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Network Modems

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About Network Modems

Network modems (modulators-demodulators) are devices or programs that allow computers to transmit data over telephone lines. They convert digital computer data to analog sound waves and then demodulate the carrier signals to decode the transmitted information. There are two form factors for network modems: internal and external. Internal modems are computer cards that attach to a computer through a slot. External modems are modules or devices that connect to a larger system through a physical port. In terms of connectivity, several device types are commonly available. Public switched telephone network (PSTN) modems transmit analog data across copper telephone wires. Integrated services digital network (ISDN) devices can transmit data over regular telephone lines or digital telephone lines. Network modems that use digital subscriber lines (DSL) support standard xDSL or variants such as asynchronous DSL (ASDL), symmetric DSL (SDSL), or high data rate DSL (HDSL). Cable modems operate over cable television lines and can achieve very high data rates. Fiber optic modems are also available.

Selecting network modems requires an analysis of bus, card, connector and interface types. Industry standard architecture (ISA) buses can handle 16-bit data transfers at clock speeds of 8 MHz. Peripheral component interconnect (PCI) buses can transfer 32 or 64 bits of data at clock speeds of 33 MHz. Universal serial bus (USB) 2.0 supports data transfer rates of up to 480 Mbps. Type II modem cards are 54 mm x 85.4 mm and up to 5.5 mm thick. Type III cards are also 54 mm x 85.4 mm, but up to 10.55 mm thick. Some network modems plug into RS232, RS422, or RS485 ports. Others interface directly with a programmable logic controller (PLC). Several connector types are commonly available. Medium interface connectors (MIC) are duplex devices used in fiber distributed data interface (FDDI) networks. RJ-45 connectors are similar in appearance to standard telephone connectors, but are twice as wide with eight wires. Straight tip (ST) connectors feature a quick release, bayonet coupling that requires only a quarter turn to engage or disengage. Many ISDN devices have a U interface that allows a direct connection to a wall jack, or an S/T interface for connections to other ISDN devices. Network modems that use IEEE 1394 or FireWire® connectors are also available. FireWire is a registered trademark of Apple Computer, Inc.

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Products & Services Related to Network Modems

Access Points
Access points are transmitter / receivers (transceivers) that connect to a network through an interface such as a bus or connector. They receive, store, and transmit data between the wireless LAN and the wired structure.
Radio Modems
Radio modems are radio frequency transceivers for serial data. They connect to serial ports (RS232, RS422, etc.) and transmit to and receive signals from another matching radio modem.
Wireless Modems
Wireless modems transmit modulated data using electromagnetic waves.

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Cable/DSL Modems > Switches > Network Adapters Cable/DSL Modems Switches Network Adapters
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Home Network Security

3Com | Routers, Switches, VoIP, Wireless, Network Management
Network Management Intelligent Management Center, Enterprise All Network Management Routers MSR 50 Series
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Part Numbers for Network Modems

Part # Distributor Manufacturer Product Category Description
USR5610B Newark US ROBOTICS Other Computers,56K Performance Pro Internal Modem,Computers,Computers Drop Ship:Yes,Network Products,56K Performance Pro Internal Modem ,Newark In One
MSCNC PLC Radwell SIEBE Not Provided NETWORK CONTROLLER W/O MODEM
MSCNCM PLC Radwell ROBERTSHAW Not Provided NETWORK CONTROLLER W/ MODEM

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