real time protocol (rtp) 2006. 5. 16 김 준 [email protected]
TRANSCRIPT
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Agenda
About RTP Data Transfer Protocol RTCP RTP Translators and Mixers SSRC identifier Security
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About Real-Time Protocol (RTP)
Purpose Transmit protocol for real time packet
Audio Video Simulation data
Function Provide end to end network transport function
For application transmitting real- time data
Characteristics Not provide RSVP Not guarantee QoS. Suitable Protocol.
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Overview of RTP
Application
RTP
UDP
IP
Physical
Transportlayer
RTP provide transport layer interface that extend UDP
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Data Transfer Protocol – Header Format
V : Version [2] P : Padding [1] X : Extension [1] CC : CSRC Count [4] M : Marker [1] PT : Payload Type [7] SN : Sequence Number [16] Timestamp : [32] SSRC identifier : Synchronization Source [32] CSRC identifier : Contributing Source [32]
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Data Transfer Protocol – Session
Session Based on Destination Address (IP and port). Each Stream translate each session.
Select encoding type Timing and Sequence number
Multiplexing multiple related source on same medium Used one session by RTP mixer. But used different SSRC number. Considered Payload Type (PT)- RFC 1890
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Data Transfer Protocol – Modify RTP header Modify RTP header by profile
PT field modified Used Payload section in packet
for specific payload type’ information
Additional header field Additional functionality
RTP header extension New functionality Independent payload type
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Real-Time Control Protocol (RTCP)
Function Provide feedback on quality of data distribution Transmit identifier for RTP source ,called CNAME
Transmit rate control RTCP function need participants send control packet. Need the rate control for large number of participants. Detect total participants by received control packet.
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RTP Translators and Mixers
Cloud Common network and transport protocol (e.g., IP/UDP) Multicast address and destination port A pair of unicast address and destination port
Translator and Mixer connect two or more cloud. Translator
Forwards RTP packets with their SSRC
Mixer Combines the stream from on or more sources.
Change data format. Forwards the combined stream.
Used mixer’s SSRC identifier for timing
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RTP Translators and Mixers
end system SSRC = 17
end system SSRC = 39
Translator MixerSSRC = 5
DVI4
L16
GSM
GSM
SSRC=5
CSRC = 17, 39
Intermediate system Situation of connection between high and low bandwidth Advantage
High performance Disadvantage
Receiver can’t control
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SSRC identifier - Collision resolution
SSRC is required globally unique within RTP session
Collision Resolution Source detect collision
Used RTCP BYE packet
Receiver detect collision SSRC value is equal CNAME or is different One accept, another discard Then used RTCP BYE packet
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Security
Application required security Confidentiality
Only intended receiver can decode packet Used encryption such as CBC, DES - RFC 1423
Authentication and integrity Not defined
They need key management infrastructure