Chapter 3: Digital Voice Technology 3-1 Copyright © 1998, Cisco Systems, Inc.

3-2CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Objectives Review, identify, and define digital telephony fundamentals and basics Contrast digital and analog signaling Identify and contrast the different digital frame formats, signaling formats, and coding

3-3CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Objectives (cont.) Compare the various levels of voice quality Categorize the various types of digital voice compression Examine ISDN and identify the basic components of this digital architecture

3-4CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Analog versus Digital Signaling Analog signals require one set of wires (2 or 4) per call Digital signals require

3-5CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Digitizing Analog Signal Sample Quantization Encode Compression (optional)

3-6CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Digitizing Voice: Nyquist Theorem Codec PCM 64 kbps = DS0 Sampling Stage Analog Audio Source

3-7CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Quantization Time Voltage Segment 0 Segment 1 Segment 2 Note: each line represents 1/8000 of a second

3-8CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Quantization Technique Linear – Uniform quantization Logarithmic quantization – Companding the signal – Uniform signal to noise ratio – Two methods A-law (most countries) Mu-law (North America, Japan)

3-9CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Quantizing Error Stage 1 Quantizing Stage Quantizing Noise A-Law (Europe) Mu-Law (USA–Japan) Mu-Law (USA–Japan)

3-10CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Coding Polarity, one bit Segment, 3 bits Step, 4 bits PSe St

Digital Voice Technology Voice Compression Methods 3-11 Copyright © 1998, Cisco Systems, Inc.

3-12CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Speech Coding Schemes Wave form coders – Nonlinear approximation of the actual wave form – Examples: PCM, ADPCM, Mu-law, A-law Vocoders – Synthesized voice – Examples: LPC, channel, phase Hybrid coders – Linear wave form approximation with synthesized voice – Examples: APC, SELP, CELP

3-13CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Voice Compression Benefits/Drawbacks Benefit: Reduce bandwidth consumption Drawbacks: Quantization distortion Tandem switching degradation Delay (echo)

3-14CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Voice Compression Techniques Wave form algorithms –PCM: Pulse code modulation –ADPCM: Adaptive differential pulse code modulation Source algorithms –LD-CELP: Low delay, code-excited linear- processing –CSA-CELP: Conjugate structure algebraic code-excited linear-processing

3-15CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Example: Wave Form Compression ADPCM Wave form coding scheme Adaptive: automatic companding Differential: encode changes between samples only ITU standards: G.721 rate: 32 kbps = (2 x 4 kHz) x 4 bits/sample G.723 rate: 24 kbps = (2 x 4 kHz) x 3 bits/sample G.726 rate: 16 kbps = (2 x 4 kHz) x 2 bits/sample

3-16CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Example: Source Compression CELP –Hybrid coding scheme High quality voice at low bit rates, processor intensive, use of DSPs G.728: LD CELP16 kbps G.729: CSA-CELP8 kbps –G.729a variant8 kbps, less processor intensive, allows two voice channels encoded per DSP

3-17CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. G.729 and G.729a Comparison Both are ITU standards Both are 8 kbps CSA-CELP G.729 more complex and processor intensive G.729 higher quality than G.729a Compression delay the same (10-20 ms)

3-18CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Compression Techniques Bandwidth Requirement Standard Bit Rate (kbps) G.711, PCM 64 G.726, G.727, ADPCM 16,24,32,40 G.728, LD CELP 16 G.729, CSA-CELP 8 G.729a, CSA-CELP 8

3-19CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Ciscos Voice Compression Technologies Bandwidth (kbps) Quality UnacceptableBusiness Quality Toll Quality * PCM (G.711) * ADPCM 32 kbps (G.721) * ADPCM 24 kbps (G.723) * ADPCM 16 kbps (G.726) * LD CELP 16 kbps (G.728) * CSA-CELP 8 kbps (G.729a) * CSA-CELP 8 kbps (G.729)

3-20CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Digital Speech Interpolation (DSI) Silence suppression and VAD Removal of voice silence Examines voice for power, change of power, frequency, and change of frequency All factors must indicate voice fits into the window before cells are constructed Automatically disabled for fax/modem

Voice Quality Measurement 3-21 Copyright © 1998, Cisco Systems, Inc.

3-22CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Telephone Voice Quality Toll quality Transparent quality Conversational quality Synthetic quality

3-23CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Mean Opinion Score (MOS) SourceImpairment Codec X Channel Simulation Test statement: Nowadays, a chicken leg is a rare dish RatingSpeech QualityLevel of Distortion 5ExcellentImperceptible 4GoodJust perceptible but not annoying 3FairPerceptible and slightly annoying 2PoorAnnoying but not objectionable 1UnsatisfactoryVery annoying and objectionable MOS of 4.0 = Toll Quality

3-24CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. MOS Rating of Digital Voice G ACELP ?

3-25CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. MOS under Varying Conditions Example: G.729 MOS Rating Average speech level:3.85 Low input level: 3.54 Two tandem codings:3.46 Three tandem codings:2.68 5% bit error rate:3.24 5% frame error rate:3.02

3-26CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Subjective Impairment Analysis: MOS kbps Subjective Quality (MOS) Hybrid Coders Vocoders Wave Form Coders ScoreQualityDescription of Impairment Excellent Good Fair Poor Bad Imperceptible Just Perceptible, Not Annoying Perceptible and Slightly Annoying Annoying but Not Objectionable Very Annoying and Objectionable

Digital Voice Technology Channel Signaling Types and Frame Formats 3-27 Copyright © 1998, Cisco Systems, Inc.

3-28CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Channel Signaling Types T1 (defines physical characteristics) – AMI/B8ZS (line coding) – 100 ohms (impedance) DS1 (describes framing characteristics) – Frame: 24 DS0s or channels – SF (superframe): 12 frames (D4 framing) – ESF (Extended Super Frame): 24 frames

3-29CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Channel Signaling Types (cont.) E1 (physical characteristics) – AMI/HDB3 (line coding) – 75/120 ohms (impedance) E1 (framing characteristics) – Frame: 32 channels or E0s – MF (multiframe): 16 frames

3-30CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. DS1 Digital Signal Format Frame #1 F Frame #2 Frame #3 Frame #12 DS0 #1DS0 #2DS0 #3DS0 #4DS0 # DS0 #1DS0 #2DS0 #3DS0 #4DS0 # DS0 #1DS0 #2DS0 #3DS0 #4DS0 # DS0 #1DS0 #2DS0 #3DS0 #4DS0 # :::::: 12 frames = Superframe (SF) 24 frames = Extended Super Frame (ESF) F F F Framing bit 24 time slots (DS0 = 64 kbps)

3-31CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Extended Super Frame

3-32CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. A and B Robbed Bit Signaling (D4) Example: DS1 FXS Auto Ringdown FXS Rx States RCV No Ringing Ringing A B * 0 * 1 idle Tx FXS States XMT Loop Open Loop Clsd A B A-bit and B-bit Signaling A-bit and B-bit Signaling FXS Tx States XMT Loop Open Loop Clsd A B Rx FXS States RCV No Ringing Ringing A B 0 * 1 * idle

3-33CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. E1 Framing and Signaling DS0 #1DS0 #2DS0 #16DS0 # DS0 in an E Mbps DS0 #1 only contains framing information DS0 #16 only contains signaling information

3-34CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. E1 Frame Format 16 Frames per Multiframe Time Slot 0 Synchronization Bits 2 to 8 16th Time Slot Contains Multiframe Alignment Signaling 32 Time Slots (125 microseconds) 031

3-35CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. E1 Line Coding Unipolar – NRZ: Nonreturn to Zero – RZ: Return to Zero Bipolar – AMI – HDB3 Violation pulse if more than three zeros Highest quality and most efficient

3-36CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Digital Channel Signaling TypesCAS Bit Frame A 6th B 12th C 18th D 24th Extended Super Frame Supervision On/Off Hook Address Signaling (Dial Pulse) Audio Address Signaling (DTMF)

3-37CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Supervision On/Off-Hook Address Signaling (Dial Pulse) Digital Channel Signaling TypesCAS Time Slot 16 Audio Address Signaling (DTMF) E1 Time Slot 0 {

3-38CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Time-Division Multiplexing (TDM) Conversion 1 Conversion 2 Conversion 3 Conversion Conversion 24/30...

Digital TelephonyT1 and E1/J1 T1 (ITU-T G.733)E1/J1 (ITU-T G.732) Sampling Frequency Channel Bit Rate Time Slots per Frame Channels per Frame Bits per Frame System Bit Rate Framing Signaling 8 kHz DS064 kbps x = x 8 = 256 D4/Superframe (12) Extended Super Frame (24) E1: Multiframe (16) J1: CRV in bit 1 of frame Framing Indicator193rd bit of frame2.048 kbps word of 7 bits in the 0 channel of odd frames 8000 x 193 = Mbps8000 x 256 = Mbps E1: CCS in time slot 16 CAS in time slot 162 channels every other frame J1: time slot 0 Robbed bit channel associated signaling D4/SuperframeExtended Super FrameLSB/channel Frame 6 and 12Frames 6, 12, 18, CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc.

3-40CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Digital Telephony Synchronization Bit synchronization Primary reference source Ones density (except for J1/CMI) Time slot synchronization Bits/byte/channel Frame alignment Basic rule 193rd bit pattern

3-41CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Digital Telephony Synchronization (cont.) 1 bit time 648 ns 3 ms One DS1 ESF Frame, 125 microseconds, 193 bits 24 time slots Channel Time slot 5.18 microseconds Framing bit }

Digital Voice Technology ISDN Overview 3-42 Copyright © 1998, Cisco Systems, Inc.

3-43CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Integrated Services Digital Network (ISDN) ISDN Part of a network architecture Definition for the access to the network Allows access to multiple services through a single access Standards based ITU recommendations Proprietary implementations

3-44CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. ISDN Network Access Customer Equipment Public packet switched network PSTN (CO lines) 800 Tie trunks FX Private line data Traditional Access Customer Equipment Public packet switched network PSTN (CO lines) 800 Tie trunks FX Private line data ISDN Access Telephone Switch (e.g., DMS-100)

3-45CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. ISDN Network Architecture Telco Switch PRI Telco Switch BRI Common Channel Signaling Network and Database Circuit Switched Services Dedicated Circuit Services Public Packet Network ISDN PBX NT1 (23 B+D) (2B+D)

3-46CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. ISDN Services: Tie Trunks ISDN PBX Telco Switch PRI ChnlBankChnlBank Analog Facilities Digital Facilities

3-47CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. ISDN Services: Packet-Switched Data ISDN NT Telco Switch PRI/BRI Host or PAD Packet Handler Public Packet Network

3-48CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. ISDN Services: Circuit Switched and Dedicated Data Telco Switch PRI Telco Switch BRI Common Channel Signaling Network and Database Circuit Switched Services Dedicated Circuit Services Public Packet Network ISDN PBX NT1 (23 B+D) (2 B+D)

3-49CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. ApplicationSessionTransportNetworkData Link Physical I.430 basic interface + I.431 primary interface LAPDLAPBI.465/V.120 X.25 Q.931 call control X.25 Further Study End to end user signaling ISDN Protocols at the User- Network Interface Control Signaling PacketTelemetryCircuit Switch Semi- permanent Packet Switched D ChannelB Channel Presentation

3-50CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Layer 3 (Q.930/931) Messages Call establishment Call information phase Call clearing phase Miscellaneous

3-51CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Q.SIG Protocol ROSE: Remote Operation Service Elements ACSE: Association Control Service Elements End-to-end protocol network transparent Basic Rate I.430 Primary Rate I.431 Copper Optical Interface Dependent Protocols Media Physical Link Layer Network Layer 4-7 Q.SIG procedures for supplementary svcs In progress ISO 11582, ETS300, 239 ECMA165 ISO 11574, ETS /172, EDMA142/143 ECMA141, ETS Q.SIG generic func- tional procedures Q.SIG basic call

3-52CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Signaling System 7 (SS7) Call establishment Billing Routing Information exchange Architecture for performing out-of-band signaling within the PSTN for the purpose of:

3-53CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. SS7 Components STP SCP SSP SCP SCP SCP Network 1Network 2 Voice Trunk Signaling Link SSP Signal switching point STP Signal transfer point SCP Signal control point

3-54CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. OMAPASEs ISUP Signaling Connection Control Part SS7 Layers Physical Layer Message Transfer Part-Level 2 Message Transfer Part-Level 3

3-55CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. SS7 Messages and Protocols ISDN User Part (ISUP) Transaction Capabilities Application Part (TCAP) Operations, Maintenance, and Administration Part (OMAP) Application Service Elements (ASEs)

3-56CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. SS7 Message Formats FLAG BSN/BIBFSN/FIBLengthCheckStatus FLAG BSN/BIBFSN/FIBLengthCheckSvc InfoSig Info Fill-In Signal Unit Link Status Signal Unit Message Signal Unit FLAG BSN/BIBFSN/FIBLengthCheck 1 to 2 bytes 8 to 272 bytes BSN/BIB - Backward Sequence Number/Backward Indicator Bit FSN/FIB - Forward Sequence Number/Forward Indicator Bit Length - Number of octets between itself and the check sum Svc Info - Is used to indicate the type of signaling message that follows

3-57CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Summary Review, identify, and define digital telephony fundamentals and basics Contrast digital and analog signaling Identify and contrast the different digital frame formats, signaling formats, and coding

3-58CVOICEDigital Voice Technology Copyright © 1998, Cisco Systems, Inc. Summary (cont.) Compare the various levels of voice quality Categorize the various types of digital voice compression Examine ISDN and identify the basic components of this digital architecture