I will setup price of this job on 30$ and delivery time on 3 days because I do not know can you solve described project. If you can solve problems please send me info about your price and delivery time.
I have android app what use voip for calling between registered user. App do not use phone number for contacts, app use usernames stored in database and search function, after finding some user using search you can call him by click on username. On server is installed kamailio for single calls and asterisk for conference calls.
1. App has voice latency - test description: when call is established and user1 say ONE - user2 hear ONE and say TWO - user1 hear TWO and say THREE - user2 hear THREE and say FOUR -...etc..etc till TEN. For this test users need 16 - 17 sec. and for the same test on Skype or Viber users need 8 - 9 sec. So I need decreased latency on same level as Skype.
2. App has problems with call connections. App usually connect first call and after ending this call next call has no connection, sometime has ring and connection ( voice ) but usually no ring, no connection, no voice. I am 95% sure it is voip server side problem. Server is Linux.