Some critics of DPNSS suggest that it is too loosely defined and allows too much latitude in its interpretation of message formats and timers. It is also sometimes mistakenly believed that DPNSS is semi proprietary and that it is only possible to connect PBXs from the same manufacturer. i.e. Siemens will connect to Siemens, Mitel to Mitel etc. Experience indicates that this is not the case and BT's FeatureNet platform (Nortel's DMS100) running DPNSS, has interconnected successfully to many PBX types available in the UK.
==Voice VPN==
A Voice VPN [http://www.voice-vpn.com/index_files/VoiceVPN.htm]combines Voice over IP and [[Virtual Private Network]] [[VPN]] technologies to offer a method for delivering voice services between site PBXs [[Private branch exchange]].
The site-based [[Voice Router]] acts as an intelligent voice switch which creams off the interesting calls and routes them over the corporate data network e.g. IP-VPN. As the voice calls are now carried over the data network then all inter-site calls now cost zero cost per minute – as you may know this could be a significant saving potential for most companies.
In addition long distance calls can also be routed over the Voice VPN [http://www.voice-vpn.com/index_files/VoiceVPN.htm]to an appropriate destination site [[Voice Router]] e.g. if the UK company calls a US-based customer then calls are re-routed over the Voice VPN to the US-sited [[Voice Router]] before exiting to the [[PSTN]]ɸ. Therefore call rates become local in-country rates rather than international rates.
''ɸ Please note that this is always subject to any local regulatory constraints.''
