You mentioned that ringing but no voice, so the signaling from outside sip endpoint to CME and internal extension to CME is ok. No voice i suggest you need to check the connectivity directly between the outside sip endpoint and internal extension. any useful port denied? layer 3 connectivity?
If the calls complete but there is no audio, or one-way audio, I usually check for something preventing the RTP stream. This could be a layer 3 problem or an ACL, as previously mentioned. But it could also be Network Address Translation, or even just a deep-packet and/or stateful-inspection firewall. Even if the firewall is configured to allow RTP traffic through, some (particularly older firewalls) just don't reassemble the RTP packet right.
Let's clarify what is and is not working. You have CME with SIP endpoints, and internally calling between all SIP endpoints is fine. You have a Nortel PBX, connected to the PSTN. Does the Nortel have any endpoints? Can the SIP endpoint on CME dial and be dialed by the Nortel endpoints? The Nortel and the CME VG have H.323 gateway service with dial-peers, correct? From your description, it sounds like the SIP endpoints can dial the PSTN and they received audio both ways. However, if the PSTN dials a SIP end point, the call connects, but there is no audio in either direction. That makes me think it's an inbound dial-peer matching issue. Do you know what dial-peer is matching the inbound call leg for calls comeing from the PSTN to the SIP phones? You also mentioned remote SIP endpoints are working? Where are this endpoints and how are they connecting to the CME and the Nortel?
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The short answer is that you don't.... That isn't entirely true while at
the same time it kind of is, but for the most part you don't configure
the softkeys. You enable or disable them via TCL. Here is the long
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Topology: IP Phone > Switches > Microsoft NPS setup to forward 802.1x
proxy to > ISE 2.1 patch 3 Authentication: EAP-TLS using Cisco MIC SANs
Phone Models 802.1X support? 802.1x flavor Addtl Comment EAP-MD5 EAP-TLS
Cisco 3905 Y Y N Cisco 6911 Y Y N Cisco ...