Patton VoIP News
Also In This Issue: Patton VoIP News | February 2009
•  Latest SmartWare firmware release R5.3
•  How-to: Register SIP phones with your SmartNode
•  How-to: Configure SIP trunking on SmartNodes
•  Please give us your feedback on this newsletter

The new "high precision clock" SmartNode models   by Marco Liechti

You might have read in the press that there are new SmartNode models featuring a "high precision" clock. These are variations of existing SmartNodes and are sold as model codes 4961, 4635 and 4639. We claim the new 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.

PBX clocked by the ISDN network

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:

PBX clocked by a SmartNode

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:

Interfaces Call capacity Standard model High precision model
1 or 4 E1 PRI 15 to 120 SN4960 SN4961
3 or 5 BRI 4 or 8 SN4634 / SN4638 SN4635 / SN4639
3 or 5 BRI with DSL modem 4 or 8 SN4654 / SN4658 SN4655 / SN4659

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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