5wyx1t Posted April 28, 2015 #1 Share Posted April 28, 2015 Over a number of years, there is an aspect of SIP trunks that I have found tricky to make work in a flexible way. This aspect is withholding numbers. On the SwyxIt! client, there is a "Hide number / URI" setting. This setting seems to work fairly well with ISDN, but with SIP trunk calls, I have not been able to make this work. I know that there are many different ways that SIP trunk providers can use for withholding numbers (e.g. w prefixes, presence flags, Set CID to zero, add a 141 prefix, ...etc).Two ways that I have commonly made use of myself are the 141 prefix and setting CID to zero. For the 141 prefix, I have used special number replacement for adding this in. Unfortunately, it means that all calls on a trunk have number withheld. This is not ideal in all circumstances, as you might want to withhold the number for some calls and not others. Likewise, if not done at trunk level, it can be messy to expect users to remember that they should dial 141 before a number to withhold their own number. For the CID to zero, I have sometimes created a dummy user account with a zero external number. I have added this account as an alternative number for other users, so that they can select it in their line settings for outgoing calls, or so that a certain line can be set for all users as a withhold number line. This works reasonably, but it is not as slick as being able to just select the "Withhold Number" setting on the client. I would be grateful for any advice on whether it might be able to be configured to work with SIP trunks. I would also be interested in any further suggestions that can be made regarding methods for number withholding on SIP trunks. I do understand, though, that these will vary between SIP carriers. Link to comment Share on other sites More sharing options...
Most Valued User Virikas Posted April 29, 2015 Most Valued User #2 Share Posted April 29, 2015 Use a supported/SIP compilant SIP trunk and anonymous calls aren't any problem. SIP RFC 3261: A UAC SHOULD use the display name "Anonymous", along with a syntactically correct, but otherwise meaningless URI (like sip:thisis@anonymous.invalid), if the identity of the client is to remain hidden. Link to comment Share on other sites More sharing options...
5wyx1t Posted April 29, 2015 Author #3 Share Posted April 29, 2015 That is very useful - Thanks - This gives me something to think about. However, in terms of supported SIP carriers, I have also encountered problems with this with supported carriers (e.g. Gamma). Link to comment Share on other sites More sharing options...
Most Valued User Virikas Posted April 30, 2015 Most Valued User #4 Share Posted April 30, 2015 "encountered problems" might be a *lil to vague regarding debugging I can only talk our (certified/supported) SIP trunks and there is no problem regarding anonymous calls. Link to comment Share on other sites More sharing options...
5wyx1t Posted May 27, 2015 Author #5 Share Posted May 27, 2015 I have now overcome this problem, so thought I would feed-back my experiences. As the withhold sets the from: information to anonymous@anonymous.invalid, I have now managed to overcome problems of withholding numbers by using special number replacement. I just replace anonymous@anonymous.invalid with the method for withholding used by the actual carrier. e.g. If this is all zeros, then I replace with all zeros. Virikas - Thanks for your input, which pointed me towards understanding how the withhold works. Link to comment Share on other sites More sharing options...
Most Valued User Virikas Posted May 28, 2015 Most Valued User #6 Share Posted May 28, 2015 No problem, I read RFCs as my personal sleep novell Link to comment Share on other sites More sharing options...
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