1. Hosted VoIP Solution

2. Image 1 PSTN Media Gateway T1 / PRI POTS lines Others SIP Servers 1.Soft Switch 2.Registration Server 3.Others Cluster A SIP Servers 1.Soft Switch 2.Registration Server 3.Others Cluster B Subscriber A Subscriber B Database Synch (Active, Active) Register to specific IP address, but this would present a scalability issue. VoIP Traffic to and from PSTN

3. DNS Based failover PSTN Media Gateway T1 / PRI POTS lines Others SIP Servers 1.Soft Switch 2.Registration Server 3.Others Cluster A SIP Servers 1.Soft Switch 2.Registration Server 3.Others Cluster B Subscriber A Subscriber B Database Synch (Active, Active) DNS Server SRV Record _sip._udp.voip.comapnydomain.com SRV Record with Load Sharing _sip._udp. 0 40 a.example.com 0 40 b.example.com 0 20 c.example.com 1 0 backup.somewhere.com VoIP Traffic to and from PSTN

4. Hosted Solution Subscriber A Subscriber B GeoDNS