Update - CallTower Support is working with affected customers to address issues related to Skype For Business (SfB) users experiencing connectivity issues, and in some cases no audio being passed on calls after these changes are made. CallTower Engineering has made call routing changes internally to resolve the majority of calls connecting with no audio. Customers are reporting services have normalized when customers verified their network firewall settings were correct, then clearing their cache and rebooting. CallTower encourages all affected customers to take these steps.

Please see below for steps necessary to take:

https://www.uc.solutions/Skype_for_Business/Skype4B_Set_Up/005Firewall_Settings
• It is recommended to whitelist the domain ct950.com on your network as well as specifying the IP addresses.
• Another more flexible approach would be to simply whitelist the following networks since we can and will add servers over time to multiple locations:
• 205.196.169.0/24
• 205.196.173.0/24
• 205.196.174.0/25
• 67.213.189.0/24
• 63.128.106.128/26
• If a SonicWall or other firewall is utilizing "DPI" Deep Packet Inspection, it is recommended to disable this feature for voice traffic. All Skype traffic is Encrypted Data traffic and this feature isn't necessary, also it will interfere with Skype/Voice services and cause call quality issues.
• If your router is not configured for the new traffic protocols that Skype for Business (Lync) will introduce to your network, you could experience packet loss, dropped calls and jitter. You must make sure that SIP inspection or SIP ALG (Application level gateway) are disabled on your routers and firewalls to prevent this from happening. You may need to contact your ISP to have this done, but make sure this is completed prior to deployment. These features in routers are intended to block SIP traffic and will interfere with Skype for Business (Lync) communications.
• Clear your Skype for Business (Lync) cache: https://www.uc.solutions/Skype_for_Business/Skype_for_Business_Client/Windows_Users/How_to_clear_Skype_for_Business_cache
• Reboot your workstation to refresh DNS settings, after the above changes are confirmed.

If you continue to have issues after these changes have been made please contact support@calltower.com or 800-347-5444.
Nov 18, 13:20 MST

Update - CallTower Support is continuing to address an issue related to Skype For Business (SfB) users experiencing connectivity issues. CallTower Engineering has taken steps to remediate issues internally. Customers are reporting services have normalized when customers verified their network firewall settings were correct and then clearing their cache and rebooting.

Please see below for steps necessary to take:

https://www.uc.solutions/Skype_for_Business/Skype4B_Set_Up/005Firewall_Settings
• It is recommended to whitelist the domain ct950.com on your network as well as specifying the IP addresses.
• Another more flexible approach would be to simply whitelist the following networks since we can and will add servers over time to multiple locations:
• 205.196.169.0/24
• 205.196.173.0/24
• 205.196.174.0/25
• 67.213.189.0/24
• 63.128.106.128/26
• If a SonicWall or other firewall is utilizing "DPI" Deep Packet Inspection, it is recommended to disable this feature for voice traffic. All Skype traffic is Encrypted Data traffic and this feature isn't necessary, also it will interfere with Skype/Voice services and cause call quality issues.
• If your router is not configured for the new traffic protocols that Skype for Business (Lync) will introduce to your network, you could experience packet loss, dropped calls and jitter. You must make sure that SIP inspection or SIP ALG (Application level gateway) are disabled on your routers and firewalls to prevent this from happening. You may need to contact your ISP to have this done, but make sure this is completed prior to deployment. These features in routers are intended to block SIP traffic and will interfere with Skype for Business (Lync) communications.
• Clear your Skype for Business (Lync) cache: https://www.uc.solutions/Skype_for_Business/Skype_for_Business_Client/Windows_Users/How_to_clear_Skype_for_Business_cache
• Reboot your workstation to refresh DNS settings, after the above changes are confirmed.

Once you have taken these steps and if you continue to have issues after these changes have been completed, please contact support@calltower.com or 800-347-5444.
Nov 18, 11:39 MST