Token-DCF, COMSNET(2013) -> MOBICOM(2014)

Introduction▣ To improve standard MAC protocol of IEEE 802.11 for WLAN.

▣ S-MAC, A-MAC, SPEED-MAC, and etc are for WSN. Close to 802.15.4 Energy Consumption is the main issue. Duty Cycling

▣ Whereas, Throughput & Latency is of most important factor for WLAN.

Motivation▣ 802.11a, b(1999), 802.11g(2003), 802.11n(2009), 802.11ac,ad(2013)

Basic CSMA/CA being improved

▣ Problems of CSMA/CA unnecessarily long idle time

– channel access delay, low channel utilization

High collision rate– Still possibe to collide even with big CW size

▣ The paper is for reducing idle time and collision rate to get better throughput and latency.

Related Works▣ Many researches for improving CSMA/CD

Optimal CW size– Set optimal CW size immediately considering network status– optimal backoff distribution

802.11e,n– Transmit Opportunity (TXOP) – multiple frames– Reverse Direction (RD) – burst response

Related Works (cont.)▣ Wireless Token Passing Protocols

Token Passing is a medium access method where a short packet called token is passed between stations to autho-rize a station for transmission.

To send data frame, it needs to possess token. No collision.

▣ Issues connectivity loss, network partitioning, token loss & duplica-

tion, network connectivity change. Round Robin Passing

Main Idea

1. not round robin scheduling. Privilege (Token) Scheduling with neighbor nodes’ queue

length >0.

2. implicit scheduling. Queue length information of source and token are collected

by each neighbor node by overhearing through MAC header. Node with same Id can transmit next.

ad hoc mode / infrastructure mode

ad hoc mode / infrastructure mode

Evaluation

Compared to 802.11g in NS-2 Wireless adhoc/infra network RTS/CTS turned off Each simulation – 30 seconds/10seconds. Averaged over 20

runs. Packet payload size – 1500 B P

Results – ad hoc

Results - infra

Ad hoc – detailed

Ad hoc – detailed (cont.)

Ad hoc – detailed (cont.)

Ad hoc – detailed (cont.)