Một khung không đánh số mang theo dữ liệu kiểm soát như yêu cầu ngắt kết nối, công nhận, và từ chối khung. Dữ liệu: Một lĩnh vực có kích thước thay đổi có chứa một gói tin được đóng gói | NMT 900 Nordic Mobile Telephone 900 MHz 338 NMT 900 Nordic Mobile Telephone 900 MHz A 1G analog cellular radio technology developed and placed into service in the early 1980s in Scandinavian countries. NMT 900 operates in the 900 MHz band employing frequency division multiple access FDMA to derive 1999 channels with a width of kHz. NMT 900 employs frequency division duplex FDD to achieve bidirectional communications with the downlink in the 935-960 MHz band and the uplink in the 890-915 MHz band. Within each channel frequency modulation FM is employed. See also 1G analog cellular radio channel downlink FDD FDMA FM and uplink. NN Network Neutrality Referring to Internet neutrality. See Net neutrality. NNI Network-to-Network Interface The boundary or point of interaction between network service NNI is both a physical and logical point of NNI serves the technical boundary where protocol issues are resolved and as the point of division between the responsibilities of the individual service providers. NNIs are defined for asynchronous transfer mode ATM and frame relay as examples. See also ATM logical frame relay physical and protocol. NOC Network Operations Center pronounced knock Also known as network control center NCC . A centralized location from which a large complex network and its component subnetworks and network elements can be monitored and faults or performance failures can be identified diagnosed isolated and often corrected. See also network network element and subnet. node 1. A junction point at which two or more circuits interconnect in a data network. A bridge for example interconnects two or more segments of a local area network LAN . See also bridge circuit LAN and network. 2. In a switched network a switching point that comprises a point of interconnection for circuits a data switch and control facilities. In the public switched telephone network PSTN for example a great many circuits terminate in a central office .
