1 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 VoIP Voice over IP

2 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

3 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

4 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 Microphone transforms acoustic waves into "current fluctuations" microphone Signal is transferred by a wire Loudspeaker transforms the signal back into sounds Loudspeaker How VoIP works The Classical Approach: Analog Transmission

5 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 How VoIP works The Classical Approach : Digital Transmission ……… 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

6 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)!

7 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

8 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 Synchronisation through Timestamp sampled 7898 Sampling Instants packetized 58 Timestamp sent received replayed How VoIP works

9 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 Site BSite A Internet PSTN Private Voice Network Voice Switch Intranet IP Router PC Phone Fax IP Router PC Phone Fax Modem Voice over IP Scenarios The Classical Approach: Separate Voice and Data Networks

10 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 IP Router PC with Voice/Fax IP Phone PSTN Gateway PSTN Gateway PC with Voice/Fax IP Phone IP Router PSTN

11 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 with Voice/Fax IP Phone PC with Voice/Fax IP Phone PSTN Gateway PSTN Gateway Voice Switch Phone Fax Voice Switch Phone Fax IP Router PSTN

12 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 Voice over IP Scenarios Site BSite A Internet Intranet PC with Headset Roger Wilco Server The Gamers Approach: Use of “Roger Wilco” PC with Headset Roger Wilco Client

13 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“

14 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

15 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)

16 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)

17 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)

18 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 Header Format |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)

19 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)

20 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 VoIP Delay Budget (example: G.711) Input queuing not relevant Jitter buffer ms Decoding1 ms *) Access (up) link transmission Backbone network transmission t Access (down) link transmission Coding and framing20 ms *) Packetization20 ms Output queuing ms Total t [ms] ITU-T G.114 Recommended (150 ms) *) depends on uses codec Real-time Transport Protocol (RTP)

21 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 H.323 : Packet-Based Multimedia Communications Systems System Control Video I/O Equipment System Control User Interface RAS Control Q.931 Call Setup H.245 Control User Data Applications T.120, etc. LAN H.323 H Layer RTP Audio Codec G.711, G.722 Audio I/O Equipment Video Codec H.261, H.263 H.323 Standard

22 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 MOS - Mean Opinion Score Speech Quality 5 - Excellent 4 - Good 3 - Fair 2 - Poor 1 - Bad Poor 2 Fair 3 Good 4 Excellent Bit Rate [kbps]

23 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 Speech Samples G kbps LPC 2.4 kbps Single Speaker Music Bit Errors 0.1% Bit Errors 1% GSM 13 kbps Speech Samples

24 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 Future Aspects

25 VoIP – Voice over Internet Protocol Patrick Hügenell, Andreas Vetter – TIM01AGR – 2003 Thanks for your attention