 Calls over Wi-Fi are particularly cost-effective on international calls. The Demarcation Point at Which Telephone Companies Wire Trunks The local telephone company brings telephone lines into buildings and wires them to interfaces. The interface is called a jack or a punch-down block. Each outside line is punched down (wired) to the connecting block. RJ11c jacks connect one line per jack. The RJ stands for registered jack. These are the jacks found in most homes. The RJ21x, which holds 25 lines, is the interface to which local telephone companies wire multiple, outside lines in businesses. The RJ21X jack is a point from which telephone lines and trunks can be tested. For instance, if there is a question with regard to where a problem lies, the telephone company can test its trunk to the RJ21X jack, and the equipment vendor can test service between the equipment or router and the www.TechnicalPDF.com interface. The RJ21X jack is the demarcation point between the telephone company line and the inside wiring. The most common data jack is the RJ48 jack. Data trunks such as Carrier Gigabit Ethernet terminate on these connectors. Both these jacks are at customer premises, and they are the points at which telephone companies test trunks if there is an outage. The most common type of high-speed trunk for incoming customer contact centers is Carrier Gigabit Ethernet for data. Information on these services is in Chapter 4, "Managing Broadband Networks." MULTI-PROTOCOL LABEL SWITCHING FOR INTEROFFICE CONNECTIONS Multi-Protocol Label Switching (MPLS) is a Virtual Private Network (VPN) network service that large and midsize organizations deploy to link their domestic and international sites together. MPLS traffic is carried on a provider's core private data network rather than on the Internet. MPLS is suitable for transmitting packetized voice (VoIP), video, and data between sites. MPLS is starting to be replaced by Wide Area Software Defined Networks (WA SDNs) services, which have more capacity and flexible treatment by typ