Introduction to Communication Networks
Introduction to Communication Networks EL ENG 122
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This 16 page Class Notes was uploaded by Kris Heathcote on Thursday October 22, 2015. The Class Notes belongs to EL ENG 122 at University of California - Berkeley taught by Staff in Fall. Since its upload, it has received 39 views. For similar materials see /class/226761/el-eng-122-university-of-california-berkeley in Electrical Engineering at University of California - Berkeley.
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Date Created: 10/22/15
Contents Realtime Transport Protocol RTP a Purpose u Protocol Stack u RTP Header u Realtime Transport Control Protocol RTCP Voice over IP VoIP 1 Motivation El H323 El SIP a VolP Performance Tests 1 Buildout Delay References 1 Computer Networks A Tanenbaum a Computer Networks L Peterson and B Davie RTP Purpose Provide a generic transport capabilities for realtime multimedia applications Supports both conversational and streaming applications a Internet radio a Internet telephony a Musicondemand a Videoconferencing a Videoondemand Applications may include multiple media streams Purpose Cont d Provides following functions a Identifies encoding scheme a Facilitates playout at appropriate times a Synchronizes multiple media streams 1 Indicates packet loss 1 Provides performance feedback 1 Indicates frame boundary Protocol Stack Normally runs over UDP Runs with the companion protocol RTCP on consecutive ports a RTCP handles feedback synchronization and user interface It s a transport protocol implemented in the application layer A Tanenbaum Ethernet IP UDP RTP header healderheaiier header User Multimedia application Space FlTP 1 Socket interface HTP Payload UDP quot 39 c 08 p lt UDP payload gt Kernel Ethernet IP payload gt Ethernet payload a b RTP Header 32 bits llllllllllllllllll LllllJl Ver P I x 00 lml Payload type Sequence number 7 Timuslarnp f Synch ron izatio n sou rce identifier e e e A e e e e e e Cunlnbuling source identi er El For each class of application RTP defines 0 Profile How to interpret header fields 0 Format How to interpret payload data EIComments o P Padding indicator if present last byte of payload is pad count 0 X Extension bit indicating presence of Extension Header 0 CC Number of Contributing Sources 0 M Marker bit eg frame with beginning of a talkspurt o Payload type Type of data eg encoding scheme 0 Timestamp Generation time of first sample relative to previous frame 0 Synchronization Source Identifier SSRC Current source 0 Contributing Source Identifier CSRC Contributing source at a mixer lRTCP Main functions 1 Provide feedback on endtoend application performance as well as network performance a Synchronize different media streams from the same sender 1 Identify sender for display on user interface RTCP Cont d Information conveyed for synchronization of different media streams a Timestamp containing actual timeofday u RTPtimestamp Information conveyed for performance feedback 1 Data packets lost a Interarrivaljitter 1 Highest sequence number received RTCP Cont d How performance feedback can be used CI If one or a few of the recipients are reporting poor performance Check resource reservation Check for network problem If many receivers are reporting poor performance Lower encoding rate I Add error resiliency Voice over IP Motivation By 2002 volume of total data traffic was an order of magnitude higher than that of voice traffic I Data traffic still growing exponentially Voce traffic growth almost flat 5 Money spent on voice services by a typical househo d is higher than that for data serVIces l Strong business case for sending voice over data networks a VolP internet Telephony provides data service providers significant revenue with minimal increase in traffic a With 80211 WiFi and 80216 WiMax wireless voice over data networks would have even higher penetration H323 El H323 is an architectural overview of internet telephony than a specific protocol El Supports G711 64Kbps voice by default El H245 let the terminals negotiate encoding algorithms bit rate etc El ITU 0931 is used for signaling El Gatekeeper controls endpoints in a Zone 0 H225 manages PCtogatekeeper channel called RegistrationAdmissionStatus El Gateway connects Internet and PSTN Gateway Zone Terminal xx VTelephone nchyork 39 I H323 Protocol Stack Speech Control G7XX RTCP H225 0931 H245 HAS Call Call RTP signaling control UDP TCP lP Data link protocol Physical layer protocol Session Initiation Protocol SIP l Designed by IETF to offer a simpler alternative Describes how to set up VolP calls video conferences etc I Designed to interwork with existing Internet applications a Defined phone numbers as URLs o Textbased protocol modeled on HTTP a Main methods are Invite Ack Bye Options Cancel and Register Runs over UDP or TCP Uses RTPRTCP for data transport SIP Example El A proxy server is used as a redirection server Proxy Callee VoP Performance Tests Mus Analysvs mum San Jase n You MUS Analms frnm Vnn TD San Jnse mmos 4 3n and a a macamn 2 my Ma 0 u him a 7 mm a n1 cndu nnunmrln Launcy mm Dlxcards Pack31 Lnu Lm Purlndl Amane mm I 43 s n ans m g 21 5 4 4 Degradation Saunas Main 5 Sam mum an m DUEm mz mu uuu Elms G 711PCM stamps 20m m pawaam sum 1 aw 11 ms m5quot um Win 2mm m Wax Z ms ZanaomLosx ms Lm PurlId Min 2 m Avg Max 2 m5 Random L05 Marina Jmur 3m n57 as w u muss quotquot5 I 443 n an thh g z 5 4 4 Degraditlnn Saunas new mum um am a mm m 32 um I s an Eudu 5m PCM m amps ZUms rm panaan sum 1 aw 511 de 1 m5 LaunEY mm Dlicards my mm Lm uvc TestYourVolPcom I VoIP Performance Tests Cont d MD Anulyxll mm m TD amnn M Annlml Hum mum Tn m Lnss Perlnds Avuraae Jmer Loss Perlnds Averagzlmar cm H 57 cm on Law m mm vawmosnv mmquot 39 whim nmmmon mm quotquot5 I 4us u quotquot5 I Lgw Bast m cm 5 4 4 355 m cm 5 4 a Dunradaunn Snurux neuradaunn snums nan cm isms no a ma mm mm u as 5 mm u as s m ammo Sam M 33 m DEzzkuD szzvds m2 mm am 1 mm mm DE mum um um Endelt a 71mm atsAkbps Endet a 11mm 21mm Z ms m pay aad 2m m Wm WWW IP aw E khws w aw RnundTrln 2m m5 Raun Trln an Ms Lamquot Lama Pack Dlscards 25 Parka DIsEards mm mm m m mm Ln 1 TestYourVol Pcom 1m Buidout Delay Synchronous Source El Packet are sent at 81 S 82 28 with interpacket spacing of 8 El Received at StD1 S2D2 El Find minimum buildout delay so that packets can be played out synchronously c Find minimum B such that 81D1B StD1BS are not smaller than the corresponding reception times 0 lmplies B Max delay D1
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