Introduction to Vo IP Lecture 1 Paul Flynn

Introduction to Vo. IP Lecture 1 Paul Flynn

Vo. IP Part 1 – Sept - Dec 1. Introduction 2. Transporting Voice over IP Network 3. Speech Coding Techniques 4. Signalling 1 – H 323 5. Signalling 2 – SIP 6. Media Gateway Control 7. Vo. IP and SS 7 8. ATM 9. QOS and Traffic management 10. Designing a Vo. IP Network

Network Components SF RTP SJ IXC CO CO - Central Office Trunk - Switch-switch connection Loop - Line from switch to phone Tandem switch - provides switch-switch interconnection IXC - interexchange carrier PBX - Private branch exchange 3

The PSTN: Separate Voice and Signaling Networks • SSP: Service Switching Point (Telephone Switch) • STP: Signaling Transfer Point (Router) Voice SSP STP Trunk SSP SS 7 Trunk Signaling (Packet) SCP (TDM) Trunk • SCP: Service Control Point (Database, Logic) SSP STP 4

Local Loop Speaker 2 wire Talker Echo S w i t c h 2 wire Listener s w i t c h 2 wire • 2 wire from phone to switch • Tip and Ring - derived from old switchboard plugs • 4 wire used at switch • Conversion performed by hybrid

Local Loop (cont. ) Problems with Analog Transmission Speaker 2 wire Talker Echo H y b r i d 2 wire Listener H y b r i d 2 wire • Several problems with analog • Attenuation - loss of signal power • Distortion - unequal loss at different frequencies • Noise - induced into line which is amplified along with signal by network components • Echo - due to 2/4 wire conversion • Physical impairments - bad lines, bridge taps, load coils

Digitizing Voice • Assumption is that human speech information is contained in the range of 300 -3400 Hz Filter & use signal below 4 k. Hz to prevent aliasing Sample and quantize signal at 8 k. Hz encoder produces 64 kbit/sec stream of data 7

Waveform Coders (codec) Voice ENCODER Sampler 2 * Fmax Samples/Sec Low Pass Filter BW = Fmax Clock Quantizer n Bits/Sample 2 n Levels Binary Encoder Voice De. CODER Pulse Detector Binary to Decimal Decoder Filter BW = Fmax

Non-Linear vs. Linear Encoding Companding (a-law vs -law) Output Input Non- Linear Encoding Closely Follows Human Voice Characteristics High Amplitude Signals Have More Quantization Distortion (Both a- & - Law) Linear Encoding Relatively Easy to Analyze, Synthesize, and Regenerate All Amplitudes Have Roughly Equal Quantization Distortion

Linear Predictive Coding Source Coding 10 20 ms 0001 0010 0011 0100 0101 0111 1000 1001 1010 1011 1100 1101 1110 1111 Actual Code 1001 1011 0001 0010 0011 0100 0101 0111 1000 1001 1010 1011 1100 1101 1110 1111 Predicted Code 10

Bandwidth Requirements Voice Band Traffic Encoding/ Compression G. 711 PCM A-Law/u-Law G. 726 ADPCM Result Bit Rate 64 kbps (DS 0) 16, 24, 32, 40 kbps G. 729 CS-ACELP 8 kbps G. 728 LD-CELP 16 kbps G. 723. 1 CELP 6. 3/5. 3 kbps Variable

Voice Quality Anything Above an MOS of 4. 0 Is “Toll” Quality Compression Method MOS Score Delay (msec) 64 K PCM (G. 711) 4. 4 0. 75 32 K ADPCM (G. 726) 4. 2 1 16 K LD-CELP (G. 728) 4. 2 3– 5 8 K CS-ACELP (G. 729) 4. 2 15 8 K CS-ACELP (G. 729 a) 3. 6 15

Voice Activity Detection - 31 dbm B/W Saved Voice Activity (Power Level) Hang Timer No Voice Traffic Sent SID Buffer SID - 54 dbm Pink Noise Voice “Spurt” Time Silence Voice “Spurt”

Applications of Speech Coding q q q q Telephony, PBX Wireless/Cellular Telephony Internet Telephony Speech Storage (Automated call-centers) High-Fidelity recordings/voice Speech Analysis/Synthesis Text-to-speech (machine generated speech) Rensselaer Polytechnic Institute 14

Different Types of Signaling (when you place a call) • Supervisory - Determines state of line/trunk whether on/off-hook EM signal leads, loop open/closed • Addressing - passes digit information for call routing DTMF, DNIS • Informational - indicates call progress Busy signal, dial tone, ring back

Summary Page Local Loop FXS/ FXO Loopstart/ Gndstart SF RTP SJ IXC CO T 1/ E 1 DTMF/ MF CAS/ CCS 16

Voice Transport Protocols 17

Voice Transport Protocol Overview Encoder/ Decoder IP Cisco Gateway T 1/E 1 CAS/CCS ATM, FR, HDLC Cisco Gateway PBX PSTN 18

Queuing • Voice always given priority over data • Real-time queue for voice and video Data queue serviced only if nothing in Real Time queue - (Exhaustive like priority queuing) • Non-real time queue (Data) WFQ by default WFQ Disabled if Frame Relay Traffic Shaping Enabled Fancy queuing disabled if voice-encap set on interface

Voice Over IP 20

Protocols Used • H. 225. 0 for Connection and Status – Q. 931 ‘derived’ messages – ‘RAS’ for Endpoint-GK signaling. • H. 245 for negotiating channel usage and capabilities • Media transport – RTP/RTCP -- standard payloads (RFC 1889/1890) – ‘native’ uni/multicast support 21

Vo. IP Camps Circuit switch engineers “We over IP” “Convergence” ITU standards Conferencing Industry Netheads “IP over Everything” H. 323 SIP ISDN LAN conferencing I-multimedia WWW Call Agent SIP & H. 323 BISDN, AIN H. xxx, SIP IP “any packet” Rensselaer Polytechnic Institute “Softswitch” Our focus 22 BICC

IP SIP Phones and Adaptors 1 Are true Internet hosts • Choice of application • Choice of server • IP appliances Analog phone adaptor 2 Implementations • 3 Com (3) 3 • Columbia University Palm control • MIC World. Com (1) • Mediatrix (1) • Nortel (4) • Siemens (5) 44 5 Rensselaer Polytechnic Institute 23

PSTN to IP Call PBX PSTN External T 1/CAS 1 Call 9397134 Gateway Internal T 1/CAS (Ext: 7130 -7139) 2 Call 7134 Ethernet Regular phone (internal) 5 3 SIP server sipc Bob’s phone Rensselaer Polytechnic Institute 24 SQL database sipd 4 7134 => bob

IP to PSTN Call PBX PSTN External T 1/CAS 5 Call 5551212 Gateway (10. 0. 2. 3) Internal T 1/CAS 4 Call 85551212 3 Ethernet 5551212 Regular phone (internal, 7054) 1 Bob calls 5551212 SIP server sipc 2 SQL database sipd Use sip: 85551212@10. 0. 2. 3 Rensselaer Polytechnic Institute 25

End-to-End Delay Sender Receiver Network First Bit Last Bit Transmitted Received A Processing Delay A Network Transit Delay Processing Delay t End-to-End Delay 26

Fixed Delay Components Propagation Delay Serialization Delay— Buffer to Serial Link Processing Delay • Propagation—six microseconds per kilometer • Serialization • Processing Coding/compression/decoding Packetization

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

Delay Variation—“Jitter” Sender Receiver Network B A C Sender Transmits t A D 1 B D 2 = D 1 C D 3 = D 2 Sink Receives t 29 85

Network Qo. S Toolkit 30

Logical Connections Call Leg 1 Call Leg 2 IP Cloud Call Leg 3 Call Leg 4 31