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Introduction

As part of the resource allocation mechanisms, each router must implement some queuing discipline that governs how packets are buffered while waiting to be transmitted. Various queuing disciplines can be used to control which packets get transmitted (based on bandwidth allocation) and which packets get dropped (based on buffer size). The queuing discipline also affects the latency experienced by a packet, by determining how long a packet waits to be transmitted. Examples of the common queuing disciplines are first-in-first-out (FIFO) queuing, priority queuing (PQ), and weighted-fair queuing (WFQ).

Network Setup

The "Queuing" folder contains all the necessary configuration files and is attached to this article. It can be downloaded and imported into NetSim. 
(refer this article https://support.tetcos.com/support/solutions/articles/14000128666-downloading-and-setting-up-netsim-file-exchange-projects to import the attached files in NetSim). To access this example, navigate to "Your Work" on the NetSim home screen, where you'll find all the configuration files associated with "Queuing."

NetSim UI displays the scenario corresponding to this experiment as shown below:

Figure: Pictorial representation of the scenario being simulated. Labels have been added for explanatory purposes.

Procedure

Sample 1: (FIFO)

The following set of procedures were done to generate this sample:

Step 1: A network scenario is designed in NetSim GUI comprising of 4 Wired Nodes and 2 Routers in the “Internetworks” Network Library.

Step 2: Wired Link Properties is set as follows:

Step 3: In the Interface WAN > Network Layer Properties of Router 1, Scheduling Type is set as FIFO. Similarly, Scheduling Type is set as FIFO for Router 2.

Step 4: Three different applications are generated as per the table given below:

Note: For Voice application set codec as Custom.

Step 5: Enable the plots and run the Simulation for 10 Seconds. Note down the Application Throughput.

The following changes in settings are done from the previous sample:

Sample 2: (Priority)

Step 1: In the Interface WAN > Network Layer Properties of Router 1, Scheduling Type is set as PRIORITY. Similarly, Scheduling Type is set as PRIORITY for Router 2.

Step 2: Enable the plots and run the Simulation for 10 Seconds. Note down the Application Throughput.

Sample 3: (WFQ) 

Step 1: In the Interface WAN > Network Layer Properties of Router 1, Scheduling Type is set as WFQ. Similarly, Scheduling Type is set as WFQ for Router 2.

Step 2: Enable the plots and run the Simulation for 10 Seconds. Note down the Application Throughput.

Measurements and output

In FIFO, packets will get served based on their packet arrival time to the router. Therefore, since link 4 is a 5 Mbps link, the throughputs of Voice, Video, and Custom applications are equal to the ratio of their generation rates i.e., 1.76 ~ (5/13.6)*5, 0.90 ~ (2.6/13.6)*5, 2.12 ~ (6/13.6)*5.

The priority scheduling technique processes packets based on their priority. Hence voice which has the highest priority takes up the complete bandwidth available. 

Weighted fair queuing (WFQ) assigns a weight to each application and hence gives a result that is in between priority and FIFO.