Call blocking is available on Lync 2010 and 2013 and Skype for Business 2015 and 2019 platforms. When the recording system is experiencing technical difficulties and is unable to record conversations, it can block all new calls and disconnect ongoing calls if possible for configured recorded users. This feature allows mitigating the risk associated with not recording a certain conversation.

Voice, video, screen and application share calls, instant messages, and P2P file transfers can be blocked.
The system blocks all calls for the configured recorded users, so it is most suitable for always-on recording scenarios.
The components participating in call blocking (SfB/Lync Call and IM Filter Service, Proxy Service) are logging details of each call that has been blocked into an audit log file (lync_im_filter_auditlog.csv, lync_call_filter_auditlog.csv).
Ongoing calls can only be blocked when proxy based recording is used, otherwise, only new calls can be blocked.

Call blocking scenarios

The table below summarizes the different failure and call blocking scenarios:

Recording method	Failure scenario	Description
Proxy server based recording	Verba Proxy Server fails	All ongoing calls will be automatically disconnected on the proxy server that went down, as it will stop relaying RTP streams. The Verba Lync Filter applications (on the Lync Front End servers) will notice the problem (in 5 seconds). If none of the proxy servers are available for a Lync Filter, the plugin will send a "SIP ERROR(603)" response to each new SIP INVITE.
Proxy server based recording	Verba Lync Filter fails	All ongoing calls will stay connected and recorded but SIP BYE messages will not be captured and the system will terminate these calls after the timeout period. New calls cannot be blocked or recorded, as the Verba Lync Filter is down.
Proxy server based recording	Verba Recording Server fails	The proxy service notices the problem (in 5 seconds). If there is at least one recorder available, the proxy service will automatically restart recording on the available recorder. If there is no available recorder left, the proxy stops relaying RTP streams and calls get disconnected. If all of the recorders are offline for the proxy, it notifies the Verba Lync Filter (on the Lync Front End server) that all of the recorders are offline for the proxy. If the associated proxy server for the new call reports that no recorders are available, the Lync Filter plugin will send a "SIP ERROR(603)" response to each new SIP INVITE.
Proxy server based recording	Verba Media Collector fails on Edge	All ongoing calls will stay connected, but recording will be stopped, and the system will end these calls after timeout. The Verba Lync Filter applications (on the Lync Front-End servers) will notice the problem (in 5 seconds). If the Media Collectors is not available which would handle the call then the filter will prevent the call setup
Mediation and/or Edge based recording	Verba Media Collector fails	All ongoing calls will stay connected, but the recording will stop and the system will terminate these calls after the timeout period. The Verba Lync Filter applications (on the Lync Front-End servers) will notice the problem (in 5 seconds). If none of the Media Collectors are available, the Lync Filter plugin will send a "SIP ERROR(603)" response to each new SIP INVITE.
Mediation and/or Edge based recording	Verba Lync Filter fails	All ongoing calls will stay connected and will be recorded but SIP BYE messages will not be captured and the system will terminate these calls after the timeout period. New calls cannot be blocked, as the Verba Lync Filter is down.
Mediation and/or Edge based recording	Verba Recording Server fails	All ongoing calls will stay connected, but the recording will stop and the system will terminate these calls after the timeout period. The Verba Lync Filter applications (on the Lync Front-End servers) will NOT notice the problem and new calls will not be blocked.

For more information refer to the Configuring Lync call blocking on recording failure article.

A basic call blocking feature is available with the 1Global (formerly Truphone) integration. If there are no recorders at the time of call establishment, the call can be blocked.

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