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Walkthrough Wednesdays

Problems with 3rd party SIP device

Hi All,

We have deployed a few 3rd party SIP devices made by Siemens.

The setup consists of Gigaset N300A IP DECT basestations with SL400H handsets.

Getting the N300A IP basestation registered was a snap and basic features seem to work fine.

Except, one featue is causing me headaches; call transfer

Now before I go any further, chances are the problem is purely caused by a firmware problem in the N300A but at the off chance I'm doing something wrong the details.

Call transfer either should work via R (hook flash) or straight from the options menu.

Problem is, if you perform a transfer the basestation crashes and resets.

There are 2 possible situations.

1 - the feature is broken, nothing will fix it

2 - the featue can work but a wrong setting will cause the basestation to reset.

In the advanced IP settings menu there quite a couple of setting available regarding call transfer, so I have a little hope that the right settings might result in a working situation.

See screenshot below for the available settings.

I already have tried most combinations with just turning on/off features but the one thing that eludes me is the Applicatuion Type and Applicatyion Signal fields which become available if check the check box for 'SIP Info'.

Any help would be appreciated.



In the mean time we've done some testing.

Apparently transfering an external call does work.

Only difference is that external calls are routed through a Cisco 2811 H323 gateway (ISDN30).


After doing some traces with WireShark while performing a transfer with the phone first connected to CUCM and second to a freeware SIP server I setup for testing, I finally found the cause:

The CUCM is sending an extra request containing a SIP/SDP header.

Obviously the N300A IP doesn't know how to handle SIP/SDP and chokes on it.

In the end, Cisco doesn't offer any means to disable SDP and Siemens probably won't add support for it so the devices is effectively useless when it comes to this feature.

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