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Published byShannon Powell Modified over 9 years ago
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Introduction to Packet Voice Technologies Cisco Networking Academy Program
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Traditional Telephony
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Basic Components of a Telephony Network
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Central Office Switches
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What Is a PBX?
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Basic Call Setup
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Supervisory Signaling
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Address Signaling –Tone telephone DTMF dialing Rotary telephone –Pulse dialing
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Informational Signaling
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Digital vs. Analog Connections
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Time-Division Multiplexing
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Frequency-Division Multiplexing
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Packetized Telephony Networks
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Packet Telephony vs. Circuit-Switched Telephony More efficient use of bandwidth and equipment Lower transmission costs Consolidated network expenses Increased revenue from new services Service innovation Access to new communications devices Flexible new pricing structures
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Call Control
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Distributed Call Control
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Centralized Call Control
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Packet Telephony Components
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Real-Time vs. Best-Effort Traffic Real-time traffic needs guaranteed delay and timing. IP networks are best-effort with no guarantees of delivery, delay, or timing. Solution is quality of service end-to-end.
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Foreign Exchange Station Interface
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Foreign Exchange Office Interface
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E&M Interface
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T1 Interface
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E1 Interface
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BRI
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Physical Connectivity Options
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Cisco IP Phone
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Analog Voice Basics
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Local Loops
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Types of Local-Loop Signaling Supervisory signaling Address signaling Informational Signaling
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On Hook
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Off Hook
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Ringing
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Ringing (Cont.)
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Pulse Dialing
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Dual Tone Multifrequency
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Informational Signaling with Call-Progress Indicators
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Trunks
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Foreign Exchange Trunks Foreign Exchange Office –Connects directly to office equipment –Used to extend connections to another location Foreign Exchange Station –Connects directly to station equipment –Used to provision local service
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Types of Trunk Signaling Loop start Ground start E&M Wink Start E&M immediate start E&M delay start
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Loop-Start Signaling
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Ground-Start Signaling
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E&M Signaling Separate signaling leads for each direction E-lead (inbound direction) M-lead (outbound direction) Allows independent signaling
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E&M Type I
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E&M Type V
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E&M Type II
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E&M Type III
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E&M Type IV
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Trunk Supervisory Signaling— Wink Start
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Trunk Supervisory Signaling— Immediate Start
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Trunk Supervisory Signaling— Delay Start
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2-Wire to 4-Wire Conversion and Echo Echo is due to a reflection. Impedance mismatch at the 2-wire to 4-wire hybrid is the most common reason for echo.
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Echo Is Always Present Echo as a problem is a function of the echo delay and the loudness of the echo.
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Echo Suppression
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Echo Cancellation
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Analog-to-Digital Voice Encoding
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Digitizing Analog Signals 1.Sample the analog signal regularly. 2.Quantize the sample. 3.Encode the value into a binary expression. 4.Compress the samples to reduce bandwidth, optional step.
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Basic Voice Encoding: Converting Digital to Analog 1.Decompress the samples, if compressed. 2.Decode the samples into voltage amplitudes, rebuilding the PAM signal. 3.Filter the signal to remove any noise.
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Nyquist Theorem
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Voice Compression Techniques Waveform algorithms –PCM –ADPCM Source algorithms –LDCELP –CS-ACELP
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Example: Waveform Compression PCM –Waveform coding scheme ADPCM –Waveform coding scheme –Adaptive: automatic companding –Differential: encode changes between samples only ITU standards: –G.711 rate: 64 kbps = (2 * 4 kHz) * 8 bits/sample –G.726 rate: 32 kbps = (2 * 4 kHz) * 4 bits/sample –G.726 rate: 24 kbps = (2 * 4 kHz) * 3 bits/sample –G.726 rate: 16 kbps = (2 * 4 kHz) * 2 bits/sample
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Compression Bandwidth Requirements
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Mean Opinion Score
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Perceptual Speech Quality Measurement
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Signaling Systems
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T1 Digital Signal Format
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Robbed-Bit Signaling
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Channel Associated Signaling— T1
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E1 Framing and Signaling
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Channel Associated Signaling— E1
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Common Channel Signaling
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ISDN –Part of network architecture –Definition for access to the network –Allows access to multiple services through a single access –Used for data, voice, or video Standards-based –ITU recommendations –Proprietary implementations
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ISDN Network Architecture
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Layer 3 (Q.930/931) Messages
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