Here’s something interesting I saw recently.
It’s a little involved, I’ll do my best to explain (there will be diagrams)… so, imagine this situation…
CLI Suppression in PSTN Calls
For security, secrecy, or customer engagement / marketing reasons – users are not supposed to give out their personal numbers… Therefore BigCorp have voice routes that hides the DDI of all their staff. All outbound calls present their main office number, lets say 0845 111 1111 (+448451111111).
Which is fine. Everyday standard stuff…
What about federated or forwarded calls?
BigCorp and LittleOrg both use Lync Enterprise Voice. Now lets say Mr Smith, BigCorp’s boss calls me in LittleOrg via Lync, and I’ve got Call Forwarding, or Simultaneous Ringing configured… I now see BigCorp’s boss’s PSTN DDI ringing my mobile.
And I can sell this to hundreds of marketing companies and retire 🙂
Lets have a look at the call flow in this situation…
The important piece of information to allow this comes from the P-Asserted-Identity header of the SIP INVITE message that leaves BigOrg. This includes the display name, SIP URI, as well as the Line URI of the caller, which gets used on the final leg of the call to my mobile.
Well, none really. If Mr Smith wants to make a Federated Lync call, he should be aware that it’s not anonymous. However, he may not realise that there is an unexpected side effect which discloses his DDI.