VoIP application for android

This question really has little to do with Android or ARM but I'll try to help out. First, you're asking a very specific questions but we have no context. We may be left to infer that you're trying to reverse engineer a VoIP protocol but if you simply need to create VoIP functionality, there are lots of open source projects that can enable you. Perhaps if you share what you're trying to accomplish, we can give you better advice.

It sounds like you might be attempting to do something that The Several Mesh (open source) and a few other projects are doing.

The Serval Mesh - Android Apps on Google Play

There are many, many other apps in the App Store that do audio intercom/phone like functions without the internet. I'll leave it to you to sort the open source from the closed though. For example:

Intercom for Android - Android Apps on Google Play

BlueFi Phone - Android Apps on Google Play 

There are also many WebRTC demos that do require an internet connection to initiate but are extremely simple, open source and open protocol so if you're looking to leverage highly open technology, I'm sure you could manage to add your own subnet broadcast/discovery system around them to eliminate the need for a server to help two nodes initiate.

WebRTC Demo

https://janus.conf.meetecho.com/demos.html

webrtc/samples · GitHub 

I think the most important open source project for you to become familiar with is Opus.

https://www.opus-codec.org/

It share a lot of common core technologies for rate adaptation and high quality audio that many well known VoIP apps use and is used in many VoIP applications. It is fully open source and unencumbered by corporate licenses.

As far as network traffic sniffing. Yes, you can monitor Android through logCat and the Android Network monitoring tool. If you simply want to have a workstation watch and decode all network activity, WireShark is quite popular: Wireshark · Go Deep.

If you have any ARM specific questions, feel free to continue this discussion here.

This question really has little to do with Android or ARM but I'll try to help out. First, you're asking a very specific questions but we have no context. We may be left to infer that you're trying to reverse engineer a VoIP protocol but if you simply need to create VoIP functionality, there are lots of open source projects that can enable you. Perhaps if you share what you're trying to accomplish, we can give you better advice.

It sounds like you might be attempting to do something that The Several Mesh (open source) and a few other projects are doing.

The Serval Mesh - Android Apps on Google Play

There are many, many other apps in the App Store that do audio intercom/phone like functions without the internet. I'll leave it to you to sort the open source from the closed though. For example:

Intercom for Android - Android Apps on Google Play

BlueFi Phone - Android Apps on Google Play 

There are also many WebRTC demos that do require an internet connection to initiate but are extremely simple, open source and open protocol so if you're looking to leverage highly open technology, I'm sure you could manage to add your own subnet broadcast/discovery system around them to eliminate the need for a server to help two nodes initiate.

WebRTC Demo

https://janus.conf.meetecho.com/demos.html

webrtc/samples · GitHub 

I think the most important open source project for you to become familiar with is Opus.

https://www.opus-codec.org/

It share a lot of common core technologies for rate adaptation and high quality audio that many well known VoIP apps use and is used in many VoIP applications. It is fully open source and unencumbered by corporate licenses.

As far as network traffic sniffing. Yes, you can monitor Android through logCat and the Android Network monitoring tool. If you simply want to have a workstation watch and decode all network activity, WireShark is quite popular: Wireshark · Go Deep.

If you have any ARM specific questions, feel free to continue this discussion here.