【正文】 al loss is a function of its diameter, dielectric construction, temperature, and operating frequency(f) 7 Cisco Systems Confidential Terms ? CarriertoNoise C/N (also CNR): The difference in amplitude between the desired RF carrier and the noise in that portion of the spectrum ? SignaltoNoise S/N (also SNR): Similar to C/N but relates to a BaseBand signal ? Ingress Noise Overtheair signals that are inadvertently coupled into the nominally closed coaxial cable distribution system. Difficult to track down and intermittent in nature. ? QPSK Quadrature Phase Shift Keying. A digital modulation method in which the there are 2 data bits represented with each baud symbol. ? QAM Quadrature Amplitude Modulation. A digital modulation method in which the value of a symbol consisting of multiple bits is represented by amplitude and phase states of a carrier. Typical QAM types are 16QAM(4 bits per symbol), 64QAM(6 bits per symbol), and 256QAM(8 bits per symbol) ? Downstream(DS) Signal flow from headend toward subscribers. Also called Forward Path ? Upstream(US) Signal flow from the subscribers to the Headend. Also called the Return or Reverse Path 8 Cisco Systems Confidential Terms ? Carrier or RF carrier. A signal on which another, lowerfrequency signal is modulated in order to transport the lowerfrequency signal to another location. ? FDM Frequency Division Multiplexing. A data transmission method in which a number of transmitters share a transmission medium, each occupying a different frequency. ? Headend The location where the Cable pany aggregates, bines, mixes, and modulates all signals in order to send them downstream and receive upstream signals ? Broadband Refers to the ability to frequency division multiplex(FDM) many signals in a wide RF bandwidth over an HFC work, and the ability to vast amounts of information. ? FEC Forward Error Correction. In data transmission, a process by which additional data is added that is derived from the payload by an assigned algorithm. It allows the receiver to determine if certain classes of errors have occurred in transmission and, in some cases, allows other classes of errors to be corrected. 9 Cisco Systems Confidential Measurement Units ? dB Decibel. A measure of the relative strength of two signals. Multiplication bees addition and Division bees subtraction. ? dBm Decibels with respect to one milliwatt. A unit of RF signal strength used in satellite work and other munications applications ? dBmV Decibels with respect to 1 millivolt in a 75ohm system. The unit of RF power used in CATV industry. ? 0 dBmV = 1 millivolt measured across an impedance of 75 ohms. 10 Cisco Systems Confidential Devices and Symbols Head End Fibre Satellite Antenna VHF/UHF Antenna RF Amplifier BiDirectional Amplifier Splitter 8Way Tap Fibre Transmitter Fibre Node 11 Presentation_ID 169。1 Presentation_ID 169。 1999, Cisco Systems, Inc. Cable Solutions Training Program For Universal Broadband Router and Cable Modem 2 Cisco Systems Confidential Visualizing a DOCSIS over HFC Network 100 Channels Headend COAX Tap Drop Node Hub Hub Node Node Cable Modem PC Node Node Node Node Node Hub Broadband Router uBR7246 Total Network Management PSTN Inter CNN HBO ESPN FNN Node DOWNSTREAM 88 880MHz UPSTREAM 5 42 MHz 3 Cisco Systems Confidential Access infrastructure Service Provider Customer Premises POTS ISP1 ISP2 Wireless SONET/ATM Backbone Comp A Comp B SwitchISDN Services: Inter Access Online Service Telemuting Cable HeadEnd D/C D/CCable HDSL ADSL VDSL Fanout Shelf D/C D/CNew Access Service 5 4 Cisco Systems Confidential Simple Lab Topology uBR7223 US DS IF RF Up convertor Diplex Filter uBR904 Legend: Downstream Upstream Bidirectional 10Base T Hub DHCP/DNS/TOD/TFTP Server Tel Connection Console Connection ATT ATT Hi Lo A D C B ATT ATT ATT Variable Attenuater 30 30 6 3 Repeat for B,C,D to US ports 1, 2, 3 5 Presentation_ID 169。 1999, Cisco Systems, Inc. Basic CATV Components, Concepts and Topology 12 Cisco Systems Confidential RF Spectrum ? Radio Frequency (RF) Above Audio to InfraRed ? Down Stream (DS) (Forward) Cable pany to subscriber 55750 (860) MHz F re q u e n cy1 1 0 / 2 2 0 VEl e ct ri ca lSi g n a l6 0 H zIF5 4 5 MH zRF ( V HF amp。 1999, Cisco Systems, Inc. DOCSIS Hardware Specifications 27 Cisco Systems Confidential DOCSIS Hardware Specifications (General) Frequency Range ?Upstream: 5 to 42 MHz ?Downstream: 88 to 860 MHz (User dependent) Bandwidth ?Upstream: 200, 400, 800, 1600, 3200 KHz ?Downstream: 6 MHz Modulation Modes ?Upstream: QPSK, or 16 QAM ?Downstream: 64 or 256 QAM Symbol Rates ?Upstream: 160, 320, 640, 1280, 2560 Ksym/sec ?Downstream: or Msym/sec