Simulation of DoD Collaboration Services

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Modeling and Simulation Final Project SYS 611 Modeling and Simulation

Simulation of DoD Collaboration Services

Aaron Griggs

11 December 2007

SYS 611 Modeling and Simulation

Stevens Institute of Technology

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Table of Contents

Background ................................................................................................................................. 3

Model .......................................................................................................................................... 3Simulation ................................................................................................................................... 3

Text Chat ................................................................................................................................. 4Attributes............................................................................................................................. 4Users ................................................................................................................................... 4

Simulated Time ................................................................................................................... 4

Results ................................................................................................................................. 4

Audio Collaboration ................................................................................................................ 7Attributes............................................................................................................................. 7

Users ................................................................................................................................... 7

Simulated Time ................................................................................................................... 7Results ................................................................................................................................. 7

Video Collaboration .............................................................................................................. 10

Attributes........................................................................................................................... 11Users ................................................................................................................................. 11

Simulated Time ................................................................................................................. 11

Results ............................................................................................................................... 11Aggregate .............................................................................................................................. 14

Attributes........................................................................................................................... 14

Users ................................................................................................................................. 14

Simulated Time ................................................................................................................. 14Results ............................................................................................................................... 14

Conclusion ................................................................................................................................ 18

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Background

The Department of Defense like other large enterprises is adopting collaboration services to

promote better communication and take advantage of a distributed workforce. The key

collaboration services include: text chat, audio, video, white boarding, file sharing and webconferencing (multi-user chat).

The first deployment of collaboration services will be centrally hosted at the Defense Enterprise

Computing Center (DECC) in Columbus, Ohio consisting of three services: text chat, audio and

video collaboration. The collaboration services (i.e., software and hardware running at theDECC) are being outsourced and can be scaled up as necessary. However, the network

performance is the DoDs responsibility and requires significant investments if the existing

infrastructure cannot support the collaboration load.

The expected concurrent user load consists of the following:

5000 users of text chat 500 users of audio 50 users of video

Prior to contracting for the collaboration services, the DoD is interested in understanding the

ability of the network to support delivering the services to the end users. Two network

performance metrics are of interest: response time and utilization. A response time of 0.1seconds or less and network utilization of 80% and below is considered acceptable.

Prior to investments in the services, the DoD needs to understand if the existing network is able

to support the services. The assumption is the DECC is connected to regional Points of Presence

(POPs) via an OC3, 155 megabits per second (Mbps). The end users (consumers) are connectedto regional POPs via a DS3, 45 Mbps.

The DoD has chosen a modeling and simulation approach to see how the network is affected by

the three collaboration services.

Model

A network model consisting of the centrally located services was simulated in OPNET. Theconsumers are assumed to be located at STRATCOM in Omaha, Nebraska, connected through a

regional POP located in Kansas City, Missouri.

A single consumer location was chosen for simplicity. In reality, the users would be distributed

all over the US (assuming continental US usage at this time). However for aggregation ofnetwork links, a single location suffices.1

SimulationEach service was simulated with a DS3 link from KC to STRATCOM as well as replacing that

link with one well under capacity for the service load to see the impact to service delivery. The

network model is shown in the diagram below.

1 Note the assumption is multicast is not used. Future models and simulations should test the affects of leveraging

multicast for UDP traffic. Multicast will not affect HTTP traffic (text chat) as that is over TCP.

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Text Chat

Text chat is assumed to be similar to Google Talk and AOL Instant Messenger (AIM). HTTP is

assumed to be the protocol used to send the chat messages.

Attributes2

Page interarrival time (seconds) Exponential(60) Object size (bytes) Uniform integer(100, 1000) Number of objects per page Uniform integer(1, 5)

Users

1 500 5000

Simulated Time

10 minutesResults

The simulation produced the results shown below. The response time in the first row of graphs is

approximately 0.02 seconds, regardless of the user load. The second row of graphs illustrate that

traffic sent is equal to traffic received which indicates successful delivery of the messages.

As shown in the third row graphs, the utilization of the DS3 is only 1%. Note, when the usersfirst start sending messages, there is a spike of 3.5% utilization. This is due to the start time of

2Text chat was replicated using the HTTP. Specifically, the page interarrival time is the chat message frequency.

The object size is the size of the chat message. Objects per page are the number of chat participants. The main

difference is the simulation entails a client requesting pages instead of what happens in an actual chat session: the

client sending chat messages. However since the assumption is a symmetric duplex link, the simulation will provide

the same usage pattern just in reverse.

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the users set between 100 and 110 seconds in the OPNET. The 100 second lag provides fornetwork convergence. The users all start sending messages at approximately the same time

initially. Then the exponential interarrival rate of 60 seconds evens out the load. Even in the

5000 user case, the network is able to support the user load.

The second set of graphs illustrates the impact of connecting the users through a 56 kbps link. As

can be seen, response time and network utilization are unacceptable.

Results for text chat over OC3-DS3: response time (1st row), network traffic (2nd row) and

network load (3rd row):

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Results for text chat over OC3-56k (starting top left, clockwise): response time, traffic

sent/received, throughput KC POP to STRATCOM, throughput DECC to KC POP:

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Audio Collaboration

Audio collaboration encodes a users voice into digital data and sends over UDP. A single frame

of audio represents one second of talk from a user and is sent as 1 frame per network packet. Ifthere is silence, a frame does not contain as much data as when the user talks (makes noise).

Attributes

Silence length (seconds) Exponential(0.65) Talk length (seconds) Exponential(0.352) Encoder G.723.1 5.3K (silence) Voice (frames/packet) 1

Users

1 VoIP-DES-1 50 VoIP-DES-2 100 VoIP-DES-3 500 VoIP-DES-4

Simulated Time

5 minutes A short duration is sufficient since audio collaboration session produceconstant network load. Note a longer simulation of a couple users for 1 hour was run toverify the validity of short runs.

Results

The simulation produced the results shown below. The response time is consistent for all users at

around 0.1 second shown in the first row of graphs. As shown in the second row of graphs,traffic sent is equal to traffic received. The third row of graphs show the network is only

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experiencing about 8% utilization for 500 users. The audio collaboration produces a load directlyproportional to the number of users. Response time is steady for all user distributions.

Shown in the second set of graphs, if a DS1 (1.544 Mb/s) was used instead of the DS3, 500 users

would saturate the link and cause significant delay. The response time is 0.45 seconds. Data

received is about one-half the data sent due to the smaller on the DS1 link.

Also, the network load is not a smooth straight line since silence suppression is used (shown asjagged line in the second row of graphs).

Results for audio over OC3-DS3: response time (1st row), network traffic (2nd row) and network

load (3rd row):

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Results for audio over OC3-DS1 (starting top left, clockwise): response time, trafficsent/received, throughput KC POP to STRATCOM, throughput DECC to KC POP:

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Video CollaborationVideo collaboration encodes a moving image into digital data. The quality of the image is based

on how many frames (snapshots) of the moving image are encoded per second. For the

simulation, 5 frames per second were used. The amount of data in each frame is based on howmuch data is needed to encode a moving picture (due to motion or scenery changes). For

example, a still object requires little data in the frames once the picture is encoded.

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Since video collaboration is between people (many times a talking head), there will be quite a bitof movement, some people move more than others. But, there will still be reduced amount of

data the frames.

This simulation illustrates a maximum load since the number of bytes for each frame is constant.

Attributes Frame interarrival time 5 frames/second Frame size 128x120 pixels

Users

1 DES-1 10 DES-2 50 DES-3 100 DES-4

Simulated Time

5 minutes A short duration is sufficient since audio collaboration session produceconstant network load. Note a longer simulation of a couple users for 1 hour was run toverify the validity of short runs.

Results

The first row of graphs shows the response time. As can be seen, the response time degrades(increases) when 100 users are participating compared with 1, 10 and 50. At 50 users, the

response time is less than 0.02 seconds. But at 100 users, the response time is over 0.2 seconds

outside the required 0.1 seconds. The degradation is due to the network load produced by 100users saturating the network link.

The second row of graphs shows the video services sending more traffic than is being received

due to the congestion. Since the consumers are connected via a DS3, the link is 100% utilized asthe bit rate approaches 45 Mbps as shown in the third row of graphs.

The second set of graphs show a simulation over a DS1 for 10 users. The response time is at 0.45seconds and the throughput reduced due to the link between the KC POP and STRATCOM only

capable of handling 1.5 Mbps.

Note the throughput and utilization graph are smooth. This is due to the constant number of bytes

in each video frame. As a reference point, a user produces a load of about 700 Kbps. The load islinear due to the constant rates. So, 50 users produce a load of 35 Mbps (80% utilization), shown

by the light green line in the third row of graphs.

Results for video over OC3-DS3: response time (1st row), network traffic (2nd row) and network

load (3rd row):

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Results for video over OC3-DS1 (starting top left, clockwise): response time, traffic

sent/received, throughput KC POP to STRATCOM, throughput DECC to KC POP:

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Aggregate

Simulation the services individually, a DS3 link was able to perform with a response time of 0.1

seconds or less and a network utilization of 80% or less. However, the services wont necessarilyrun separately and it is important to simulate the aggregate load.

Attributes

Text chat Same as individual simulation (above) Audio Same as individual simulation (above) Video Same as individual simulation (above)

Users

Text Audio Video Simulation Name

1 1 1 DES-1

500 100 10 DES-2

5000 500 50 DES-3

Simulated Time

10 minutesResults

The simulation produced the results shown below. When aggregated, the network is unable tohandle the user load that was handled in the single service cases. Specifically, when text, audio

and video are at 5000, 500 and 50 users, respectively, the network is incapable of operating

within 0.1 seconds response time as shown in the first row of graphs.

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The cause of the delay is mainly due to the video load as shown in the second row of graphs. Thevideo traffic sent is much more than the traffic received. Whereas, the text and audio services are

close to equal although slightly degraded. However, unlike the video single service case above

the utilization is not at 100% as shown in the third row of graphs. This is due to the fact that therouters at the DECC, KC POP and STRATCOM drop packets as shown in the third graph in the

third row.


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Results for aggregate over DS3: response time (1st

row), network load (2nd

and 3rd

rows):


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Conclusion

Three collaboration services were simulated: video, audio and text chat. By simulating each

service individually and varying the number of users, it was shown that the network utilization

increases linear based on the number of users. The response time remains constant as long as the

network load does not approach 100% utilization. At 100% utilization, the network fails todeliver the service to the users in a timely manner.

As shown in the table below for the individual simulations, the maximum number of simulated

users were supported with the following response times, network throughput and utilization.

Service

Type

Users Response Time

(seconds)

Throughput

(megabits/second)

Utilization (%)

Text 5,000 0.02 0.4 1

Audio 500 0.1 3.5 8

Video 50 0.02 35 80

The aggregate simulation illustrated that none of the services operated within the requiredresponse time as shown in the table below.

Service

Type

Users Response Time

(seconds)

Throughput

(megabits/second)

Utilization (%)

Text 5,000 35

Audio 500 4

Video 50 4

Total 13 30

The recommendation is the DoD not proceed with the full deployment of the collaboration

services at this time. There is too much risk that the network will not be able to support the user

load. Instead, the DoD should pilot the collaboration services at 10-20% of the user load togather empirical data on the network characteristics. It was shown that 500 text users, 50 audio

users and 10 video users running concurrently operated within the performance parameters. Alsothe simulation did not model any background network traffic which will have an affect on the

network load. By deploying a scaled down version of the services, the DoD can get a better

understanding of the impact to the network and promote a more successful deployment in the

long run.

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Documents

Simulation of DoD Collaboration Services