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

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

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

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

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

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)

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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