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Figure 6.1 |
The waveform of a typical carrier. The carrier oscillates continuously, even when no data is being sent. |
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Figure 6.2 |
(a) A digital signal, and (b) the wave that results from amplitude modulation using the signal in (a). The carrier is reduced to 2/3 full strength to encode a 1 bit and 1/3 strength to encode a 0 bit. |
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Figure 6.3 |
An illustration of phase shift modulation. Arrows indicate points at which the carrier abruptly jumps to a new point in the cycle. |
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Figure 6.4 |
The use of two modems for long-distance communication across a 4-wire circuit. The modulator in one modem connects to the demodulator in the other. A pair of wires is needed for each connection. |
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Figure 6.5 |
Illustration of dialup modems that use the voice telephone system to communicate. To the telephone system, a dialup modem appears to be a telephone. |
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Figure 6.6 |
The concept of frequency division multiplexing. Each pair of source and destination can send data over the shared channel without interference. In practice, each end requires a multiplexor and demultiplexor for 2-way communication, and a multiplexor may need circuitry to generate the carrier waves. |
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Figure 11.1 |
Optical fibers and fiber modems used to provide a connection between a computer and a distant Ethernet. The computer and Ethernet hub both use conventional signals. |
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Figure 11.6 |
A bridge connecting LAN segments in two buildings. An optical fiber is used to connect the bridge to a remote LAN segment. |
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Figure 12.7 |
ADSL modems connected to existing local loop wiring. The modems can use a pair of wires simultaneously with analog telephone service. |
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Figure 26.5 |
Illustration of a dedicated NAT device that provides connections for multiple computers. The NAT box connects to an ISP (e.g., through a DSL connection or a cable modem). |
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Photo 1_001 |
Modem showing RS-232 connector for serial connection to computer |
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Photo 1_003 |
Computer system with modem |
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Photo 1_010 |
Serial cable to RS-232 connector |
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Photo 1_012 |
Dial-up voice line modem, showing RS-232 connector |
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Photo 1_014 |
RS-232 connectors, showing wiring for three-wire connection |
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Photo 1_024 |
RS-232 connector with control and data wiring |
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Photo 1_025 |
RS-232 connector with control and data wiring |
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Photo 1_042 |
Dial-up modem for voice lines |
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Photo 1_047 |
Dial-up modem for voice lines |
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Photo 1_048 |
An RS-232 cable tester |
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Photo 2_001 |
Modems in a computer center for dial-up access to the organization network |
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Photo 2_008 |
Modems in a computer center for dial-up access to the organization network |
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Photo 2_011 |
Modems in a computer center for dial-up access to the organization network |
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Photo 2_020 |
A serial connection switch that interconnects RS-232 serial cables |
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Photo 3_055 |
A rack holding a dial-in modem pool consisting of 16 modems. |
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Photo 3_056 |
A rack holding a dial-in modem pool consisting of 16 modems. |
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Photo 3_057 |
A rack holding a dial-in modem pool consisting of 16 modems. |
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Photo 3_058 |
Two Ascend Pipeline ISDN modems. |
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Photo 3_059 |
An Ascend Pipeline ISDN modem. |
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Photo 3_060 |
An Ascend Pipeline ISDN modem. |
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Photo 4_001 |
A dial-in pool of 96 modems. The six rectangular devices near the middle are terminal servers. Each terminal server connects 16 modems to the local area network. |
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Photo 4_002 |
A dial-in pool of 96 modems. The six rectangular devices near the middle are terminal servers. Each terminal server connects 16 modemsto the local area network. |
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Photo 4_003 |
A dial-in pool of 96 modems. The six rectangular devices near the middle are terminal servers. Each terminal server connects 16 modems to the local area network. |
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Photo 4_004 |
Closeup of modems in rack with a terminal server below. |
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Photo 4_005 |
Closeup of modems in rack with a terminal server below. |
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Photo 4_006 |
The rear of a terminal server. A serial line connects each modem to a terminal server. |
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Photo 4_007 |
The rear of a terminal server. A serial line connects each modem to a terminal server. |
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Photo 4_008 |
Rear view of a dial-in pool of 96 modems (see photo img4_001). |
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Photo 4_009 |
Rear view of a dial-in pool of 96 modems (see photo img4_001). |
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Photo 4_075 |
Two examples of PCMCIA fax/modem/Ethernet adapters. |
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Photo 4_076 |
Two examples of PCMCIA fax/modem/Ethernet adapters. |
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Photo 4_077 |
Two examples of PCMCIA fax/modem/Ethernet adapters. |
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Photo 4_103 |
A PCMCIA modem being inserted into a laptop computer. Attached to the card is an adaptor which connects the card to a standard RJ-11 telephone line. |
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Photo 4_104 |
A PCMCIA modem being inserted into a laptop computer. Attached to the card is an adaptor which connects the card to a standard RJ-11 telephone line. |
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Photo 4_107 |
A standard desk fax modem. In the middle are seen two RJ-11 telephone jacks. One connects the modem to a telephone line while the other is empty. On the far right is a serial line connecting the modem to a computer. |
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Photo 4_108 |
A standard desk fax modem. In the middle are seen two RJ-11 telephone jacks. One connects the modem to a telephone line while the other is empty. On the far right is a serial line connecting the modem to a computer. |
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Photo 4_109 |
The front of a standard desk fax modem showing its various indicators. |
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Photo 4_110 |
The front of a Motorola cable modem showing its various indicators. |
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Photo 4_111 |
The back of a Motorola cable modem. On the left is a standard coaxial television cable connector. The modem sends and receives data over the existing cable system infrastructure through this connection. On the right is an RJ-45 Ethernet jack which connects the modem to a computer. |
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Photo 5_001 |
Motorola CyberSurfer Wave cable modem |
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Photo 5_002 |
Motorola CyberSurfer Wave cable modem |
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Photo 6_029 |
A Fujitsu DSL modem. |
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Photo 7_002 |
A Cisco 673 DSL modem. |
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Photo 7_006 |
Cisco DSL products, including DSLAM and DSL modem. |
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Photo 7_008 |
A twisted pair interface card for a Cisco DSLAM. This device is the modem in the service provider's DSLAM, typically located in the service provider's office. |
