Chapter 16 VoIP
Management Switch Card User’s Guide
611
•
G.711
is a Pulse Code Modulation (PCM) waveform codec. PCM measures analog signal
amplitudes at regular time intervals (sampling) and converts them into digital bits (quantization).
Quantization “reads” the analog signal and then “writes” it to the nearest digital value. For this
reason, a digital sample is usually slightly different from its analog original (this difference is
known as “quantization noise”).
G.711 provides very good sound quality but requires 64kbps of bandwidth.
•
G.723.1
uses Low-Delay Code-Excited Linear Prediction (LD-CELP) to code audio in 30-
millisecond frames. The standard supports two bitrates, 6.3 kbps and 5.3 kbps.
4
G.723.1
provides toll-quality sound and requires very little bandwidth.
•
G.726
is an Adaptive Differential Pulse Code Modulation (ADPCM) waveform codec that uses a
lower bitrate than standard PCM conversion.
Differential (or Delta) PCM is similar to PCM, but encodes the audio signal based on the difference
between one sample and a prediction based on previous samples, rather than encoding the
sample’s actual quantized value. Many thousands of samples are taken each second, and the
differences between consecutive samples are usually quite small, so this saves space and
reduces the bandwidth necessary.
However, DPCM produces a high quality signal (high signal-to-noise ratio or SNR) for high
difference signals (where the actual signal is very different from what was predicted) but a poor
quality signal (low SNR) for low difference signals (where the actual signal is very similar to what
was predicted). This is because the level of quantization noise is the same at all signal levels.
Adaptive DPCM solves this problem by adapting the difference signal’s level of quantization
according to the audio signal’s difference level. A low difference signal is given a higher
quantization level, increasing its signal-to-noise ratio. This provides a similar sound quality at all
signal levels.
G.726 operates at 16, 24, 32 or 40 kbps.
•
G.729
is an Analysis-by-Synthesis (AbS) hybrid waveform codec. It uses a filter based on
information about how the human vocal tract produces sounds. The codec analyzes the incoming
voice signal and attempts to synthesize it using its list of voice elements. It tests the synthesized
signal against the original and, if it is acceptable, transmits details of the voice elements it used
to make the synthesis. Because the codec at the receiving end has the same list, it can exactly
recreate the synthesized audio signal.
G.729 provides good sound quality and reduces the required bandwidth to 8kbps.
16.1.7 PSTN Call Setup Signaling
PSTNs (Public Switched Telephone Networks) use DTMF or pulse dialing to set up telephone calls.
Dual-Tone Multi-Frequency (DTMF) signaling uses pairs of frequencies (one lower frequency and
one higher frequency) to set up calls. It is also known as Touch Tone®. Each of the keys on a DTMF
telephone corresponds to a different pair of frequencies.
Pulse dialing sends a series of clicks to the local phone office in order to dial numbers.
5
16.1.7.1 VoIP VLAN
Virtual Local Area Network (VLAN) allows a physical network to be partitioned into multiple logical
networks. Only stations within the same VLAN can communicate with each other.
4.
At the time of writing, the VOP supports the 5.3 kbps bitrate only.
5.
The VOP supports DTMF at the time of writing.
Summary of Contents for MSC1000G Series
Page 38: ...Table of Contents Management Switch Card User s Guide 38...
Page 39: ...39 PART I Introduction...
Page 40: ...40...
Page 54: ...Chapter 1 Getting to Know Your MSC Management Switch Card User s Guide 54...
Page 61: ...61 PART II Web Configurator...
Page 62: ...62...
Page 80: ...Chapter 3 The Web Configurator Management Switch Card User s Guide 80...
Page 162: ...Chapter 5 Alarm Screens Management Switch Card User s Guide 162...
Page 178: ...Chapter 6 Diagnostic Screens Management Switch Card User s Guide 178...
Page 184: ...Chapter 7 Maintenance Screens Management Switch Card User s Guide 184...
Page 204: ...Chapter 8 Multicast Screens Management Switch Card User s Guide 204...
Page 226: ...Chapter 9 Subscriber Port Setup Screens Management Switch Card User s Guide 226...
Page 227: ...Chapter 9 Subscriber Port Setup Screens Management Switch Card User s Guide 227...
Page 330: ...Chapter 10 IMA Screens Management Switch Card User s Guide 330...
Page 412: ...Chapter 11 Profile Screens Management Switch Card User s Guide 412...
Page 512: ...Chapter 12 Statistics Screens Management Switch Card User s Guide 512...
Page 560: ...Chapter 13 Switch Screens Management Switch Card User s Guide 560...
Page 598: ...Chapter 15 VLAN Screens Management Switch Card User s Guide 598...
Page 636: ...Chapter 16 VoIP Management Switch Card User s Guide 636...
Page 638: ...Chapter 17 Config Save Management Switch Card User s Guide 638...
Page 639: ...639 PART III Commands...
Page 640: ...640...
Page 646: ...Chapter 18 Commands Management Switch Card User s Guide 646...
Page 682: ...Chapter 19 acl Commands Management Switch Card User s Guide 682...
Page 690: ...Chapter 20 alarm Commands Management Switch Card User s Guide 690...
Page 696: ...Chapter 22 config Commands Management Switch Card User s Guide 696...
Page 754: ...Chapter 28 multicast Commands Management Switch Card User s Guide 754...
Page 840: ...Chapter 29 port Commands Management Switch Card User s Guide 840...
Page 924: ...Chapter 30 profile Commands Management Switch Card User s Guide 924...
Page 926: ...Chapter 31 redundant Commands Management Switch Card User s Guide 926...
Page 1062: ...Chapter 35 vlan Commands Management Switch Card User s Guide 1062...
Page 1103: ...1103 PART IV Troubleshooting Specifications Appendices and Index...
Page 1104: ...1104...
Page 1134: ...Chapter 39 Product Specifications Management Switch Card User s Guide 1134...
Page 1146: ...Appendix B Legal Information Management Switch Card User s Guide 1146...