Android SIP Functionality Resolution

I'm looking for an expert in VOIP and Android development. My project revolves around fixing bugs in an Android app, specifically problems with its SIP functionality.

The key issues I'm experiencing are:
- The SIP registration automatically stops. This tends to happen when the app is runing .
- Certain SIP functions related to incoming and outgoing calls and call quality issues are not working as expected.

An ideal candidate would possess the following skills and experience:
- Proficiency in Android app development
- In-depth understanding and experience of VOIP and SIP communication protocol
- Experience in troubleshooting and resolving SIP registration issues
- Experience in debugging and problem-solving SIP related call issues.

Your primary task will be to fix these bugs to ensure that SIP registration is seamless, and calls made or received via the app using the network simcard are effective and efficient. I look forward to working with someone who can swiftly and successfully resolve these issues.