We often receive requests to connect & configure third party SIP devices to CallManager. This is often because people feel a third party device is cheaper than a Cisco handset, or because the third party device has a function/feature not available on a Cisco handset. As CallManager supports SIP (and 95% of our handsets are running SIP), this shouldn't be a problem. However, the devil is in the detail.
- SIP Compatibility
- Despite what vendors claim, SIP is not a well defined standard. Third party suppliers often have to implement different dialects of SIP to support different manufacturer's equipment. We occasionally look at third party devices that look interesting, and we can spend several days trying to get the devices to work in a meaningful way with CallManager.
- We've yet to come across a third party device that supports CallManager's resiliency model. Telecoms have put a lot of effort into making sure the core phone system is resilient, and our colleagues in Network Systems have done a lot of work to ensure the CUDN is resilient too.
- Each manufacturer has their own way of configuring their device. Most devices are configured from a web interface, and only from a web interface. This means that any changes have to be made twice: Once in CallManager and a second time on the device. Telecoms achieves its low costs by economies of scale. If we have to support numerous different devices each by different manufacturer, all manually controlled, this increases our costs.
We have considered running a second SIP phone system just for these third party devices, but the idea has never left the drawing board.