Simulation report-Cosmin Caba

8/7/2019 Simulation report-Cosmin Caba

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Simulation Report

Student: Cosmin Caba


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1. IntroductionTelecommunication sector evolves rapidly, especially mobile communication networks

because there is an increasing demand for high quality for applications running on mobile

terminals. The applications and services offered to mobile users ask for more and more

bandwidth , for less delay and this has to be somehow sustained by the mobile network

infrastructure. In order to keep the pace with this trends, mobile operators try to improve their

infrastructure permanently. Standardization bodies have a very important role because they

release standards for future improvements which can facilitate interoperability between

different manufacturers thus helping mobile operators to get rid of being dependent on one

vendor.

Before implementing the newest technologies, that can support the very best quality of

services, mobile operators and not only them, have to go through one or more simulation

steps. Simulation is useful because it helps testing and investigating some technologies orprotocols leading to capital savings and also time. It is very hard and expensive to implement a

newly standardized technology in reality, to test it, to investigate what benefits can bring

beyond the already implemented technology. That is why simulation comes with a lots of

advantages to help in this situation:

1) It is very easy to control and to reproduce: simulation typically takes place inside of acomputer thus only one person can controlit andrun it. Also it can be reproduced as

many times as it needs to get the desired result.

2) It is easy adaptable to several traffic loads: it can be very easy set up with differenttraffic loads to visualize how the networks topology reacts in case of a future high load

from the customers side.

3) It is possible to simulate even protocols or technologies not available yet on the market.4) Also it is possible to design very complex systems to simulate, which in reality can be

extremely difficult.

Of course there are many other advantages and this is why most (if not all) operators

prefer to simulate the behavior of their networks or future network implementations before

deploying them.

What is a simulation in fact ? In order to talk about this I have first to mention about

modeling. A model is a imitation of a real-life system, it doesnt try to reproduce the real-life

system. Having the model of the system built it is possible to find answer about that model by

testing it , by performing experiments on the model and this is what is called a simulation.

Basically the simulation helps people to find answers about a system just by performing tests

on a imitation of that system in a computer environment.


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For our simulation exercise we used CommWyse IMNS 3000 network simulator. The

exercise comprises three main parts :

- GPRS/EDGE simulation setup;- UMTS simulation setup;- HSDPAsimulation setup.2. GPRS/EDGE simulation setup and resultsGPRS has been introduced in communication networks as an enhancement for the GSM

network to transport data. In the present exercise we try to simulate a site with three cells

each of them containing three TRX units. Eight time slots that are able to support EDGE and

the data time slot strategy is to allocate dynamically 1 to 8 slots. The third cell has poor radio

conditions in comparison with cell 1 and 2.Traffic on the network consists of a mix with the

following ratios : 40% HTTP traffic, 30% FTP, 30% Email. The mobile terminals are 60% of them

EDGE enabled and 40% GPRS.

After loading the network topology and assigning the traffic profile to it we run the

simulation with the specified parameters.

The first task is to analyze and compare both technologies GPRS and EDGE with respect

to the HTTP page response time, Email retrieval time and FTP download response time .I have

plotted the three graphs which depict the Cumulative distribution function (CDF) for the GPRS

and EDGE enabled mobile stations in the three cases I mentioned above. I have to say that

both types of mobile stations involved in the simulation are class 10 GPRS/EDGE.

EDGE is meant to be an improvement for the GPRS networks thus it should provide

better QoS for the applications running on the MS. Surprisingly enough the graphs show that

EDGE does not always perform better than GPRS. Lets take as an example the first graph with

HTTP page response time. It can be seen that in the first part of the curve EDGE really performs

slightly better than GPRS. For the probability of 0.8 for both technologies the response time is


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less than 75 sec. From this point GPRS is a little bit better then EDGE meaning that for the same

probability ( 0.9) the response time for GPRS(


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The next figure illustrates the differences between two of the cells within the same technology

namely EDGE : one with poor radio conditions (Cell2G-3) and the other with good radio

conditions(Cell2G-1). It is easy to see from the plot that cell number three really pulled down the

performance of the EDGE system. There is a penalty of at least 20 seconds for the cell 3 with respect to

the application considered (FTP).

To better observe the influence of the retransmissions on the load of the time slots we have

next two figures. They show the load on the time slots for the cell 1 and 3 as an instantaneous value and

a mean value.

It can be observed in the first graph compared to the second that the sessions are shorter in

time and this is because the radio conditions facilitate the data transfer thus no or very few

retransmissions are needed. In the second figure, below, sessions take more time to be completed ,

increasing the burden over the radio link. This can be easily proved by the fact that the mean value

forthe allocated time slots in the first case is 4.6 while for the cell number 3 is 5.4. So transmitting the

same amount of data requested 0.8 of a time slot more in third cell than in the first one.


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Having the present case fully analyzed we proceed to an improved test case for which the good

radio conditions have been selected for all the three cells in the site not only for the first two as it was

until now. The scenario is the same with the only modification that I mentioned above.

The first thing to verify is the improvement added by the modification in the present scenario

compared to the previous one. The following picture only takes into consideration the EDGE enabled

MSs and plots the first network topology with cell 3 having poor radio conditions and the second

network topology with all the cell having good radio conditions. So we will see the impact of good radio

conditions only on the EDGE mobile terminals in the case of FTP application.

As it can be seen the curve for the improved case of GPRS/EDGE is very steep this time thus

many clients will experience a better response time than in the previous case. Going further the

following graph depicts the same comparison but this time only for cell number 3 for which we have

switched to good radio conditions. A significant improvement in quality has been achieved for this

cell by changing the radio conditions and this can be seen from the plot : there is a time interval of at

least 20 s between the two curves thus many more users will experience better services.


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Now that we saw how the third cell influenced the QoS for the EDGE users it is time to have a

look at how EDGE can improve data transfer comparing it with the GPRS system. It is the same

comparison we have made in the beginning of this section but now for good radio conditions selectedfor cell number 3.

This last figure illustrates the difference in performance between the two systems. We can

conclude now that EDGE really brings quality to the data transfer but only if the radio conditions allow

that the mechanisms designed for EDGE to work properly. For the case of the poor radio conditions and

only for one of the three cell , the GPRS proves to be almost the same as EDGE concerning the quality of

the services. So we can talk about an improvement in EDGE system only for good radio conditions.

3. UMTS simulation setup and resultsIt is very important for a mobile operator to evaluate several strategies for configuring the RAB

(Radio Access Bearer) and resource allocation for his UMTS network. Also a very important aspect when


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purchasing new equipment is to assess the quality of service that it can provide, the Radio Resource

Management configurations from different vendors, before buying.

The network topology that we use in this part of the exercise consists of two Node Bs each

serving one UE. One of the UE runs FTP and the other runs HTTP. Also the data pattern is set up to be

deterministic(fixed). There are two network topologies from different vendors to help us analyze bothstrategies.

After loading the scenario and setting up the parameters required for the simulation, we run the

simulation and proceed to the next step of plotting and analyzing the results. First we focus on the first

vendor (Vendor X) and plot the FTP download response time and the HTTP page response time. The

following two figures comprise this.

For the first picture, we can infer that the usual response time is around 9.5 seconds but itvaries from 8.5 to 12.5 seconds. For the HTTP application the response time is significantly lower ,

around 3.5 to 4 seconds.


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The next two pictures show the same FTP and HTTP response time but for the other vendor

(Vendor Y). Comparing this two figures with the ones above it is very useful for an mobile operator who

wants to purchase equipment because it gives an ideea about the performance, from both sides and

helps to take the decision.

As we can see for the Vendor Y the FTP download response time is mostly around 12.5 second

which is a little bit more longer than for the Vendor X equipment. As for the HTTP page response time

it is almost the same , around 3.5 seconds.

In the following we will examine the Rate Adaptation behavior for the Vendor X equipment for

both cases of FTP Download response time and HTTP page response time. First we put on the same

graph the curves for DCH allocation (bit rate allocation ) for downlink and the Throughput also for

downlink direction.


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This picture shows the sessions for FTP download application. For a better understanding I

zoomed in one of the spikes and captured in the next figure . From the figure it can be concluded that

the vendors choice for allocation of bit rate in the downlink is to allocate at the beginning a lower bitrate and when the application reaches the maximum of this , then the total amount of available speed

will be allocated to the UE.

I have zoomed only the top part of the spike and captured in the next picture. The allocation

reaches 384 kbps which is the maximum speed for download link in UMTS.


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This means that at the beginning the UE is allocated a higher spreading factor and after the

spreading factor is set to 8 which means that only 8 users can communicate with this speed of 384 kbps.

After the session has been finished there is a timer and then the equipment turns of the allocatedbandwidth. In this particular case the timer is around 5 seconds.

The next two pictures illustrate the same phenomenon but for the case of HTTP application.

The time interval between two consecutive sessions for HTTP is smaller than for FTP. Taking a

closer look to only one of the sessions it can be noticed that the profile of throughput for HTTP is very

different from the one of FTP. The bit rate allocation is exactly the same mainly because the equipment

is not able to distinguish different types of traffic. It is all data traffic. But HTTP sessions dont make use

of the allocated bandwidth very efficiently. The sessions end very quick and the timer seems to take

around 20 seconds to trigger the bandwidth closure. As I said previously the equipment is not able to

distinguish between types of packets but as we see the timer is different for FTP and HTTP applications.

In my opinion the time interval should be the same and it is just a matter of simulation, resolution or

maybe of how many samples weve selected for running the simulation.


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The next two pictures also show the bit rate allocation technique but for Vendor Ys equipment

for FTP application.


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As we can see from the second figure the allocation scheme this time is different. The

equipment gives the maximum speed of 384 kbps from the beginning to the UE which is equivalent to a

spreading factor of 8. The next two pictures shows the same thing but for HTTP application. The same

conclusion we draw in the case of Vendor X , that HTTP sessions are shorter than FTP sessions ,applies

here . Also the bandwidth in case of HTTP is scarcely utilized .

In this case, of Vendor Xs equipment, the time interval between the last packet sent on the

link and the closure of the allocated bandwidth is a little bit smaller around 5 to 10 second for both

applications, FTP and HTTP.

It can be inferred that these different bit rate allocation schemes have a great impact on

response time for FTP and HTTP applications and that is why we obtained slightly different values for

different vendors.


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The following section provides an analyze for the dynamic rate adaptation in a hot spot case.

The scenario is the same as the previous one with the amendment that we have 6 UE now, and the

traffic is stochastic not deterministic. The traffic is 50% HTTP and 50% FTP.After running the simulation

with the specified parameters we compare the QoS End to End for the two networks with respect to

the two application simulated : FTP and HTTP. First we take the case of HTTP page response time . The

next figure illustrates this case.

The graph shows that the vendor Xs equipment performs better for this case. 75% of the UEs

attached to Vendor Xs equipment will experience a response time less than 10 seconds while for the

Vendor Y is 60%. For the case of FTP application we have the following figure.

In the case of FTP the situation is a little bit different. The same percentage of 67 of the UEs will

experience a response time less than 20 ms for both vendors.


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The last case for UMTS is to analyze the HTTP session initialization and HTTP successful sessions

for the two networks. First figure shows the sessions initialized and as it can be seen the number of

sessions fluctuates during the simulation the reveals the stochastic nature of traffic but in the end the

number of sessions turns to the same for both vendors .

As for the case of successful sessions the situation is that the vendor Xs equipment performs

better because in the end it can provide more successful sessions than the vendor Ys equipment.

The success rate for the vendor X is roughly 0.835 as for the vendor Y we have the success rate

of 0.929. As a conclusion for the UMTS simulation I can say that the configuration of the equipment can

influence the QoSEE for different applications running on UE. These configurations consist of Bit Rate

allocation scheme, timers etc. Overall the vendor Xs equipment performed slightly better but it is also

a need to take the costs in consideration when purchasing an equipment.


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4. HSDPA simulation setup and resultsHSDPA came as an improvement for the UMTS networks for the data traffic. In order to assess

its benefits , in this exercise , we will compare two scenarios : one UMTS scenario and one HSDPA

enabled scenario. Also we will run into inspecting the advantages of packet scheduling and the burden

of adding more terminals in the network.

Having the UMTS topology ready we duplicate the topology and add the HSDPA profile to the

UE. Then we run the simulation and have a look at the results . First we analyze the FTP response time

for the two cases: with and without HSDPA.

From this graph we can see that n the case of HSDPA networks the response time for FTP

download is significantly improved from above 30 seconds to less than 10 sec. Also the speed is

increasing very much for the HSDPA case , from 384 kbps (UMTS) to 1.1 mbps in our case. The nextpicture can illustrate this, we plotted the DL throughput for our HSDPA network. This first scenario for

HSDPA is set to use Round Robin packet scheduling.


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Next, we inspect the influence of adding more terminal to the network and changing the scheduling to

optimized Round Robin. We add another 5 UEs and rerun the simulation. Following figure shows the

comparison between the three scenarios we have : UMTS, HSDPA and HSDPA with many UEs and

optimized RR.

We can still see an improvement for the case of HSDPA RR but is performing worse than the

previous HSDPA case with only one UE. This is mainly because HSDPA uses a shared channel and with

many users sharing this channel the speed for each of them becomes lower. The last figure is about

observing the throughput for the three cases. Although the speed for one user has decreased we can

see that the throughput for the HSDPA RR case has increased compared to HSDPA case to 1.4 mbps.

In conclusion HSDPA really bring advantages in terms of speed and cell utilization but it is also

illustrated that because of the shared channel when many users use HSDPA services the speed per user

is decreasing . Also scheduling can help to improve the speed thus the QoS End to End .


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5. Iub capacity considerationsIub is the interface (link ) between the RNC and Node B .A very important issue in mobile

networks is dimensioning of the Iub link because it transports the aggregated traffic from Node B to the

core network. We will see if increasing the capacity of the link will bring QoS improvements for the data

traffic. The scenario used in this experiment consists of one Node B with 3 cells each of them carrying

some HSDPA traffic. The base scenario has an Iub link with the capacity of 2048 kbps (E1 ). From this

base scenario we duplicate another one for which we set the Iub capacity to be twice as much as the

first , namely 4096 kbps (2* E1). We run the simulation for these two scenarios and compare them.

First we analyze the FTP download response time for the two cases. The next picture shows the

CDF :

For the case with the upgraded link the is a slightly improvement in the response time. Let us plot the

graph that illustrates the throughput for the two cases.


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In the first figure the case for the base scenario is presented. For both cases the average load on

the link is around 125 kbps which is much less than the capacity of the link 2 Mbps. However we still can

see an improvement for the response time . The explanation lies in the fact that the peak values of the

throughput also have a great influence on the link load. As it can be noticed from the first picture the

peak values of throughput reach almost the 2Mbps value. So there exists the possibility that the link

limits the throughput for these peak values. This is confirmed by the next picture from which we can

see that the peak values reach 2.5 Mbps for the same number of UEs thus the same amount of traffic

also. This tells us that in the first case the link somehow cut the peaks of throughput so having a

negative impact on QoS and increasing the response time.

In conclusion I can say that because of the bursty nature of the data traffic , the behavior cant

be predicted. Even if the average throughput is around 125 kbps , increasing the Iub capacity can still

provide some improvement in the QoS for different applications.

Simulation report-Cosmin Caba

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