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Shared vs. Switched Ethernet (Modeling and Simulation using OPNET). Dr. Khaled Salah. Objectives. Show basic features and capabilities of OPNET by example Ethernet background How to: Build a small Ethernet LAN types Generate traffic: Poisson & Bursty Examine performance

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Presentation Transcript
objectives
Objectives
  • Show basic features and capabilities of OPNET by example
  • Ethernet background
  • How to:
    • Build a small Ethernet LAN types
    • Generate traffic: Poisson & Bursty
    • Examine performance
      • Choose statistics
      • Data collection
      • Animation

K. Salah

issues to investigate
Issues to Investigate
  • How many users/node can be supported?
  • Identify congestion and bottlenecks
  • Node placement and load balancing
  • Assess the health of existing network
    • Resource utilization
    • Delays
  • Capacity planning
  • Test different vendor Ethernet products
  • “what-if” scenarios

K. Salah

ethernet network topology

Bus

Point-to-point

Star

Ring

Ethernet Network Topology

K. Salah

shared ethernet protocol csma cd

Sense channel (1)

Station is

ready to send

Transmit data and sense channel

(4)

Transmit

jam signal

(5)

Wait according to backoff strategy

(6)

Station is ready to send

Station is ready to send

Station is ready to send

Station is ready to send

Channel free (2)

Channel busy (3)

Collision detected

New attempt

Shared Ethernet Protocol – CSMA/CD

K. Salah

csma cd
CSMA/CD
  • Step 1.“Listen before talking”.
  • Step 2. If channel is quiet for a certain time, called interframe gap (IFG), then transmit. “Talk if quiet”.
  • Step 3. If channel is busy, monitor the channel until it is quiet for IFG period before transmitting. “Wait for quiet before talking.”
  • Step 4. Monitor the channel continuously during transmission to detect collisions. “Listen while talking”.
  • Step 5. If collision occurs, the first node recognizes it will send a jam signal to ensure that all other stations detect the collision. Transmitters should stop immediately, receivers should reject data, and others wishing to transmit should recalculate their backoff period. “A buzzer sounds off indicating we have more than one talker at a time.”
  • Step 6. All nodes wish to transmit must now wait a random period called “backoff” and attempt again to spread out collisions. “Backoff” is based on BEB algorithm (Binary Exponential Backoff). After 16 collisions, drop the frame to be transmitted.

K. Salah

shared ethernet component
Shared Ethernet Component
  • Coaxial Cable
    • Shared medium with BNC or vampire taps
  • Repeater
    • Layer 1 device that provides physical and electrical connections.
    • It receives signals from one cable segment, regenerates, retimes, and amplifies them, and then transmits these “revitalized” signals to another cable segment.
    • Transmits in both directions
    • Joins two segments of cable
    • No logical isolation of segments
    • Greater distance is achieved
  • Hub
    • Used to describe a repeater
    • Can be “repeater hub”, “switching hub”, bridging hub”.
  • NIC
    • Performs layer-2 functions: framing, error detection, and flow control.
    • Performs layer-1 functions by converting the bits into electrical signals using appropriate coding scheme.

K. Salah

switched ethernet
Switched Ethernet
  • Point-to-point
  • No Collision
    • Larger Network diameter
      • 10GbE that can go more than 50 km over SMF.
    • Higher Throughput
    • Smaller Latencies
    • No Congestion Collapse

K. Salah

csma cd model in opnet
CSMA/CD Model in OPNET

Process Model

Node Model

K. Salah

bursty traffic model in opnet
Bursty traffic model in OPNET

Node Model

Process Model

K. Salah

creating network topologies
Creating Network Topologies
  • Importing the topology
  • Placing each individual node from the Object Palette into the workspace
  • Crating a new network topology by using Rapid Configuration

K. Salah

statistics
Statistics
  • Two ways to collect statistics
    • Object statistics
      • from individual nodes
    • Global statistics
      • From the entire network as whole

K. Salah

data collection
Data Collection
  • Vector
    • Time-dependent series of values
  • Scalar
    • Parametric relationships
  • Animation
    • visualization

K. Salah

vector vs scalar
Vector vs. Scalar

Vector data graphs

Scalar data graph

K. Salah

opnet animation
OPNET Animation
  • Used for debugging
    • Extremely useful for new or modified protocols
  • Allows to visualize a simulation while running it.
  • Gives insight how a certain protocol works (RIP, BGP, OSPF, IPv4, IPv6, etc.)
  • The animation can also be run after the simulation is over, from a history file.

K. Salah

setup animation
Setup Animation
  • To view animation, click on Simulation and select Record Animation For Subnet. You have to do this before you do a simulation run.
  • Animation Viewer/Player
    • Slow
    • Fast
    • Step
    • Pause

K. Salah

an example
An Example

K. Salah

debugging
Debugging
  • A good debugging tool is the Simulation Log. You can check for warnings and errors
  • Click on Results
  • Then Click on Open Simulation Log

K. Salah

coming up examples
Coming up examples
  • Shared Ethernet with bus topology
    • Coaxial cable
  • Shared Ethernet with star topology
    • Hub
  • Switched Ethernet with star topology
    • Switch
  • Mix
    • Hub and Switch

K. Salah