Skype resolvers can also be used to track users location as they travel between cities.
This type of privacy issue can be mitigated by relaying Skype signal traffic through proxies. Although, there remain other methods of eavesdropping on traffic. The problem - the maximum tolerable Round Trip Time (RTT) of VoIP users is 300 milliseconds (ms) whereas the propagation delay in a fiber optical cable is 200ms. Therefore, when a user in France calls another one in India, the proxy service must incur less than 100ms additional RTT.