Wireless Application Protocol
Transport Layer Performance
G.Kahraman, ASELSAN Inc., Turkey,
gahraman@ mst.aselsan.com.tr,
ASELSAN Inc. P.O. Box: 101, Yenimahalle, 06172 Ankara/TURKEY, Phone: (90-312) 385 19 00, Fax: (90-312) 354 52 05
S.Bilgen, METU, Turkey,
Semih-Bilgen@metu.edu.tr
Middle East Technical University, 06531 Ankara/TURKEY, Phone: (90-312) 210 23 19, Fax: (90-312) 210 12 61
Abstract:
In this paper, simulation-based performance evaluation of the Wireless Application Protocol (WAP) Transport Lay er
Protocol, which may be suitable for Combat Net Radio (CNR), is presented. In the simulations, the Wireless Transaction Protocol
(WTP) Layer that is the transport layer of WAP is modeled in detail according to WAP Forum specifications. Wireless Transport
Layer Security (WTLS) layer is excluded in this paper. The User Datagram (UDP) Protocol is modeled for the bearer adaptation
protocol of the transport layer of WAP. The Wireless Session Protocol (WSP) layer is modeled with some basic features. The OPNET
model of MIL-STD-188-220B standard is used for the bearer network of WAP. Some user profiles are constructed for the application
layer. These profiles are modeled implicitly with source generators and/or explicitly by implementing their process model. These user
profiles simulate FTP, HTTP and E-MAIL applications. The protocols are simulated on “OPNET Modeler Radio”. Frequency hopping
radios are assumed during the simulations.
Keywords: Wireless Transaction Protocol, Wireless Application Protocol, MIL-STD-188-220B, Packet Radio, Transport -Layer,
Session-Layer, Source Traffic Model.
Introduction
The Wireless Application Protocol (WAP) is at the convergence of two rapidly evolving
network technologies, wireless data and the Internet [1]. In particular, in the military
context, there is a great interest to use commercial Internet Protocol (IP) based
applications for tactical packet radio networks. In the battlefields of the future,
tremendous amounts of information is going to be transported and processed at
unprecedented speeds. One example of a tactical military packet radio network is CNR
1
(Combat Net Radio) Area Network. Mainly MIL-STD-188-220B protocol [2] is used for
the operation of CNR Networks. Tactical requirements demand that the CNR Networks
be flexible to different types of command and control structures. Also, a CNR Network
must be autonomous, that is, deployable in a remote area where no core network is
available. If all infra-structure is destroyed, communication between units within good
radio coverage should be possible. Mobility is another critical issue, the network should
not only support point-to-point communication but also efficient broadcast and
multicasting [2]. Two important characteristics of a communication link in a mobile
packet radio network are unreliability and variability [3]. Today, widely used application
and transport protocols are taken into account for military applications. The WAP
protocol stack is one of these. Hence, it is of interest to study the behavior of WAP in the
context of ad hoc networks and evaluate the effect of dynamic topology on WAP
performance. In [4] and [5], some commonly addressed problems of WAP are outlined.
Current military applications use TCP or UDP for IP networks, even if WAP is deemed
to be successful or not, WTP seems to be a viable candidate for military applications due
to the fact that TCP has known problems in wireless networks and UDP provides
unreliable service [6].
This study aims to examine the viability of using WAP over a MIL-STD-188-220B
packet radio network. Due to the limited bandwidth, unpredictable availability and
unfavourable physical conditions, the delay in these networks becomes rather high and
throughput is quite low. In this paper, WTP is evaluated with respect to the performance
metrics of delay, goodput, efficiency and success under mobility and packet loss
conditions. Details on this study can be found in [7].
2
Simulation Methodology
We performed the simulations for 2 to 15 nodes. The nodes move around in a rectangular
region of NxN meters according to a mobility model. Node mobility consists of discrete
steps. Each node chooses a direction and moves with a distance of X meters at each
mobility period T. N has a range of 276 to 1000 meters to implement high and low
connectivity, respectively, between nodes. Also, X has a range of 100 meters for
simulation of changes of connections. In order to satisfy different classes of mobility, T
has a range of 15 to 480 seconds. The nodes have constant radio range of 391 meters. In
networks such as MIL-STD-188-220B with very high communication density, partial
band jammers are assumed to exist. The effect of a partial band jammer is modeled by
discarding the packets with a certain probability called as Packet_Loss_Probability.
Therefore, simulations were performed without packet drops in order to measure the
performance of the WTP protocol under noiseless conditions and with a set of low to
high rate of packet drop (for both directions). We set the Packet_Loss_Probability as a
simulation parameter in a range of 0% to 40%.
The whole communication protocol stacks separated as blocks can be seen in Figure 1.
Figure 1 Node Model
3
The node model consists of modules, which have one or more processes. In our model,
Ideal Generator, Custom Profiles, E-MAIL, HTTP and FTP modules represent the upper
layers of WAP communication protocol suite, that is WAE (Wireless Application
Environment) layer. These modules construct different user profile classes, and they are
considered as the source of data packets, which will be transmitted to the other nodes.
MIL-STD-188-220B protocol was chosen as a bearer of WAP network in simulations.
The WSP module has a process model that simulates the Wireless Session Protocol Layer
of WAP protocol stack. The Wireless Transaction Protocol Layer of WAP protocol stack
is fully implemented in this module. The WDP module has a process model that
simulates the Wireless Datagram Protocol Layer of WAP protocol stack. For IP networks
WDP is simply UDP. The model of WTP module consists of three processes, one
wireless transaction protocol layer process (WTP Root) and WTP Initiator process and
WTP Responder process as child processes.
At the transport layer, WAP provides a connectionless, unreliable datagram service
(WDP – Wireless Datagram Protocol), replaced by UDP when used over an IP network
layer. Over that transport protocol, WAP defines a Transaction Layer (WTP) that
provides reliable data transfer based on the request/reply paradigm. Due to the fact that
WAP has well defined layered architecture based on OSI Reference model, it can be used
for client/server interactions, as well as peer-to-peer communication (e.g. wireless ad-hoc
tactical networks).
Simulation Results
Figure 2 indicates the response time, goodput and efficiency versus file size with respect
to the maximum group size. From all of the graphs, we see that response times, goodput
4
and efficiency metrics get worse when the maximum group size decreases. But there is a
threshold value, and from these figures, we can choose the Maximum_Group_Size
attribute equal to 4 as best value for WTP over MIL-STD-188-220B network with respect
to the file sizes.
Max_
Group_
Size
0.99
6000
1
0.97
1
5000
2
0.96
2
4000
3
3000
4
2000
5
0.94
5
1000
6
0.93
6
9000
7000
0
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0.95
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0.92
3214
160000 320000 480000 640000 800000
File Size (bytes)
0.07
3214
160000 320000 480000 640000 800000
File Size (bytes)
Max_
Group_
Size
0.065
Goodput (x 16Kbps)
Max_
Group_
Size
0.98
Efficiency %
Response Time (sec)
8000
0.06
1
0.055
2
0.05
3
0.045
4
0.04
5
0.035
6
0.03
3214
160000 320000 480000 640000 800000
File Size (bytes)
Figure 2 Effect of File Size wrt Maximum Group Size
Figure 3 shows response times, goodput and efficiency versus the number of nodes with
respect to the maximum group size. From all of the graphs, we see that response times,
goodput and efficiency metrics get worse with decreasing maximum group size.
Especially when the number of nodes in the network is high, the effect of maximum
group size is seen well, higher values of max group sizes result in increasing file transfer
delays and decreasing goodput values when the number of nodes increase. The threshold
value of Maximum_Group_Size is determined as 4 or 5 as best value for WTP over MILSTD-188-220B network with respect to the number of nodes in network.
5
4000
3000
1
2500
2
0.986
1
0.984
2
0.982
3
0.98
4
5
0.978
5
6
0.976
6
2000
3
1500
4
1000
500
0.974
0
2
5
7
10
Number Of Nodes
2
15
0.25
5
7
10
Number Of Nodes
15
Max_
Group_
Size
0.2
Goodput (x 16Kbps)
Max_
Group_
Size
0.988
Efficiency %
Response Time (sec)
0.99
Max_
Group_
Size
3500
1
0.15
2
3
0.1
4
5
0.05
6
0
2
5
7
10
Number Of Nodes
15
Figure 3 Effect of Number of Nodes wrt Maximum Group Size
Simulations for the effect of Packet Loss Ratio were performed for two different sets of
Quality-Of-Service values over MIL-STD-188-220B network. The first simulation was
performed for Type1 [8] service of MIL-STD-188-220B protocol, that is, no ACK
procedure in MIL-STD-188-220B protocol is used. The second simulation is performed
for Type1 and 3 [8] services, that is, coupled ACK procedure in data link layer of MILSTD-188-220B protocol is used.
Figure 4 shows the response times, goodput, efficiency and success for the values of
maximum group size for no ACK procedure in MIL-STD-188-220B network. It is seen
that the response times get the worst values when the maximum group size is 1. If the
maximum group size is set to a value higher than 1, the values of response times decrease
sharply, especially for high values of packet loss probability. Due to the fact that WTP
responder confirms every segment explicitly by sending an ACK when the maximum
6
group size is set to 1, loosing a segment results in retransmissions by WTP provider.
Therefore, because of the type of medium access method used and redundant delays in
the network, the response times get higher when the maximum group size decreases in a
lossy environment. Similarly, we can see that goodput, efficiency and success metrics get
worse when the maximum group size decreases. In our simulations, we saw that WTP
900
800
700
600
500
400
300
200
100
0
Efficiency (%)
1
2
3
4
5
0.8
Max_
Group_
Size
0.6
1
2
0.4
3
4
0.2
5
0
0
5
10
15
20
Packet Loss Probability (%)
25
0.25
Goodput (x 16Kbps)
1
Max_
Group_
Size
0
0.2
Max_
Group_
Size
0.15
1
2
0.1
3
4
0.05
5
10
15
20
Packet Loss Probability (%)
25
1
Success (rspns/rqst)
Response Time (sec)
protocol operates very badly when there is no lower layer that gives a reliable service.
0.8
Max_
Group_
Size
0.6
1
2
0.4
3
4
0.2
5
5
0
0
0
5
10
15
20
Packet Loss Probability (%)
0
25
5
10
15
20
Packet Loss Probability (%)
25
Figure 4 Effect of Packet Loss Probability wrt Maximum Group Size
Although the bearer network causes additional delays and overhead, response times,
goodput, and especially efficiency and success metrics are satisfactory with a reliable
MIL-STD-188-220B network [8].
Figure 5 indicates the response times, goodput, efficiency and success versus the network
size with respect to the maximum group size. The value 276m of network size means that
even if the nodes are mobile, all nodes have links with each other, because the radio
7
range is equal to 391m for each node. These figures show the effects of connectivity of
nodes on performance. The values of 1 and 2 of max group size give higher response
times and smaller goodput values respectively when compared to the other values of max
group size parameter, as the WTP layer generates more ACK packets for every group.
When the max group size increases, the decrease on response times and the increase on
goodput values are negligible. However, for max group size values of 8 and 16,
efficiency is lower than that for 2 and 4. Also, response time and goodput show the same
behavior for the value of 8 and 16 of max group size. The reason for this behavior is that
when the network size increases, decreasing the connectivity between nodes, the load
over every network node decreases relatively, although the total offered load is constant.
1400
1200
Max_
Group_
Size
0.9
1000
0.8
Efficiency (%)
Response Time (sec)
1
Max_
Group_
Size
1
800
2
600
4
2
4
0.6
8
400
1
0.7
8
0.5
16
200
16
0.4
276
376
476
576
676
Network Size (meters)
776
0.21
276
776
Max_
Group_
Size
1
Success (rspns/rqst)
Goodput (x 16Kbps)
0.17
476
576
676
Network_Size (meter)
1.2
Max_
Group_
Size
0.19
376
0.8
0.15
1
0.13
2
0.11
4
0.09
8
0.07
16
1
0.6
2
4
0.4
8
0.2
0.05
16
0
276
376
476
576
676
Network_Size (meter)
776
276
376
476
576
676
Network Size (meter)
776
Figure 5 Effect of Connectivity wrt Maximum Group Size
For higher values of the max group size, WTP protocol sends many more segments. As
the nodes move in the network with constant intervals and sizes in random directions, the
8
probability that the number of segments sent to reach their destination successfully is
high when the value of the max group size is high. It is obvious tha t this situation reduces
efficiency for high values of max group size. However, we get better results for response
times and goodput metrics when the maximum group size increases, because then, WTP
sends all segments in a group in one batch, lowering the probability of loosing an ACK
sent by the Responder.
The success metric decreases with increasing network size. The change in performance of
the WTP protocol does not present a deterministic behavior when the connectivity
between nodes decreases, but for a max group size of 4, best results are achieved.
The Responder caches old TID (Transaction ID) values for each different Initiator. The
old TID value is called LastTID. The TID in the received invoke message is called
RcvTID. When the Responder receives an invoke message it takes some actions
depending on whether the Responder is caching old TID values or not, and the depth of
the TID cache size. Higher cache size values result in higher resource requirements,
smaller cache size values result in redundant (unnecessary) transactions.
400
Response Time (sec)
350
TID_
Cache_
Depth
300
250
0
200
1
150
2
100
3
50
15000
20000
25000
30000
35000
File Size (bytes)
Figure 6 Effect of File Size wrt TID(Transaction Identifier) Cache Depth
9
From Figure 6, we see that if the WTP caches the last two TID values, the response times
are reduced. But also, higher values from that do not result in smaller response times.
Therefore the best value seems to be 1.
We have suggested two methods for determining the value of Retry Interval given in
Figures 7 and 8. The value of Retry Interval depends not only on applications but also on
network parameters such as number of nodes and load. By making consistent
measurements with respect to the Max Group Size, a set of values of Ack Receive
Interval can be constructed so that the optimum value of Retry Interval can be chosen
according to the requirements of application used over WTP.
Ack Receive Interval
(sec)
70
Max_
Group_
Size
60
50
1
40
2
30
3
20
4
10
5
0
2
3
4
5
6
7
8
9 10 11 12 13 14 15
Number of Nodes
Figure 7 A method for Retry Interval (Considering number of nodes)
Ack Receive Interval
(sec)
120
Max_
Group_
Size
100
80
1
60
2
40
3
20
4
5
0
0.01 0.03 0.05 0.08 0.1 0.13 0.15 0.18 0.2 0.23 0.25
Load
Figure 8 A method for Retry Interval (Considering load)
In Figure 9, we can see that the value of Success metric decreases when the packet loss
ratio increases. In addition, the Success metric gets worse values when the value of
10
MAX_RCR decreases. But there is a threshold value that the optimum value for
MAX_RCR can be chosen as 2 in these network configurations for small file sizes.
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
Success (rspns/rqst)
MAX_
RCR
0
1
2
3
4
5
0
5
10
15
20
25
30
35
40
45
Packet_Loss_Ratio %
Figure 9 Success for Packet_Loss_Ratio wrt MAX_RCR (Max. Retransmission Count)
For long file sizes, we have seen that the Success metric shows the same behavior. But at
this time the value 3 was chosen as optimum value for MAX_RCR. This difference
comes from the inc reasing probability that a segment is lost when segmentation is used.
28
26
24
22
20
18
16
14
12
10
OFF
ON
0
5
10
15
Efficiency %
Response Time (sec)
UserAck
0.95
0.9
0.85
0.8
0.75
0.7
0.65
0.6
0.55
0.5
UserAck
OFF
ON
0
20
Packet Loss Probability %
5
10
15
20
Packet Loss Probability %
0.19
1.001
UserAck
0.15
0.13
OFF
0.11
ON
0.09
UserAck
1
Success (rspns/rqst)
Goodput (x 16Kbps)
0.17
0.07
0.999
0.998
OFF
ON
0.997
0.996
0.995
0
5
10
15
20
0
Packet Loss Probability %
5
10
15
Packet Loss Ratio %
Figure 10 Effect of Packet Loss Ratio wrt User Acknowledgement
11
20
In Figure 10, we can see that the values of Response Time, Efficiency, Goodput and
Success metrics get better whe n UserAck attribute is ON [9].
In Figure 11, a method for investigation of NACK Timer Interval is shown. When the
GTR or TTR packet has been received and one or more packets of the group are missing,
the WTP provider sets the NACK Timer before returning the Nack PDU with the
sequence numbers of the missing packet(s). To determine the optimum value for NACK
Timer Interval, we have presented a new metric named as “Average number of segments
received in NACK Timer Interval” for corresponding transaction. From the Figure 11, we
can see that, the value for the metric gets 0 value when the value of NACK Timer
Interval is between 0 and 4 sec. It means that the value of NACK Timer Interval should
be increased. When the NACK Timer Interval increases starting at 4sec, the value of this
new metric increases. But again there are threshold values for every values of Packet
Loss Ratio that to increase the value of NACK Timer Interval does not make sense for
performance, even makes the value of Response Time high.
3.5
Packet_
Loss_
Ratio_%
Average # of
Segments in
NACK Interval
3
2.5
5
2
1.5
10
1
15
20
0.5
25
18
16
14
12
10
8
6
4
2
0
0
NACK Timer Interval (sec)
Figure 11 A method for investigation of NACK Timer Interval
12
We compare the performances of FTP, EMAIL and HTTP user profiles over WTP
protocol with respect to Packet Loss Ratio and Mobility when offered load is same for all
profiles. Simulations were run for the value of Max. Group Size 3 and UserAck ON.
Results are collated with respect to Response Time s and Success metrics. Figure 12
shows the results for Packet Loss Ratio and Mobility.
600
500
Packet_
Loss_
Ratio
400
300
0%
200
15%
100
Mobility_
Pause_
Time
500
Response Times (sec)
Response Times (sec)
600
0
400
300
0
60
200
100
0
FTP
EMAIL
HTTP
FTP
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Packet_
Loss_
Ratio
0%
15%
FTP
EMAIL
EMAIL
HTTP
Offering Same Load
Success (rspns/rqst)
Success (rspns/rqst)
Offering Same Load
HTTP
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Mobility_
Pause_
Time
0
60
FTP
Offering Same Load
EMAIL
HTTP
Offering Same Load
Figure 12 Comparison of Profiles in Fixed Load
For the same offered load, the response time for FTP profile shows the worst value in
lossy environment. Although the response time under HTTP in lossy environment is
higher than the response time for EMAIL, the increase in the value of response time in
EMAIL is higher than HTTP when packet losses are experienced. This is an expected
situation as Class 2 transactions created by FTP profile use large number of segments to
transmit the data to the destination, therefore if a packet loss occurs, the last segment is
sent to the destination for every timeout of retransmission timer in WTP. Also the
13
number of segments indicated in the header field of Nack PDU when WTP Responder is
to send Nack to WTP Initiator is high in FTP profile. Actually, the difference between the
response times of FTP and EMAIL user profile is just one Class 2 transaction created for
get or put command for FTP profile. In HTTP profile, due to the fact that the number of
segments sent to the destination is low, and due to the burst traffic provided HTTP profile
channel is used efficiently.
The success value for FTP is higher than the success value for EMAIL. Also, for HTTP
profile, the success value is best. In addition, the value of response time metric is smaller
for EMAIL profile than FTP profile when nodes are mobile in similar to the packet loss
ratio case. But it is very interesting that the response time decreases again when mobility
is presented to the network for HTTP profile.
2150
Packet_
Loss_
Ratio
1650
ftp_0%
1300
ftp_15%
1150
email_0%
email_15%
650
150
56
112
168
224
900
ftp_0
700
ftp_60
500
email_0
email_60
http_0%
300
http_15%
100
280
Packet_
Loss_
Ratio
Success(rspns/rqst)
0.7
ftp_0%
0.6
ftp_15%
0.5
email_0%
0.4
email_15%
0.3
http_0%
0.2
http_15%
56
112
168
224
http_60
112
168
File Size (Kbytes)
280
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
280
Mobility_
Pause_
Time
ftp_0
ftp_60
email_0
email_60
http_0
http_60
56
File Size (Kbytes)
112
168
File Size (Kbytes)
Figure 13 Comparison of Profiles wrt File Sizes
14
224
Success (rspns/rqst)
1
0.8
http_0
56
File Size (Kbytes)
0.9
Mobility_
Pause_
Time
1100
Response Times (sec)
ResponseTimes(sec)
2650
224
280
We compare the performances of FTP, EMAIL and HTTP user profiles over WTP
protocol with respect to Packet Loss Ratio and Mobility when offered load is same for all
profiles for different file sizes. Figure 13 shows the results for Packet Loss Ratio and
Mobility for different file sizes. Simulations were run for the value of Max. Group Size 3
and UserAck ON. Results are plo tted for Response Times and Success metrics.
It is seen that FTP profile give s the worst performance when packet losses occur. If there
are no packet losses, EMAIL profile gives the smallest value for response time. For
HTTP profile the difference between the values of response times for no- loss
environment and lossy environment is disappearing when the file size increase. Also, the
worst value for success when packet losses occur is given by EMAIL profile. In addition,
the worst value for response time when nodes are mobile is given by FTP profile, and the
change in the value of response time in a mobile medium has undeterministic behavior.
4 0 0 0
N u m _
Of_
N o d e s
= 7
Response Times (sec)
3 5 0 0
3 0 0 0
2 5 0 0
2 0 0 0
1 5 0 0
1 0 0 0
http_15%
http_0%
email_15%
a l l s e r v e r
email_0%
ftp_0%
0
o n e s e r v e r
ftp_15%
500
U s e r P r o f i l e s w r t P L P
1
Num_
Of_
Nodes
= 7
Success (rspns/rqst)
0.8
0.6
0.4
0.2
all server
User Profiles wrt PLP
Figure 14 Comparison of Profiles wrt File Sizes
15
http_15%
http_0%
email_15%
email_0%
one server
ftp_15%
ftp_0%
0
We compare the performances of FTP, EMAIL and HTTP user profiles over WTP
protocol with respect to Packet Lo ss Ratio when offered load is same for all profiles, for
the number of servers in the network.
Simulations were run for the value of Max. Group Size 3 and UserAck ON. Results are
collated with respect to Response Times and Success metrics. Figure 14 shows the results
for Packet Loss Ratio with respect to the number of servers in the network.
For all profiles, due to the effect of medium access control algorithm used in MIL-STD188-22B network, when the traffic topology changes, the performance values are change
too.
Conclusion
In this paper, the performance of the Wireless Transaction Protocol (WTP) operating
over packet radio networks is investigated. WTP is the heart of WAP in the sense that it
represents the communication protocol layer of WAP. As a bearer network for WTP,
simulation model of MIL-STD-188-220B protocol operating over packet radio networks
is used. Topology update procedure in intranet layer of MIL-STD-188-220B is used to
handle mobility. Also a simple model of a frequency hopping radio was used. WSP and
WDP layers are modeled to create transactions and to service the requests from WTP
respectively. In order to see the performance of WTP on different classes of user
behaviors, three different types of user classes have been modeled: FTP, HTTP, EMAIL.
In this paper, the full functionality of WTP is modeled with the exception of the extended
version of SAR.
16
From the simulation results, we can see that network topology represented by number of
nodes and the status of mobility and packet losses in network effect the performance of
WTP seriously.
First, we have investigated the Maximum Group Size parameter with respect to the
network parameters and file sizes. For increasing file sizes, higher values of Maximum
Group Sizes give better performance. Also, the higher values of Maximum Group Sizes
give better performance, when the effects of mobility, network connectivity and packet
loss ratio increase. But it is seen that there is a threshold va lue for Maximum Group Size.
In other words, when we continue to increase the value of Maximum Group Size
parameter more than a threshold value, the performance of WTP starts to degrade,
especially for efficiency metric. From all simulation results we have seen that the value 4
for Maximum Group Size is the best value to be chosen for WAP over MIL-STD-188220B network.
Second, the value of TID Cache Depth is investigated. We have seen that under various
network conditions caching the TID value increases the performance of WTP, especially
with respect to response times and efficiency. The value 1 for TID Cache Depth has been
chosen as the best value. It is seen that while caching a single transaction ID makes
significant difference, increasing that number does not give significant change in
performance.
Also, we investigate the effect of UserAck. We have seen that using UserAck increase
the performance especially in small file sizes and high loads. We have seen that network
parameters do not change significantly the effect of UserAck on performance.
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In our simulations, we have seen that using Nack Timer increases the efficiency. But the
value of Nack Timer is dependent on other parameters, especially Maximum Group Size
parameter of WTP and network parameters.
For the values of Maximum Retransmission Counter and Retry Interval, we could not
find exact values, because these parameters are strictly dependent on the network
topology and the characteristics of the network.
We also presented a method for determining optimum values of NACK Timer Interval,
MAX_RCR and Retry Interval with respect to the network configurations.
Finally we investigated the performance of WTP under various user profiles. FTP, HTTP
and EMAIL user profiles were constructed. From the simulation results we have seen that
FTP and EMAIL user profiles give worse performance than HTTP profile. It has been
seen that HTTP profile gives better performance than the other profiles if the network is
mobile whereas it gives worse performance than the other profiles if the network has
packet losses with respect to response times. We have seen that for FTP profile, effect of
packet loss ratio in performance degradation in low load and medium load is smaller than
the effect of mobility whereas the effect of mobility in performance degradation high in
load is smaller than the effect of packet loss ratio.
Also we have seen that for HTTP profile, effect of packet loss ratio in performance
degradation in low load and medium load is smaller than the effect of mobility whereas
the effect of mobility in performance degradation in high load is smaller than the effect of
packet loss ratio.
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Also we have seen that for EMAIL profile, effect of packet loss ratio in performance
degradation for all loads is smaller than the effect of mobility.
If the user application traffic is similar to FTP profile we defined, in high loads
performance of WTP degrades significantly when the network presents packet losses. On
the other hand, in high loads, the performance of WTP degrades very slightly when the
network presents mobility.
If the user application traffic is similar to HTTP profile we defined, as independent from
the load, the performance of WTP degrades smoothly when the network presents packet
losses. On the other hand, in high loads, the response time metric for HTTP profile gets
better values when mobility is supplied.
In order to keep the performance of WTP over MIL-STD-188-220B protocol stable,
some adaptation procedures should be implemented between WAP and MIL-STD-118220B. Due to the fact that network conditions can be changed during the life of the
network and WTP protocol has no congestion algorithms or strict flow control
mechanism, QoS parameters are to be important.
As a further study, E-SAR procedure which is excluded in this thesis can be investigated
with respect to the performance. Also, for various user QoS requirements, correct
mapping between WTP and MIL-STD-188-220B protocol can be investigated. Optimum
values of MIL-STD-188-220B parameters such as delay, throughput, reliability,
precedence should be determined for implementing WAP over actual MIL-STD-188220B packet radio networks. Furthermore, other medium access control algorithms
beside DAPNAD, investigated in this work, should be examined for possible
improvements in functionality and performance.
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In general, while this work has intended to provide a preliminary study of the possibilities
of supporting WAP services over a military packet radio system, much work remains to
be done in the direction of determining how to do this most effectively and efficiently.
References
[1]
The WAP Forum, “WAP White Paper”, October 1999, http://www.wapforum.org
[2]
Nilsson, Jan, Architectural Issues for Integrating Tactical Radio Access Networks
in Civilian Infrastructure, 1999 IEEE
[3]
Nilsson, Jan, Routing for Multimedia Traffic in Wireless Frequency -Hop
Communication Networks, IEEE Journal On Selected Areas In Communications, VOL.
17, NO.5, May 1999
[4]
Rohit Khare. W* Effect Considered Harmful. 4K Associates, April 1999. Online
document is available at http://www.4K-Associates.com/4K-Associates/Library.html or
IEEE Internet Computing, pp 89-92, july-august 1999.
[5]
S.Gordon and J. Billington, WAP Forum Input Document: Inconsistencies in the
Wireless Transaction Protocol. Submitted to the WAP Forum, 19 March 1999
[6]
Chandran, Kartik, A Feedback-Based Scheme for Improving TCP Performance in
Ad Hoc Wireless Networks, IEEE Personal Communications, February 2001
[7]
Kahraman, Gokhan, An Investigation of WAP Transaction Protocol Performance
for Packet Radio Networks, Master Thesis, Electrical and Electronics Engineering,
Graduate School of Natural and Applied Sciences, The Middle East Technical
University, Ankara, Turkey, April 2002
[8]
Military Standard – Interoperability Standard for Digital Message Transfer
Device Subsystems (MIL-STD 188-220B), 20Jan1998.
[9]
The WAP Forum, “Wireless Transaction Protocol”, Version 10-Jul-2001,
http://www.wapforum.org
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