The Sentinel isn't needed if on the same net. It is used as a proxy to translate external addresses to internal addresses. Especially if the phones are coming from the same external address. Sentinel will assign those different internal addresses so the UGW can sort out who is who. The 2427 (MGCP) and the 5060 (SIP) ports are control signaling. The Audio is in the RTP packets, 16400 thru 16700 for MGCP negotiated with SIP.
