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OPNET IT Guru Academic Edition
Chapter 2 - Ethernet
N. AbedpoorInternational Imam Reza University of Mashhad
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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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