Lync recognizes Cisco ISR as a PSTN gateway connected by SIP. So we need to add Cisco ISR to the Lync topology by adding it as a PSTN gateway.
1. To add a PSTN gateway to the Lync topology, run Lync Server Topology Builder as a user in the CSAdministrator group. Then add the Cisco ISR Gateway to the PSTN gateway topology
Figure 2: Configure PSTN Gateway -1
2. Set FQDN: This is the IP Address or FQDN of the Cisco ISR Gateway.
Figure 3: Configure PSTN Gateway -2
3. Set Trunk Name: This is the FQDN of the ISR
4. Set Listening port for IP/PSTN gateway: 5060 for TCP
5. Set SIP Transport Protocol: TCP
6. Set Associate Mediation Server: Assign this PSTN gateway to the Mediation Server. Medpool.lynclabkm2013.local is used here for example.
Figure 4: Configure PSTN Gateway -3
7. Publish topology to make the changes effective, refer to below screen capture for the process.
Figure 5: Publish Topology