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Media: Voice and Video in your SIP EnvironmentJitendra Shekhawat
Agenda
• Common Audio and Video Codecs • Media/Codec Negotiations • Tuning Your Network for Voice and Video • QoS issues, metrics and user quality
expectations
Objective: Introduction of Media in the SIP environment.
SIP
RTP
SIP
RTP
IP Audio/Video Telephony Network
IPRTP
SIP
SIP Soft Phone
SIP Desk Phone
PC – Email Client
Applications• Video Mail• Video Portal• Live content
streaming
Broadband Users
Multimedia Server
SIP Video Endpoints
SIP Proxy Server
SIP
RTSP Streaming
Server
CNN, ESPN, Bloomberg, live feed
RTP
•Call Control: SIP
•Media: RTP
•Video: H263, H264, MPEG4
•Audio: G711, G723, G729, G726, AMR-NB, etc.
RTSP
SIP Call Example
Audio Video Codecs and Payload Types
• RFC 3551• Some codecs
PT encoding name0 pcmu3 gsm4 g7238 pcma9 g722
18 g72934 h263
Dynamic iLBCDynamic AMRDynamic AMR-WBDynamic AMR-WB+
Media Transport
• RTP – Real Time Transport Protocol– media packet transport– One stream per direction between endpoints
• RTCP– RTP Control Protocol– Provides quality information– Generate reports to the network
RTP Packet
RTP Datagram RTP Datagram RTP Datagram
IP Header 20 bytes
UDP Header 8 bytes
RTP Header 12 bytes
RTP Payload N bytes
Version 2 bits
Padding 1 bit
Extension 1 bit
CSRC count 4
bits
Marker 1 bit
Payload Type 7 bits
Sequence Number 2
bytes
Time stamp 4 bytes
Source Identifier 4 bytes
RTCP Packet
• Receiver of RTP stream sends periodic updates to the originator
• Packet count• Byte count• Packet loss• Timestamps to assess
round-trip delay• Jitter
RTP Packet Payload size
Example: g.711, 20 ms frames: 64000 bps X 20 msec / 8 = 160 byte payload
Payload size =
Function of: codec speed, frame-size
Frequency packets sent
codec speed X frame size
bits/byte
8 X 1000
msec / sec
Media Stream (RTP) Bandwidth:
Packet size := Header + Payload
Header := Ethernet + (IP + UDP + RTP) = 38 + (20 + 8 + 12) = 38 + 40 bytes
Payload := depends on codec
Example: g.711, 20 ms frames (50 packets/s)160 byte payload + (38 + 40) byte header
IP bandwidth: 200 byte/packet = 80,000 bps 160 kbps for 2 way
Ethernet bandwidth: 238 byte/packet = 95,2000 bps 190.4 kbps for 2 way
• Ethernet: Preamble (8) + Ethernet Header (14) + Ethernet CRC (4) + Inter-frame gap (12) = 38
Codec BandwidthsCoder Bitrate Encoded bandwidth
G.711 64 kbps 200-3400 Hz
G.723 5.4 or 6.3 kbps 200-3400 Hz
G.729A (20ms Packet) 8 kbps 200-3400 Hz
AMR 4.75 to 12.2 kbps 200-3400 Hz
AMR-WB Variable: 6.6 up to 23.85 (non-continuous)
50 to 7000 Hz
AMR-WB+ Variable: 6-36 kbps (mono) or 7-48 kbps (stereo)
50 Hz – 7.2 kHz up to 50 Hz – 19.2 kHz
iLBC 13.33 kbps for 30 ms, 15.20 kbps for 20ms
200-3400 Hz
Codec Bandwidths
Coder IP Bandwidth / RTP stream
G.711 (30 ms Packet) 74.6 kbps
G.711 (20ms Packet) 80 kbps
G.711 (10 ms Packet) 96 kbps
G.723.1 (30ms Packet) 15.7 kbps
G.729A (20ms Packet) 24 kbps
AMR (20 ms) 20.4 - 28 kbps
AMR-WB (20ms) 22.4 – 39.6 kbps
AMR-WB+ (20ms) 22 – 52 kbps
iLBC (20ms or 30ms) 31.2 kbps or 24 kbps
Video streams
Frame Sequence
I-frames (Key frames) P-frames (predicted frames)
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
1 18 35 52 69 86 103 120 137 154 171 188 205 222 239 256 273 290 307 324 341 358 375 392 409 426 443 460 477 494 511 528 545 562 579 596 613 630 647 664 681 698
Frame Number
Fram
e S
ize
Video Formats (IP vs. 3G) • High resolution for IP networks
– More bandwidth available– SIP Video Phones are generally CIF size (352 × 288 pixels) – Recommended: CIF, 15 or 30fps, up to 384kbps
• Low resolution for 3G networks– Total bandwidth limited to 64kbps – Generally video + audio is approx 52kbps (12.2kbps AMR + 40kbps
H263) – 3G Mobile phones are generally QCIF size (176 × 144 pixels)
CIF
QCIF
4
3
Performance Issues
• Propagation DelayTime required to travel end to end across the network
• Transport DelayTime required to traverse network equipment
• Packetization DelayTime to digitize, build frames and undo at destination
• Jitter DelayFixed delay by receiver to hold 1 or more packets to damp
variations in arrival times
• Packet LossPacket size impacts sound quality
Jitter Delay
• Calculated on inter-arrival time of successive packets– Average inter-arrival time– Standard deviation
• Goal inter-arrival time = inter-arrival time on emitted packets
• 3 phenomena effecting jitter– Packet loss (threshold 5%)– Silence suppression– Out of sequence packets
• Can be configured on most VoIP equipment
Packet Fragmentation
• Audio RTP packets– Not generally fragmented since packet size is less
than MTU
• Video RTP packets– A large frame is fragmented into a series of packets
for transmission over network– I-Frame fragmentation
• Receiver must receive all fragments to properly reconstruct frame
Packet Loss
• Audio– Packet Loss Concealment (PLC)
• Mask effect of lost or discarded packets• Replay previous packet or use previous packets to estimate missing
data• Key method for improving voice quality
– Packet Loss Recovery (PLR)– Packet Redundancy
• Increased bandwidth
• Video– I-Frame
• If a fragment is lost, subsequent P-Frames will not be sufficient to reconstruct image at receiver
• Video conversion tools available to generate files more suitable for real-time transmission
G.107 to MOS mapping
Codec Bandwidth and Voice Quality Comparison
Codec Payload Bit Rate Voice Quality
G.711 64 Kbps Excellent(MOS 4.2)
G.723 6.4 Kbps / 5.3 Kbps Good (MOS 3.9)
Fair (MOS 3.7)
G.729 8 Kbps Good (MOS 4.0)
G.726 or
G.721
16/24/32/40
Kbps
2/3.2/4/4.2
iLBC 13.33/15.2 kbps Good
(MOS 4.0)
AMR-WB+ 6-36 kbps Good (MOS near 4.0)
Network Issues?
Network Issues – Now What
• Determine the source of delay– Codec’s?– Too many hops?– Not enough bandwidth?
• Define means to reduce delay– Provision smaller packet sizes– Reduce hop count– Change routing protocols used
• Keep monitoring– Find problems first– Objectively identify issues
IP Header
Traffic Shaping
• DiffServ• RSVP• MPLS
Conclusion
• Reliability– Can calls be made when needed? – Will call setup time match current environment?– Will calls be disconnected?
• Quality– Is the voice quality of the calls the same?– Can the users tell the difference?
• Cost– What are the cost benefits of VoIP?– What equipment will be needed?
Wrap-up
Q & A / Quiz
Frame Sizes
Format Dimension (H x W, pixels)
>1 bits/pixel
Sub-QCIF (SQCIF) 128 x 96
Quarter-CIF (QCIF) 176 x 144
CIF (Common Intermediate Format)
352 x 288
4CIF (4 x CIF) 704 x 576
16CIF (16 x CIF) 1408 x 1152