Chapter 1 - Traditional Telephony Basic Components of a...

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Traditional Telephony Basic Components of a Telephony Network This topic introduces the components of traditional telephony networks. 3 © 2005 Cisco Systems, Inc. Al rights reserved. Cisco Public IP Telephony v1.0 Basic Components of a Telephony Network A number of components must be in place for an end-to-end call to succeed. These components are shown in the figure and include the following: ± Edge devices ± Local loops ± Private or central office (CO) switches ± Trunks Edge Devices The two types of edge devices that are used in a telephony network include: ± Analog telephones: Analog telephones are most common in home, small office/home office (SOHO), and small business environments. Direct connection to the PSTN is usually made by using analog telephones. Proprietary analog telephones are occasionally used in conjunction with a PBX. These telephones provide additional functions such as speakerphone, volume control, PBX message-waiting indicator, call on hold, and personalized ringing. ± Digital telephones: Digital telephones contain hardware to convert analog voice into a digitized stream. Larger corporate environments with PBXs generally use digital Copyright © 2005, Cisco Systems, Inc Introduction to Packet Voice Technologies > Traditional Telephony 1-3
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PBX or key system of that vendor only. Local Loops A local loop is the interface to the telephone company network. Typically, it is a single pair of wires that carry a single conversation. A home or small business may have multiple local loops. Private or CO Switches The CO switch terminates the local loop and handles signaling, digit collection, call routing, call setup, and call teardown. A PBX switch is a privately owned switch located at the customer site. A PBX typically interfaces with other components to provide additional services, such as voice mail. Trunks The primary function of a trunk is to provide the path between two switches. There are several common trunk types, including: ± Tie trunk: A dedicated circuit that connects PBXs directly ± CO trunk: A direct connection between a local CO and a PBX ± Interoffice trunk: A circuit that connects two local telephone company COs Example: Telephony Components The telephone installed in your home is considered an edge device because it terminates the service provided by your local telephone company. PBXs or key systems installed in a business would also be considered edge devices. The local loop is the pair of wires that come to your house to provide residential telephone service. Trunks are the interconnections between telephone switches. They can be between private switches or telephone company switches. 1-4
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Chapter 1 - Traditional Telephony Basic Components of a...

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