No ringback from Cisco IP phone to Lync server 2010

Problem Description
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No ringback when call from Cisco IP phone to Lync server via SIP trunk.

Resolution Summary
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Applied command “voice-class sip block 183 sdp absent” under dial-peers as from the debugs we do not receive SDP with session progress 183.

And you had command “voice-class sip block 183 sdp present”.

As per IETF draft, the 183 session progress after 180 ringing signals not to play local ringback signal.
http://www.jdrosen.net/papers/draft-donovan-mmusic-183-00.txt
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The introduction of the 183 informational response message would allow a called user agent to indicate to the calling user agent whether or not the calling user agent should apply local alerting for the session. The existing 180 Ringing message would indicate that the calling user agent has the option of providing local alerting (and generally should). The 183 Session Progress message would indicate that the calling user agent should not provide local alerting and should establish a media session to be used by the called user agent to indicate the status of the session setup request as part of the indicated media stream.

So my dial peers ended up looking like this

dial-peer voice 15 voip
description **Incoming Call from LYNC**
b2bua
session protocol sipv2
session target ipv4:10.x.x.x:5068
incoming called-number .%
voice-class codec 1
voice-class sip dtmf-relay force rtp-nte
dtmf-relay rtp-nte
no vad

dial-peer voice 16 voip
description ** SIP Trunk to Lync for Lyn users**
translation-profile outgoing LYNC_ADD_PLUS
destination-pattern [3,4]8..
notify redirect ip2pots
session protocol sipv2
session target ipv4:x.x.x.x:5068
session transport tcp
voice-class sip block 183 sdp absent
dtmf-relay rtp-nte
codec g711ulaw
fax rate disable
fax protocol pass-through g711ulaw
no vad

About Alexis Katsavras

Working as Freelance Cisco Unified Communications Consultant in the UK. www.NetPacket.co.uk