components:

>LTE phone / data terminal > linux based computer, running Android framework

The phone section exposes certain features to the Android section through a defined interface – see the following link:

http://www.kandroid.org/online-pdk/guide/telephony.html

For obvious security reasons, the "telephone" end in 2G and 3G devices exposes a relatively simple and very limited set of interfaces. For example, even if the "telephone" part itself contains all the functions required to set up calls and negotiate the use of radio resources, it does not provide an API that allows Android Applications to observe or manipulate these mechanisms or messages, Interaction of basic call establishment beyond the definition of a finite set

In the 3G world, the details of the mechanism for sending call establishment messages are therefore hidden from Android applications - it can make advanced requests for establishing calls, but it can not actually control GSM or 3G signaling, request rails resources, send initial call messages, etc. in LTE, in order to ensure that this is also hidden, Android applications cannot access IMS connections, I think this is what you might mean by observed behavior