DND & FWD on T46G

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Hi, We have a number of different Yealink handsets connected to our PBX at Voipfone. We have a specific problem with the T46G handsets in that DND and Call Forwarding don't appear to be working.

If we call the T46Gs and either DND or FWD is enabled (both icons display on the screen) the phones ring normally as if DND or FWD isn't enabled. If we enable the same features on our older T22P handsets, a W56P dect or a T49G that we have then both features work perfectly (so it's clearly not a problem at the Voipfone PBX).

We've tried several different firmwares from 28.73.179.4 all the way up to the latest 28.81.0.20 and this doesn't make any difference.

We did some tests with the guys at Voipfone and no matter whether DND or FWD is enabled or not the phones respond as 180 RINGING.

********
vf1-sov 2016-11-24 17:01:17 xxx.xxx.xxx.xx:8699 xx.xx.xxx.xxx:5061 xx.xx.xxx.xxx:5062 374 xxxxxxxx*202 xxxxxxxx*205
close

���Q!�.��SIP/2.0 100 Trying
Via: SIP/2.0/UDP xx.xx.xxx.xxx:5060;branch=z9hG4bK0eeb855c;rport=5060
From: "xxxxxxxx*202" <sip:xxxxxxxx*202@xx.xx.xxx.xxx>;tag=VF03dfc337a13ee1e5d08a08b32ae0
To: <sip:xxxxxxxx*205@xxx.xxx.xxx.xx:41844>
Call-ID: VF090393cb92cfe577e2f4563efbdf3c@voipfone
CSeq: 102 INVITE
User-Agent: Yealink SIP-T46G 28.81.0.15
Content-Length: 0

vf1-sov 2016-11-24 17:01:17 xxx.xxx.xxx.xx:8699 xx.xx.xxx.xxx:5061 xx.xx.xxx.xxx:5062 610 xxxxxxxx*202 xxxxxxxx*205
close

���Q!�.��SIP/2.0 180 Ringing
Via: SIP/2.0/UDP xx.xx.xxx.xxx:5060;branch=z9hG4bK0eeb855c;rport=5060
From: "xxxxxxxx*202" <sip:xxxxxxxx*202@xx.xx.xxx.xxx>;tag=VF03dfc337a13ee1e5d08a08b32ae0
To: <sip:xxxxxxxx*205@xxx.xxx.xxx.xx:41844>;tag=3411456143
Call-ID: VF090393cb92cfe577e2f4563efbdf3c@voipfone
CSeq: 102 INVITE
Contact: <sip:xxxxxxxx*205@xxx.xxx.xxx.xx:41844>
Allow: INVITE, INFO, PRACK, ACK, BYE, CANCEL, OPTIONS, NOTIFY, REGISTER, SUBSCRIBE, REFER, PUBLISH, UPDATE, MESSAGE
User-Agent: Yealink SIP-T46G 28.81.0.15
Allow-Events: talk,hold,conference,refer,check-sync
Content-Length: 0
********

On the T46G phones themselves we've experimented with different options under Features, General Information, "Return Code When DND" - 480 / 486 / 603 - and this makes no difference either.

Does anyone have any ideas what the problem may be?

Thanks

Clive