4. VoIP
(1) VoIP benefits
 Some important benefits of VoIP implementation are as follows:
l Cost savings --- By m...

         VoIP Migration for Private Network

Conventional                                                        ...

                           VoIP Application for PSTN
                                               Protocol H.323


                                       VoIP Terminals
                                              IP Telephone Typ...

                                      VoIP Protocols

    Call Control and Signaling                          Signal...

                  H.323 & SIP Protocol Stack
OSI References                              H.323 Protocol Suite       ...
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Wireless IP Networks


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Wireless IP Networks

  1. 1. VoIP 4. VoIP (1) VoIP benefits Some important benefits of VoIP implementation are as follows: l Cost savings --- By moving voice traffic to IP-based networks, companies (or users) can reduce the toll charges associated with transporting calls over PSTN. VoIP service providers and companies can also conserve by investing in additional capacity only when it is needed. This is made possible by the distributed nature of VoIP and by reduced operations costs as companies combine voice and data traffic onto one network. l Open standards and multi vendor interoperability --- By adopting open standards, both companies and service providers can purchase equipment from multi vendors and eliminate their dependency on proprietary solutions. l Integrated voice and data networks --- Companies (or users) can build truly integrated networks for voice and data. These integrated networks not only provide the quality and reliability equivalent to PSTN, they also enable companies to quickly and flexibly take advantage of new opportunities within the changing world of communications. (2) Total VoIP and PSTN Traffic 1997 - 2001 The chart shows the global PSTN traffic growth. The data of 2001 recently updated is that the PSTN voice traffic grew just over 10% – the slowest rate of growth in 20 years. On the other hand, VoIP traffic has exceeded more than this chart in 2001, about 10% of global market. VoIP traffic here is all cross-border voice calls carried on IP networks but terminated on public switched telephone networks. From: www.telegeography.com 37
  2. 2. VoIP VoIP Migration for Private Network Conventional Migration Voice Network Migration Phase Completed 4.1 VoIP Migration for Private Network At the early stage, VoIP was applied to the private business networks to get clear benefits of operation cost reduction by integrating with voice (including FAX) and data traffics into single network. Traditional private networks have PBX (Private Branch Exchange) and connected to PSTN (Public Switched Telephone Network) for analog telephones. When VoIP is introduced, the interface to PBX is required to bridge the existing network and VoIP network with Gateway. When the usage of ordinary telephones becomes obsolete, PBX is eliminated and only VoIP network will work. 38
  3. 3. VoIP VoIP Application for PSTN Protocol H.323 PSTN PSTN •Signal Conversion H.323 H.323 •Packeting of Voice Gateway Gateway ITSP IP Network ITSP • Conversion between Telephone Number & H.323 GateKeeper IP address • Routing ITSP=IP Telephony Service Provider 4.2 VoIP Application for PSTN The network configuration for VoIP service by ITSP is shown here. As the access networks, the existing subscriber lines are used and the lines are connected through the existing local exchanges to Internet by ITSP. Features of the application of VoIP to PSTN are described as follows: ² Internet prosperity Because of Internet prosperity, VoIP has been applied for public telephone use. Although the existing analog telephone subscriber line and Local PSTN are used initially, the main transmission is relied on Internet. ² Breakaway from POTS (Plain Old Telephone Service) Because of competitive de facto standardized facilities and operations, Internet can carry the voice traffic much cheaper than POTS, the traditional telephone network and service are being broken away and even old players are entering in the VoIP market. ² Competition among Carriers New comers having VoIP technologies have emerged on the telephone service market. The operator called Greenfield Operator in general who have no existing network, provides VoIP service by use of entirely IP-based backbone network as shown below. Severe telephone competition decreases the telephone charge drastically, so that it becomes clear to keep the infrastructure on healthy financial background for most of network providers. Backbone Customer Greenfield Greenfield Customer Broadband IP Network Broadband IP Access IP Access 39
  4. 4. VoIP VoIP Terminals IP Telephone Type Network Device ISP IP Telephone Soft Phone Type PC Net Phone Network Dial Device ISP Soft Phone Call Channel TA Type Multi Ports Type Network Network Router Device Router Device Telephone ISP ISP PBX Multi Ports IP Phone VoIP PSTN PSTN TA 4.3 VoIP Terminal There are several types of VoIP terminal depending on usage of resources and configurations. In the case of IP Telephone, entire VoIP functions are accommodated in the set, of which block diagram is shown below. The voice coding methods are summarized in the table below. Compression Sample Typical end-to-end delay MOS Method (ms) Rate (kbps) Size (ms) Score (excluding channel delay) G.711 PCM 64 0.125 <<1 4.1 G.726 ADPCM 32 0.125 60 3.85 G.728 LD-CELP 16 0.625 <<2 3.61 G.729 CS-ACELP 8 10 25 – 35 3.92 G.729a CS-ACELP 8 10 25 - 35 3.7 G.723.1 MP-MLQ 6.3 30 97 3.9 G.723.1 ACELP 5.3 30 67 3.65 ADPCM: Adaptive Differential Pulse Code Modulation, LD-CELP: Low Delay Code Excited Linear Predictive CS-ACELP: Conjugates Structure Algebraic Code Excited Linear Predictive, MP-MLQ: Multi Pulse, Multi Level Quantization 40
  5. 5. VoIP VoIP Protocols Call Control and Signaling Signaling and Media Gateway Control H.323 Audio / Video H.225 H.245 Q.931 RAS SIP MGCP RTP RTCP RTSP TCP UDP IP H.323 Version 1 and 2 supports H.245 over TCP, Q.931 over TCP and RAS over UDP. H.323 Version 3 and 4 supports H.245 over UDP/TCP and Q.931 over UDP/TCP and RAS over UDP. SIP supports TCP and UDP. 4.4 VoIP Protocols For VoIP control protocols, there are two categories of protocols; one for call control (e.g. H.323 and SIP) and the other is gateway control (e.g. MGCP/Megaco, H.248). The details of those protocols are shown in the table below. H.323 SIP MGCP/H.248/Megaco MGCP/Megaco—IETF; Standards body ITU IETF H.248—ITU Architecture Distributed (Peer-to-peer) Distributed (Peer-to-peer) Centralized (Master/Slave) Current version H.323v4 RFC2543-bis07 MGCP 1.0, Megaco, H.248 Call agent/media•@ gateway Call control Gatekeeper Proxy/Redirect Server controller Endpoints Gateway, terminal User agent Media gateway Transmission Control MGCP—UDP;•@ Signaling transport Protocol (TCP) or User TCP or UDP Datagram Protocol (UDP) Megaco/H.248—both Multimedia capable Yes Yes Yes H.245 (signaling) or RFC RFC 2833 (media) or•@Signaling or RFC 2833 (media) DTMF-relay transport 2833 (media) INFO (signaling) Fax-relay transport T.38 T.38 T.38 Supplemental services Provided by endpoints or Provided all control by endpoints or call control •@ c Provided by call agent SIP: Session Initiation Protocol MGCP: Media Gateway Control Protocol, also known as Megaco and H.248, for handling the signaling and session management during a multimedia conference. The protocol defines a means of communication between a media gateway, which converts data from the format required for a circuit- switched network to that required for a packet-switched network and the media gateway controller. RTP: Real-Time Transport Protocol that specifies a way for programs to manage the real-time transmission of multimedia data over either unicast or multicast network services. RTCP: Real-Time Transport Control Protocol, RTSP: Real Time Streaming Protocol 41
  6. 6. VoIP H.323 & SIP Protocol Stack OSI References H.323 Protocol Suite SIP Protocol Stack 7. Application Audio Video Codecs Codecs 6. Presentation RAS H.245 Q.931 (H.225.0) (H.225.0) 5. Session RTP/RTCP SIP 4. Transport UDP TCP UDP TCP 3. Network IP IP 2. Data Link 1. Physical 4.5 H.323 & SIP Protocol Stack Both SIP and H.323 define mechanisms for call routing, call signaling, capabilities exchange, media control, and supplementary services. SIP is a new protocol that promises scalability, flexibility and ease of implementation when building complex systems. H.323 is an established protocol that has been widely used because of its manageability, reliability and interoperability with PSTN. SIP session setup for VoIP is illustrated as follows: Proxy Location Server Server (SIP Server) (SIP Server) Caller Callee Softphon SIP Phone e INVITE INVITE 100 ( Trying) INVITE 100 ( Trying) 180 ( Ringing) Pick-up 180 ( Ringing) handset 180 ( Ringing) 200 ( OK) 200 ( OK) 200 ( OK) ACK Media Session (Telephone Conversation) Hang up BYE 200 ( OK) SIP session setup example with SIP trapezoid 42