Voice Data Integration Cisco do Brasil Jonio Cavalcanti

Agenda • Introduction • Codecs • Voice Over Packets • Characteristics for Vo. IP,

Vo. Coders (AUDIO CODECS) • Quality often measured using MOS • Standards vs Entrepreneurial

Voice Quality: Compression Standards Unacceptable Utility Business Toll Bandwidth (kbps) 64 PCM 56 48 40 ADPCM 32 (G. 723) 32 LD CELP 16 (G. 728) 24 16 8 LPC 4. 8 ADPCM 16 (G. 726) MPMLQ (G. 723. 1) LDCELP 16 (G. 728) CS-ACELP 8 (G. 729) 0 Quality Presentation_ID © 1999, Cisco Systems, Inc. 5

Route Replacement PBX PSTN T 1, E 1 PBX Telco Switch Voice GW V

Vo. X Transport PSTN PBX Telco Switch Analog/Digital V Voice GWs V Branch Office

Enterprise Voice VPN PSTN PBX T 1, E 1 PBX Telco Switch V V Qo. S WAN (Intranet/Internet) Typical Building Call Comes In Presentation_ID © 1999, Cisco Systems, Inc. Data Center V V PSTN Phoenix Charlotte V PSTN Philadelphia Bypass PSTN 9

Dial Plan Design 1111 PSTN 1111 NXX 555 -xxxx V NXX 556 -xxxx V 3600 A. 3 3600 B . 4 IP Qo. S WAN 10. 1. 5. 0 AS 5300 1111 PBX . 2 1111. 10 Netmeeting PC NXX 559 -xxxx 7 and 7 digits for Local PSTN 71 and 10 digits for Long Distance to PSTN 7 digits of “on net” Location NXX 557 -xxxx Presentation_ID © 1999, Cisco Systems, Inc. 10

Vo. FR, Vo. ATM, Vo. IP Quality Unacceptable Utility Quality Business Quality Cellular Cost ($) Toll Quality PSTN VOICE Vo. ATM (8 Kbps) (PCM/AAL 1) Vo. FR, Vo. ATM, Vo. IP Quality Internet Intranet Vo. IP CS-ACELP 8 Kbps (G. 729) Quality Presentation_ID © 1999, Cisco Systems, Inc. 12

L 3/L 2 Transport Characteristics • L 3—Vo. IP Flexible—IP is ubiquitous “Soft” form of Qo. S IP/UDP/RTP overhead (RTP compression) Quickly emerging technology Presentation_ID © 1999, Cisco Systems, Inc. • L 2—Vo. FR, Vo. ATM “Hard” Qos Infrastructure can be rigid Better suited for high volume bulk voice 13

Voice Transport Requirements • Subjective quality (MOS) MOS • Delay and delay variation • Background noise • Silence suppression Comfort noise • Echo cancellation • Language sensitivity Vo. IP Challenges in the WAN Loss Bandwidth Delay Presentation_ID © 1999, Cisco Systems, Inc. 15

Vo. IP (G. 729) Is Tolerant of “Occasional” Packet Loss missing packet G. 729 vocoder algorithm • The friendly “retransmission” is of no use in the Voice world… late is as good as never • Complex “concealment strategy” in algorithm interpolates lost packets based on context Presentation_ID © 1999, Cisco Systems, Inc. 16

How Does Echo Happen? Echo is due to a reflection Central Office 2 Wire Local Loop Rx & Tx Superimposed Receive Direction 2 w-4 w Hybrid Impedance mismatch at the 2 w-4 w hybrid is the most common reason for echo Transmit Direction Echo is always present and as a problem is a function of the echo delay, and the magnitude of the echo Presentation_ID © 1999, Cisco Systems, Inc. 17

Delay—How Much Is Too Much? Cumulative Transmission Path Delay CB Zone Satellite Quality Fax Relay, Broadcast High Quality 0 100 200 300 400 500 600 700 800 Time (msec) Delay Target ITU’s G. 114 Recommendation = 0 – 150 msec 1 -way delay Presentation_ID © 1999, Cisco Systems, Inc. 18

Fixed Delay Components Propagation Delay Serialization Delay— Buffer to Serial Link Processing Delay • Propagation—six microseconds per kilometer • Serialization • Processing Coding/compression/decoding Packetization Presentation_ID © 1999, Cisco Systems, Inc. 19

Fixed Frame Serialization Delay Matrix Frame Size Link Speed Presentation_ID 1024 Bytes 1 Byte 64 Bytes 128 Bytes 256 Bytes 512 Bytes 56 kbps 143 us 9 ms 18 ms 36 ms 72 ms 144 ms 214 ms 64 kbps 125 us 8 ms 16 ms 32 ms 64 ms 128 ms 187 ms 128 kbps 62. 5 us 4 ms 8 ms 16 ms 32 ms 64 ms 93 ms 256 kbps 31 us 2 ms 4 ms 8 ms 16 ms 32 ms 46 ms 512 kbps 15. 5 us 1 ms 2 ms 4 ms 8 ms 16 ms 23 ms 768 kbps 10 us 640 us 1. 28 ms 2. 56 ms 5. 12 ms 10. 24 ms 15 mss 1536 kbs 5 us 320 us © 1999, Cisco Systems, Inc. 640 us 1500 Bytes 1. 28 ms 2. 56 ms 5. 12 ms 7. 5 ms 20

Variable Delay Components Queuing Delay Dejitter Buffer • Queuing delay • Dejitter buffers •

Delay Variation—“Jitter” Receiver Sender Network A B C Sender Transmits t A D 1

Qo. S Networking Tools • Congestion Management (WFQ) • Qo. S Signaling (IP Prec / RSVP) • Packet Residency (MLPPP/MTU Size Reduction) • Bandwidth (RTP Header Compression, Silence Suppression, VAD) • Generic Traffic Shaping Presentation_ID © 1999, Cisco Systems, Inc. 23

Voice over IP Protocols Presentation Session G. 729(A)/G. 723(. 1)/G. 711 H. 323/SIP/SGCP/IPDC Transport Network RTP/UDP IP Link MLPPP/FR/ATM AAL 1 Physical – – – Constant - Voice Packets ride on UDP/RTP Variable - Several Signaling Methods Presentation_ID © 1999, Cisco Systems, Inc. 24

ITU H. 323 Infrastructure Gatekeeper H. 323 Terminals e V - User Interface Intranet © 1999, Cisco Systems, Inc. H. 320 (Over ISDN) Telephone Network - Gateway - Video Terminal Presentation_ID Gateway Proxy H. 324 (Over POTs) Speech Only (PSTN) Real-Time Network 25