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What IP telephony architecture is all about. The hard facts on softswitches.

<<<... Line cards and handsets therefore become switch ports and IP handsets or, if you want to keep some of your existing analogue phones, you plug analogue to digital gateway boxes into your LAN and hang your phones off that. And for trunk connections, whether to the PSTN or to an existing PBX, you install media gateways that will convert your E1 PRIs to an RJ-45 based LAN port and do all the clever stuff to translate things. Watch this last part though, especially if you want to integrate an IPT deployment into your existing PBX system. These gateways can be used to connect the IP environment to a PRI on your PBX so the two systems can be linked. Although this can work well, with feature transparency and common dial plans, not all types of inter-PBX connectivity are supported fully.

For example, DPNSS, which is commonly used to interconnect PBXs in the UK, isn't an international standard, so some gateways and softswitches don't understand the signalling and formatting, in which case you need to add in third party gateways extra to do the translation for you. Phone operation While a softswitch works much the same way as the processor on a PBX, letting you configure route selection, digit translation, access rights, hunt groups etc, the handsets are significantly different. They've become, in effect, baby PCs, with operating systems, IP addresses and, on some, screens that offer web browser functionality. IP phones have MAC addresses, which is about all they know when they boot up. Remember those diskless workstations that used to broadcast for a server to download what they needed to get them going? An IP phone will broadcast for a DHCP address and typically (though this can be vendor-dependent) will also be given other information such as a server that it can get new firmware loads from, if required, and a list of the softswitches it should communicate with. more>>>