1. Team: Aaron Sproul Patrick Hamilton
A Unified Architecture for the Design and Evaluation of Wireless Fair Queueing Algorithms
Team:
Aaron Sproul
Patrick Hamilton

2. Introduction Context: Problem Addressed: Solution:
Addresses fairness issues in Wireless Networks
Problem Addressed:
Location-dependent errors
Bursty errors
Channel contention
Joint scheduling
Solution:
Unified wireless fair queueing architecture

3. Introduction Results Overview: Presents a wireless fair service model
Unified wireless fair queueing architecture
Creates unified rule set
Future specifications
Simulate and analyze 7 algorithms
2 Algorithms fulfill all requirements for wireless fair service

4. Background and Motivation
Background – fluid fair queuing model
Motivation:
Growth of wireless networks brought about issue of fair wireless channel arbitration
TCP uses losses to determine congestion
Fluid fair queueing assumes error free channel or not location dependent errors
No study of current wireless fair queueing algorithms
No single rule set for wireless fair queuing algorithms

5. The Problem Statement
Failure of fluid fair queueing when location-dependent channel errors occur
Flows that perceive channel error
Channel access fairness impact from full separation/compensation trade off

6. Key Terms What basic feature does fluid fair queueing (TCP) provide?
Provides full separation between flows
error-free service – service that flow would have received at same instant if all channels were error-free
leading – received channel allocation in excess of its error-free service
lagging – received channel allocation less than its error-free service
in sync – flow that is neither leading nor lagging
backlogged – accumulated packets in queue (backed up flow)

7. Wireless Channel Model
Channel capacity is dynamic
Channel errors are location-dependent and bursty
Contention in channel among multiple hosts
Mobile hosts do not have global channel state
Scheduling must do both up and down link flows
Mobile hosts constrained by battery power and processor power

8. Wireless Fair Service Model
Short-term fairness
Long-term fairness
Channel-conditioned delay bounds
Short-term throughput bounds
Long-term throughput bounds
Support of both Delay sensitive and Error sensitive data flows
Optimization of the schedulable region (optional)

9. Unified Wireless Fair Queueing Architecture
error-free service
Defines an ideal fair service model assuming no channel errors
lead and lag model
Determines which flows are leading or lagging their error-free service and by how much
compensation model
Compensates lagging flows at expense of leading flows
slot queues and packet queues
Support of both delay sensitive and error sensitive flows
Decouples connection-level packet management policies from link-level packet scheduling policies
channel monitoring and prediction
Provides reliable and accurate measurement and estimation of channel state at any time instant for each backlogged flow

10. Interaction of components in the unified wireless fair queueing architecture
Bold boxes indicate programmable components

11. Channel State Dependent Packet Scheduling (CSDPS)
error-free service
Weighted round robin
lead and lag model
If channel error, skip flow and reallocate slot
compensation model
Policed by outside mechanism
implementation complexity
Depends on the number of flows
impact and limitations
No guarantee for long-term and short-term fairness

12. Idealized Wireless Fair Queueing (IWFQ)
error-free service – uses WFQ
lead and lag model
Arriving packets are tagged similar to WFQ
Service tag set to finish tag of its head-of-line packet
Head-of-line packet for flow with least service tag is transmitted
compensation model
Lagging flows have low service tags
implementation complexity
Sorting service tags = O(n log n)
WFQ computation = O(n)
impact and limitations
Coarse short-term fairness
Coarse throughput bounds
Long-term fairness
Bounded delay channel access

13. Wireless Packet Scheduling (WPS)
error-free service
WRR with spreading of slots
lead and lag model
A frame with multiple slots
compensation model
Slot swapping within frames
Leading flows suffer
implementation complexity
WRR-spreading = O(n)
Intra-frame swaping = O(n)
impact and limitations
Coarse short-term fairness
Throughput bounds
Bounded delay channel access
Long term-fairness

14. Channel-condition Independent Fair Queueing (CIF-Q)
error-free service
Start Time Fair Queueing
V(t) is set to start tag of transmitting packet
Applied to active flows (leading or backlogged)
lead and lag
Difference error-free and real service
compensation model
Leading flows backs off and allow lagging flows additional service
Lagging flow can capture channel and starve other flows
implementation complexity
Sort the service tags = O(n log n)
Computation of Virtual time, V(t) = O(1)
Slot allocated to flow with channel error, find another flow = O(n)
impact and limitations
Short-term fairness
Long-term fairness
Bounded delay channel access
Problems with lagging flows

15. Enhanced Class Based Queueing with Channel State Dependent Packet Scheduling
(CBQ-CSDPS)
error-free service
Modified Class Based Queueing with Channel State Dependent Packet Scheduling
lead and lag model
A leading flow has transmitted more bytes than a given normalized weight
A lagging flow has transmitted less bytes
compensation model
Lagging flows given precedence which can lead to channel capture
implementation complexity
WRR (error-free service) = O(n)
impact and limitations
Long term fairness
Throughput bounds
Link sharing
No short-term fairness
In sync and leading flows can be affected if a lagging flow captures channel
CBQ-CSDPS is not simulated in this paper because it is still in progress

16. Server Based Fairness Approach (SBFA)
error-free service
Generic framework for service disciplines to be adapted to wireless from wired
lead and lag model
Lagging flow with channel error, submits a slot request to compensation flow
Lag is number of slot request in compensation flow
No concept of leading flows
compensation model
A fraction of the channel bandwidth
Treated like all flows
If allocated a slot, compensation flow gives slot to requested flow
implementation complexity
Depends on error-free service
Compensation = constant
impact and limitations
Long term fairness and throughput bounds for error-free flows
No short-term fairness or throughput bounds
Very coarse worst case delay bounds
Leading flows are not monitored, do not release lead
Performance based on compensation flow

17. Wireless Fair Service algorithm (WFS)
error-free service
Enhanced version of WFQ
Transmission
Earliest deadline first or WFQ or WF2Q
lead and lag model
Bounded by per-flow parameters
compensation model
A leading flow releases a number of slots to lagging flows based on its lead and a lead bound
implementation complexity
Sort service tags = O(n log n)
Compute lagging flow to transmit = O(n)
impact and limitations
Tightest short term fairness
Throughput bounds
Long-term fairness
Delay bounded channel access
Graceful degradation of leading flows
Optimal schedulable region

18. Performance Evaluation Model
Simulation Environment
Simulation run for 50,000 time units
Results averaged over 40 simulation runs
Short time windows: 10 different windows, 200 time units each for 5 distinct runs
Parameters used:
Pl : loss probability – fraction of packets dropped
Dmax : max delay of successful packet transmitted
Davg : average delay
σD : standard deviation of delay
dnq : maximum queue delay
Delay and throughput parameters expressed in terms of slots

19. Performance Evaluation Model
Algorithms performance evaluated on:
Separation between flows
Decoupling of rate and delay
Size of the schedulable region
Short term throughput and fairness guarantees for error-free flows
Long term throughput and fairness guarantees for all flows
Graceful service degradation for leading flows

20. Examples (1 and 2) Flow 3 Suffers Low delay BAD
Example 1 – error-free service
Shows that each algorithm performs according to its error-free service model
Delay-bandwidth decoupling in WFS
Example 2 – Error-sensitive vs. Delay-sensitive flows
Delay-sensitive flow drops packets from queue when they are there for a time larger than specified delay bound
Error-sensitive flow drops packets when it tries to retransmit a packet for a specified number of times and encounters channel error
3 sources: 1,2 MMPPs sources; 3 constant source
Loss rates and delay for flows:
Flow 3 Suffers
Low delay
BAD
However, SBFA is good with error free channel 3

21. Examples (3) Example 3 – Graceful service degradation
Service degradation of leading flows
Flow 1: error till time t=100
Flow 2 and 3: error-free
Service degradation plots
Number of packets transmitted vs. time

22. Takes longer to compensate
Examples (3 continued)
Bad for short term
throughput
Takes longer to compensate

23. Example (4, 5, and 6) Example 4 – Channel prediction:
Exactly like example 2, except that the errors are uncorrelated between slots
Results: the worse the channel prediction the more performance degrades
Example 5 – Identical Behavior
Details a situation where all algorithms behave in a similar fashion
Results: similar delays, except for SBFA
Example 6 – Adaptive Sources
Effect of latency of adaptation on the throughput for a flow in the presence of channel error
Throughput increases with smaller time windows
If delay is reduced, up to 10% increase in throughput

24. Related Work Related work in wireless fairness:
Unified WLAN architecture for real and non-real time
Distributed fair scheduling in WLAN
Fair medium access protocols using adaptive flow-rate control in WLAN
Packet fair queueing algorithms for WLAN
How is it different from this work?
Aimed at more specific areas of research into wireless fairness

25. Critique Technical flaws
No definition of parameters or terms used
Results were not clearly stated or proven
Failure to maintain consistency (i.e. lead and lag model)
Approaches you would have used instead of those presented
Described algorithms, key terms, simulations, and results more clearly

26. Summary and Conclusions
WFS and CIF-Q achieve all the properties of wireless fair queueing
Were you paying attention?
WFS = ?
Wireless Fair Service
CIF-Q = ?
Channel-condition Independent Fair Queueing