alls the service for the rest of the enterprise. (Because of technical and network management incompatibilities, MPLS requires that the same carrier supply end-to-end service for each site on the network.) This is particularly problematic in underdeveloped areas such as parts of Africa and outside of most populated cities in Latin America. Many companies with offices in less developed countries or rural areas have a mix of MPLS services for which their carrier has a presence, but they use the Internet for communications to the rest of their organization. However, Internet access in many less developed and rural areas is prohibitively expensive, costing thousands of dollars monthly for even T1 speeds of 1.54Mbps. Multi-Protocol Label Switching for Interoffice Connections Prioritizing Traffic via Classes of Service When customers want to differentiate certain traffic for specific treatment, they select from their carrier's list of classes of service. These classes of service are used to define the priority given to traffic for each class. For example, there might be three classes for data, one for voice, and another (the most expensive) for video. Voice and video are generally assigned higher priorities than data. Routers at customer sites add bits to packet headers with Class of Service (CoS) designations. At the MPLS edge router, these designations are added to the MPLS labels, along with addressing data. Some organizations use the lowest-priced CoS for most data and higher-priced CoS for database lookups. This can vary by industry. Retail organizations that depend on point-of-sale credit card lookups for revenue might assign these applications highest priority. One aspect behind the popularity of MPLS for multisite organizations is the grow- ing adoption of centralized Unified Communications (UC). UC denotes the use of one server to deliver e-mail, voicemail, and fax messages, as well as audio and video confer- encing through a single computer desktop application. Because it's centralized, all sites depend on co