06-02-2013, 04:25 PM
A Direct Link Network with Media Access Control
A Direct Link Network with Media Access Control.pdf (Size: 379.55 KB / Downloads: 20)
Objective
This lab is designed to demonstrate the operation of the Ethernet network. The simulation
in this lab will help you examine the performance of the Ethernet network under different
scenarios.
Overview
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 “carrier sense” in CSMA/CD means that all the nodes can distinguish
between an 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.
In this lab you will set up an Ethernet with 14 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 the
throughput of the network is affected by the network load as well as the size of the
packets.
Create a New Project
To create a new project for the Ethernet network:
1. Start OPNET IT Guru Academic Edition ⇒ Choose New from the File menu.
2. Select Project ⇒ Click OK ⇒ Name the project <your initials>_Ethernet, and
the scenario Coax ⇒ Click OK.
3. In the Startup Wizard: Initial Topology dialog box, make sure that Create Empty
Scenario is selected ⇒ Click Next ⇒ Choose Office from the Network Scale list
⇒ Click Next ⇒ Assign 200 to X Span and keep Y Span as 100 ⇒ Click Next
twice ⇒ Click OK.
4. Close the Object Palette dialog box.
Configure the Network Nodes
To configure the traffic generated by the nodes:
1. Right-click on any of the 30 nodes ⇒ Select Similar Nodes. Now all nodes in the
network are selected.
2. Right-click on any of the 30 nodes ⇒ Edit Attributes.
3. Check the Apply Changes to Selected Objects check box. This is important to
avoid reconfiguring each node individually.
4. Expand the Traffic Generation Parameters hierarchy:
a. Change the value of the ON State Time to exponential(100) ⇒ Change
the value of the OFF State Time to exponential(0). (Note: Packets are
generated only in the "ON" state.)