VoIP & Mobile VoIP 梁紀翔 NETLab

2 Topics ► Voice over Internet Protocol  H.323, SIP, Skype  Adoption  Benefits  Challenge ► Mobile VoIP  Generic Access Network

3 Voice over Internet Protocol ► Family of transmission technologies for delivery of voice communications over IP networks ► Talks to other IP phone or PTSN ► Use codecs convert analog voice into digital audio stream ► Video, text, file, conference, voice mail … etc

4 Common protocols ► H.323 (ITU-T) ► Session Initiation Protocol (RFC 3261) ► Skype (Propritary)

5 H.323 ► First VOIP standard (Feb. 1996) ► Part of H.32x family ► Audio-Video communication on packet network ► Call singling & control, multimedia transport & control, bandwidth control for P2P and multipoint conference ► Based on Q.931 of ISDN

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9 SIP ► Application Layer protocol for controlling multimedia communication session over IP ► Client-Server HTTP like Text-based control message request/response ► Depend on SDP (RFC 2327), RTP

10 Request Messages Type Description REGISTERRegisters the user agent INVITE Initiates a call by inviting user to participate in session ACK Confirms that the client has received a final response to an INVITE request CANCELCancels a pending request BYE Indicates termination of the call OPTIONS Used to query the capabilities of a server Response Messages Type Description 1xx Informational Responses ex. 180 Ringing 2xx Successful Responses ex. 200 OK 3xx Redirection Responses ex. 302 Moved Temporarily 4xx Request Failure Responses ex. 404 Not Found 5xx Server Failure Responses ex. 503 Service Unavailable 6xx Global Failures Responses ex. 600 Busy Everywhere

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13 Skype ► Proprietary P2P model, written by KaZaA developers ► Decentralized user directory ► AES encrypted

14 Adoptions ► Many implementations of H.323 & SIP  Analog Telephone Adapter connects old phone and IP network  Dedicated IP phone  Softphone on PC

15 Benefits ► Reducing communication and infrastructure costs  Charged per amount of data not per time  Free/Open-source IP-PBX software integrate legacy phone system ex. Asterisk ► Flexibility  Easy to encrypt, location independence  Integration with other services

16 Challenge ► QoS  Latency and Jitter ► Power failure ► Emergency call ► Lack of redundancy ► Number portability ► Security ► Fax and other telephony devices

17 Mobile VoIP ► Extension of mobility to VoIP network ► Mobile device with SIP client ex. fring  High speed IP communication 3.5G, WiFi, WiMax  Some company may block SIP ► Use softswitch to bridge SIP and RTP to cell phone network  Handset still use GSM or CDMA

18 Generic Access Network ► 3GPP standard to let dual-mode handset to seamlessly roam or handover between WLAN and WAN(GPRS) ► GAN Controller  Inside cellular core network, as another base station ► When detects WLAN, establish secure IP connection to GAN Controller

19 Questions ?

20 References ► VoIP ► H ► SIP ► Asterik ► Skype ► GAN ► GAN ► “ 行動網際網路電話之研製與實現 ”, 李昆達, 2005 ► “ H.323 網路電話視訊監控與錄製系統之研製 ”, 曾致皓, 2008 ► “ H.323 網路電話音訊監控與錄製系統之研製 ”, 黃威穎, 2008 ► “ 客製化 H.323 協定之智慧型網路電話監控與錄音系統 ”, 蔡家瑞, 2009