Post on 29-Dec-2015
transcript
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
VoIP
Voice over IP
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
• Introduction• How VoIP works• Voice over IP Scenarios• The „Pros and Cons“• RTF (Real-time Transport Protocol)• H.323 Standard• Speech Samples• Future Aspects
Contents
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
What is VoIP ?
• VoIP = Voice over Internet Protocol
• Transmission of voice and video over data-networks (internet, intranet), using the Internet protocol (IP)
• Possible variants using VoIP :– PC to PC– PC to Phone and the other way around– Phone to Phone using the Internet / Intranet
Introduction
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
Microphone transforms acoustic waves into "current fluctuations"
microphone
Signal is transferredby a wire
Loudspeaker transforms the signal back into sounds
Loudspeaker
How VoIP works
The Classical Approach: Analog Transmission
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
How VoIP works
The Classical Approach : Digital Transmission
0111000111000001………
In time intervals the amperage is measured and its value is transferred
Microphone transforms acoustic waves into "current fluctuations"
Usual: 256 different values (256=2^8, => 8 bit);8000 measures per second => 64 kBit/s
transmission of 0 and 1 as on and turn-off processes;nearly error free
Converted back into current fluctuations and acoustic waves
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
How VoIP works
Tomorrow (?): Voice over IP
The Internet works package-oriented: data stream is distributed on packets, which are sent independently to the target
Transmission of media (audio,video) over the Internet Protocol:
This means for the media (speech), like you would:- record it on a tape- cut the tape into pieces- put the pieces in envelopes- at the destination paste the pieces in the correct order and play the tape
… and this all in real-time (almost)!
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
How VoIP works
• General approach in case of submitting speech:– Recording and digitalisazion of speech– Segmentation of data packets– The packets are transported over the internet to the receiver– The receiver‘s hardware turns the data back into speech– Timestamp guarantees correct time and order
How VoIP works
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
Synchronisation through Timestamp
56 57 58 59 75 76 77 78 79 95 9697 98 99
sampled
78 98
Sampling Instants
packetized58
Timestamp
sent58 78 98 118 138 158
received58 1581381189878
58 78 98 118 138 158 replayed
How VoIP works
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
Site BSite A
Internet
PSTN
Private VoiceNetworkVoice
SwitchVoice
Switch
Intranet
IPRouter PC
Phone
Fax
IPRouterPC
Phone
Fax
Modem Modem
Voice over IP Scenarios
The Classical Approach: Separate Voice and Data Networks
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
Voice over IP Scenarios
The Future Approach: Voice/Fax over IP - A Unified Network
Site BSite A
Internet
Intranet
IPRouter
PC withVoice/Fax
IP Phone
PSTNGateway
PSTNGateway
PC withVoice/Fax
IP Phone
IPRouter
PSTN
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
Voice over IP Scenarios
The Intermediate Approach: Voice/Fax over IP - A Unified Network
Site BSite A
Internet
Intranet
PC withVoice/Fax
IP Phone
PC withVoice/Fax
IP PhonePSTNGateway
PSTNGateway
VoiceSwitch
Phone
Fax
VoiceSwitch
Phone
Fax
IPRouter
IPRouter
PSTN
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
Voice over IP Scenarios
Site BSite A
Internet
IntranetPC with Headset
Roger Wilco Server
The Gamers Approach: Use of “Roger Wilco”
PC with HeadsetRoger Wilco Client
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
• Advantages– Cost savings on long distance calls– Less (no) need for private telephone networks– Single RJ-45 connector at the workplace for all services– Enables new multimedia features, e.g. human operator assisted
e-commerce
• Problems / Open Questions– Control of delay, jitter and packet loss over IP-based networks– QoS guarantees– Bandwidth
The „Pros and Cons“
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
• Introduction• How VoIP works• Voice over IP Scenarios• The „Pros and Cons“ • RTF (Real-time Transport Protocol)• H.323 Standard• Speech Samples• Future Aspects
Contents
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
Real-time Transport Protocol (RTP)
• RTP version 2 is specified by RFC 1889 • RTP covers functions such as
– Payload type identification (which codec and Framing)– arranging the packages by sequence numbers synchronisation by time stamps
(playing time of the individual Samples or Frames; – Synchronisation of several Media Streams – quality control and statistics
• RTP is defined independent of transportation protocol, sets however typically on UDP/IP
• RTP contains no mechanisms to the safety device of the quality of service (QoS)
Real-time Transport Protocol (RTP)
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
RTP and RTCP
• The concept covers two closely linked protocols– RTP (real-time transport Protocol): transport the Media Stream
– RTCP (real-time transport control Protocol): informed about the participants attached at the Media Stream and the quality of service (QoS)
• For each Media Stream and each direction, received from them, a separate RTP session opens, you get– an IP address (multicast address for Conferencing)
– a pair of UDP ports • n for the Media Stream (default 5004) • n+1 for RTCP (default 5005)
Real-time Transport Protocol (RTP)
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
RTCP: Paket-Typs and scalability
• RTCP reports are generated by all transmitters and receivers of the session in regularly intervals (statistic information)
• the interval must be selected in such a way that the total load remains within limits (recommended: approx.. 5% of the range of the session)
• very large groups to make possible (with thousands of participants), the interval computed due to the – amount of active participant – the extent of the individual report
Real-time Transport Protocol (RTP)
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
Header Format
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V=2|P|X| CC |M| PT | sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | timestamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | synchronization source (SSRC) identifier | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | contributing source (CSRC) identifiers | | .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | optional header extension | | .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Real-time Transport Protocol (RTP)
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
Overhead und Header Compression
• RTP header Overhead: Example – compressed language - 8 kbps
– every 20 ms a RTP package with 20 oktetts Payload
– 40 oktetts header per package - 24 kbps
• RTP header compression: – reduces Overhead
– router decompression necessarily - > high processor load
– Slow i-net connection (e.g. VoIP over V.34 modem)
Payload (20) 24 kbit/s
~10 kbit/s
IP (20) UDP (8) RTP (12)
Payload(20)compressed RTP (2 ... 4) cRTP
Real-time Transport Protocol (RTP)
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
VoIP Delay Budget (example: G.711)
• Input queuing not relevant
• Jitter buffer 4 ... 40 ms
• Decoding 1 ms *)
• Access (up) link transmission
• Backbone network transmission t
• Access (down) link transmission
• Coding and framing 20 ms *)
• Packetization 20 ms
• Output queuing 0 ... 8 ms
Total 45 ... 89 + t [ms]ITU-T G.114 Recommended (150 ms)
*) depends on uses codec
Real-time Transport Protocol (RTP)
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
H.323 : Packet-BasedMultimedia Communications Systems
System Control
Video I/OEquipment
System ControlUser Interface
RAS Control
Q.931 Call Setup
H.245 Control
User Data Applications T.120, etc.
LAN
H.323
H.225.0Layer
RTPAudio CodecG.711, G.722
Audio I/OEquipment
Video CodecH.261, H.263
H.323 Standard
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
MOS - Mean Opinion Score
Speech Quality
5 - Excellent4 - Good3 - Fair2 - Poor1 - Bad
Poor 2
Fair 3
Good 4
Excellent 5
64 32 16 8 4.8 2.4
Bit Rate [kbps]
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
Speech Samples
G. 71164 kbps
LPC2.4 kbps
Single Speaker
Music
Bit Errors0.1%
Bit Errors1%
GSM13 kbps
Speech Samples
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VoIP – Voice over Internet Protocol
Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003
Future Aspects
Future Aspects