IEEE JSAC Special Issue
Adaptive Media Streaming
Submissions by April 1
Details at
http://www.jsac.ucsd.edu/Calls/adaptivemediastreamingCFP.pdf
Packet Video Workshop 2013
San Jose, CA (@ Cisco)
December 12/13, 2013 (Right after PCS 2013)
Submissions by mid June
http://pv2013.itec.aau.at/
Server-Based Traffic Shaping for
Stabilizing Oscillating
Adaptive Streaming Players
Saamer Akhshabi, Lakshmi
Anantakrishnan, Constantine Dovrolis
Ali C. Begen
Briefly …
• Problem
• When multiple adaptive streaming players compete for
bandwidth, we have several problems:
• Instability
• Unfairness
• Bandwidth underutilization
• Objective
• A server-based traffic shaping solution to mitigate the
oscillation problem without significant loss in utilization
4
Outline
•
•
•
•
•
Overview of adaptive streaming over HTTP
Multiple-player competition
Stabilization method and demonstration
Results
Conclusions
5
Outline
•
•
•
•
•
Overview of adaptive streaming over HTTP
Multiple-player competition
Stabilization method and demonstration
Results
Conclusions
6
Adaptive Streaming over HTTP
• Media is split into “chunks”
• Each chunk corresponds to
a certain amount of content
• Each chunk is encoded at
multiple bitrates
• Clients request chunks
based on their estimate of
available bandwidth
From IIS Smooth Streaming Website
7
Typical Behavior of a Player
• One chunk per HTTP request
• Two states:
• Buffering
• Request chunks as fast as
possible
• Build up the playback buffer
• Steady
• Request a new chunk every T
seconds
• Keep buffer size constant
• ON-OFF download pattern
• Estimate avail-bw with running
average of per-chunk TCP
throughput measurements
8
Outline
• Overview of adaptive streaming over HTTP
• Multiple-player competition
• Instability
• Bandwidth underutilization
• Unfairness
• Stabilization method and demonstration
• Results
• Conclusions
9
Simple Model: Two Competing Players
• Ideal TCP
• A single active
connection gets entire
capacity C
Shared link
Capacity C
Fair share = C/2
• Two active connections
share the capacity fairly
receiving C/2 each
• Based on the temporal overlap of the
ON-OFF periods of the players three
performance problems can arise
• Instability
• Unfairness
• Bandwidth underutilization
• Two competing
adaptive streaming
players
• Steady-State
• Full buffers
10
The Root Cause of Oscillations
ON
ON
ON
ON
ON
ON
ON
• Both players measure per-chunk throughput of more than C/2
• Overestimate the fair share (f=C/2)
• They will request bitrate greater than f, if available
• Oscillations
• Bandwidth underutilization
• Unfairness
11
Outline
• Overview of adaptive streaming over HTTP
• Multiple-player competition
• Stabilization method and demonstration
• Server-based shaping solution
• Experimental setup
• Stabilization method
• Results
• Conclusions
12
Outline
• Overview of adaptive streaming over HTTP
• Multiple-player competition
• Stabilization method and demonstration
• Server-based shaping solution
• Experimental setup
• Stabilization method
• Results
• Conclusions
13
Traffic Shaping Solution: Basic Idea
• A server-side stabilizer module
• Client independent
• Basically, a reactive and adaptive traffic shaper
• The stabilizer
• Remains inactive if there is no client-side instability
• When instability is detected, stabilizer shapes requested
video chunks at the rate of a lower profile
• Client will then measure lower throughput, and it will return (and
hopefully stabilize) to a lower profile
14
Outline
• Overview of adaptive streaming over HTTP
• Multiple-player competition
• Stabilization method and demonstration
• Server-based shaping solution
• Experimental setup
• Stabilization method
• Results
• Conclusions
15
Experimental Methodology
DummyNet
Stabilizer
• DummyNet
• Sets the capacity of the share
bottleneck
• Wireshark
• Captures the traffic for offline
analysis
• Server
• Hosts the video content in
multiple bitrates
• Host for stabilizer
• Clients
• Simpler player
• Logs internal
parameters
• Does not
render video
• Smooth
Streaming player
16
Implementation
• Server: Smooth Apache module:
• http://smoothstreaming.code-shop.com/trac/wiki/ModSmooth-Streaming-Apache
• Shaping done with Apache mod_bw module:
• http://bwmod.sourceforge.net
• Shaping module is modified to implement the
stabilizer
17
Outline
• Overview of adaptive streaming over HTTP
• Multiple-player competition
• Stabilization method and demonstration
• Server-based shaping solution
• Experimental setup
• Stabilization method
• Results
• Conclusions
18
Relation between Shaping Rate
and Chunk Encoding Rate
ON
ON
ON
ON
ON
ON
ON
ON
ON
ON
ON
•
•
•
Eliminate OFF periods by shaping each chunk so that its download takes about T
seconds
Shape the chunk to the average encoding rate for that chunk
In practice, the shaping rate is set to a slightly higher value than the encoding rate (r/c)
•
Shaping slack parameter c (0.7 in this study)
19
Relation between Shaping Rate
and Chunk Encoding Rate
ON
ON
ON
ON
ON
ON
ON
ON
ON
ON
ON
•
•
•
Eliminate OFF periods by shaping each chunk so that its download takes about T
seconds
Shape the chunk to the average encoding rate for that chunk
In practice, the shaping rate is set to a slightly higher value than the encoding rate (r/c)
•
Shaping slack parameter c (0.7 in this study)
20
Outline
21
Oscillation Detection
• Detecting direction changes
• Direction change defined as a change in the requested profile (upshift or
downshift) that is different than the last such change
• When two or more direction changes occur within W successive chunks,
an oscillation is detected and the player is flagged as unstable
• Parameter W is the detection window size
22
Oscillation Detection
23
Initial Shaping Rate Selection
• Goal is to find the highest sustainable profile
• Consider a set of candidate profiles
• Highest profile is obviously not sustainable
• Shaper starts by setting the initial shaping rate to the next highest profile
24
Experiment with the Simpler Player
• Six video profiles
between 0.7 and 5
Mbps
• Bottleneck capacity 10
Mbps
• Four players are
competing
Player-1
starts
streaming
Three more
player join
Two players
leave
25
Shaping Rate Decrease
Short-term
available
bandwidth
drops
detected
•
During shaping the server distinguishes between oscillations
•
Due to OFF periods
•
•
Due to short-term avail-bw reductions
•
•
Shaping rate should be decreased
No reason to modify the shaping rate
How to distinguish between the two cases?
•
Based on the requested profiles in the last W chunks
26
Shaping Rate Increase
Two players
leave
Avail-bw
increases
Abort
procedure
activated
Shaping rate
increases
• The server occasionally estimates the available bandwidth
• De-activates shaping for randomly chosen chunks
• Measure the connection’s throughput by looking at the ratio cwnd/rtt
• Increase the shaping rate if the estimated available bandwidth
is higher than the shaping rate
27
Shaping Rate Increase
28
Outline
29
Outline
•
•
•
•
Overview of adaptive streaming over HTTP
Multiple-player competition
Stabilization method and demonstration
Results
•
•
•
•
Performance metrics
Number of competing players
In the presence of a TCP bulk transfer
Mix of players
• Conclusions
30
Outline
•
•
•
•
Overview of adaptive streaming over HTTP
Multiple-player competition
Stabilization method and demonstration
Results
•
•
•
•
Performance metrics
Number of competing players
In the presence of a TCP bulk transfer
Mix of players
• Conclusions
31
Performance Metrics
• Instability
• Fraction of successive chunks in which the requested
bitrate is not constant
• For each client:
• Increase: 1, Decrease: -1, Constant: 0
0
0
1
0
-1
-1
0
0
1
-1
• The number of 1’s and -1’s divided by the total number of
chunk requests
• Utilization
• Aggregate throughput of all players divided by avail-bw
32
Outline
•
•
•
•
Overview of adaptive streaming over HTTP
Multiple-player competition
Stabilization method and demonstration
Results
•
•
•
•
Performance metrics
Number of competing players
In the presence of a TCP bulk transfer
Mix of players
• Conclusions
33
Number of Competing Players
Instability
• Unshaped players
• Instability metric peaks at some mid-range N value
• Shaped players
• Instability metric significantly lower
• We cannot reject the hypothesis that the mean instability is constant as N is
increased
34
Number of Competing Players
Utilization
• Between shaped and unshaped players
• For some values of N, the utilization metric does not show a
statistically significant difference
• For other values of N, the difference in the actual utilization is not
large
35
Outline
•
•
•
•
Overview of adaptive streaming over HTTP
Multiple-player competition
Stabilization method and demonstration
Results
•
•
•
•
Performance metrics
Number of competing players
In the presence of a TCP bulk transfer
Mix of players
• Conclusions
36
In the Presence of a TCP Bulk Transfer
BW=10 Mbps
3 players
(shaped
or
unshaped)
Greedy
• Instability metric is much less in the shaped case
• Aggregate utilization is high in both cases
• The TCP flow tends to fill up the bottleneck
• TCP connection takes up the largest share of the bottleneck’s capacity
37
Outline
•
•
•
•
Overview of adaptive streaming over HTTP
Multiple-player competition
Stabilization method and demonstration
Results
•
•
•
•
Performance metrics
Number of competing players
In the presence of a TCP bulk transfer
Mix of players
• Conclusions
38
Mix of Players
BW=12 Mbps
Two
shaped
and
two
unshaped
players
• Shaped players
• have the lowest instability
• Their presence helps to also stabilize the competing unshaped players
• Utilization is slightly less in the mixed-player experiments
39
Outline
•
•
•
•
•
Overview of adaptive streaming over HTTP
Multiple-player competition
Stabilization method and demonstration
Results
Conclusions
40
Conclusions
• Competition between adaptive streaming players can
lead to performance problems
• Instability, unfairness and bandwidth underutilization
• Root cause is the ON-OFF behavior of players during
Steady-State
• Players overestimate the fair share if their ON periods are not
perfectly synchronized (which is rarely the case)
• Traffic shaping can help mitigate instability
• (Upon oscillations) by shaping chunks at a lower bitrate pushing
players to switch to the lower profile
• Without incurring significant loss in bandwidth utilization
41