Drive-thru Internet: IEEE 802.11b for “Automobile” Users

Jorg Ott and Dirk KutscherBremem University, Germany

IEEE INFOCOM 2004Reporter: 鄭伊騏 (JOE)

Outline

Introduction What is “Drive-thru” Measure Scenarios Measurements Experimental finding and analysis Applications Conclusion

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WiFly 架構 Access 層

IEEE 802.11b/g ，是目前使用者端較為成熟且普及的。 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 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 a

s 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 calle

d connectivity island. Several connectivity island maybe int

erconnected 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 ava

ilable 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 cl

ose 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 4.38 Mb/s

Fixed to mobile 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 PCMCIA IEEE 802.11b adapter. (Orinoco gold card)With External Antenna on the right hand side of car.

A laptop with a built-in Ethernet adapter.

The same ESSID, Neither WEP nor DHCP.

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

Channel used and beacon transmission rate Using different hardware component

APs and WLAN card with different firmware and driver version.

Using 802.11 a/g to impliment

Applications on Internet connectivity

Continuous communication IP telephony, database access

Transaction based information 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

Multicast UDP trigger message and listen new connections on specified port.

Client mode 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 flo

ws adapt quickly.