Transcript Tunneled multiplexed Compressed RTP ("TCRTP")

Tunneled multiplexed
Compressed RTP ("TCRTP")
Compress and Multiplex RTP Streams
Over the Network
1
RTP and Voice
40
RTP
IP/UDP/RTP Headers
10
RTP
payload
• Problem: Large header, Small payload
– Poor utilization of bandwidth
• Need end-to-end solution
– Compress the Headers
– Multiplex packets
2
CRTP Compression
(RFC2508)
40
RTP
10
IP/UDP/RTP Headers
RTP
payload
2 10
CRTP
C
I
D
RTP
payload
CRTP Header
3
CRTP End to End = TCRTP
(Tunneled CRTP)
20
IP hdr
1
TCRTP
Protocol
Type=FH
FULL_HEADER
40
IP/UDP/RTP Headers
CID
SEQ
Len
10
RTP
payload
COMPRESSED_RTP
2 10
CID associated with:
src host-id and port#
dst host-id and port#
SSRC
IP hdr
TCRTP
Protocol
Type=CR
C
RTP
I
payload
D
Len
4
Multiplexing TCRTP
20
IP hdr
10
TCRTP
Protocol
C
RTP
I
payload
D
40
IP/UDP/RTP Headers
CID
SEQ
20
RTP
payload
10
RTP
payload
5
10
RTP
RTP
payload payload
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RTP
payload
• Multiplexed packets
– Can be from different RTP streams
– Same Destination IP
5
Multiplexing 10
20
IP hdr
TCRTP
Protocol
C
I
D
10
10
10
10
RTP
payload
RTP
payload
RTP
payload
RTP
payload
10
10
10
10
RTP
payload
RTP
payload
RTP
payload
RTP
payload
10
RTP
payload
10
RTP
payload
10 IP/UDP/RTP headers = 400
Multiplexed = 20 + 40 = 60
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TCRTP MULTIPLEXING
CID1 = (h1,p1,h4,p4,SSRC1)
CID2 = (h2,p1,h5,p5,SSRC2)
(h1, p1)
(h4, p4)
CID3 = (h3,p3,h6,p6,SSRC3)
RTP
RTP
(h5, p5)
(h2, p2)
TCRTP
(h3, p3)
IP: G1,G2
G1
G2
(h6, p6)
CID1,RTP-Payload1 CID2,RTP-Payload2 CID3,RTP-Payload3 7
CRTP Advantages
• Very good compression (40 --> 2)
– Is already a standard (RFC2508)
– CID stores essentials of RTP stream
• Easy to deliver data at destination
• No need to use SSRC for delivery
• Very strong multiplexing capabilities
– Multiple streams
– Multiple sources and destinations
– Streams parameters not related
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TCRTP not only for RTP
• TCRTP can be used to compress and
multiplex any UDP streams by using only
FULL_HEADER (FH) and
COMPRESSED_UDP (CU) packet types
10 IP/UDP headers = 280
Multiplexed = 20 + 40 = 60
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Voice over a Network
• ‘Reasonable Network’
– Limited loss and misordering
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Network Quality Level: N
• At most N adjacent packets may get lost
• Misordering is of order N
– Sequence number may skip N
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CRTP Limitations
• CRTP algorithm is sensitive to
– Lost packets
– Packets delivered out of order
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Which packets make CRTP
vulnerable
• Packets that change the state of the
decompressor
– COMPRESSED_RTP with DeltaT
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The CRTPX packet (CX)
CR
The CRTPX
header is
added to CR
and CR+
packets
to yield the CX
packet type
CRTP
hdr
RTP
payload
CRTPX
hdr
CR+
CX
CX
CRTP+
hdr Delta
CRTPX
hdr
CRTPX
hdr
RTP
payload
CRTP
hdr
CRTP+
hdr Delta
RTP
payload
RTP
payload
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The CRTPX packet (CX)
CX
CX
CRTPX
hdr
CRTPX
hdr
RTP timestamp
CRTP
hdr
CRTP+
hdr Delta
RTP
payload
RTP
payload
RTP sequence
RTP
Type
CRTP
DeltaT
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Why CRTPX
• The CRTPX header includes the RTP
header fields that are missing in a CR
packet, and the current DeltaT
• Upon receipt of a CX packet, the
decompressor can fully recover to a good
state
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When are CX packets sent
• Each packet that changes the state at
the decompressor will be followed by N
packets of type CX
– COMPRESSED_RTP with DeltaT
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TCRTP Functionality
• IP Tunneling of CRTP
• Multiplexing
• Complement CRTP to adopt to an end to
end IP network
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Additional CX types
• Checksums
• Error correction bits
• Add bits to CRTP sequence number
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The End
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CRTP packet format (PPP)
FULL_HEADER
FH
IP hdr
COMPRESSED_UDP
COMPRESSED_RTP
COMPRESSED_RTP
CID
UDP
SEQ
hdr
RTP
hdr
RTP
payload
CRTP
hdr
RTP
hdr
RTP
payload
CU
CR
CR+
CRTP
hdr
CRTP+
hdr Delta
RTP
payload
RTP
payload
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