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The Influence of Proportional Jitter and Delay on End to End Delay in
Differentiated Service Network
Thu Ngo Quynh (*)
Holger Karl (**)
Adam Wolisz(**)
Klaus Rebensburg (*)
(*) Interdepartmental Research Center
(**) Telecommunication Networks Group
for Networking and Multimedia Technology
Department of Electrical Engineering
PRZ / FSP-PV / TUBKOM
and Computer Science
Technical University of Berlin
Strasse des 17. Juni 136 10623, Berlin, Germany.
Email: {thu, klaus}@prz.tu-berlin.de, {wolisz,karl}@ee.tu-berlin.de
Abstract
There exist some studies in Proportional Scheduling
Algorithms for Differentiated Service Network which
schedules the packets between different classes
proportionally based on some metrics as bandwidth,
loss, delay. In this paper, the behaviors of RJPS
(Relative Jitter Packet Scheduler) and another
proportional delay scheduler (WTP), as well as its
influence at the Playout Buffer which uses Concord
Delay Adjustment Algorithm are examined. Our
simulations show that RJPS is more converging and
produces smaller delay than WTP via the same
network with the same loss rate. Finally, we propose a
network using both RJPS and WTP for minimizing the
network delay of each class.
Keywords: Differentiated
proportional scheduling.
1.
Service,
jitter,
delay,
Introduction
There exist some proportional scheduling studies in
order to achieve proportional bandwidth (WFQ and
others), proportional delay (MDP [1], BPR [2], WTP [2]),
proportional loss (LHB [3]) for Differentiated Service.
And our earlier work [4] showed that it is possible to meet
the requirement of Relative Proportional Differentiated
Service Model in terms of delay jitter by using a simple
new scheduling algorithm called RJPS (Relative Jitter
Packet Scheduling).
An interesting question is not only examine the
behaviors of jitter proportional scheduler, but the
behaviors of proportional delay and jitter separately in a
same network to verify which can produce better network
delay, too. Furthermore, the influence of these network
delays at the playout buffer algorithm should be examined
because the playout buffer delay is adjusted with the
variation of network delay and loss rate. We will compare
network delays and end to end delays (with Concord
Playout Buffer Adjustment Algorithm) of two topologies
using RJPS and WTP separately. After that we could
conclude which scheduler provides smaller end to end
delay under which conditions. Another interesting
question is whether we should use both of RJPS and WTP
in the same network for providing proportional jitter and
delay simultaneously and for minimizing the network
delay at the same time?
The rest of the paper is organized as follows. In Part 2,
the performances of a network which uses RJPS and WTP
separately were examined. Part 3 proposes a network
which uses both RJPS and WTP simultaneously for
gaining its advantages.
2. Comparison of delays of a network using
RJPS and WTP separately
Among some proportional delay schedulers (BPR,
MDP, WTP) we believe that WTP is the best scheduler
because WTP can estimate delay differentiation very well.
Furthermore we choose Concord algorithm described in
[5] for adjusting the playout buffer delay at the receiver.
This algorithm computes a Probability Delay Distribution
over a window of packets. From this distribution they can
easily find the value of total end to end delay if there is a
predefined loss rate ratio. Our simulation study uses the
ns-2.1b7 Simulator [6]. The simulation model is as
follows. The RJPS scheduler uses packet sources of type
on-off traffic. The topology used is shown in Figure 1.
The links are 6Mps with a latency of 10ms. There is a
total of 3 classes 0, 1, 2. Flow 1 (S1- D1), 2 (S2- D2), 6
(S6-D1) and 9 (S9- D1) are belonging to class 0, while
flow 3 (S3- D3) , 4 (S4- D4), 7 (S7- D2) and 10 (S10- D2)
are belonging to class 1 and flow 5 (S5- D5), 8 (S8- D3)
and 11 (S11- D3) belongs to class 2. The weights of class
0, 1, 2 are 2.0, 1.0, 1.5 respectively. We will compare the
network delays and end to end delays of two topologies:
the first one uses only RJPS in its three routers (R17, R18,
1
R19) and the second one uses only WTP in these routers.
The Concord algorithm is used at the receivers. The others
are just FIFO routers. It is necessary to note that we
should maintain a window of packets in order to calculate
the PDD function. In our simulations, we use PDD taken
over a moving packet window of size 3000 packets for
Concord algorithm and this window is calculated once pro
200 packets for saving the cost of the computations. The
predefined loss rate is chosen 5%.
Our graphs (Figure 1a, 1b and 1c) show the actual
network delays at the case of RJPS or WTP for each class.
The result shows that RJPS produces smaller network
delays. The end to end delay of this topology (Figure 1d,
1e, 1f) shows that our algorithm produces better quality of
service in terms of delay. But as we can see, RJPS
fluctuates much more than WTP which is a very stable
proportional delay scheduling algorithm.
S1
R1
S2
R2
Note that when we have only WTP in a network, we will
receive proportional delay between all classes, and that is
why we will receive proportional jitter, too. When we
have RJPS as ingress router and the others are WTP, we
will receive only proportional jitter and approximately
proportional delay between all classes. Finally, when we
have RJPS as egress router and the others are WTP, we
will receive proportional jitter and approximately
proportional delay too.
3.1 RJPS as ingress Router
There is a total of 3 classes. We compare the network
delay of each class of this topology with the same
topology which uses only the WTP algorithm at all
routers. The result is shown in the Table 1. A
differentiated service network which uses RJPS as ingress
router and WTP at core routers is shown in Figure 2. We
S6
S7
S8
R11
R12
R13
R17
RJPS
WTP
R18
RJPS
WTP
R19
RJPS
WTP
R6
D1
R7
D2
R8
D3
S3
R3
S4
R4
R14
R15
R16
R9
D4
S5
R5
S9
S10
S11
R10
D5
Figure 1
3. Use of both RJPS and WTP simultaneously
in the same network
As shown in previous sections, RJPS could produce a
smaller delay than WTP in some cases, but the delay in a
RJPS network fluctuates much more than in a WTP
network. WTP is a very stable scheduler and it works well
even though the different load distribution between classes
is very asymmetric. Hence we choose WTP for using at
the core routers in a Differentiated Service network. RJPS
which oscillates more than WTP, but could produce
smaller delay in some cases, should be used in egress or
ingress routers for minimizing network delay and
providing both proportional jitter and approximately
proportional delay. We believe that such a network could
generate proportional jitter, approximately proportional
delay, reduce the end to end delay while still keeping of
the price of implementation small.
simulate different cases while the number of hops (K=3, 4,
5) is varied.
Class 0
With Withou
RJPS t RJPS
Class 1
Class 2
With Without With Witho
RJPS
RJPS RJPS ut
RJPS
K= 3,0580 3,2066 6,1953 6,591 4,188 4,374
3
3
5
K= 6,5512 6,6688 13,700 14,0725 9,141 9,331
4
3
7
2
K= 9,1627 9,688 18,934 20,068 12,33 13,19
5
51
79
Table 1
In this simulation class 0 is the most important one. The
result in table 2 shows that a network which uses RJPS as
ingress router could provide smaller delay for the most
important class than a network using only WTP at all
routers. The performance of the network delay of other
classes (class 1 and 2) in case of RJPS as ingress router is
better at all cases, too.
2
S1
S6
S7
S8
R1
S2
S3
R2
RJPS
R1
WTP
R2
S4
S9
WTP
R3
WTP
Rk
S10
S11
S5
Figure 2
3.2 RJPS as egress Router
Another interesting question is to compare the network
delay of two networks which use RJPS as egress router
and another network which uses only WTP at its nodes.
We simulate for a similar topology as the Figure 2, but the
scheduler RJPS is used in egress router. The performance
is shown in Table 2. Table 2 compares the average
network delay between different classes in two cases with
different number of hops. The number of hops in this case
plays an important roll because performance of network
delay depends on this number. For example, when we
have only two hops (K=2) the network delay of class 0, 1
and 2 stay similar, and the delay of the most important
class (class 0) of a network with RJPS as egress router is
smaller. But when the number of hops increases (K=3 or
5) the delay of the RJPS network is increased too and the
performance of the RJPS network is not good as the
performance of WTP network. We could say that the
performance of the RJPS egress network decreases with
the number of hops.
Class 0
With Withou
RJPS t RJPS
Class 1
Class 2
With Witho With Without
RJPS RJPS
RJPS
ut
RJPS
2,823 2,8112 1,87
1,8655
K 1,359 1,3854
=2
9
K 3,190 3,2067 6,6996 6,591 4,357
=3
6
1
K 10,57 10,164 21,535 20,444 14,29
=5
5
1
34
Table 2
4,374
14,0855
4. Conclusion
In conclusion, we have examined the behaviors of RJPS in
different contexts. The performance of the delay of
networks which use only the RJPS algorithm at its core
R3
Class 0
Class 1
Class 2
R4
R5
routers is examined and compared to a network which
uses only the WTP in its core routers. We conclude that
RJPS could provide a smaller delay than WTP and
fluctuates more than WTP in some case. That is why we
proposed a network which uses both, WTP and RJPS, at
the routers for gaining the advantages of these schedulers.
We conclude that a network with RJPS as ingress router is
better than a network with only WTP in terms of network
delay. And the performance of a network with RJPS as
egress router, compared to a network which uses only
WTP is examined too.
5. Acknowledgement
The authors would like to thank Nguyen Huu Thanh,
Thomas Wolfram and Irina Piens for their useful help and
comments.
6. References
[1] T. Nandagopal, Narayanan Venkitaraman, R. Sivakumar and
V. Bharghavan. Delay Differentiation and Adaptation in Core
Stateless networks. IEEE Infocom 2000, Tel Aviv, Israel. March
2000.
[2] C. Dovrolis, D. Stiliadis and P. Ramanathan. Proportional
Differentiated Services: Delay Differentiation and Packet
Scheduling. In Proceedings of the 1999 ACM SIGCOMM
conference, Cambridge MA, September 1999.
[3] C. Dovrolis and Parmesh Ramanathan. A Case for Relative
Differentiated Services and the Proportional Differentiation
Model. In IEEE Network, 13(5):26-34, September 1999 (special
issue on Integrated and Differentiated Services in the Internet).
[4] T. N. Quynh, H, Karl, A. Wolisz, K. Rebensburg. Relative
Jitter Packet Scheduling for Differentiated Service. In
Proceeding of 9th IFIP Working Conference on Performance
Modelling and Evaluation of ATM & IP Networks IFIP
ATM&IP 2001.
[5] N. Shivakumar, C. J. Sreeman, B. Narendran and P.
Agrawal. The Concord algorithm for synchronization of
networked multimedia streams. International Conference on
Multimedia Computing and Systems, 1995.
[6] UCB/LBNL/VINT Network Simulator-ns (version 2),
http://www-mash.cs.berkeley.edu/ns/ns.html.
3
Appendix: Graphes
Figure 1a: Network Delay for Class 0
6
D
e
l
a
y
(
s
)
5
4
Class 0- W TP
Class 0- RJPS
3
2
1
0
8
9
8
,
5
8
8
,
6
7
8
,
8
6
9
5
9
,
1
4
9
,
3
3
9
,
4
2
9
,
5
1
9
,
7
9
,
8
5
0
0
1
T im e (s)
Figure 1b: Network Delay of Class 1
10
D
e
l
a
y
(
s
)
8
6
Class 1- W TP
Class 1- RJPS
4
1
1
2
1
0
2
9
1
,
6
8
1
,
4
7
1
,
3
6
1
,
1
5
0
,
9
4
0
,
7
3
0
,
5
2
0
,
4
0
0
1
0
,
2
2
Tim e (s)
Figure 1c: Network Delay of Class 2
6
D
e
la
y
(
s
)
5
4
Class 2- W TP
Class 2- RJPS
3
2
1
0
8
9
8
,4
8
8
,6
7
8
,8
6
8
,9
5
9
,1
4
9
,2
3
9
,4
2
9
,5
9
,8
5
0
0
1
9
,7
1
T im e (s)
Figure 1d: End to End Delay , Loss 5%
1
1
5
1
0
4
9
3
,8
8
3
,4
7
3
6
2
,6
5
2
,1
4
1
,7
3
1
,3
2
0
,9
1
0
,4
Class 0- RJPS
Class 1- W TP
0
D
e
la
y
(
s
)
3,5
3
2,5
2
1,5
1
0,5
0
Tim e (s)
Figure 1e: End to End Delay, Loss 5%
6
D
e
la
y
(
s
)
5
4
Class 1- W TP
Class 1- RJPS
3
2
1
0
8
9
8
,6
8
8
,7
7
8
,9
6
9
5
9
,2
4
9
,3
3
9
,4
2
9
,6
1
9
,7
9
,8
6
0
0
1
T im e (s)
Clas s 2- WTP
1
1
0
9
9
,1
8
8
,1
7
7
,1
6
6
,1
5
5
,1
4
4
3
3
2
2
Clas s 2- RJPS
1
1
3,5
3
2,5
2
1,5
1
0,5
0
0
D
e
la
y(s
)
Figure 1f: End to End Delay, Loss 5%
Time (s)
4