RTP Redundancy Up date Colin P erkins < c.p - - PowerPoint PPT Presentation

▶
rtp redundancy up date colin p erkins c p erkins cs ucl
SMART_READER_LITE
LIVE PREVIEW

RTP Redundancy Up date Colin P erkins < c.p - - PowerPoint PPT Presentation

Nov 28, 2022 272 likes •370 views

RTP Redundancy Up date Colin P erkins < c.p erkins@cs.ucl.ac.uk > Depa rtment of Computer Science Universit y College London Go w er Street London W C1E 6BT Status RTP redundancy mechanism published as RF C2198

slide-1
SLIDE 1 RTP Redundancy Up date Colin P erkins <c.p erkins@cs.ucl.ac.uk> Depa rtment
  • f
Computer Science Universit y College London Go w er Street London W C1E 6BT
slide-2
SLIDE 2 Status
  • RTP
redundancy mechanism published as RF C2198 in Septemb er 1997.
  • Simple
pack et fo rmat, allo ws bundling
  • f
multiple frames
  • f
audio into a single pack et as a fo rm
  • f
media sp ecic FEC.
  • 2

1

  • 3

2

  • 4

3 1

  • Optimised
fo r audio data, but can b e used fo r
  • ther
media t yp es. Colin P erkins/RTP Redundancy Up date/1
slide-3
SLIDE 3 Example pack et 1 2 3 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+
  • +-+-+-
+-+-+-+- +-+-+-+
  • +-+-+-+
  • +-+-+-+
|V=2|P|X| CC |M| PT | sequence number
  • f
primary | +-+-+-+-+-+-+-+-+-+-+-+-+-+
  • +-+-+-
+-+-+-+- +-+-+-+
  • +-+-+-+
  • +-+-+-+
| timestamp
  • f
primary encoding | +-+-+-+-+-+-+-+-+-+-+-+-+-+
  • +-+-+-
+-+-+-+- +-+-+-+
  • +-+-+-+
  • +-+-+-+
| synchronization source (SSRC) identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+
  • +-+-+-
+-+-+-+- +-+-+-+
  • +-+-+-+
  • +-+-+-+
|1| block PT=7 | timestamp
  • ffset
| block length | +-+-+-+-+-+-+-+-+-+-+-+-+-+
  • +-+-+-
+-+-+-+- +-+-+-+
  • +-+-+-+
  • +-+-+-+
|0| block PT=5 | | +-+-+-+-+-+-+-+-+ + | | + LPC encoded redundant data + | | + +-+-+-+-+-+-+-+-+-+-+-+-+
  • +-+-+-+
| | | +-+-+-+-+-+-+-+-+-+-+-+-+-+
  • +-+-+
+ | | + + | DVI4 encoded primary data | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+
  • +-+-+-
+-+-+-+- +-+-+-+
  • +-+-+-+
  • +-+-+-+
Colin P erkins/RTP Redundancy Up date/2
slide-4
SLIDE 4 Problem: Sta rt
  • f
T alkspurt
  • The
redundant (FEC) data is t ypically piggy-back ed
  • ne
pack et after the p rima ry .
  • The
rst pack et in a talkspurt cannot contain FEC data, since there a re no p receeding pack ets.
  • This
causes t w
  • p
roblems: 1. Changing pa yload t yp e 2. Unkno wn buering requirement Colin P erkins/RTP Redundancy Up date/3
slide-5
SLIDE 5 Issues: P a yload T yp e
  • In
a standa rd RTP session, all pack ets sent b y a source will have the same pa yload t yp e.
  • Ho
w ever, senders using redundant audio send the rst pack et in a talkspurt with no FEC data (ie: pa yload t yp e
  • f
the p rima ry co dec) and the follo wing pack ets with the redundancy pa yload t yp e.

R R R N R R Talkspurt 1 Talkspurt 2

  • This
mak es implementations needlessly complex, since they have to asso ciate pack ets with dierent pa yload t yp es into a single stream. Colin P erkins/RTP Redundancy Up date/4
slide-6
SLIDE 6 Issues: Buer Space
  • The
FEC data can b e sent any numb er
  • f
pack ets after the p rima ry . This dela y isn't kno wn until a pack et containing FEC data is received...
  • ...b
y which time the pla y
  • ut
buer length fo r this talkspurt has already b een calculated.
  • Adapting
the pla y
  • ut
buer mid-talkspurt will cause an glitch in the audio. Not adapting ma y mak e it imp
  • ssible
to use the FEC data (since it a rrives to
  • late)
Colin P erkins/RTP Redundancy Up date/5
slide-7
SLIDE 7 Solution
  • Send
all pack et with the redundancy pa yload t yp e.
  • F
  • r
those at the sta rt
  • f
the talkspurt, advertise the FEC
  • set
and set the blo ck length to zero. 1 2 3 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 +-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+- +-+-+-+- +-+-+-+
  • +-+-+-+
  • +-+-+-
+ |V=2|P|X| CC |M| PT | sequence number
  • f
primary | +-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+- +-+-+-+- +-+-+-+
  • +-+-+-+
  • +-+-+-
+ | timestamp
  • f
primary encoding | +-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+- +-+-+-+- +-+-+-+
  • +-+-+-+
  • +-+-+-
+ | synchronization source (SSRC) identifier | +-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+- +-+-+-+- +-+-+-+
  • +-+-+-+
  • +-+-+-
+ |1| block PT | timestamp
  • ffset
| block length = | +-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+- +-+-+-+- +-+-+-+
  • +-+-+-+
  • +-+-+-
+ |0| block PT | | +-+-+-+-+-+-+-+-+ + | ...Media data... | : : Colin P erkins/RTP Redundancy Up date/6
slide-8
SLIDE 8 Solution
  • This
solves b
  • th
p roblems noticed.
  • Requires
a change to the usage
  • f
the p roto col, but not to the p rotcol sp ecication itself.
  • Believed
backw a rds compatible with existing implementations... Colin P erkins/RTP Redundancy Up date/7