TCP with Adaptive Pacing for Multihop Wireless Networks

Sherif M. EIRakabawy, Alexander Klemm, Christoph Lindemann

University of Dortmund GermanyProceedings of the 6th ACM international symposium on Mobile ad hoc networking and computing

2005

Presented by JIUN-JAU CHIOU

Outline

Introduction Motivation TCP-AP Performance

– FTP-like data transfer– Variable length flows

Conclusion

Introduction

TCP with Adaptive Pacing (TCP-AP):– A congestion control algorithm for TCP over multi

hop IEEE 802.11– TCP-AP provides a rate-based control by motnitor

ing RTTs to shrottles transmission rate to avoid congestion-related loss.

Motivation

TCP’s window-based congestion control increase contention on 802.11.– Spatial reuse constraint of wireless channel in IEE

E 802.11– Packet loss due to hidden terminal problem.

TCP identifies congestion when packet lossed.– This behavior result in increased congestion.

TCP-AP

Rmax : upper bound of transmission rate

Two parameters of TCP-AP to get Rmax

– covRTT (coefficient of variation) :Quantifies the degree of contention on the network.

– FHD (4-hop propagation delay):The transmitting time between Sorce node and Des node whitch lies 4 hops away.

covRTT

– N is number of RTT samples– /RTT is the mean of samples– RTTi denotes i-th RTT sample

Justify the applicability of covRTT:

FHD:

Hidden terminal effects depend mainly on the characteristics of the network :– Interference range– Transmission range

This paper consider “FHD” for the calculation of the transmission rate.

Rmax = 1 / FHD

TCP - Adaptive Pacing :

Parameter Tuning and Responsiveness:– Responsiveness:

How quickly this algorithm adapts to changing network conditions.

2 parameters :– N : samples of RTT for calculation– α: averaing weight– (N, α) = (50 , 0.7)

Performance (FTP-like)

Chain topology :

Symmetric Parallel Chains Topology:

Asymmetric Parallel Chains Topology:

Grid Topology

Random Topology

Performance (variable length flows)

Symmetric Parallel Chain Scenario:

Random Scenario:

Pause = 1 sec

Conclusion

Quntification of congestion by measuring the fluctuation of RTT samples using covRTT

Based on covRTT and FHD, TCP-AP adaptively calculates the rate for pacing.