Problems adding phone numbers to a conference call

I’ve recently had some problems with an OCS 2007 R2 installation where the users were complaining that they couldn’t add external phone numbers to a conference call. Internal numbers and SIP contacts were working fine.

I did some tracing, and noticed that the service provider gateway returned a 404 Not found when answering to the SIP Invite of the phone number. I checked the number, and it seemed correct.

But the FROM: field of the INVITE was populated with the users SIP URI not the users TEL URI, which the service provider didn’t handle. Normally a call through the mediation server will use the TEL URI, but turns out that it doesn’t in this case. There is AFAIK no way to handle this in OCS 2007 R2. (There might be in Lync, but I’ll need to lab that. The conference call behaves the same way in Lync, but you have the option to substitute the dialed from number on the route.)

This means that the service provider needs to handle this and substitute all unknown URI’s in the FROM: field with some known number, ex. the Dial In conference number or the main number of the organization, unless the service provider wants to maintain a database of the users and their corresponding TEL URI.

It might also be a solution to put some kind of gateway between the PSTN and OCS that does the conversion.

Has anyone else seen this?

One thought on “Problems adding phone numbers to a conference call

  1. (cynic on)
    Yes, and is not a bug but a feature 🙂
    (cynic off)

    If you are in an existing OCS/Lync conference call and you invite the N+1 participant into that existing call, you are inviting this participant into a conference. That’s obvious. In this case, who shall be the source of such invite? The “CONFERENCE” entity itself or the guy who drag@dropped the new participant’s number into the conference roster? And the answer is: the CONFERENCE entity. Remember, Lync is tuned for IP networks, and it prefers all participants are Microsoft PC clients, and those can handle conference IDs. As this conference entitiy is a temporary entity (the full ID is valid only for that particular conference), its ID cannot be a phone number (as this conference entitiy does not have any own phone number) so the solution is: to put there the full conference ID. This consists of the organizer’s SIP address followd by some GRUU-like string.

    The gateways however simply crop the GRUU-like string, so you will see only the following: call FROM the SIP address, instead of a phone number.

    Solution? There is not any I am aware of. It is up to the provider to handle this situation (as far as I know the attitude of arrogant providers, they a) dont care or b) their limited infrastructure does not support such custom hacking, so you may have to live with this.)

    Workaround? Try to call first the PSTN number. That will be a valid 1:1 phone call, with valid source and destination phone numbers. Add the Lync participant AFTER this, as the Lync participant is more flexible in terms of signaling as the PSTN participant. And everyobdy will be happy.

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