Boštjan Šteiner VIDEOTELEFONIJA PREKO IP OMREŽJA Diplomska naloga Maribor, februar 2010 I Diplomska naloga univerzitetnega študijskega programa VIDEOTELEFONIJA PREKO IP OMREŽJA Študent: Boštjan ŠTEINER Študijski program: UN ŠP Telekomunikacije Mentor: red. prof. dr. Zdravko KA ČIČ Somentorica: doc. dr. Mirjam SEPESY MAU ČEC Maribor, februar 2010 II III ZAHVALA Zahvaljujem se mentorju dr. Zdravku Ka čič in somentorici dr. Mirjam Sepesy Mau čec za pomo č in vodenje pri opravljanju diplomskega dela. Posebna zahvala velja staršem, ki so mi omogo čili študij in ženi, saj me je vsa ta leta vzpodbujala ter mi stala ob strani. IV VIDEOTELEFONIJA PREKO IP OMREŽJA Klju čne besede: videotelefonija, SIP, H.323, IP omrežje, Asterisk UDK: 621.39(043.2) Povzetek V diplomskem delu opišemo delovanje videotelefonije. Opis je podan na na čin, ki ga ponujajo globalni ponudniki in na na čin za doma čo uporabo. V uvodu je podana zgodovina videotelefonije in njen razvoj po svetu. V nadaljevanju smo se osredoto čili na signalizacijske protokole, kodirnike in na kratko opisali njihovo delovanje. Posvetili smo se strukturi videotelefonije, ki jo imajo realizirano razli čni ponudniki v Sloveniji. Na koncu smo se lotili še problema izvedbe domače centrale za videotelefonijo s pomo čjo odprtokodnega telekomunikacijskega sistema Asterisk. V VIDEO TELEPHONY OVER IP NETWORK Key words: video telephony, SIP, H.323, IP network, Asterisk UDK: 621.39(043.2) Abstract In our diploma work we have described the video telephony. The description is presented as given by global providers and for home usage. In the introduction we have presented the history of the video telephony and her worldwide development. Hereinafter we have focused on signal protocols, encoders and shortly described their functioning. We have focused on the structure of video telephony, which is realised by various providers in Slovenia. At the end we have tackled with the problem of implementing the video telephony home exchange with the help of the open source telecommunication system Asterisk. VI KAZALO 1 UVOD ................................................................................................................................ 1 2 VIDEOTELEFONIJA PO SVETU ................................................................................. 3 2.1 Zgodnja zgodovina ...................................................................................................... 3 2.2 Razvoj protokolov ....................................................................................................... 5 2.3 Videotelefonija danes .................................................................................................. 5 3 SIGNALIZACIJSKI PROTOKOLI ............................................................................... 7 3.1 H.323 standard ............................................................................................................. 7 3.1.1 Kaj je H.323? ........................................................................................................ 7 3.1.2 Arhitektura H.323 ................................................................................................. 8 3.1.3 Pregled protokolov H.323................................................................................... 12 3.1.4 Naslavljanje H.323 ............................................................................................. 14 3.1.5 Signalizacija RAS ............................................................................................. 15 3.1.6 Klicna signalizacija............................................................................................. 16 3.2 P rotokol za zagon seje ............................................................................................. 21 3.2.1 Arhitektura SIP ................................................................................................... 21 3.2.2 Vzpostavljanje klica SIP ..................................................................................... 25 3.2.3 Prednosti SIP-a pred drugimi signalizacijskimi protokoli .................................. 26 3.2.4 Zahteve SIP ........................................................................................................ 28 3.2.5 Odgovori SIP ...................................................................................................... 31 3.2.6 Naslavljanje SIP ................................................................................................. 31 3.2.7 Čela sporo čila ..................................................................................................... 32 3.3 Protokol za opis seje ................................................................................................ 34 3.3.1 Zgradba opisov SDP ......................................................................................... 34 3.3.2 Skladnja SDP ...................................................................................................... 36 4 KODIRNIKI ................................................................................................................... 38 4.1 AUDIO KODIRANJE ............................................................................................... 38 4.1.1 Metode kodiranja govora ................................................................................. 38 4.1.2 Vrste kodekov za govor ...................................................................................... 38 4.1.3 G.711 .................................................................................................................. 39 4.1.4 Adaptivni diferen čni PCM - ADPCM .............................................................. 40 VII 4.1.5 Kodeki z analizo s sintezo - AbS ....................................................................... 41 4.1.6 Izbira kodekov .................................................................................................... 43 4.2 VIDEO KODIRANJE ............................................................................................... 45 4.2.1 H.261: Kodek za osnovno video konferenco...................................................... 45 4.2.2 H.263: Video kodek za srednje kvalitetno video konferenco ............................ 46 4.2.3 H.264 / MPEG-4: Video kodek za visoko kvalitetne video konference ............ 50 5 VARNOST ....................................................................................................................... 53 6 STRUKTURA OMREŽJA ............................................................................................ 55 6.1 Globalna uporaba ....................................................................................................... 55 6.2 Doma ča uporaba ........................................................................................................ 58 6.3 Prikaz grafov razli čnih video klicev .......................................................................... 62 7 GRADNIKI OMREŽJA ................................................................................................ 66 7.1 Asterisk ...................................................................................................................... 66 7.2 Videotelefon Leadtek BVP 8882 ............................................................................... 68 7.3 Usmerjevalnik Netgear WGR614 .............................................................................. 69 7.4 Primerjava programske opreme VoIP central ........................................................... 70 8 SKLEP ............................................................................................................................. 74 VIRI, LITERATURA ..................................................................................................... 75 PRILOGE ........................................................................................................................ 76 VIII KAZALO SLIK Slika 2.1: Prvi videotelefon ................................................................................................... 3 Slika 2.2: VideoPhone 2500 .................................................................................................. 4 Slika 3.1: Arhitektura H.323 ................................................................................................. 8 Slika 3.2: Primer cone ......................................................................................................... 10 Slika 3.3: Centralizirana konferenca ................................................................................... 11 Slika 3.4: Decentralizirana konferenca ................................................................................ 11 Slika 3.5: Mešana konferenca .............................................................................................. 12 Slika 3.6: Logi čni kanali ...................................................................................................... 13 Slika 3.7: Klic, ko ni vratarjev ............................................................................................. 17 Slika 3.8: Klic z vratarji ....................................................................................................... 18 Slika 3.9: Klic z vratarji ....................................................................................................... 19 Slika 3.10: Arhitekturni model H.323 za internetno telefonijo ........................................... 20 Slika 3.11: Signalizacijski podatki .....................................................................................