POP kết nối cuộc gọi thông qua một máy chủ và một kết nối an toàn với tường lửa khuôn viên trường. Một mức độ bảo mật được cung cấp bởi IPsec. Các doanh nghiệp đã nhận ra rằng Internet là một, trung bình trên toàn thế giới giá cả phải chăng có thể | The Last Mile 147 In many loops remote terminals RTs are set up at some distance from the wire center. Here 96 672 or some other number of channels are aggregated and transmitted over optical fibers between the MDF and the remote terminals. Called digital loop carrier DLC the channels are distributed from the RTs to customers in the carrier serving area CSA over distribution and drop cables. The carrier serving area is limited to 9 000 feet from the RT. Any DSLs home on DSLAMs located at the RT. Optical Fibers in the Local Loop In the local loop carriers have installed fiber to carry multiplexed signal streams close to their destination. They terminate in optical network interfaces ONIs where twisted pairs are used to complete the connection to residences or small businesses. Several acronyms are used to identify such installations FITL fiber in the loop FTTC fiber to the curb FTTH fiber to the home. They are used without precision to indicate various levels of fiber availability. Most carriers are awaiting the development of demand for residential wideband services before making major commitments to these facilities. SONET rings are employed to connect the main switching center remote switches remote terminals distribution interfaces and other traffic collection points. Figure illustrates the principle of applying SONET in the local communication environment to replace feeder cables. In the figure a star-star arrangement is compared to ring-based structures that employ SONETs. The ring-bus structure is constructed from the combination of cable television and incumbent local exchange Star-star Ring-bus SAP SONET Wire center SONET Ring-star ADM Distribution lant FDI Feeder plant CO Remote switch Service access point SAP Feeder distribution interface FDI or Feeder plant Feeder plant Distribution plant SAP DM Add-drop multiplexer ADM Figure Alternative architectures for loop plant. SAP Cable Distribution plant 148 The Convergence of Voice and Data
