Transcript PPT

CS 414 – Multimedia Systems Design
Lecture 22 –
Multimedia Session Protocols
Klara Nahrstedt
Spring 2014
CS 414 - Spring 2014
Administrative
MP1,HW1, Midterm graded
 Pick up your HW1 and midterm from TA
during office hours or by appointment
 Regrading: meet with TA or email TA
asking for regarding

 He
will facilitate the regarding with the graders
 Deadline until Wednesday, March 19 (one
week)

If you can’t make the deadline, email to TA and
Instructor
CS 414 - Spring 2014
Outline
Error Control
 Multimedia Protocols – Standards

– Transmission Protocol
 RTCP Control/Negotiation Protocol to RTP
 RTP/UDP/IP
CS 414 - Spring 2014
Covered Aspects of Multimedia
Image/Video
Capture
Audio/Video
Perception/
Playback
Audio/Video
Presentation
Playback
Image/Video Information
Representation
Transmission
Audio
Capture
Transmission
Compression
Processing
Audio Information
Representation
Media
Server
Storage
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A/V
Playback
Error Detection

Ability to detect the presence of errors
caused by noise or other impairments during
transmission from sender to receiver
 Traditional
mechanisms: check-summing, PDU
sequencing


Checksum of a message is an arithmetic sum of message code words
of a certain word length (e.g., byte)
CRC – Cyclic Redundancy Check – function that takes as input a data
stream of any length and produces as output a value (commonly a 32bit integer) – can be used as a checksum to detect accidental alteration
of data during transmission or storage
 Multimedia
mechanisms: byte error detection at
application PDU, time detection
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Design of Error Correction Codes

Automatic repeat-request (ARQ)
 Transmitter
sends the data and also an error
detection code, which the receiver uses to check for
errors, and requests retransmission for erroneous
data
 The receiver sends ACK (acknowledgement of
correctly received data)

Forward Error Correction (FEC)
 Transmitted
encodes the data with an error-correcting
code (ECC) and sends the coded msg. No ACK
exists.
CS 414 - Spring 2014
Error Control

Error Correction
 Traditional
mechanisms: retransmission using
acknowledgement schemes, window-based flow
control
 Multimedia mechanisms:
Go-back-N Retransmission
 Selective retransmission
 Partially reliable streams
 Forward error correction
 Priority channel coding
 Slack Automatic Repeat Request

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Go-back-N Retransmission
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Internet Multimedia Protocol Stack
APPLICATION
Media encaps
(H.264, MPEG-4)
DASH
SIP
RTSP
RSVP
RTP
HTTP
KERNEL
TCP
DCCP
UDP
IP Version 4, IP Version 6
AAL3/4
Layer 5
(Session)
RTCP
AAL5
MPLS
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Layer 3
(Network)
Layer 2
(Link/MAC)
Ethernet/WiFi
ATM/Fiber Optics
Layer 4
(Transport)
Internet Multimedia Protocol Stack
APPLICATION
Media encaps
(H.264, MPEG-4)
DASH
SIP
RTSP
RSVP
RTP
HTTP
KERNEL
TCP
DCCP
UDP
IP Version 4, IP Version 6
AAL3/4
Layer 5
(Session)
RTCP
AAL5
MPLS
CS 414 - Spring 2014
Layer 3
(Network)
Layer 2
(Link/MAC)
Ethernet/WiFi
ATM/Fiber Optics
Layer 4
(Transport)
Service Requirements for Realtime Flows (Voice/Video)
Sequencing
 Intra-media synchronization
 Inter-media synchronization
 Payload identification
 Frame indication

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Real-time Transmission
Protocol (RTP)


RTP provides end-to-end transport functions
suitable for real-time audio/video applications
over multicast and unicast network services
RTP companion protocol – Real-time Transport
Control Protocol (RTCP)
RTP
RTCP
User Datagram Protocol
Internet Protocol
Ethernet 802.13 or Wi-Fi 802.11
PHY (Wired or Wireless)
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Layer 4
Relation between RTP and RTCP
Application
Decoding
Coding
RTP
RTCP
Application
Coding
RTCP
UDP/IP
UDP/IP
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Decoding
RTP
RTCP: Control and Management

Out-of-band control information for RTP flow.
 Monitors
QoS for RTP in the delivery and packaging of
multimedia data
 Used periodically to transmit control packets to
participants in a streaming multimedia session.
 Provides feedback on the quality of service being
provided by RTP.
 Gathers statistics on media connection


Bytes sent, packets sent, lost packets, jitter, feedback and
round trip delay.
Application may use this information to increase the quality of
service, perhaps by limiting flow or using a different codec.
CS 414 - Spring 2014
RTCP Functions

There are several type of RTCP packets:
 Sender
report packet,
 Receiver report packet,
 Source Description RTCP Packet,
 Goodbye RTCP Packet and
 Application Specific RTCP packets.

RTCP itself does not provide any flow encryption
or authentication means. SRTCP protocol can be
used for that purpose.
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RTP Services

Payload Type Identification
 Determination
of media coding
 Source identification
 RTP works with Profiles


Profile defines a set of payload type codes and their
mappings to payload formats
Sequence numbering
 Error

Time-stamping
 Time

detection
monitoring, synchronization, jitter calculation
Delivery monitoring
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RTP Services – Support of Heterogeneity

Mixer service
 Allows
for resynchronization of incoming audio packets
 Reconstructs constant 20 ms spacing generated by
sender
 Mixes reconstructed audio streams into single stream
 Translates audio encoding to lower bandwidth
 Forwards lower bandwidth packet streams

Translator service
 Allows
for translation between IP and other high speed
protocols
 May change encoding data
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Difference between Mixers and
Translators
S3
S1
M1
T
S2
S4
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M2
R1
RTP Common Header
0 0 0 0 0 0 0 0 0 0 1 1 1 1 11
0 1 2 3 4 5 6 7 8 9 0 1 2 3 45
1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
Ver
Sequence Number
P X CC
M PT
Timestamp
SSRC
CSRC [0..15] :::
Ver – Version 2
P – Padding
X – Extension, if set, the fixed head is followed by exactly one
header extension
CC – CSRC count
M – Marker – intended to allow significant events such as
frame boundaries to be marked (defined by profile)
PT – Payload type
SSRS – synchronization source, CSRC – contribution source
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Payload Formats

Static Payload formats
 Established
in RTP Profile
 Payload type 0 := µ-law audio codec

Dynamic Payload formats
 Applications
agree per session on payload
format
 H.263, JPEG, MPEG
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Conclusion





RTP usage – in several application audio and
video tools (vat, vic)
RTP follows the principle of application level
framing and integrated layer processing
RTP/UDP/IP is being used by the current
streaming session protocols such as RTSP
Session protocols are actually
negotiation/session establishment protocols that
assist multimedia applications
Multimedia applications such as QuickTime,
Real Player and others use them
CS 414 - Spring 2014