Network Topology without NAT
As long as you have no NATs between the sipXecs server and all the phones and gateways there should be no challenges from a network topology perspective. As long as all the hosts are reachable a routed network works fine and also network segments reachable via VPN are not a problem.
Network Topology with NAT
NAT traversal at the near-end or far-end represents a significant challenge for the SIP protocol as both signalling (SIP) and media (RTP) needs to be mapped to traverse NATs successfully. Up to and including sipXecs release 3.10 an external Session Border Controller (SBC) is required for NAT traversal. Typically we have used either an Ingate SIParator or an Intertex IX-67 SOHO SIP firewall/router. Other products might have but we have not done any extensive testing. In particular it is said that Patton Electronics SmartNodes might work.
sipXecs Release 4.0: As of release 4.0 sipXecs includes native support for both remote worker configurations as well as SIP trunking.
External Session Border Controllers
For releases earlier than 4.0, an external SBC is needed for operation behind NATs.
Remote worker configurations require both near-end and far-end NAT traversal assistance. Some products, such as the Ingate SIParator provide support for both. Therefore, at the far-end there is no special equipment required and phones connected behind a traditional firewall/router will work fine. Other products might require NAT traversal assistance at the far-end as well.
SIP Trunking requires both near-end NAT traversal as well as interoperability with the ITSP providing the SIP trunking service. An SBC is required and we have typically used Ingate SIParators for this purpose.
Network Services
sipXecs does not work unless DNS and DHCP services are properly configured. It is possible to use the sipXecs server for such network services. The single CD ISO installation disk provides for automated installation and configuration of such services. However, more often you already have DNS and DHCP services deployed on your network. Please consult the respective information on how to configure such services to work with sipXecs. sipXecs uses DNS SRV records, which require proper setup. If you deploy sipXecs in a high-availability configuration the complexity of the DNS SRV configuration increases dramatically.
The sipXecs administration portal (sipXconfig) provides automated tests that allow the verification of proper configuration of all such network services. Make sure the tests pass immediately after installation and before you file a trouble ticket.