Netlab

Data Networks Lab.

Wireless MAC

Data Networks Lab.Data Networks Lab.윤정균윤정균

jyun@netlab.snu.ac.kr

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Outline

Protocols with NCR (Neighborhood-aware Contention Resolution)

NAMA, LAMA, PAMA

IEEE 802.11 MAC Overview CSMA/CA IEEE 802.11 for QoS support

Distributed Scheduling

Rate-Adaptive MAC Protocol RBAR(Receiver-Based Autorate)

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Protocols with NCR

NAMA, LAMA, and PAMA

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Contents

Neighborhood-aware Contention Resolution(NCR) Algorithm

Channel Access Protocols Node Activation Multiple Access (NAMA) Link Activation Multiple Access (LAMA) Pairwise-link Activation Multiple Access (PAMA)

Results

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Neighborhood-aware Contention Resolution

Assumption Every entity knows the set of its contenders. Each contention context (time slot) is

identifiable

NCR Algorithm (in contention context

t)1. (1) Rand( ) is pseudo-random number2. Exit unless (2)3. may access the common channel during

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Channel Access Protocols

Undirected Graph Each node is assigned a unique ID number

Remind the Assumption Nodes already know their neighborhood

Example of Collision Types

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①Node Activation Protocol - NAMA

Based on NCR Node activation Distributed time division multiplexing

Time Division in NAMA

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NAMA Frame Format for Membership

Signal Frame Format in

Membership Section

Data Frame Format in Regular

Section

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NAMA Algorithm

NAMA:

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②Link Active Protocol - LAMA

Based on NCR Time-slotted code division access using

DSSS Link activation (receiver-oriented code

assignment)

Code assignment Orthogonal code pool A receiver is assigned a pseudo-noise

code by the hashing operation

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LAMA Algorithm

The contender set

LAMA:

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LAMA Example

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③Pairwise Link Activation Protocol - PAMA

Based on NCR Time-slotted code division access using DSSS Link activation (transmitter-receiver pair- oriented c

ode assignment)

Contending entities are LINKs, not nodes

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PAMA Algorithm

PAMA:

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Results

Fully Connected - Delay

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Results

Fully Connected - Throughput

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Results

Multihop - Delay

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Results

Multihop - Throughput

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IEEE 802.11 MAC

CSMA/CA & QoS support

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CSMA/CA Example

Source Dest

NAV set NAV setData

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Basic Access Method : CSMA/CA

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IEEE 802.11 QoS support (IEEE 802.11e 에서 표준화 작업 중 )

Using Backoff time Replace by .

Using DIFS

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Distributed Scheduling

Distributed Priority Scheduling

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Contents

Introduction

Distributed Priority Scheduling Proposed Algorithm

Multi-Hop Coordination

Results

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Introduction

Distributed Priority Scheduling Using piggybacked priority tag Each node’s scheduling table will be incomplete →

define probability q

Multi-Hop Coordination Better satisfy end-to-end QoS target across multipl

e nodes

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Distributed Priority Scheduling

Two Scheduler Earliest Deadline First (EDF) → t+d Virtual Clock (VC) → max(t, pk-1) + L/r

802.11 Differentiation backoff timer distribution the defer time (DIFS)

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Algorithm

Priority

Broadcast

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Modified Backoff Policies

Effect of q (available information)

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Multi-Hop Coordination

Definition

Index Assignment Scheme Deadline Targets

Time To Live (TTL) Fixed Per-Node Allocation Uniform Delay Budget (UDB)

Rate Targets

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Simulation Results

Topology

Delay performance

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Rate Adaptive MAC

RBAR(Receiver-Based Autorate)

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Contents

Introduction

Previous Works The Lucent ARF Protocol

The RBAR Protocol Incorporation of RBAR into 802.11

Results

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Introduction

Need for Rate Adaptation

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The Lucent ARF Protocol

Two consecutive ACKs are not received by sender, then drops the rate Timer expires or 10 consecutive ACKs are received, then raises the rat

e

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The Receiver-Based Autorate Protocol

Receiver selects the appropriate rate for the data packet during the RTS/CTS packet exchange (more accurate selection)

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Overview of the RBAR Protocol

S sends a RTS to R with rate r1 and packet-size n.

A hears the RTS and tentatively calculates the reservation duration.

R selects r2 using channel estimation and sends a CTS.

B hears the CTS and calculates the reservation using r2 and n

S puts r2 in the data packet header and transmits at the rate r2.

A hears the data packet and recalculates the reservation.

A S R Br1, nr1, n

r2, n

r2, n r2, n

r2, n

ACK

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RBAR Example

Source Dest

NAV: NAV:DataNAV: 10NAV: 7 NAV: 7

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Incorporation of RBAR into 802.11

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Simulation Results

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Multi-Hop Performance

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Summary

Protocols With NCR New Approach → Using 2-hop neighbor

inform. No need to contend or schedule broadcast

Distributed Priority Scheduling Priority-Based Medium Access Multi-Hop Priority Access

Rate-Adaptive MAC A modified version of 802.11 Improve network throughput

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References

[Protocols with NCR] Lichun Bao and J.J. Garcia-Luna-Aceves, “A New Approach to Channel Access Scheduling for Ad Hoc Networks,” Mobicom 2001.

[IEEE 802.11] Brian P. Crow, Indra Widjaja, Jeong Geun Kim, and Prescott T. Sakai, “IEEE 802.11 wireless local area networks,” IEEE Communication magazine, September 1997.

[802.11 QoS support] Imad Aad and Claude Castelluccia, “Differentiation mechanisms for IEEE 802.11,” Infocom 2001.

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References

[Distributed Scheduling] V. Kanodia, C. Li, A. Sabharwal, B. Sadeghi, and E. Knightly, “Distributed Multi-Hop Scheduling and Medium Access with Delay and Throughput Constraints,” Mobicom 2001.

[Rate-Adaptive MAC] Gavin Holland, Nitin Vaidya, and Paramvir Bahl, “A Rate-Adaptive MAC Protocol for Multi-Hop Wireless Networks,” Mobicom 2001.