CAC and Scheduling Schemes for Real-time Video Applications in IEEE Networks Ou Yang UR 10/11/2006

Outline Overview of IEEE Networks Motivation Proposed CAC Scheme Proposed Scheduling Scheme Simulation Results Conclusion

Overview

Overview of IEEE Networks

Brief Introduction to Fixed Wireless Broadband Access Networks - Line of sight Connection Oriented - Block incoming calls when QoS fails Medium Access Mechanism - TDMA Differentiated Quality of Service - Support real-time video application

Motivation

Real-time video applications demands high bandwidth efficiency and guaranteed QoS IEEE standard defines a frame of MAC but leaves CAC and scheduler open to discuss Varying bit-rate and stringent delay bound make the design of CAC and scheduler difficult

State of the Art CAC - Determines throughput - Influences delay performance Scheduler - Determines fairness - Influences delay performance No reference focuses on throughput, delay performance and fairness simultaneously.

State of the Art -CAC Make decision as soon as incoming flows arrive Conservative bandwidth reservation. Reserve bandwidth according to the maximum I frame These cause low throughput

State of the Art - Scheduling Earliest Deadline First (EDF) - Maximizing throughput under delay constraint - Unfair - Commonly used FIFO + Weighted Fair Queuing (WFQ) - Unfair under delay constraint - Low throughput under delay constraint - Seldom used None achieve good delay performance and fairness simultaneously

Solution – Utilize Traffic Traits Periodicity: - I B P frames constitute a GOP - Control the bandwidth occupancy Regularity: - I frame bigger than non-I frame - I frame less than non-I frame - Consider I and non-I frame separately in bandwidth reservation

Proposed CAC Scheme

Pending Period Decision is made in the pending period Less traffic burst causes delay violation

Consider I and non-I separately Detect delay violation until find out a proper access time or the pending period expires Step 1: Accessed I vs. Incoming I - Utilize periodicity to predict the arrival of I frames Step 2: Accessed non-I vs. Incoming I - Estimate the average bit-rate of non-I frames - Reserves bandwidth based on estimation Effect: Adjust estimation to balance delay performance and throughput

Proposed Scheduling Scheme

EDF - > Earliest LST First LST (Latest Starting Time) - latest time to start transmission in order to catch up with deadline Effect - Being scheduled = Meet delay constraint - The same deadline, larger frame will be scheduled first in result of earlier LST

Loose Constraint on ELSTF Enlarge the Pool of Prospective Packets Consider fairness

Effect ELSTF improve the delay performance Loose constraint improves fair service L is adjustable, compromising delay and fairness

Simulation Results

Analysis Throughput, delay performance and fairness are involved in two trade-offs, handled by Re and L Re↑ Throughput↓ Delay performance↑ L ↑ Fairness ↑ Delay performance ↓

Conclusion

The proposed CAC introduces a pending period and utilizes traffic traits to compromise throughput and delay performance The proposed scheduler applies loose constraint on ELSTF to balance fairness and delay performance Simulation results show the proposed schemes significantly improve the throughput with acceptable delay performance and fairness.

Thank You