OPNET Chapter 2 N. Abedpoor (Ethernet)

8/13/2019 OPNET Chapter 2 N. Abedpoor (Ethernet)

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OPNET IT Guru Academic Edition

Chapter 2 - Ethernet

N. AbedpoorInternational Imam Reza University of Mashhad

N. AbedpoorInternational Imam Reza University of Mashhad

Nov. 2013


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Ethernet Model Description

Model Scope and Limitations

Model Architecture

Process Models

Model Interfaces

Packet Formats

ICI Formats

Ethernet Addressing

Lab 1 - Ethernet

Chapter 2

Lab1- Ethernet

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Background / Operational Description

Ethernet is a bus-based local area network (LAN) technology

commonly used in the technical and business communities.

Detailed information about the Ethernet protocol is in the IEEE

802.3 Standard.

Ethernet Model Description

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The Ethernet MAC model provided with OPNET implements the carriersensing, collision detection, and retransmission mechanisms specified inthe IEEE 802.3, IEEE 802.3u, and IEEE 802.3z Standard. Explicitmodeling is performed for all features other than serialization of bittransfers to and from the physical layer.

The following list itemizes the features provided in this model:

FIFO processing of Transmission Requests

Propagation Delay based on Distance Between Individual Stations

Carrier Sensing from Physical Layer

Collision Detection from Physical Layer

Truncated Binary Exponential Backoff

Transmission Attempt Limit of 16

Interframe Gap Timing for Deference Jam Sequence Transmission after Collisions

802.3 Minimum and Maximum Frame Sizes

Frame Bursting (1000BaseX Ethernet operating in half-duplex only)

Full- and half-duplex transmissions

Model Scope and Limitation

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You can configure port-based VLANs on all generic bridge

and switch models, and on any vendor-specific models that

support this technology. Ethernet link models allow you tosimulate point-to-point trunk links; a single trunk link can carry

traffic for multiple VLANs as specified by IEEE 802.1q.

To configure a VLAN, set the VLAN Scheme attribute to Port-

based VLAN on the bridge or switch supporting the VLAN.You can assign VLAN identifiers to specific port numbers in

the VLAN Port Configuration Table. (To find a links port

numbers, use Link Interfaces on the Edit Attributes

(Advanced) dialog box.)

Note that you can assign only one VLAN identifier to a specific

port. However, multiple ports can belong to the same VLAN.

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The Ethernet models also support Fast EtherChannel

technology. This allows multiple Ethernet point-to-point links to

be bundled into one logical full-duplex channel of up to 800Mbps (for Fast Ethernet) or 8000 Mbps (for Gigabit Ethernet).

You can use a Fast EtherChannel or Gigabit EtherChannel

link in place of any regular Ethernet link (10BaseT, 100BaseT,

or 1000BaseX). EtherChannel links support flow-based

balancing of traffic, and are useful for upgrading bottleneck

links in Ethernet LAN networks.

NoteYou can only use EtherChannel links when Ethernet is

running in full-duplex mode.

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The Ethernet models can be deployed either in a bus

(10Base2) or a hub (10BaseT, 100BaseT or fast ethernet, and

1000BaseX or gigabit ethernet) configuration. The followinglist itemizes the main differences between these two

configurations:

Connections from the MAC processes to the hub are via

duplex point-to-point links, as opposed to a bus medium. Collision Detection in the hub configuration is handled by

the hub, rather than individual MAC processes.

Deference mechanism is handled by the hub, rather than a

separate deference process.

Ethernet hubs cannot be directly connected to one another.Instead, a bridge must be used to link two or more hubs

together.

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The following diagram illustrates the relevant portions of a typical

10Base2 node model using the process models defined for the

Ethernet model suite.

Figure 2-1 Node Model Structure Surrounding Ethernet

Model Architecture

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The following diagram illustrates the relevant portions of a typical

node model.

Figure 2-2 Node Model Structure Surrounding Ethernet Hub

Model Architecture

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The following diagram illustrates the relevant portions of a typical hub

node model.

Figure 2-3 Node Model Structure Surrounding Ethernet Hub

Model Architecture

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The following table enumerates the process models used by

the Ethernet model suite. Additional details on these processmodels are provided in subsequent sections.

Table 2-1 Ethernet Process Models (Part 1 of 2)

Process Model

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Table 2-1 Ethernet Process Models (Part 2 of 2)

Process Model

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Packet Formats

The following table enumerates the packet formats used in theEthernet model suite.

Table 2-2 Ethernet Packet Formats

Model Interface

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ICI Formats

The following table enumerates the interface control information (ICI)formats used in the Ethernet model suite.

Table 2-3 Ethernet ICI Formats

Model Interface

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Ethernet Addressing

Each MAC entity has a physical address, specified by thestation_address attribute of the eth_mac_v2 (and ethernet_mac_v2)

process models. When using these models in conjunction with the

Spanning Tree Bridge models, the Ethernet addresses must be unique

for the entire OPNET network to support correct bridge address learning.

The addresses can be automatically assigned to meet this requirement.

Model Interface

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The Ethernet is a working example of the more general

Carrier Sense, Multiple Access with Collision Detect

(CSMA/CD) local area network technology. The Ethernet is a

multiple-access network, meaning that a set of nodes sends

and receives frames over a shared link. The carriersensein

CSMA/CD means that all the nodes can distinguish betweenan idle and a busy link. The collision detect means that a

node listens as it transmits and can therefore detect when a

frame it is transmitting has interfered (collided) with a frame

transmitted by another node. The Ethernet is said to be a 1-

persistent protocol because an adaptor with a frame to send

transmits with probability 1 whenever a busy line goes idle.

Lab1- Ethernet

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In this lab you will set up an Ethernet with 30 nodes connected

via a coaxial link in a bus topology. The coaxial link is

operating at a data rate of 10 Mbps. You will study how thethroughput of the network is affected by the network load as

well as the size of the packets.

NOTES:

Create Project: Name the project _Ethernet

Name the scenario Coax

make sure that Create Empty Scenario

Choose Office for Network Scale

X,Y = 100

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NOTES:

Create the Network:

Use Rapid Configuration. BUS Topology

Choose ethcoax

from Model List

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NOTES:

Configure Coaxial BUS

Advanced Edit Attributes

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NOTES:

Configure the Network Nodes

Select Similar Nodes

Edit Attributes

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NOTES:

Configure the Simulation

Select Similar Nodes

Edit Attributes

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NOTES:

Configure the Simulation

To examine the network performance under different loads, you need

to run the simulation several times by changing the load into the

network. There is an easy way to do that. Recall that we promoted

the Interarrival Time attribute for package generation.

Object Attributes Tab

Office Network.node_0.Traffic Generation

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Make Sure Office Network.*.Traffic Generation Parameter

added in the list of simulation object attributes

Click the Values button and Add all nine values.

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Save Scalar file

Assign _Ethernet_Coax to the Scalar file text field.

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NOTES:

Choose the Statistics

Choose Individual Statistics - Expand the Global Statistics

hierarchy

a) Traffic Sink check theTraffic Received (packets/sec) box

b) Traffic Source - check theTraffic Sent (packets/sec) box

to collect the average of the above statistics as a scalar value by the

end of each simulation run:

Simulation menu - Statistics (Advanced)

be sure Traffic Sent and Traffic Received appeared under the

Global Statistics Probes.

Set the Values.

Save.

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NOTES:

Run the Simulation

Click Configure/Run Simulation button

Duration 15 Second

RUN

Close and Save Project

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NOTES:

Rerun the Simulation

When you rerun the simulation, OPNET IT Guru will append the

new results to the results already in the scalar file. To avoid that,delete the scalar file before you start a new run. (Note: Deleting the

scalar file after a run will result in losing the collected results from

that run.)

File Model Files Delete Model Files (.os): Output ScalarsSelect the scalar file to be deleted

In this Lab : _Ethernet_Coax

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NOTES:

View the Results

View Results (Advanced) from the Results menu

Load Output Scalar File Select _Ethernet-

Coax

Create Scalar Panel from the Panels menu

Horizontal : Traffic Source.Traffic Sent (packets/sec).average

Vertical : Traffic Sink.Traffic Received (packets/sec).average

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The resulting graph should resemble the one below:

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OPNET Chapter 2 N. Abedpoor (Ethernet)