【正文】 TFTP Server Cable Modem Termination System Rack DHCP/DNS Network Registrar Security Server Remote Access Server Rack Routers, etc. Int er Time Server Log Server 43 Presentation_ID 169。 registration was refused due to bad mic reject(c) modem did attempt to register。 Timing ? MPEG Frames 188 Byte, 4 Byte header ? Synchronous Transmission Clock Synch messages from HE (613 per sec) One source per DS Multiple sources per US, requiring time sharing Cable modems identified by 13 bit Service ID (SID) Downstream supports 8175 SIDs with additional 16 reserved. ? Upstream Time Sharing ? Time allocation MAP from HE (periodic) ? US time allocated for Cable modems in mini slots (Mini Slot = 8 ticks, Tick = 181。 UHF )5 5 7 5 0 M HzMi cro w a veAb o ve 1 G H zI n f ra R e d V i si b l eL i g h tU l t raV i o l e tXR a ys G a m maR a ysCB2 7 MH zCh a n n e l 25 5 M HzS a t e ll it eFre qu e nc y S pe c t rum? Up Stream (US) (Reverse) ? Subscriber to Cable pany ? 542 (30) MHz Note: Non North American systems can have different cutoff frequencies such as 65 MHz, 88 Mhz 105 Mhz etc. 13 Cisco Systems Confidential COAXIAL CABLE TRANSMISSION SYSTEMS COAXIAL CABLE and PROPERTIES DIRECT CURRENT ALTERNATING CURRENT Increasing Frequency For Direct Current, electron flow is distributed uniformly throughout the conductor. As frequency increases, electron flow radiates to the outer circumference. This is known as “skin effect” and is an important property in coaxial cable design. COAXIAL CABLE FOAM DIELECTRIC CABLE CHARACTERISTICS (dB per 100 ft ) SIZE (OD) LOSS LOSS ( INCHES) (54 MHz) (500MHz) RG 6 RG 59 Frequency Loss (dB) slope CENTER CONDUCTOR EXTERNAL JACKET DIELECTRIC OUTER CONDUCTOR Coaxial Cable 14 Cisco Systems Confidential COAXIAL CABLE TRANSMISSION SYSTEMS COMMON EQUIPMENT AND APPLICATIONS SPLITTER SPLITS SIGNAL INTO TWO EQUAL SIGNALS LOSS = 10 LOG 1 / 2 = 3 dB + Insertion loss = dB Available with MULTIPLE EQUAL or NON EQUAL PORTS. Available for Electrical or Optical Applications 0 dBmV dBmV dBmV SUBSCRIBER TAP TWO BASIC TYPES POWER PASSING POWER BLOCKING A B C A B Insertion Loss decreases as drop loss increases A C Insertion Loss higher, and varies with number of drops Number of drops typically 2, 4, 8 C B Isolation increases as drop loss increases 0 dBmV dBmV 36 dBmV 36 dB drop loss 15 Cisco Systems Confidential EQUALIZATION and ATTENUATION 55 750 MHZ INPUT EQUALIZER SHAPE 55 750 MHZ OUTPUT Slope Adjust { cable equalizer Frequency Loss (dB) COAXIAL CABLE TRANSMISSION SYSTEMS BASIC ONE WAY AMPLIFIER AC Coupler AC Coupler Forward Equaliser ATT Power Module ATT INTERSTAGE TILTING 16 Cisco Systems Confidential COAXIAL CABLE TRANSMISSION SYSTEMS BASIC ONE WAY AMPLIFIER BASIC TWO WAY AMPLIFIER AC Coupler AC Coupler Forward Equaliser ATT Power Module ATT High Pass Low Pass High Pass Low Pass ATT ATT Forward Equaliser Power Module ATT Reverse Equaliser 17 Cisco Systems Confidential COAXIAL CABLE TRANSMISSION SYSTEMS Forward Equaliser ATT Power Module ATT High Pass Low Pass High Pass Low Pass ATT Reverse Equaliser CPLR CPLR High Pass Low Pass Signal Director BASIC TWO WAY AMPLIFIER with BRIDGER 18 Cisco Systems Confidential Up Converter / Optical Node Frequency Synthesizer ATT IF RF Upconverter Optical Node Optical Electrical Diplexer 19 Cisco Systems Confidential COAXIAL CABLE TRANSMISSION SYSTEMS COMMON EQUIPMENT AND APPLICATIONS AMPLIFIER (FORWARD) AMPLIFIER ( TWO WAY) INPUT + 12 dBmV INPUT + 12dBmV OUTPUT + 34 dBmV OUTPUT + 34 dBmV CABLE LOSS 22dB GAIN + 22 dB GAIN + 22 dB CABLE LOSS 22dB DOWN STREAM DOWN STREAM UP STREAM ONE WAY TRANSMISSION TWO WAY TRANSMISSION 20 Cisco Systems Confidential COAXIAL CABLE TRANSMISSION SYSTEMS AFFECTS OF TEMPERATURE and COUNTERMEASURE LOSS (dB) TEMPERATURE (deg F) relative to reference frequency AGC (Autmatic Gain Control ) is the countermeasure Output signal is sampled, and fed back to the input of the amplifier to pensate for temperature, and to maintain a constant output. AGC functionality is distributed when needed to achieve stability at minimal cost. DISTRIBUTION OF AGC FUNCTION AMP 1 (AGC) AMP 2 (MAN) AMP 3 (MAN) AMP 4 (AGC) TEMP OUT CABLE IN OUT CABLE IN OUT CABLE IN OUT deg F PUT LOSS PUT PUT LOSS PUT PUT LOSS PUT PUT +90 +40 + +