Download Time Diversity

Fault-Tolerance of Capillary
Multi-Path Routing for RealTime Multimedia Streaming with
Forward Error
Correction
Emin Gabrielyan
Switzernet Sàrl and Swiss Federal
Institute of Technology (EPFL)
[email protected]
2006-04-25
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Fault-Tolerance of Capillary
Multi-Path Routing for RealTime Multimedia Streaming with
Forward Error
Correction
ICTTA 2006 – 2nd IEEE International
Conference on Information & Communication
Technologies: from Theory to Applications April 24 - 28, 2006, Umayyad Palace,
Damascus, Syria
2006-04-25
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Off-line streaming

Digital Fountain Codes
A file can be chopped into equally sized source packets
…
…
…
Digital fountain code can generate an unlimited number of
different checksum packets of the size of the source packets
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Off-line streaming

Digital Fountain Codes
…
…
…
It is sufficient to collect almost as many checksum packets as
there are source packets in the file – and the file can be
recovered
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Off-line streaming

Digital Fountain Codes
Exactly like in a fountain: you need
to collect just a sufficient number
of drops to fill your cup
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Off-line streaming

Application of large file transmission
through a lossy network
Delivery of a large data file to a
motor vehicle through a satellite
broadcast channel without a
feedback – for example a recurrent
updates of GPS maps
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Off-line streaming

Reliable data file transmission
through a satellite channel
As far as the car is permanently
visible by the satellite there are no
problems
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Off-line streaming


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However the visibility of a car is usually
fragmented and is arbitrary due to:
Tunnels
Whether conditions
Underground parking
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Off-line streaming

Reliable data file transmission with
digital fountain code - carousel
One of the solutions is to broadcast
the file in a carousel, so if the
reception of the file is interrupted the
car can retry it at the next go
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Off-line streaming

Large file transmission with
carousel
However with a sufficiently large file
the probability that there will be
interruption at every go is very high
– there is a risk that the car never
receives its file
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Off-line streaming

Large file broadcast with digital
fountain code
With digital fountain code
everything is easy. The car
just needs to collect a
sufficient number of drops
(any of transmitted
checksum packets) to
recover the file
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Off-line streaming

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Digital fountain codes:
Raptor Codes: satellite broadcast, MBMS in 3G
communications
Amin Shokrollahi, “Raptor codes”, International
Symposium on Information Theory 2004, ISIT’04
LT codes: film footage transmission (Hollywood)
Michael Luby, “LT codes”, Symposium on
Foundations of Computer Science 2002, FOCS’02
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Off-line streaming – unlimited
buffering

The benefice of off-line applications
from FEC codes is spectacular

The common thing in all off-line streaming applications:

there is no hurry in receiving a piece of
information and passing it further to
the user
Off-line applications using FEC employ
Time Diversity:
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Off-line streaming

Time diversity: if data for information
recovery is not collected at the present
period of time…
The remaining data
can be collected later
2006-04-25
Later…
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
And later…
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Real-time streaming


In off-line streaming the receiver is
permitted to hold data in a practically
unlimited playback buffer
In real-time streaming the situation is
different: the fresh packets have a
limited life time and must be delivered
to the user ASAP
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Real-time streaming

In real-time streaming the
receiver is not permitted to
keep data too long in the
playback buffer
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Real-time streaming
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Several authors reported that:
In real-time streaming FEC is applicable if
the packet loss rate is below 5%
Efficiency of FEC can be improved if
combined with retransmissions
FEC is not efficient during bursts
The side effect from application of FEC
(that is increase of congestion rates) is
stronger than the improvements
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Real-time streaming – references
on application of FEC


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Several references on poor effect of FEC in real-time streaming :
Ingemar Johansson, Tomas Frankkila, Per Synnergren, “Bandwidth
efficient AMR operation for VoIP”, Speech Coding 2002 (FEC is efficient if
losses are below 5%)
Yicheng Huang, Jari Korhonen, Ye Wang, “Optimization of Source and
Channel Coding for Voice Over IP”, Multimedia and Expo 2005, ICME’05
(combine FEC with retransmissions)
Chinmay Padhye, Kenneth J. Christensen, Wilfrido Moreno, “A new
adaptive FEC loss control algorithm for voice over IP applications”,
Performance Computing and Communications Conference 2000,
IPCCC’00 (not efficient during bursts)
Eitan Altman, Chadi Barakat, Victor M. Ramos, “Queueing analysis of
simple FEC schemes for IP telephony”, Twentieth Annual Joint Conference
of the IEEE Computer and Communications Societies INFOCOM 2001
(not efficient for real-time streaming at all)
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Real-time streaming versus
Off-line streaming - résumé
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Application of FEC may result in slight
performance
… due to limited playback buffer
In any case it is clear that: If a failure or a full congestion lasts longer than the
playback buffer limit, even an infinite amount of redundant FEC packets
cannot save the communication
Failure time
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
Playback
buffer
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Real-time streaming – time
diversity?


Time diversity: that was turning FEC
into a powerful method in off-line
streaming
Is useless for real-streaming
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Real-Time streaming
Playback buffer limit
Reliable realTime streaming
Path diversity

Real-time
streaming
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

Data lost at the present period of time can be
received at another period of time (buffering
time scale)
But it can be also received via another path
(path diversity scale)
All previous studies stressing the poor FEC
performance assumed that the real-time
communication follows a single path route
Reliable Off-line
streaming
Time diversity
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Path diversity

Path diversity

Buffering time is a scalar value
– easy to imagine along an ax
Path diversity depends on the
multi-path routing topology …
Time diversity
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Path diversity

Intuitively we imagine the
path diversity ax as shown:
zero
Path diversity
Single path
routing
2006-04-25
Multi-path
routing
Multi-path
routing
Multi-path
routing
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Path diversity ax
Single path
routing
2006-04-25


zero
There are already
other studies
showing that in
real-time streaming
FEC becomes
applicable when an
extra path is added
to the single path
Intuitively we imagine the
path diversity ax as shown:
The single path routing does
not interest us and we
remove it from our study
Path diversity
Multi-path
routing
Multi-path
routing
Multi-path
routing
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Applicability of FEC in twopath routes - references
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Qi Qu, Ivan V. Bajic, Xusheng Tian, James W. Modestino, “On the
effects of path correlation in multi-path video communications using
FEC over lossy packet networks”, GLOBECOM’04
Tawan Thongpook, “Load balancing of adaptive zone routing in ad
hoc networks”, TENCON 2004
Rui Ma, Jacek Ilow, “Reliable multipath routing with fixed delays in
MANET using regenerating nodes”, LCN’03
Rui Ma, Jacek Ilow, “Regenerating nodes for real-time transmissions
in multi-hop wireless networks”, LCN'04 (coding at each intermediary
node)
Thinh Nguyen, Avideh Zakhor, “Protocols for distributed video
streaming”, Image Processing 2002 (streaming from multiple servers)
Thinh Nguyen, P. Mehra, Avideh Zakhor, “Path diversity and
bandwidth allocation for multimedia streaming”, ICME’03
(transmission with Reed-Solomon codes via shortest path and an
alternative – possibly corelated path)
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Gabrielyan
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Capillary routing


As a method for obtaining multi-path routing
patterns of various path diversity we relay
on capillary routing algorithm
For any given network and pair of nodes it
produces layer by layer several multi-path
routing patterns of increasing path diversity
Path diversity = Layer of Capillary Routing
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Capillary routing - introduction
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Capillary routing is constructed layer by
layer
First it offers a simple multi-path routing
pattern
At each successive layer it recursively
spreads out the individual sub-flows of the
previous layer
The path diversity develops as the layer
number increases
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Capillary routing – definition


Reduce the maximal load of all links

2006-04-25
Capillary routing is
discovered by an
iterative LP process
First take the
shortest path flow
and minimize the
maximum load of all
links
This will split the
flow over a few
main parallel routes
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Capillary routing – second
layer

Reduce the load of
the remaining links
2006-04-25

At the second layer
identify the
bottleneck links of
the first layer
…and minimize the
flow of all links,
except the
bottleneck links of
the first layer
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Capillary routing – min-flow vs
max-flow
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This LP formulation is completely valid,
but is numerically instable
We use another mathematically
equivalent LP model to achieve the
same results without numerical
instabilities
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Network samples
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The network samples for applying capillary
routing are obtained from a random walk
MANET
Nodes are moving in a rectangular area
If the nodes are sufficiently close and are
within the range of the coverage there is a
link between the nodes [diagram]
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Capillary routing examples
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Here is an example of capillary routing
on a small random walk ad-hoc
network with 9 nodes [diagram]
An example of capillary routing on a
larger network with 130 nodes
[diagram]
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Redundancy Overall
Requirement (ROR)

To evaluate how good a given multipath routing pattern is for real-time
streaming we measure the amount of
adaptive FEC codes that the sender
needs to transmit in order to combat
non-simultaneous failures of all
individual links in the given multi-path
routing
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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ROR – static FEC
We assume an application streaming
the media with a little constant static
tolerance for combating weak failures
source
packets
redundant
packets

FEC block
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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source
packets
redundant
packets
ROR – static FEC
FEC block



The real-time streaming constantly
tolerates packet loss rate 0<t<1
The FEC block length is FECt
We assume Reed-Solomon MDS code
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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ROR – static FEC

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When the packet loss rate observed at the
receiver exceeds the tolerable limit t …
… the sender increases the FEC block size
by adding more redundant packets and
increasing the transmission rate
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Redundancy Overall
Requirement
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The overall amount of FEC packets during
communication time is proportional:
to the usual packet transmission rate of the
sender
to the duration of communication
to the single link failure rate
to the single link failure time
and to a coefficient characterizing the
given multi-path routing pattern
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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ROR - equation
 FECr (l ) 
ROR   
 1
lL | t  r ( l )1  FECt




This routing coefficient is computed
according the above equation, where
FECr(l) is the FEC transmission block
size in case of the failure of link l
FECt is the usual FEC block size of the
real-time streaming
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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ROR coefficient
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Smaller the ROR coefficient of the multipath routing pattern, better the multi-path
routing is suited for real-time streaming
For a given pair of nodes, by measuring the
ROR coefficient of different layers of the
capillary routing – we can evaluate the
benefice from the capilarization
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ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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ROR as a function of
capilarization
Average ROR rating

60
55
50
45
40
35
30
25
20
15
10
5
0

3.3%
3.9%
4.5%
5.1%
6.3%
7.5%



capillarization
2006-04-25
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
Here is ROR as a
function of the
capillarization level
It is an average
function over 25
different network
samples (obtained from
MANET)
The constant tolerance
of the streaming is
5.1%
Here is ROR function
for a stream with a
static tolerance of 4.5%
Here are ROR
functions for static
tolerances from 3.3% to
7.5%
40
ROR rating over 200 network
samples


2006-04-25
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
ROR function of the
routing’s
capillarization
computed on several
sets of network
samples
Except a few
pathological cases
capillarization of the
routing results in
reduction of overall
FEC codes needed
from the sender
during the
communication
41
Conclusions (1 of 2)

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Commercial real-time streaming applications do not
relay on packet level FEC, since even heavy FEC
cannot protect communication against a long failure
on a single path
Recent studies have shown applicability of FEC in
real-time streaming if the media is streamed via two
paths
By studying a wide range of routing topologies we
have shown that a proper choice of multi-path
routing can make FEC extremely efficient
2006-04-25
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Conclusions (2 of 2)
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We introduced capillary routing algorithm
offering steadily diversifying patterns
We introduce ROR – a method for rating a
routing pattern by a single scalar value
Capillary routing can be applicable:



2006-04-25
to ad-hoc or sensor networks
to mobile networks where the wireless content
can be streamed to and from user via multiple
base stations
or to the public lossy internet (directly or with
relay nodes)
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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Thank you !



Fault-Tolerance of Real-Time
Streaming with Capillary Routing and
FEC
Emin Gabrielyan
[email protected]
Switzernet Sàrl and Swiss Federal
Institute of Technology (EPFL)
2006-04-25
ICTTA 2006 – Capillary routing with FEC - Emin
Gabrielyan
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