Android App for sending-receiving Voip - No signalling required, only voip packets sending and receiving

INTRODUCTION I'm developping a software that needs, among various other functionalities, to perform Voip communications. I have some applications on PC side (server, clients) and another on Android (clients). I tried several Voip library; on Android clients the libraries "sipdroid" and native "[login to view URL]"; on Pc clients the library "mjsip". The voice quality is not good, moreover on Android side. TARGET - According to my Android simple app, enclosed to this specs, target for Developper is to fills the code inside the 6 methods contained in "VoipManager_Jingle" class (a "DEVELOPPER" tag is included inside the class); that code of course will invoke other classes or libraries that the developper will have to provide. - No signalling is needed for call setup, it is already done by my main application. - The job is done and specs 100% satisfied when this app, installed in 2 android smartphones, will allow to have a voip call with very good quality, without any voice lost or delay . - The application must work with whatever Android device, with Android 4.0 version or later - On transmitting, the voice trasmission (then the Voip packet sending) must start immediately after the method is invoked, without any delay. - On receiving, the voice playing on speaker must start immediately after the method is invoked and packet are received, without any delay. - The voip comunication must be pure peer-to-peer, so it must work without any server. - The application could also run in a private network, without public internet connectivity. Therefore the voip library used must work without any external server. - The codecs to be used/implemented must be: Opus, GSM, PCMA, PCMU COMPLETE SPECS INSIDE THE .RTF FILE HERE ENCLOSED