VoIP and IP Telephony

VoIP and IP telephony allows PC users to make phone calls over the Internet or other packet networks via gateways and standard telephones. VoIP is an abbreviation for voice over Internet protocol. Types of network equipment that allow VoIP and IP telephony functions include hubs, switches, routers, repeaters, bridges, gateways, multiplexers, transceivers, and firewalls.  Network hubs serve as the central location for attaching wires to workstations.  A data switch connects computing devices to host computers, allowing a large number of devices to share a limited number of ports.  A router is a protocol-dependent device that connects subnetworks together.  A repeater is a device that connects 802.3 network cable segments.  A bridge is a device that interconnects local or remote networks.  A gateway is a device that can interconnect networks with different, incompatible communications protocols.  A multiplexer is a telecommunications device that funnels multiple signals onto a single channel.  A transceiver (transmitter-receiver) is a device that both transmits and receives analog or digital signals. A firewall is a system or group of systems that enforces an access control policy between an organization's network and the Internet for purposes of security. 

Protocol is an important specification to consider when searching for VoIP and IP telephony devices. This fundamental mechanism for network communications specifies the software attributes of data communications, including the structure of a packet and the information contained. Protocols may also prescribe some or all of the operational characteristics of the hardware on which they will run. Popular network protocols include IPX, TCP/IP and AppleTalk^®.  Other protocol choices include ATM, CANbus, ControlNet, DeviceNet, ARCNET, Ethernet, 10Base-T Ethernet, 10Base-2 Ethernet, 10/100 Ethernet, Fast Ethernet, Gigabit Ethernet, Fibre Channel, FDDI, Fieldbus, Frame Relay, INTERBUS, ISDN, PROFIBUS^®, SONET, Token Ring, and xDSL. Some VoIP and IP telephony devices can be configured to work in wireless systems.  AppleTalk is a registered trademark of Apple Computer. PROFIBUS is a registered trademark of PROFIBUS International.

Additional specifications to consider when searching for VoIP and IP telephony devices include port, form factor, performance specifications, and features.  Choices for port types include AUI, BNC, FireWire^® (IEEE 1394), GBIC, MIC, RJ-45, SC, serial, ST, ISDN BRI S/T, ISDN BRI U, and USB.  The number of ports is also important to consider. The form factor for VoIP and IP telephony devices can be chip, board, or module. Important performance specifications to consider include data rate, users, and operating temperature.  Data rate is the maximum data transfer speed.  Users refer to the number of users the device is designed for.  The operating temperature is the operating temperature range of the network equipment.  Common features for VoIP and IP telephony equipment includes light emitting diode (LED) indicators, integrated firewalls, IP addressing, and alarms.

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• Practical Power Guidelines for Cisco VoIP and Internet Telephony Applications (.pdf)
  Voice over IP (VoIP) is exploding in popularity as an application for business data networks. VoIP promises to consolidate a company's data and telecommunications infrastructure as well as its support...
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