The Lync client requires a high quality network connection. If the connectivity between your VisitorLink Kiosk and your Lync server is overtaxed or under-engineered, you will experience dropped calls and errors – particularly during peak periods of traffic on your network.
Please be aware that real time communications are dependent not just on sufficient bandwidth in your connectivity, but other quality and speed factors such as minimal dropped packets and low latency connections. To evaluate whether your kiosk has sufficient connectivity to your Lync server, you can run the Lync 2013 Pre-Call Diagnostics. The PCD tool can be downloaded at http://www.microsoft.com/en-us/download/details.aspx?id=40733
If your network connection cannot sustain MOS scores of very near or at 4.0, with minimal packet loss or jitter in the PCD tool, your Lync client may occasionally disconnect unexpectedly, which can cause errors in VisitorLink.