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Network Emulators
CNDS site

cnds challenge - network modelling
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Background

The network topology gives a good sign on how well a network will cope with traffic flows. As we have seen, token ring provides excellent sharing and prioritization on a network, whereas in a bus system, nodes contend to get access to the network. Networks, though, are typically inter-connected with other networks to give an overall network architecture. This defines how the networks are interconnected, and the routes that the data will take to get from a source to a destination. It is important that the architecture is modelled, as this can highlight problems with bottlenecks in the data flow, and any potential problems for the future. The Napier network provides an excellent example of this, as it receives peaks in data throughout the day, which varies from month to month. Thus, it is important to understand the flow of the data, and identify if routes are over-burdened, or even if they are under-burdened. An over-burdened route can be eased by providing alternative paths around the route. Another important factor of network modelling is to provide an indication of how the network architecture responds to faults, and if the network will cope with the fault.

It is possible to run a complex model of the network, but the worst-case situation can often be modelled using simple methods. One way to do this is to estimate the peak flows that occur from sources to destinations, and estimate the routes that they take. For example if we have networks A, B, C, D, E and F, which are interconnected with data points of 1, 2, 3, 4, 5, 6 and 7, then we can draw the network architecture given in Figure Ch3.1.

Figure Ch3.1: Example network architecture

If we modelled the network we could estimate the data streams, such as:

Source

Destination

Data flow (Mbps)

1

7

10

2

5

  1

1

4

  5

5

7

  4

3

6

 10

Next we can model the data streams across each of the known routes:

 

A

B

C

D

E

F

17

10

10

 

 

10

10

25

 

1

1

1

 

 

14

5

5

5

 

 

 

57

 

 

4

4

4

4

36

 

 

 

 

10

 

Total

15

16

10

5

24

14

It can be seen from this that the heaviest data flow is on Network E, which has a flow of 24Mbps. If this flow was too high for this network, we could create a new route in parallel with Network E, and share the data flow. This is known as load sharing, and an example is shown in Figure Ch3.2. With this the router sends data through Network E for half the time, and through Network G for the other half of the time.

Figure Ch3.2: Example network architecture with loading sharing

Thus in the network architecture in Figure Ch3.1, loading sharing can be applied between Network E and Network G, this will cause 12Mbps to flow through Network E, and the same for Network G. This will thus reduce the loading on Network E.

We can then determine the loading on each network, but determining the maximum bandwidth of each network, and then using:

PDF Version

Thus, using the previous example, if the bandwidth of Network A, Network B and Network E is 40Mbps, and the bandwidth of the other networks is 20Mbps then:

Network

Bandwidth (Mbps)

Actual Flow

Utilization (%)

A

40

15

37.5

B

40

15

37.5

C

20

10

50.0

D

20

5

25.0

E

40

24

60.0

F

20

14

70.0

Now we can see that the most utilized network route is actually Network F, with a 70% utilization, thus it may be better to load share on this network, rather that Network E, as it only has a 60% utilization.

Challenge 2

The network architecture in Figure Ch3.3 has the following data flows:

Source

Destination

Data flow (Mbps)

1

4

   5

1

3

   3

2

5

   7

2

6

  2

3

7

  3

3

4

  1

4

5

10

6

7

  2

Challenge A Determine the network(s) with the largest data flow?

Challenge B If the maximum data flow for networks A, C, E and F is 20Mbps, and Networks B and D are 40Mbps. Determine the most utilized network and the least utilized network route?


Figure Ch3.3: Network architecture

Name:

Email:

Matriculation number:

Programme:

Institution:

Determine the network(s) with the largest data flow?

Network A Network B Network C
Network D Network E Network F

Determine the most utilized network route(s)?

Network A Network B Network C
Network D Network E Network F

Determine the least utilized network route(s)?

Network A Network B Network C
Network D Network E Network F