Systems, methods, and software are described herein for operating a RTP server including receiving a session request from a user communication device indicating the user communication device has packet format switching capability, transferring an acknowledgement to the user communication device wherein the acknowledgement comprises at least a header-free packet string length, transferring a RTP stream using bundled packet format, transferring a packet format switch triggering event, and transferring the RTP stream using header-free packet format for at least as long as the header-free packet string length.