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Why does my SmartNode need a high precision clock and what does it do?
Article Id #: 460

You might have read in the press that there are SmartNode models featuring a "high precision" clock. These are variations of existing SmartNodes and are sold as model codes 4971/81/91, 4635 and 4639 based on Smartware and with the “HP” attribute in the model code which are based on the Trinity Operating System. We claim these models eliminate interoperability failures that typically occur with DECT, PBX and FAX equipment when converting ISDN systems to IP telephony.

To understand why Patton received a recent Product of the Year Award for these models, and to see where YOU might want to use them (keywords: DECT and fax), let‘s start with a little background in telecom network clocking.

In normal ISDN telephony networks, the public network ("Amt") provides an 8kHz clock signal to all connected equipment. This clock is ultra-stable and precise, as it derives from an atomic master clock.

In the picture above, the entire PBX system is clocked from the atomic master clock. Now, there is a little think we have to know: For SME PBX systems with integrated DECT base station, it happens to be best practice to use the ISDN clock and derive the DECT base frequency from it. This way, PBX manufacturers save in cost - they don‘t have to include in their system an expensive frequency generator for the DECT base frequency.


So what happens when an enterprise moves to VoIP? You got it. A SmartNode VoIP gateway replaces the ISDN line. Now, the SmartNode provides clock to the PBX - and thus, the DECT base frequency is derived from the SmartNode‘s internal clock:

Is this an issue? Yes it is. VoIP gateway‘s clocks are standardized to an accuracy of 50ppm. This is way enough to allow for best-quality voice conversations. But it‘s not enough to be used as source to generate a DECT base frequency. The resulting DECT frequency is not precise enough, resulting in the handset not being able to register to the base station.


Patton enables you to solve this problem in two ways:

       1)  Through the most flexible clocking configuration in the industry on SmartNodes, it is possible to select any ISDN port as clock source. The clock from the clock source is then distributed to all other ISDN ports. Thus it is possible to either keep one public ISDN line as clock master, or to feed a clock signal from another source to the SmartNode.   

       2)  Through use of the new high precision models it is possible to increase the SmartNode internal clock accuracy to Stratum 3. This is very precise and way enough to serve as source for the DECT frequency.


Here is an overview of the SmartNode models that are available with high precision clock:

 Compared to high precision solutions from other vendors, which are modular based systems, SmartNode‘s integrated system design offers a very cost effective solution. 

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