IP Telephony – Where are we today? IP Telephony – Where are we today? Aarti Iyengar Aarti Iyengar Solutions Architect Solutions Architect Polycom Polycom
Table of Contents Table of Contents • Technology Technology • • Performance challenges Performance challenges • • Policies Policies • • Deployment Deployment • • The Indian Scene The Indian Scene •
Technology Technology
Brief Introduction … Brief Introduction … • Legacy Telephony • Legacy Telephony • • TDM/SS7 based infrastructure TDM/SS7 based infrastructure • Traditional Class 5/Class 4 switches • Traditional Class 5/Class 4 switches • Voice over IP • Voice over IP • IP- -based packet infrastructure for PSTN voice transport based packet infrastructure for PSTN voice transport • IP Analog voice encapsulated in IP packets • • Analog voice encapsulated in IP packets • New elements that collectively perform traditional New elements that collectively perform traditional • telephony functions and more telephony functions and more • And what is IP Telephony? • And what is IP Telephony? • Voice + Messaging + Video + Data over IP networks = IP • Voice + Messaging + Video + Data over IP networks = IP Telephony Telephony • Public Internet : Best Effort Service • Public Internet : Best Effort Service • Managed IP Network : SLA based Service • Managed IP Network : SLA based Service
Traditional PSTN Network Traditional PSTN Network SS7 signaling SS7 network Call Control, Signaling, Legacy Legacy Legacy Class 4/5 Class 4/5 Bearer/Media Class 4/5 Switch Switch Switch and Features TDM network TDM bearer
VoIP Network VoIP Network SS7 signaling SS7 network Call Control Signaling Soft IP Phones IP signaling Signaling + Media Gateway IP bearer Gateway Controller IP Phones Integrated Access IP network Application Analog Phones Media Device Server Server Media (conferencing) Media Media Features Gateway Gateway Bearer/ Media TDM TDM network bearer
The Elements .. The Elements .. • Terminals or Endpoints • Terminals or Endpoints • IP Phones • IP Phones • Soft Phones/PC Phones • Soft Phones/PC Phones • Media converter • Media converter • Media Gateway/PSTN Gateway • Media Gateway/PSTN Gateway • Call Processor • Call Processor Media Gateway Controller or Gatekeeper or Proxy Server or or • • Media Gateway Controller or Gatekeeper or Proxy Server Softswitch Softswitch • Signaling Gateway • Signaling Gateway • Application Server Application Server • • Media Server • Media Server
Network Paradigms Network Paradigms Centralized Distributed Distributed Central Model Model Intelligence Intelligence Intelligent Server Master Intelligent Controller Server Dumb Slave Dumb GWs Slave GWs Intelligent Client Intelligent Client Intelligent Intelligent Dumb Server Intelligent Slave Client Server GWs Dumb Dumb Slave Slave Which paradigm suits your network? GWs GWs
IP Telephony Protocol Soup IP Telephony Protocol Soup H.323 MGCP SIP-T SIP Megaco/H.248 BICC Call Control/Signaling Call Control/Signaling Gateway Control T R Softswitch-Softswitch I P RTP ENUM SDP Bearer More …….
Putting All Ingredients of the Soup together ! Putting All Ingredients of the Soup together ! Protocol selection is a strategic decision. Depends on existing network and future services planned Ultimately, one winner will make it easy for all ! Media Application Server Server Media P Gateway I S MGCP/H.248 Controller Signaling Media Gateway Gateway SS7 Sigtran (M3UA/SCTP) SIP-T/BICC Controller IP Network (SS7) P C M T Media RTP/RTCP R / G PSTN P T C R a P i d / (TDM) e H M . 2 4 8 SIP/H.323 M D Media T IP Phone (H.323/SIP) Gateway
Performance Challenges Performance Challenges
IP Telephony Performance Challenges IP Telephony Performance Challenges • Need to engineer network appropriately for good • Need to engineer network appropriately for good quality IP Telephony services (voice, video) quality IP Telephony services (voice, video) • Adequately provisioned core with proper traffic and • Adequately provisioned core with proper traffic and congestion management methods congestion management methods • Sufficent bandwidth in the access bandwidth in the access • Sufficent • Video is a bandwidth hog. Require about 384 kbps for a good Video is a bandwidth hog. Require about 384 kbps for a good • quality video connection quality video connection • Reliability/Availability • Reliability/Availability • ~ 99.999% availability through implementation methods ~ 99.999% availability through implementation methods • yielding Redundancy, Resilience, Survivability, Robustness yielding Redundancy, Resilience, Survivability, Robustness
IP Telephony Performance Challenges IP Telephony Performance Challenges • Network requirements for high performance • Network requirements for high performance • Coding Algorithms: what codec codec, what bit rate? , what bit rate? • Coding Algorithms: what • Greater the compression, more the encoding delay • Greater the compression, more the encoding delay • Determine appropriate packetization packetization times and packet length times and packet length • Determine appropriate • VAD and CNG (for voice) • VAD and CNG (for voice) • At the transmitter: Detection of voice activity, silence suppression sion • At the transmitter: Detection of voice activity, silence suppres • At the receiver: Comfort Noise generation, Voice playback • At the receiver: Comfort Noise generation, Voice playback • • Latency/Delay Latency/Delay • Components: Packetization Packetization, Propagation, Network Processing, Jitter , Propagation, Network Processing, Jitter • Components: buffer delay and speech playback delay buffer delay and speech playback delay • • PLCs add about 5ms PLCs add about 5ms- -10ms delay in multimedia transmission 10ms delay in multimedia transmission • Impact on perceived audio/video quality • Impact on perceived audio/video quality – Echo (RT delay > 50ms), Talker overlap (RT delay > 250ms) – Loss of audio-video synchronization, checker-celled picture, hazy motion Latency Benchmark: Toll quality PSTN- -like voice: 150ms RTT (ITU G.114) like voice: 150ms RTT (ITU G.114) Latency Benchmark: Toll quality PSTN Occasional packet loss is tolerable ; Delay > 300ms completely unacceptable
IP Telephony Performance Challenges IP Telephony Performance Challenges Jitter • • Jitter • • Jitter = Delay Variation ( Jitter = Delay Variation ( MUST AVOID in multimedia networks! MUST AVOID in multimedia networks! ) ) • • Jitter Buffer compensates for jitter on the receiver side: Choose optimal Jitter Buffer compensates for jitter on the receiver side: Choos e optimal size!! size!! Rule of thumb: Jitter Buffer size = atleast atleast 2 x speech frame size 2 x speech frame size Rule of thumb: Jitter Buffer size = Packet loss • • Packet loss • • Packet loss should be < 1% for acceptable quality Packet loss should be < 1% for acceptable quality • • Use Codecs Use Codecs with packet loss concealment algorithms (E.g G.729, with packet loss concealment algorithms (E.g G.729, G.723.1, H.263/H.264 – – built built- -in PLC; G.711, G.726 in PLC; G.711, G.726 - - add add- -on on PLCs PLCs) ) G.723.1, H.263/H.264 • Packet loss is mostly bursty bursty in nature. Hence, packet loss in nature. Hence, packet loss • Packet loss is mostly performance is directly related to packet size, the shorter the better better performance is directly related to packet size, the shorter the • • Impact on perceived audio/video quality : Clipped speech and Impact on perceived audio/video quality : Clipped speech and distorted image distorted image
IP Telephony Performance Challenges IP Telephony Performance Challenges Transcoding/ /Tandeming Tandeming: Parameters to : Parameters to transcode transcode • • Transcoding • • Audio codecs Audio codecs (G.729A. G.711 ) (G.729A. G.711 ) – Audio Transcoding: Two or more encodings of a signal through different types of non-G.711 codecs separated by G.711 e.g G.726 to G.711 to G.729A – Audio Tandeming: Two or more encodings of a signal through same types of non-G.711 codecs separated by G.711 e.g G.729A to G.711 to G.729A • Video Codecs Codecs (H.261, H.263, H.264) (H.261, H.263, H.264) • Video Bandwidths (128 kbps, 384 kbps, 512 kbps etc.) • • Bandwidths (128 kbps, 384 kbps, 512 kbps etc.) Video formats (CIF, QCIF etc.) • • Video formats (CIF, QCIF etc.) • • Video frame rates (30 fps, 14 fps etc.) Video frame rates (30 fps, 14 fps etc.) • • Every participant must get his optimal capability!! Every participant must get his optimal capability!! Transcoding increases distortion and delay. Transcoding increases distortion and delay. Beyond one transcode Beyond one transcode, network performance drops to unacceptable , network performance drops to unacceptable levels for most codec codec combinations. combinations. levels for most
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