1. Maximizing Audio Quality
(A Linear programming Problem)
Team Members:
• Shailendra Shankar Gautam
• Abhay Kumar
• Ankit Katiyar
• Dharm Jaiswal
• Sharad Srivastava
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2. Problems
 Current Internet still provides best efforts service
 No Guarantee of performance for real time multimedia application
 Multimedia typically uses UDP
 Not reliable
 No congestion control
 Multimedia traffic is normally subject to
 Restricted available bandwidth
 Delay, Delay jitter
 Loss of packets

3. Control Mechanisms
 Mechanisms which
 Dynamically adapt the behavior of the audio application to
maximize the audio quality under the constraints of
• Restricted bandwidth
• Delay
• Packet Loss
• Jitter
present in the network at that point of time

4. Audio Compression Techniques
(codecs)
 Current codecs have a diverse range in terms of
degree of compression (bitrates) and underlying
technologies
 Thus the quality of an IP telephony call is highly
dependent on the codecs and their reaction to
available bandwidth, link delays and packet loss.

5. Mean Opinion Score (MOS)
 Described in ITU recommendation P.800
 Formal subjective measure if voice quality
 Real number – Between 1 to 5
 Toll Quality – Quality with MOS between 4 and
4.3
 Communication Quality – Between 3.5 and 4
 Lower bound for acceptability of a speech – 3.5
 MOS has been determined for every codec under
the ideal condition of no loss.

6. Examples of codecs
Codec
Technology Bitrate (ms) MOS
PCM µ-law
Waveform
64
4.3
G.721
Waveform
32
4.0
GSM fullrate
RPE-LTP
13
3.7
G.728
LD-CELP
8
4.0
G.723.1
MP-MLQ CELP
5.6
3.9

7. Bandwidth Constraint
 End to End available bandwidth – the maximum
rate that the path can provide to a flow
 Depends upon the utilization of various links in the
path in presence of cross traffic
 Less than or equal to capacity of the path – The
maximum rate a path can provide to a flow, wwhen
there is no other traffic in the path

8. Bandwidth Constraint (contd..)
 In underutilized network we can use high bitrate codecs
 which will consume more bandwidth
 but will generate high quality
 But switch to low bitrate codecs when available
bandwidth gets tighter
 It is possible to mix multiple codecs in a certain ratio for
bandwidth optimization ensuring that the audio quality
provided is optimum for the user.

9. Delay Constraint
 Delay of the path
 Propagation delay of individual links
 Queuing delay at individual hops/routers
 Delay inherent to the codec
T(codec) = T(enc.) + T(dec.) + T(LA)
 Total delay must be under the constraint of tolerable
Mouth-to-Ear (M2E) delay
 The time that elapses between the moment the talker utters the
words and the moment the listener hears them
 Must be under 400 ms (ITU recommendation G.114 & G.131)

10. The LP Problem
Maximizes the audio quality under the constraint of available bandwidth and link delay
Maximizes MOS (z) = c1x1 + c2x2 + ….. + cnxn
Subject to;
b1x1 + b2x2 + ….. + bnxn <= B
/*bandwidth constraint*/
d1x1 + d2x2 + ….. + dnxn <= D
/*delay constraint*/
c1x1 + c2x2 + ….. + cnxn <= 4.3
/*max possible MOS attainable by codec*/
c1x1 + c2x2 + ….. + cnxn >= 3.5
/*lower bound of acceptable MOS score*/
x1 + x2 + ….. + xn= 1
/*total of all percentage*/

11. The LP Problem (contd..)
Where
x1, x2 ….., xn = percentage of each codec in transmission mixing
c1, c2 ….., cn = MOS value for each codec
b1, b2 ….., bn = bitrates for each codec
d1, d2 ….., dn = (packet size in bytes)*(encoding/decoding delay
to create/decode 1 byte)
B = Available bandwidth
D = 400 ms (link one way delay)

12. Implementation
Codec
Bitrate
(kbps)
MOS
Delay for Packet
1 byte
size
(ms)
(bytes)
PCM µ-law
64
4.3
0.50
200
G.721
32
4.0
1.00
200
GSM fullrate
13
3.7
2.42
198
G.728
8
4.0
2.50
200
G.723.1
5.6
3.9
6.00
210
The delay values for each codec has been determined based on existing literature and
experiment.

13. Implementation (contd..)
The formulation of this particular linear programming problem is
thus:
Maximizes MOS (z) = 4.3x1 + 4.0x2 + 3.7x3 + 4.0x4 + 3.9x5
Subject to;
64x1 + 32x2 + 13x3 + 8x4 + 5.6x5 <= B
0.1x1 + 0.2x2 + 0.48x3 + 0.5x4 + 1.26x5 <= D
4.3x1 + 4x2 + 3.7x3 + 4x4 + 3.9x5 <= 4.3
4.3x1 + 4x2 + 3.7x3 + 4x4 + 3.9x5 >= 3.5
x1 + x2 + x3 + x4 + x5 = 1
Xi >= 0 where i = 1,2,3,4,5

14. Solution
High bandwidth availability (500) and low delay (40)

15. Solution
High bandwidth availability (500) and low delay (40)

16. Result
Sr. No. Network
Condition
Available
1 way
bandwidth delay (ms)
Solution
Optimum
MOS value
1
High available bw/Low
Delay
500
40
X1=1, X2=0,
X3=0, X4=0,
X5=0
4.30
2
High available bw/High
Delay
100
150
X1=1, X2=0,
X3=0, X4=0,
X5=0
4.30
3
Med available
bandwidth/High delay
50
140
X1=0.75, X2=0,
X3=0, X4=0.25,
X5=0
4.225
4
Low available bw/Low
Delay
30
40
X1=0.39, X2=0,
X3=0.61, X4=0,
X5=0
4.11
5
Low available bw/High
Delay
30
150
X1=0.083,
X2=0.722, X3=0,
X4=0.194, X5=0
4.025
6
Very Low available
bw/High delay
20
150
Infeasible!!
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17. Thank You!! 