| 摘要 |
<p>An SIP server (18) in an IP-based infrastructure supporting wireless telephones determines whether, based on the destination address in a call request, the call is an intrasystem call or an intersystem call. For intrasystem calls the SIP server routes VOIP packets directly between the originating and destination devices. For intersystem calls, however, and in particular encrypted calls, instead of routing the VOIP packets through the public Internet, the SIP server instantiates a circuit-switched call using a local modem bank (22) connected to the PSTN (24). In this way, quality of service assurance is obtained and latency reduced.</p> |
