Cisco call manager express
Cisco Networking Academy Program
IP Telephony
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1
Overview of Cisco CME
IP Telephony
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2
What is Cisco CallManager Express?
Cisco CME
Trunks PSTN
WAN
• Call processing for small to mediumsized deployments • VoIP integrated solution • Up to 120 IP phones • IOS based solution
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What is Cisco CallManager Express? (Cont.)
• Select IOS based platform • Multiservice access routers
2600XM
3700
1700
IP Telephony
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How DoesCisco CallManager Express Work?
Connection(s) to PSTN
• Analog • Digital
PSTN
IP Telephony
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How Does Cisco CallManager Express/Cisco Unity Express Work? (Cont.)
PSTN
H.323 H.323 H.323 between Cisco CME systems
WAN
H.323 SIP
WAN
PSTN Gateway and IP to IP Gateway functionality
PSTN
PSTN
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6
Differences between Traditional Telephony and VoIP
IP Telephony
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7
Basic Components of a Telephony Network
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8
Central Office Switches
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What Is a PBX?
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10
What Is a Key System?
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11
Basic Call Setup
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12Digitizing 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 (multiplexing), optional step
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13
Nyquist Theorem
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14Quantization
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Quantization Techniques
• Linear
Uniform quantization
• Logarithmic quantization
Compands the signal Provides a more uniform signal-to-noise ratio
• Two methods
α-law (most countries) μ-law (Canada, U.S., and Japan)
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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 samplesonly
• ITU standards:
G.711 rate: 64 kbps = (2 x 4 kHz) x 8 bits/sample G.726 rate: 32 kbps = (2 x 4 kHz) x 4 bits/sample G.726 rate: 24 kbps = (2 x 4 kHz) x 3 bits/sample G.726 rate: 16 kbps = (2 x 4 kHz) x 2 bits/sample
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Example: Source Compression
• CELP
Hybrid coding scheme
• High-quality voice at lowbit rates, processor intensive • G.728: LDCELP—16 kbps • G.729: CS-ACELP—8 kbps
G.729A variant—8 kbps, less processor intensive, allows more voice channels encoded per DSP Annex-B variant –VAD and CNG
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G.729 and G.729A Comparison
• Both are ITU standards • Both are 8 kbps CS-ACELP • G.729 more complex...
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