Internet Video Protocols

1
Internet Video Protocols Applications
2003. 5. 27
2
Contents

• Introduction
• Building loss tolerant video delivery system
• Handling Delay mechanism
• Congestion Control
• RTP RTCP
• Case Study SALSA
• Conclusion References

3
Introduction

• Video delivery applications on Internet
• Video as a part of Information-on-demand(IoD)
• Applications involved transport of live video
• Bi-directional interactive video applications
• Video highest tolerance to packet losses
• To make the best use of this loss tolerance in
  dealing with the delivery impairments
• Important impairments of packet delivery over
  internet
• Loss
• Delay

4
Loss Tolerant Video Delivery System

• Application Layer Framing (ALF)
• Constrain the effect of a packet loss to a single
  packet
• Increase error resilience
• Fragmentation smaller than Max. Transmission Unit
  (MTU)
• Repetition of higher layer headers within each
  packet
• Reference Picture Selection
• Proper Key Frame Updates
• Increasing key frame rate ? reduce waiting time
  for playback
• Slices or MBs instead of complete frames
• Layered coding
• Useful for addressing the heterogeneity issue
• Not only video information is contained in base
  layer

5
Handling Delay Mechanism

• Propagation delay on the wires
• Queuing delay on the routers
• Play-out buffers size management
• Determine the initial minimum buffer size
• Implement a mechanism to change the buffer size
  in real-time with minimal effect on the quality
  of the playback
• Effective sampling rate modification based on
  frame repeat/drop
• Global synchronization will be need
• Synchronous delivery channels with low loss rate
• Not suitable for multicast of heterogeneous
  receivers

6
Congestion Control

• Bottleneck bandwidth
• Upper limit on the speed of delivering data from
  end to end
• Obstacles of rate control
• Busty nature of the Internet traffic
• Multicast applications
• Rate adjustment algorithm based on a combination
  of the RTCP reports from all receivers
• Sending different layers of the output of a
  layered codec to different multicast groups
• Rate control of stored video
• Require real-time transcoding
• ? Increase the computational complexity
• Storing the same video encoded at several rates

7
RTP RTCP

• Payload type identification
• Special field at the packet header
• Packet sequence numbering
• Packet loss detection, packet re-ordering
• Randomly selected initial sequence number
• Time Stamping (32 bit)
• Encoder/decoder clock matching
• Synchronization of several sources
• Measuring packet arrival jitter
• Source identification
• Synchronization SouRCe identifier (SSRC)
• RTCP
• Periodic transmission of control packets from
  participants of a session

8
RTP RTCP (Cont.)

• Feedback on the quality of distribution and
  timing
• RTP reports among sender and receivers
• Fraction of the lost RTP packets since the last
  report
• Cumulative of packets lost since the beginning
  of reception
• Packet inter-arrival jitter
• Delay since receiving the last senders report
• Not defined explicit flow control of RTP
• Capable of generating high traffic rates causing
  network congestion
• Receiver specific feedback for error recovery
• Periodic RTCP
• Contain 64bit Network Time Protocol (NTP)
  timestamps
• Intra or inter-media synchronization with
  synchronized NTP timestamps

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RTP RTCP (Cont.)

• Participant Identification
• Connection between the real identification of an
  RTP source
• Using Canonical name (CNAME) current SSRC
• Scale the control packet transmission
• Less than 5 of the bandwidth allocated for a
  session

10
SALSA (System for Audio/visual Live Services and
Applications)

• Two way interactive video over cable TV
• Many applications of bi-directional video
• Personal, tutoring, shopping, etc.
• Layered coding to protect the video from packet
  losses
• Temporal scalability
• QoS guarantee between end points
• Cable Modem Termination System (CMTS) located at
  the cable head-end
• Data-over-Cable Service Interface Specification
  (DOCSIS) 1.1
• H.263 G.728 ? transmitting base layer over QoS
  channel
• Usable video under a 30 packet loss rate on the
  best effort channel

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Summary Conclusion

• Outline the Internet packet video delivery
• Review some possible remedies to address
  feasibility of using the Internet video
• To design a cost effective video delivery system
  for the Internet is needed
• QoS guaranteed network infrastructure for
  interactive applications
• Associated price structure
• Familiarity with the transport protocol is
  essential for video codec designers

12
References

• M. R. Civanlar, "Internet video - Protocols
  applications," in Proc. Packet Video Workshop
  2001, 2001

13
Real-Time Internet Video using resilient
Scalable Compression and TCP-Friendly Transport
Protocol
2003. 5. 27
14
Contents

• Introduction
• Error-resilient bandwidth-scalable video
  compression
• TCP-friendly transport protocol
• Conclusion
• references

15
Introduction

• Discrete Wavelet Transform (Subband Coding)
• DC subband contains most of the energy
• Generate several layers ? various spatial and
  quality resolutions
• Multi-priority system

downsample
upsample
?2
?2
H0(z)
G0(z)
X(z)
Y(z)
?
?2
?2
H1(z)
G1(z)
Coding transmission
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Hierarchical block coding (HBC)

• Significance Map
• Binary map indicating whether each coeff. is
  significant at the current bit-plane
• 44 ? 22 ? indicating each bit

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Bandwidth Scalable Packetization

• Each component contains coeff. Blocks which are
  independently compressed using progressive
  quantization by hierarchical block coding
• Successive bit-planes of a coeff. Block are
  intercoded to produce small codewords
• ? Fine granularity for layered packetization

18
Encoding procedure

• Every time the encoder finishes subband analysis,
  it computes and parametized the energy
  distribution of the subbands into 8 parameters
  compactly transmitted per packet

19
Two source of latency in TCP

• Backlog of data when throughput temporarily drops
  below the data generating rate
• ? filtering a scalable video bit-stream to meet
  the instantaneous throughput
• Retransmission delay
• ? not performing retransmission

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Throughput estimation of TCP

• On a lightly loaded network,
• TCP sending window ? amount of buffer space (B)
• ? Calculating average throughput (T) with
  buffer space
• TCP throughput to the packet loss rate (p)
• (kconstant, MSS Max. segment size)

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Throughput estimation of TCP (Cont.)

• Packet losses within one RTT are considered as a
  single congestion event, then
• C of congestion events in an observation
  window
• D amount of data in units of MSS (Max. Segment
  Size) transmitted in the same observation window
• Throughput estimated by (1) and (2) will show
  large variability
• ? Throughput is calculated using an additional
  RTT estimate that is measured using an accurate
  clock

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TCP Friendly Transport Protocol

• Modulated by flow controller not to exceed
  throughput given by (1) and (2)
• If source attempts to make a fixed of
  transmissions per second
• If the size of each transmission
• Reduce transmission overhead by combining
  consecutive small transmission

23
Performance comparison
(proposed)
(T) compared
(T) scalable compression scheme producing
linearly dependent packet
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FEC Packet Replication
(P) Ave. MSE 100.53
(T) Ave. MSE 201

• Higher ave. distortion of scheme (T) compared
  with scheme (P) with or without FEC

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Conclusion

• Low latency video transmission scheme consisting
  of a TCP-friendly flow controller
• By elimination of buffering in flow control
• Overall latency propagation delay decoding
  time
• Bandwidth-scalable compression scheme producing
  individually decodable packets
• Produce relatively constant video quality in face
  of packet losses as compared to MPEG and other
  schemes
• Independently decoded packets reduces the
  resulting distortion even after an adaptive FEC
  scheme is applied to protect the non-resilient
  bitstream

26
References

• Wai-tian Tan and Avideh Zakhor. "Real-Time
  Internet Video Using Error Resilient Scalable
  Compression and Tcp-Friendly Transport Protocol",
  in IEEE Trans. on Multimedia, 1999