1. Why Is There a Need to Implement a Weighted Fair Queue?
Requirement for transmitting different data types :
-Video, voice, data
Quality of service requirement
-Delay, jitter and loss
Optimize utilization of resources

2. Differences Between a FIFO Queue and a Weighted Fair Queue
All traffic in the queue is treated similarly S
Queue
Output link
How does it work?
Optimum way to implement the WFQ would be to visit the queues in repeated sequences. In each cycle, the scheduler should serve number of bits equal to the queue weight of each queue.

3. Weighted Fair Queue Each queue handles a certain traffic category
WFQ makes use of extra capacity in serving active queues S1 S2 S3
Queue 1
Queue 3
Queue 2
Output link

4. Advantages WFQ Queues WFQ can have a control on the delay
Better utilization of resources in WFQ

5. Description of System to Be Modeled
N sources
N Queues
Output link
Scheduler

6. Description of System to Be Modeled
3 queues fed by 3 different sources
Each queue is given a weight, which assigns its relative share of the bandwidth when all queues are active

7. Description of System to Be Modeled
For each queue, the share is calculated using the following equation:

8. Description of System to Be Modeled
Why do we need a scheduler ?
Scheduler determines the sequence in which the data should be sent to the output link

9. Concept of Virtual Finish Time (VFT)
Packets have to be served as they are
VFT solves this problem

10. Concept of Virtual Finish Time (VFT)
SVT is the system virtual time

11. Flowchart for Queue Was the queue empty when packet arrives YES
Update queue status and increase the number of active queue
Calculate the packet Virtual Finish Time (VFT)
Attach the VFT to the packet and insert the packet in the queue
Wait for a new packet to arrive

12. Flowchart for WFQ Scheduler
Access the VFT for the packet at the head of each queue
Get the packet with smallest VFT. Update SVT and send the packet on the link
Update queue status and decrement the number of active queues
Go to serve the next packet
Are there active queues
If queue becomes empty
Set SVT = 0 and wait till a queue becomes active
YES

13. Our Modeling Approach
Started from single queue design previously implemented
Changes made to accommodate our design

14. Our Modeling Approach SINGLE QUEUE WFQ -Simple FIFO queue
-OPNET commands on queues
-3 queues (or N queues)
-OPNET commands on subqueues and queues
-No need for calculation of VFT and SVT (no need for scheduling packets)
-Need to calculate VFT and SVT in order to schedule packets
-Created a formatted packet

15. Our Design Finite State Machine - (2 minutes) - explain interrupts
-     -    explain how going from green state to red state is a condition
-     -    the arrow for initial state
-     -    event driven and not clock driven
-     -    explain the path of the packets, explain what each state does

16. Overview of the Code Previous knowledge of C
Use of library functions in OPNET

17. Some OPNET Functions Used
Queue package:
op_q_empty ()
Subqueue package:
op_subq_pk_access(subqueue_index, OPC_QPOS_HEAD)
op_subq_pk_remove (subqueue_index, OPC_QPOS_HEAD)
Packet package:
op_pk_get(op_intrpt_strm())
op_pk_total_size_get(pkptr)
op_pk_send_forced (pkptr, stream_index)

18. Challenges in implementation – Formatted Packet
Problem
- Attach virtual finish time to packet
- Best solution

19. Overview of Code – Formatted Packet
How?
Field 1: “Packet”
Size: inherited
Field 2: “VFT”
Size: 0
( draw the formatted packet and explain the fields)
(attach virtual finish time to packet, flow chart of the queue)
(it was the best solution because it does not influence the length of the packet, and statistics)

20. How Did We Debug the Code?
Proved the sequence of the states by writing to an output file (fprintf commands)
Checked the values of the variables
Tested the content of the packets by printing it to the console

21. Sample Output File INITIAL op_sim_time(): 0.0000 weight0 : 8
IDLE STATE
op_sim_time():
ARRIVAL
packet number (sequence in which they arrive): 1
subqueue 0 active : 0
subqueue 1 active : 1
subqueue 2 active : 0
number of active queues : 1
weight of the active queue : 4.00
which queue became active now : 1
length of the packet :
calculate the total weight :4.000
the virtual service time :0.333
svt :0.0000
virtual finish time :0.333
Time when packet is inserted :0.2233
Insert_ok:1
SCHEDULER
queue1 is active, here is the VF1 :0.333
max_possible_virtual_time :1.333
min vft : 0.333
Current queue from which the packet will be send (my_queue1) 1
packet length (to determine service time) pk_len1 :
service_rate :

22. Our Strategies for Testing
Simulation using a SIMPLE SOURCE
Three test cases used to illustrate the performance of the WFQ:
1. All queues with the same weight
2. All queues with different weights
3. Priority queue

23. CASE 1: All Queues With the Same Weight (Using Exponential Source)
1024 bps
3072 bps

24. CASE 1: All Queues With the Same Weight (Using Exponential Source)
Traffic
Packets
Time

25. CASE 1: All Queues With the Same Weight (Using Exponential Source)
Delay
Delay
Time

26. CASE 1: All Queues With the Same Weight (Using Exponential Source)
Source & Sink
Packets
Note: Similar to FIFO queue
Time

27. CASE 2: All Queues With Different Weights (Using Constant Source)
1024 bps
3072 bps
Weight of Queue 0: 8
Weight of Queue 1: 4
Weight of Queue 2: 3

28. CASE 2: All Queues With Different Weights (Using Constant Source)
Delays
Delay
Delays are proportional to the weights of the queues
Time

29. CASE 2: All Queues With Different Weights (Using Constant Source)
Table
Arrival Sequence
Queue
# of Active Queues
Send Sequence
2(q0,q1) 2
1(q1) 1
3(q0,q1,q2) 3 4 1
2(q0,q2) 6 5 2
2(q0,q2) 8 2 9 7

30. CASE 2: All Queues With Different Weights (Using Constant Source)
Table
Arrival Sequence
Queue
# of Active Queues
Send Sequence
Arrival Sequence
Queue
# of Active Queues
Send Sequence
1(q1) 1 5
2(q0,q1) 2
2(q0,q1) 2 10
3(q0,q1,q2) 2 3 6
3(q0,q1,q2) 2 4 3 1 8
2(q0,q2) 5
2(q0,q2) 11
2(q0,q2) 6 4 2 11
2(q0,q2) 2 7 7
2(q0,q2) 8 9
2(q0,q2) 2 9
2(q0,q2) 12

31. CASE 2: All Queues With Different Weights (Using Constant Source)
Output File
IDLE STATE
op_sim_time():
ARRIVAL
sequence : 1
which queue is active : 1
virtual finish time :0.3333
op_sim_time():
sequence : 2
number of active queues : 2
which queue is active : 0
virtual finish time :0.5OO
op_sim_time():
sequence : 3
number of active queues : 3
which queue is active : 2
virtual finish time :
IDLE STATE
op_sim_time():
ARRIVAL
sequence : 4
number of active queues : 3
which queue is active : 2
virtual finish time :
op_sim_time():
SEND
Queue from which the packet is sent: 1
# of active queues before sending: 3
New svt :0.0222
op_sim_time():
sequence : 5
which queue is active : 0
svt :0.0222
virtual finish time :0.9583

32. CASE 3: Priority Queue (Using Exponential Source)
1024 bps
0 bps
2078 bps
Weight of Queue 0:
Weight of Queue 1:
Queue 2 not active

33. CASE 3: Priority Queue (Using Exponential Source)
Delays
Delay
Time

34. Analysis
When the weights for all queues are the same, the delays for the queues are very similar
When the weights are different, the delays and the queue size vary accordingly to the weights

35. Analysis
In the case of the priority queue, the delays for the queue with the highest weight is very small, and the delay for the queue with the lowest weight is very large
In summary, the delays for the weighted fair queue are inversely proportional to their weights

36. Conclusion Designed a WFQ in OPNET using 3 queues
Made it dynamic ( N queues )
Tested it with output file
Showed the effect of the weights of queues which are fed with similar sources