Wireless Switch Protocol

Wireless Switch Protocol

課程 : 行動計算學號 :M9129023

學生 : 陳德翰

Outline

IntroductionWireless Switch Protocol (WSP)

• An overview of the IWLAN • Complex Wireless Switch Protocol (CWSP) • Challenges in CWSP • Simple Wireless Switch Protocol (SWSP)

Simulation Model And ResultsConclusions

Introduction

IEEE 802.11 supports two kinds of network topologies:

• Infrastructure WLAN (IWAN) Access point is the bridge between wired and wireless networks • Ad hoc WLAN Collection of STAs , data exchange network without the centralized administration

Introduction

IEEE 802.11 2.4 – 2.4835 GHz 83.5MHz are Divided into 14 partially overlapping channels

IEEE 802.11b suggest at least 25 MHz or 30 MHz guard band for any two overlapping WLANs • In North American Center at 2.412 GHz , 2.437GHz , 2.462GHz • In Europe center at 2.412GHz , 2.442GHz , 2.472GHz except Spain and France

Introduction

In small/medium enterprises or home environments one IEEE 802.11b AP often can covering the service area ; this implies that one channel is mandatorily us

ed and the other two channels are useless

This paper propose a new CSMA based media access control (MAC) protocol named wireless switch protocol (WSP) for promoting the IEEE 802.11

network throughput


The MAC is defined to operate in single channel and the coverage area of the channel logically forms a basic service set (BSS)The RTS/CTS handshaking which occurs between STAs and APHidden terminal


1. STA A issue RTS control frame to AP

2. Wait for CTS control frame replied from AP

3. All STAs in the BSS are aware of the channel and STA A send data frame

4. STA A receive the acknowledgement (ACK)



Disadvantages

1. The channel bandwidth is consumed twice 2. Additional contentions and collisions and average

access delay is increased

3. AP needs extra buffer spaces for these data

frames

4. The data frames destine to wired hosts will be blocked by the data frames destine to

neighboring

wireless hosts


Propose two kinds of WSPs

1. Complex WSP (CWSP) : Designed for solving the potential hidden terminal situation in large space

2. Simple WSP (SWSP): Designed for pure environment where every STAs can here with each other


Complex WSP (CWSP): 1. STA A will issue the M-RTS1 (Multi-channel RTS Type 1) control frame to AP 2. AP detects the M-RTS1 , it retrieves the DA and issues a new M-RTS2 (Multi-channel RTS Type 2) with the assigned data channel c and time stamp t 3. STA B receives the expected M-RTS2 , it replies an M-CTS 4. STA A and STA B will complete the data transfer 5. STA B reply the standard ACK





Challenges in CWSP 1. How to tell a data frame is belonging to Internet or Intranet traffic? 2. How to distinguish the case that sender and receiver are hidden to each other? 3. If the handshaking is failure by interference , how to avoid the unnecessary bandwidth wastage? 4. How to maintain the frame sequence between sender and receiver?


First problem: Maintain a status table , which records the associated STAs in AP , it will refer the status table to decide whether the DA is one of the STAs in the BSS and whether they have exchanged data before if so M-RTS1-> M-RTS2-> M-CTS->Data->ACK If the DA is not in BSS or hidden to each other M-RTS1->CTS(A)->Data->ACK(A)


Second problem: After STA A issues the M-RTS1 control frame to STA B the AP will generate the M-RTS2 control frame to

STA B after passing SIFS if STA B only receives the M-RTS2 and miss the M-RTS1 , it is aware that STA A

is the hidden node and it will reply this situation to AP , if the STA A detects the M-RTS2 but fails in receiving the M-CTS or CTS before timeout it also find STA B is a hidden node


Third problem: From our observations , it is hard to distinguish the hidden-node or channel noise , use the standard ap

proach to prevent from unnecessary bandwidth wastage A

Last problem: the timing of STA issues M-RTS1 control frame is at the moment that a precedent data frame has been successfully


Simple Wireless Switch Protocol (SWSP):

It is particularly suitable for home or office environment , hidden terminal probability in such environment is very small , we can assume that STAs are staying in a fully connected network


Simulation Model And Results

Simulation Model And Results

Conclusions

We proposed two kind of wireless switch protocol , which base on CSMA/CA protocol with RTS/CTS handshaking mechanismSimulation results demonstrated that the proposed WSP significantly outperforms the standard CSMA/CA protocol under the constrain the network traffic include partial Intranet traffic , and the throughout gain can be even up to 400%

Documents

Wireless Switch Protocol