Incentive-Oriented Downlink Scheduling for Wireless Networks with Real-Time and Non-Real-Time Flows I-Hong Hou, Jing Zhu, and Rath Vannithamby

Motivation Wireless networks are increasingly used to serve real-time flows –VoIP, video streaming, online gaming In addition to throughput, these flows require strict per-packet delay guarantees Most current mechanisms belong to the paradigm of DiffServ

DiffServ Serve different flows differently Usually, real-time flows get higher priorities than non-real-time ones Can be unfair to non-real-time flows Non-real-time flows may lie about its category to gain more service Solution: charge real-time flows more

I am a real-time flow. I need small delay You need to pay more I require small throughput. Can I sacrifice throughput for delay?

Goal of the paper Design a scheduling policy that allows flows to tradeoff between high throughput and low delay by themselves

Desired Properties Incentive-compatibility: Flows optimize their own performance by reporting true category Versatility: The policy can work with various protocols in other layers –Different traffic patterns, different MAC, etc. Deadline awareness: The policy respects the deadlines of real-time flows Work conservation

Incentives of clients Non-real-time clients: Aim to maximize throughputs Real-time clients: Aim to maximize timely- throughput Timely-throughput: throughput of packets with delay < D

Basic Idea of Design Assume each client n has a weight of w n Each client n is entitled to have w n / Σw n channel time Allocating channel time proportional to w n maximizes and achieves proportional fairness Deficit of client n : (The amount of channel time that it is entitled) – (actual channel time)

Joint Deficit-Deadline (JDD) Policy A thin layer between Network layer and MAC layer Provides two functions: enqueue and dequeue –Interface defined by ns-2 enqueue: a packet is labeled with deadline and put in the queue when it arrives from Network layer dequeue: forward a packet to MAC

Architecture of JDD

Enqueue When a packet arrives from Network layer Mark the deadline of the packet –Deadline of real-time flow = current time + D –Deadline of non-real-time flow = current time + a large value (~ TCP timeout) Place the packet in the queue

Dequeue Delete all expired packets Forward the packet with the earliest deadline with the constraint that the corresponding client has positive deficit Earliest deadline: real-time packets usually got served first, and non-real-time packets need to wait Positive deficit: real-time packets receive smaller channel time

Ns-2 Simulation 10 clients, 5 of them are real-time ones, and the other 5 are non-real-time ones Real-time flows require a delay bound of 100ms All flows are generated by TCP Use IEEE for the MAC Weight of non-real-time clients = 1 Weight of real-time clients varies

Simulation Results

Delay Distributions

Performance Comparison Compare against two other policies: –Earliest deadline first (EDF) –Weighted round robin (WRR) 10 clients, 5 real-time and 5 non-real-time The distance between clients and the base station is evenly distributed Performance metric: = throughput/timely-throughput

Simulation results for TCP

Simulation results for TFRC

Simulation results for Interfering Network Add an additional link that causes interference

Conclusion We propose the JDD scheduling policy The policy allows strategic clients to choose between high throughput and low delay The policy does not make any assumptions on other layers, and can work with a wide range of different systems Simulation results show that JDD outperforms other policies