onsdag den 6. juli 2016

PSTN Calls from mobile - wrong "from" header in hybrid voice

I recently discovered a minor issue at a customer site with Cloud Connector Edition deployed connecting SKYPE for Business online in Office365 to onprem PSTN (SIP Trunk)

The issue has been replicated and confirmed by Office365 engineer team - there is at the moment no solid workaround - but issue is being looked in to.

The problem occurs when you dial out to PSTN from the Skype for Business mobile client on Android/ iOS / WinPhone. The FROM header that is sent in the invite from the Mediation server component in the CCE to the PSTN Gateway  is missing the LineUri in the FROM field - and also the ;user=phone is also missing - instead the users sip-address is sent.
Meaning that From header for my test user is

"FROM: sip:username@vanitydomain.com"
Where it should be
"FROM: sip:+45xxxxxxxx@PSTNGatewayFQDN;user=phone"

So what does this mean ? - Well 2 things.

When sending this info to a SIP Trunk provider or ISDN - they cannot forward the user name as a valid E.164 number, and also on many platforms calls will be rejected  because the FQDN is not contained in the FROM field - so unless the provider has knowledge of the Vanity domain call will fail - because the property ;user=phone is missing
The latter, can be fixed easily by the provider -so they will accept the call - bu the primary issue is that calls originating in the mobile client will show up a callee as "Private number" or unknown.

Only workaround would be 1:1 regex replacement in the gateway - and unless the customer has only a few employees, this is not a feasible solution in my opinion.

By the way - a small "note from the field" always include Wireshark and enable Telnet in the BaseVM before running install-ccinstance :) Saves a few minutes when troubleshooting issues like this.
As always Happy (cloud) SKYPE'ing.

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