Understanding Voice Over IP Protocols - Miralishahidi.ir

Understanding Voice over IPProtocolsCisco Systems—Service Provider Solutions EngineeringFebruary, 20024426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.1

Topics to Discuss History of VoIP VoIP—Early Adopters VoIP—Standards and Standards Bodies VoIP—Making Sense of the Protocols “The Great Voice Myth” VoIP—Protocol Challenges Summary4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.2

Why Move to VoIP? Cost savings—toll bypass Open standards—H.323, SIP, MGCP Multi-vendor interoperability Integrated IP voice and data networks4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.3

Cisco Packet Voice ArchitectureOpen ServiceApplication LayerLineConcentrationDigital TrunkSubsystemSwitching NetworkTDM/Circuit Switch(JAIN, AIN, TAPI,JTAPI, XML etc.)Open/StandardInterfaceCall ControlConnection ControlFeaturesCommon ChannelSignaling ComplexOpen Call Control Layer(SIP, H.323, MGCP, InterfaceStandards-BasedStandardsPacket Infrastructure Layer(IP, ATM)4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.4

Topics to Discuss History of VoIP VoIP—Early Adopters VoIP—Standards and Standards Bodies VoIP—Making Sense of the Protocols “The Great Voice Myth” VoIP—Protocol Challenges Summary4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.5

Early Adopters—Advanced Services and Toll-Bypass Regulatory opportunitiesallowed for toll-bypass PC-to-phone, calling-cardand international faxservices Cisco-based carriers usedstandard protocols, but notall carriers implementedstandards Inter-carrier connectionshad protocolinteroperability challenges4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.6

Topics to Discuss History of VoIP VoIP—Early Adopters VoIP—Standards and Standards Bodies VoIP—Making Sense of the Protocols “The Great Voice Myth” VoIP—Protocol Challenges Summary4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.7

Making the Rules for VoIP IETF (Internet Engineering Task Force)The community of engineers that standardizes theprotocols that define how the Internet and InternetProtocols work. http://www.ietf.org/ ITU (International Telecommunications Union)An international organization within the United NationsSystem where governments and the private sectorcoordinate global telecom networks and services.http://www.itu.int/home/index.html4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.8

Defining the VoIP Protocols H.323An ITU Recommendation that defines “Packet-based multimediacommunications systems”. H.323 defines a distributed architecture forcreating multimedia applications, including VoIP SIPDefined as IETF RFC 2543. SIP defines a distributed architecture forcreating multimedia applications, including VoIP MGCPDefined as IETF RFC 2705. MGCP defines a centralized architecture forcreating multimedia applications, including VoIP H.248An ITU Recommendation that defines “Gateway Control Protocol”. H.248 isthe result of a joint-collaborate with the IETF. H.248 defines a centralizedarchitecture, and is also known as “Megaco” MegacoDefined as IETF RFC 2885. Megaco defines a centralized architecture4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.9

Topics to Discuss History of VoIP VoIP—Early Adopters VoIP—Standards and Standards Bodies VoIP—Making Sense of the Protocols “The Great Voice Myth” VoIP—Protocol Challenges Summary4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.10

H.323 ComponentsH.323MCUGKScope .323GatewayPSTNV.70Terminal4426 02 2002 c1H.324Terminal 2002, Cisco Systems, Inc. All rights inal11

Scope of H.323 RecommendationVideo I/OEquipmentAudio I/OEquipmentUser DataApplicationsT.120, etc.Video CodecH.261, H.263Audio CodecG.711, G.722,G.723, G.728,G.7294426 02 2002 c1RTPUDPRTCPH.225LayerIPSystem ControlH.245 Sync)TCPCall ControlH.225.0RAS ControlH.225.0 2002, Cisco Systems, Inc. All rights reserved.UDP12

H.323 SignalingVVH.323Endpoint AH.323Endpoint BSetupAlerting / ConnectCapabilities Exchange / MSDOpen Logical ChannelH.225 (TCP Port 1720)H.245 (TCPDynamic Port)Open Logical Channel AcknowledgeRTP StreamRTP StreamRTCP Stream4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.Media (UDP)13

Basic H.323 CallGatekeeper ALRQGatekeeper BLCFACFACFIP NetworkRRQ/RCFARQH.225 (Q.931) SetupRRQ/RCFARQH.225 (Q.931) Alert and ConnectH.245VGateway APhone A4426 02 2002 c1RTPVGateway BPhone B 2002, Cisco Systems, Inc. All rights reserved.14

Deploying H.323 NetworksDGKGKLAGW #1WestZoneMinimizes GK configurationAddition of new zonesAddition of new NPAsAddition of new rate centersGKLAGW #2Rate Intra-LATA RateCenter #1 Toll Center #14426 02 2002 c1 2002, Cisco Systems, Inc. All rights STNEastZone15

MGCP/H.248/Megaco—ArchitecturesCall AgentCall AgentSS7PSTNPSTNIMTPSTNPRIAccessGatewayMGCP / H.248 / MegacoRTP4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.16

Deploying d RIBilling viceProvider'sPacketNetworkNAS/VoIPTraditional TDM TrafficModem Dial-up Traffic4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.17

SIP ArchitectureINTELLIGENTSERVICES4426 02 2002 IP Proxy, Registrar& Redirect ServersSIPSIPSIPSIP UserAgents (UA)PSTNCAS or PRIRTP(Media)Legacy PBX 2002, Cisco Systems, Inc. All rights reserved.18

SIP SignalingPSTNPSTNSIP VoIP NetworkINVITECalling PartySIP Signalingand SDPSignaling(UDP or TCP)100 TryingINVITE100 Trying180 Ringing180 Ringing200 OK200 OKACKACKMedia (UDP)4426 02 2002 c1Called Party 2002, Cisco Systems, Inc. All rights reserved.SignalingBearer OrMediaRTCP Stream19

SIP IPServers/Services“Where is thisname/phone#?”REGISTER“Here I am”3xx Redirection“They moved,try this address”SIP ProxyProxied INVITE“I’ll handle it foryou”INVITE“I want to talkto another UASIP UserAgents4426 02 2002 c1SIP UserAgents 2002, Cisco Systems, Inc. All rights reserved.SIP-GW20

Deploying SIP NetworksPSTN312PSTN212ChicagoPOPCentral ZoneNYPOPEast ZoneIP NetworkWest ZoneSFPOPPSTN4154426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.21

Topics to Discuss History of VoIP VoIP—Early Adopters VoIP—Standards and Standards Bodies VoIP—Making Sense of the Protocols “The Great Voice Myth” VoIP—Protocol Challenges Summary4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.22

Voice MythsMythsFacts Networks can only bebuilt one way VoIP allows centralizedor distributedarchitectures Networks will only useone protocol All networks willconverge H.323, SIP, MGCP andH.248/Megaco will all bepresent in VoIPnetworks Networks will convergeto IP4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.23

Topics to Discuss History of VoIP VoIP—Early Adopters VoIP—Standards and Standards Bodies VoIP—Making Sense of the Protocols “The Great Voice Myth” VoIP—Protocol Challenges Summary4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.24

Interconnecting VoIP Networks32H.3SIP?MGCPH.248Megaco4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.25

Connecting VoIP to SS7/C7 NetworksIAM4426 02 2002 c1H.323H.225 Setup DP 2002, Cisco Systems, Inc. All rights reserved.26

VoIP Interworking Issues Service interworkingE.g.: H.450 - SIP - MGCP Media interworkingEnd-to-end codec negotiation Bearer interworkingEnd-to-end fax, modem, DTMF4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.27

VoIP Interworking Bearer levelModem (relay/passthru)Fax (relay/passthru) Service translationissuesCall deflectionT.38Park/holdT.37 Signal issuesDTMF (relay/passthru) Media levelSDPH.245Codec (negotiation,selection)4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.28

Fax and Modem Passthru Mechanisms Modem and fax are control mechanisms basedon PLL (Phase Locked Loops) They are both time sensitive Highly sensitive to packet network impairments:JitterPacket lossDelay Susceptible to clock slew (clock sync differencesbetween gateways)4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.29

Passthru SimplifiedVoice GatewayPCMG.711µDSPG.711µG.729IPCloudVoice GatewayG.711µDSPPCMG.711µG.7294426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.30

What Is Modem Passthru? It is the transport of modem signals(modulation, error correction andcompression) through a packet networkusing PCM encoded packets4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.31

Modem Passthru (Cont.) Modem tone detection ( V.90) Switchover signaling No VAD EC off RTP payload redundancy (10mspacketization) RFC2198 (optional)4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.32

Modem Passthru Issues Consecutive packet drops(loss) cause retrain Consecutive drops duringretrain causes disconnect Variation of delay (jitter) hasquite an effect Jitter (at 10%) is aconservative estimate—Since jitter mostly impactsperformance with packet loss4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.33

What Is Modem Relay? Modem relay involvesdemodulating the modemsignal at ingress gateway Passing this data as packetdata to terminating gateway Re-modulating the data andpasses it to the receivingmodem4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.34

Fax Relay—T.38T.30UDPPSTNT.30PSTNIP Real-time Also called demod/remod Can be used in H.323/MGCP/SIP signaling Delivers fax data over UDP streams (uses same RTP port)—reuses voice UDP ports Fallback to proprietary mode Method of encoding the T.30 and T.4 into packets4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.35

DTMF What is DTMF Why is it required?and where is it used? How do you transportit in IP? DTMF implementation4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.36

DTMF (Cont.) In TDM world, all voice traffic is sent asuncompressed 64Kbs PCM streams; anythingsent on that circuit is an untouched stream ofbits; (e.g., voice speech, modem tones, faxtones, and DTMF digits) DSP codecs designed to interpret humanspeech, can distort DTMF tones (machine-tones) High b/w codecs less likely to distort Distortion causes problems with voicemail andIVR systems4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.37

DTMF Schemes with VoIP ProtocolsH.323MGCP, andCisco RTP,H.245 Alphanum,H.245 Signal, AVTTones RFC2833Cisco RTP,NSE, NTE,RFC2833RFC28334426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.38

Topics to Discuss History of VoIP VoIP—Early Adopters VoIP—Standards and Standards Bodies VoIP—Making Sense of the Protocols “The Great Voice Myth” VoIP—Protocol Challenges Summary4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.39

Summary Understand the possibilitiesand the issues Avoid protocol/productbased bias Decide on application Consider market and businessdrivers Deploy what’s possible today Choose signaling protocoldepending on services intended tobe offered Many possibilities—stay tuned4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.40

Crystal Ball on VoIP All three protocols (or its variations)are here for the long run Changes/enhancements will be made IP will be the core4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.41

Reference URLs ITU:www.itu.org IETF:www.ietf.org SIP:www.cs.columbia.edu/ hgs/sip/ H.323: www.packetizer.com/iptel/h323/ p?page techlibrary4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.42

4426 02 2002 c1 2002, Cisco Systems, Inc. All rights reserved.43

Voice Myths Networks can only be built one way Networks will only use one protocol All networks will converge VoIP allows centralized or distributed architectures H.323, SIP, MGCP and H.248/Megaco will all be present in VoIP networks Networks will converge to IP Myths Facts