All Lync Users Need a Destination on No Answer: Call Forwarding When No Endpoint Registered


If you are implementing Lync users that don't have voicemail you might be forgetting about the caller experience when a Lync client or phone is not registered.  Have you thought about what the caller will experience when no IP phone or Lync client is registered? (or if they have portable WIFI phone and it is powered off?)

When a Lync endpoint is registered and that Lync user is called things will work as you expect: the call will ring for the length of time defined in the “Call Forwarding” dialog (up to 60 seconds) and then fail.

Where it gets more confusing and inconsistent for the caller is when the Lync user in question has a DID and external/PSTN users are calling the Lync user directly. If the Lync user has no IP phone/Lync client registered the caller can get various messages depending on their own telco:

  • The number you have reached is not in service. This is a recording (SIP trunk provider)
  • sorry, this mobile number is not available at this time. (mobile
  • this number is no longer connected
  • busy
  • etc. (in other words, a very inconsistent and confusing caller experience)

Technically What is Happening?

Lync to Lync User: The caller is getting a SIP 480 “Temporarily Unavailable” (below)


PSTN to Lync DID


So this brings up the point that every Lync user needs to have a destination on no answer even if there is no voicemail (voicemail is effectively a global destination on no answer) for this user.

What are several options?

  • setup the Lync user(s) to forward to a Response Group (RGS will need an extension# or DID to configure this in Lync client call forwarding settings) that says something like “Sorry, no one is available at this time.” and then disconnects  (you can set this up centrally using SEFAUtil)
    • Notes
      • with this method, if there is no voicmail and no client registered the call will be answered immediately by the “message” RGS
    • Cons
      • if call forwarding is enabled for this user they could change call forwarding to nothing and forget to set it back reintroducing the problem
      • if they have a snom UC Edition phone forward and clear forward, the forward on no answer is cleared
      • If you disable call forwarding using a Voice Policy obviously user can no longer forward to distination *they* want to forward it to and they may be confused by fact that Lync client still presents forwarding options (see: Click Here)
  • another possible option: have SBC/Gateway reroute call on message from Lync
    • cons:
      • only calls going through sbc/gateway will be rerouted
  • MSPL script
    • I did not sit down and write an MSPL script, but this could be quite elegant. If someone has such a script, I’d be glad to post it/link here.
    • Perhaps this script could be modified? Click Here

If you think “Destination on No Answer” functionality should be built into Lync you may want to vote for it here:

The following professionals have contributed to this blog: @lyncdialog @patrichard @Matt_Friedrichs @wangshoulun @jveldh

1 comment:

  1. Hi Matt,
    Almost all of my users have a mailbox. But when I try to set: "unanswered calls go to: mobile phone", the voicemail always takes the call. When I apply the call immediately or simultaneous redirect, the redirection works fine.
    Can you explain why the missed calls always go to voice mail?
    Greetings from Germany


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