Chapter 4 - Call Establishment Principles What Are Call...

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Call Establishment Principles What Are Call Legs? This topic describes call legs and their relationship to other components. 3 © 2005 Cisco Systems, Inc. Al rights reserved. Cisco Public IP Telephony Dial-Peer Call Legs Call legs are logical connections between any two telephony devices, such as gateways, routers, Cisco CallManagers, or telephony endpoint devices. Call legs are router-centric. When an inbound call arrives, it is processed separately until the destination is determined. Then a second outbound call leg is established, and the inbound call leg is switched to the outbound voice port. Example: Call Legs Defined The connections are made when you configure dial peers on each interface. An end-to-end call consists of four call legs: two from the source router perspective (as shown in the figure), and two from the destination router perspective. To complete an end-to-end call from either side and send voice packets back and forth, you must configure all four dial peers. Dial peers are used only to set up calls. When the call is established, dial peers are no longer used. 4-4 Cisco Networking Academy Program: IP Telephony v1.0 Copyright © 2005, Cisco Systems, Inc.
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End-to-End Calls This topic explains how routers interpret call legs to establish end-to-end calls. 4 © 2005 Cisco Systems, Inc. Al rights reserved. Cisco Public IP Telephony End-to-End Calls An end-to-end voice call consists of four call legs: two from the originating router (R1) or gateway perspective, and two from the terminating router (R2) or gateway perspective. An inbound call leg originates when an incoming call comes into the router or gateway. An outbound call leg originates when a call is placed from the router or gateway. A call is segmented into call legs and a dial peer is associated with each call leg. The process for call setup is listed below: 1. The plain old telephone service (POTS) call arrives at R1 and an inbound POTS dial peer is matched. 2. After associating the incoming call to an inbound POTS dial peer, R1 creates an inbound POTS call leg and assigns it a Call ID (call leg 1). 3. R1 uses the dialed string to match an outbound voice network dial peer. 4. After associating the dialed string to an outbound voice network dial peer, R1 creates an outbound voice network call leg and assigns it a Call ID (call leg 2). 5. The voice network call request arrives at R2 and an inbound voice network dial peer is matched. 6. After R2 associates the incoming call to an inbound voice network dial peer, R2 creates the inbound voice network call leg and assigns it a Call ID (call leg 3). At this point, both R1 and R2 negotiate voice network capabilities and applications, if required. Copyright © 2005, Cisco Systems, IncVoice Dial Plans, Configuring Voice Interfaces and Dial Peers > Configuring Dialer Peers 4-5
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When the originating router or gateway requests nondefault capabilities or applications, the terminating router or gateway must match an inbound voice network dial peer that is configured for such capabilities or applications.
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This note was uploaded on 11/10/2009 for the course INT 662 taught by Professor Tholstrup during the Spring '09 term at Fort Hays.

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Chapter 4 - Call Establishment Principles What Are Call...

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