 systems to one another over existing data networks is a major motivating purchasing factor. In addition to carrying packetized voice, these networks carry signals for centralized voicemail, UC systems, and contact center applications. Contact center signals might indicate that all agents are busy and that calls should be sent to another site. Signals can also indicate the level of traffic at sites SO that calls are distributed to alternate sites based on traffic volumes or the number of agents logged in to the system. Often, customers with private lines or Multi-Protocol Label Switching (MPLS) networks between their locations use these connections for IP voice and video as well as data. (MPLS networks connect locations together via carriers' private data networks; for more information, see Chapter 5.) Customer calls answered in a central location can be transferred over these data links along with data traffic. The most important issue in extending IP and video between sites is ensuring that the links between locations are engineered with enough capacity to support voice and video and that Quality of Service (QoS) is implemented. The data connections are Data Centers and IP Private Branch Exchanges often upgraded for more capacity to handle voice traffic. The upgrade is less costly than separate per-site links for voice and individual voicemail and contact center systems. Combining voice, video, and data traffic between sites has resulted in cost sav- ings on long-distance fees. This is particularly true for organizations with international locations because data lines and calling rates are higher between intercontinental sites. Worldwide headquarters might be located in London, whereas regional headquarters are in the United States. They usually use managed network services such as MPLS, which can provide QoS for voice. These MPLS services are also used to carry video- conferencing signals between sites. Small and midsize organizations might use lower cost options such as Skype for international voice and video