Transcript Drive-thru Internet: IEEE 802.11b for

Drive-thru Internet: IEEE
802.11b for “Automobile” Users
Jorg Ott and Dirk Kutscher
Bremem University, Germany
IEEE INFOCOM 2004
Reporter: 鄭伊騏(JOE)
Outline







Introduction
What is “Drive-thru”
Measure Scenarios
Measurements
Experimental finding and analysis
Applications
Conclusion
預計94年底，台北市全區無線上網
基本服務
VoWLAN，網內互打完全免費
市府便民服務
．無線文化快遞
WiFly加值服務

．即時路況、停車資訊
報你知
．遠距動物園、家庭天
文館
．市立圖書館館藏查詢
．市立醫院線上掛號與
門診時間查詢
．市政地理資訊E點通
．線上戶政諮詢系統
．北市府資訊中心快速
入口
視
電視頻道即時播映
音
圖鈴與MP3下載
訊 行動簡訊隨身發送
http://www.wifly.com.tw/
加值服務
PDA 加值服
務
財
股匯市財經資訊
學
遠距教學知識分享
遊
線上參訪動物園
控
遠端監控居家安全
視
電視頻道即時播映
遊
線上參訪動物園
藝
文化局藝文資訊
財
股匯市財經資訊
控
遠端監控居家安全
（實際狀況
將視工程建
置進度而有
所調整，以
上資訊僅供
參考）
資料來源：
http://www.wifly.com.tw/
首航期：

93年底市中心
28個捷運站及
其周邊150公
尺商圈
接續期：

94年6月底涵括市
中心主要住商區
域

北界:民權東西路
西界:環河南北路
東界:基隆路、塔
悠路
南界:和平西路、
羅斯福路
廣佈期：

94年12月底覆
蓋北市各行政
區人口密集區
域
WiFly 架構

Access層


AP間串連


透過Mesh的無線串連AP技術，解決都市內鋪設管線必
須挖馬路的麻煩。Mesh的佈點主要還是以燈桿、交通
號誌、或天橋等公共點為主。
Hub Site端


IEEE 802.11b/g，是目前使用者端較為成熟且普及的。
透過無線的方式連接到Hub Site端，這之間採用的技術
為802.16a或802.16-like。
連接IDC

利用光纖線路連結ISP的IDC (Internet Data Center)。
Introduction (1/4)

Ubiquitous network connectivity

Cellular wide-area networks (GSM, GPRS)



Full coverage (most parts of country)
10 to 100 kbps
Wireless Local Area Network (802.11 a/b/g)


Provide selected hot spots or larger areas such as
enterprise premises or campus.
10 to 54 Mbps
Introduction (2/4)

WLAN Applications

Volunteers provide free WLAN access.




http://www.nodedb.com/
http://wifimap.com/
Side effect from WLANs inside buildings.
Location based service


Local information in mall
Advertisement of restaurant
Introduction (3/4)

Today’s deployment for WLAN access


Indoor users who are mobile with a limited
range
Outdoor users who are expected to stop or
to move most slowly.
Introduction (4/4)

Scenario for mobile users


Providing network service in mobile
environment. (NEWS)
Investigating ad-hoc network with several
mobile users to establish cooperation
environments (Without Internet accessing)
“Drive-thru”



Provide hot spots along the road.
One or more interconnected APs called
connectivity island.
Several connectivity island maybe
interconnected and cooperate to
provide WLAN access for a larger area.
“Drive-thru”



User may move at varying speeds
ranging from a less than 1 to some 70
m/s.
APs provided at each street corner,
traffic light or emergency phones.
APs may be obscured by tree, user’s
own vehicle’s bodywork and buildings.
Connect to AP

Permanently scan for signals from
available APs.





Power consumption isn’t an issue in car
Associate with the AP when signal is
detected
Network access and IP configuration.
Security service (VPN tunnel or WEP)
Ready to hand-off
Measure Scenarios

Reference Measurement


A wireless station which is immobile and
close to AP in the LAB.
Highway Measurement


1 AP and 1 MS at lower speed (40-80 km/h)
2 APs and 1 MS at higher speed (80-180
km/h)
Reference UDP Measurement
Reference UDP
Measurement Note (1/2)

Difference of sender



Mobile sender is almost no packet loss
Fixed sender’s loss rate is depending on
nominal sending rate.
Effective throughput is 5 Mb/s

DCF in WLAN
Reference UDP
Measurement Note (2/2)



From mobile to fixed, we can limit the
sending rate to a nominal rate of 5
Mb/s
Form fixed to mobile, 2.5 Mb/s can
already reach the limit of the network’s
capacity
For sending from fixed to mobile, we
can expect very high loss rates for
higher sending rates.
Reference TCP
Measurement Note

Mobile to fixed


Fixed to mobile


4.38 Mb/s
4.44 Mb/s
TCP performs significantly better than
UDP (3.79 Mb/s). We ascribe this to
TCP’s congestion control.
Highway Scenario
A laptop with a
built-in Ethernet
adapter.
The same ESSID, Neither WEP
nor DHCP.
A laptop with a PCMCIA
IEEE 802.11b adapter.
(Orinoco gold card)
With External Antenna on the
right hand side of car.
Autobahn Scenario (1/2)
Autobahn Scenario (2/2)
Autobahn UDP Measurement
TCP time sequence graph
Experimental finding and
analysis (1/3)


802.11b communication with MS is
essentially feasible.
Useful connectivity is about 200 m in
diameter



9 secs at 80 km/h
6 secs at 120 km/h
4 secs at 180 km/h
Experimental finding and
analysis (2/3)



UDP flows have little packet loses.
TCP congestion control makes TCP
flows adapt quickly to provide reliable
communication.
No handoff occurs.



Irrespective speed and direction.
Associated with the closer AP.
Due to the scanning rate is too low for a
fast handoff.
TCP connectivity Phase
Experimental finding and
analysis (3/3)



Use external antennae for AP
Increasing the distance of APs
Changing AP parameters


Using different hardware component


Channel used and beacon transmission rate
APs and WLAN card with different firmware
and driver version.
Using 802.11 a/g to impliment
Applications on Internet
connectivity

Continuous communication


Transaction based information access


IP telephony, database access
E-mail, file transfer.
Further Approach


Extending the connectivity period
Enhancing the applications to better deal
with intermittent connectivity
Applications on
transmission characteristics

TCP




TCP connection splitting
1 connection from the MS to the island
Another is from host to Internet.
UDP

FEC (Forward error correction)
Conclusion



Connectivity is poor at the edge of a
connectivity island.
Transmit 9 Mb in a single session.
TCP despite abruptly changing network
characteristics.
~The End~
Sentence

The transmission delay increases until the
maximum queue size is reached, and
subsequently, packets will be dropped,
which becomes visible by an increased
packet loss rate.
Measurement Tools-UDP



Configure packets transmission: rtpsend.
Generate Logs for packets: rtpspy.
RTP protocol:


Sequence NO: assess throughput and loss
rate
Timestamps: monitor relative delays
Measurement Tools-TCP

Tcpx

Server mode


Client mode



Multicast UDP trigger message and listen new
connections on specified port.
Wait a trigger from server
Ethereal
Tcptrace
Experimental finding and
analysis (1/3)

Useful connectivity is about 200 m in
diameter





9 secs at 80 km/h
6 secs at 120 km/h
4 secs at 180 km/h
UDP flows have little packet loses.
TCP congestion control makes TCP
flows adapt quickly.