Alternative VoIP telecommunication systems

Although the MDA Pro is equipped with all modern popular radio technologies - GSM / GPRS, UMTS, Bluetooth and WLAN, the company T-Mobile, apparently does not want her clients to use them for voice over IP, because the VoIP device itself is not supported. For testing, we provided him with softphone X-PDA 2.2 SIP-based company from Counterpath (formerly Xten), whose development was recently involved in Global IP Communications. He became one of the first soft phone, officially running Windows Mobile 5. Unfortunately, the version provided to us is not integrated into other possibilities MDA Pro. So, switching to the widescreen format is not supported (need the function keys on the screen simply absent), to dial a number from the standard menu of contacts is not possible, but the buttons for the construction and the disconnection is only available on an integrated phone, GSM. VoIP telephone systems All three finite VoWLAN devices without problems related to our laboratory alternative telecommunication systems VoIP: Open Source PBX Asterisk 1.2.5 and gateway VoIP Lancom 1821. Asterisk solution with a wide range of functions can be quickly installed in the form of preconfigured bootable CD-ROM Asterisk @ Home 2.7 (asteriskathome.sourceforge.net /) with the distribution Linux CentOS 4.2 (clone of Red Hat Enterprise Linux 4), VMware Workstation 5.5 for each required PC with Windows. Pre-configured virtual machine image of Asterisk @ Home 2.7 for VMware is available free from the site at: http://www.voip-info.org. Lancom 1821 Wireless ADSL - this is an access point c ADSL modem and the port of ISDN, which, thanks to new support options VoIP has become a small VoIP telecommunications system for branch offices and small (or home) offices. Router as a gateway to SIP / RTP combines Wi-Fi phone with an integrated ISDN port or redirects it through the Internet service provider SIP and / or a higher corporate telecommunications system IP. To ensure the confidentiality of negotiations on the Internet when connecting branches in 1821 is capable of building a transparent tunnel virtual private network based on IPSec. Already using WLAN for VoIP only noticeable significant differences as a voice transmitted through the tested device: if the two specialized VoWLAN phone provide acceptable quality of speech, it is the case with softphone XC-PDA MDA Pro on time shift becomes so large that scarcely can freely engage in dialogue. In addition, the network analyzer Observer 11 from Network Instruments has identified a very low value of the averaged ratings of speech intelligibility (Mean Opinion Score, MOS) when evaluating its quality. Meanwhile, MDA Pro is equipped with Intel PXA270 processor with a clock frequency of 520 MHz, ie has the necessary capacity to support VoIP.