Wireless Internet The Good The Bad and The

Wireless Internet: The Good, The Bad, and The Ugly Carey Williamson Professor and i. CORE Chair Department of Computer Science University of Calgary 1

Introduction n n It is an exciting time to be an Internet researcher (or even a user!) The last 10 -15 years of Internet evolution have brought us: n n n World Wide Web (WWW) Media streaming applications Peer-to-peer (P 2 P) applications “Wi-Fi” wireless LANs and hotspots Mobile/pervasive/ubiquitous computing 2

Main Messages of this Talk n Wireless Internet is wonderful! n n n Wireless Internet is scary n n n Affordable, convenient, and easy to use Widely available, useful, exciting, and fun Security risks, naïve users, vulnerable data “Wireless Security” is an oxymoron Wireless Internet ain’t perfect n n Slow, inefficient, inconsistent, and unfair Subtle and unique performance anomalies 3

Talk Outline n Wireless Internet Technology The Good: Wonderful Things (10 min) The Bad: Scary Things (10 min) The Ugly: Wacky Things (10 min) Summary and Conclusions n Questions? n n 4

Internet Protocol Stack n Application: supporting network applications and end-user services n n Transport: end to end data transfer n n IPv 4, IPv 6, BGP, RIP, routing protocols Data Link: frames, channel access, flow/error control n n TCP, UDP, RTP, SCTP, XTP Network: routing of datagrams from source to destination n n FTP, SMTP, HTTP, DNS, NTP, . . . PPP, Ethernet, IEEE 802. 11 a/b/g Application Transport Network Data Link Physical 001101011. . . Physical: raw transmission of bits 5

What Is Wireless Networking? n n The use of infra-red (IR) or radio frequency (RF) signals to share information and resources between devices A hot computer industry buzzword: n n Wireless Broadband, 3 G wireless, 4 G, WAP, i. Mode, Bluetooth, Wi. Fi, Wi. Max, . . . Enabler for Mobile Internet, M-Commerce, Pervasive Computing, Nomadic Computing n Ubiquitous; Global; Revolutionary 6

IEEE 802. 11 Standards Chart 7

Where does 802. 11 fit? Telnet, FTP, Email, Web, etc. Application TCP, UDP Transport IP, ICMP, IPX Network Logical Link Control - 802. 2 (Interface to the upper layer protocols) MAC Wireless lives at Layers 1 & 2 only! Data Link 802. 3, 802. 5, 802. 11 Physical Layer Convergence Protocol LAN: 10 Base. T, 10 Base 2, 10 Base. FL Physical WLAN: FHSS, DSSS, IR 8

Selected Features of 802. 11 n n Infrastructure mode and “ad hoc” mode Access Point (AP) sends “beacons” n n Multiple channel access protocols allowed n n n Choose AP based on signal strength CSMA/CA (DCF) and RTS/CTS MAC-layer can provide error control, retransmission, rate adaptation, etc. Direct Sequence Spread Spectrum (DSSS) n signal spread across 14 22 -MHz channels 9

Infrastructure Mode cnn. com Internet Access Point (AP) Carey 10

Ad Hoc Mode n Multi-hop “ad hoc” networking John Carey 11

The Good n Wi. Fi is convenient and flexible n n Wi. Fi is widely available, easy to use, and cheap (often free!); becoming social norm n n Email on the go: airports, hotels, coffee shops, … Innovative ways of deploying/using Wi. Fi n n n Supports tetherless computing, mobility Guerilla. net: power to the people! Portable networks, Community Nets, Wi. Mesh, … Wi. Fi is an enabling technology n Especially in developing regions 12

Wireless Mobility 1 1 6 11 11 1 Computers can roam between cells 13

Wi. Fi is Widely Available From www. smartmobs. com 14

Wireless Community Networks n n n Install wireless AP on your house Offer free public Internet access for your neighbours, colleagues, visitors, … “Open networks”: owned and operated by the people that use them Popular grass roots movement started years ago in Boston, San Francisco, … Cheap (free) access, and reciprocity Power to the people! 15

Portable Networks (1 of 2) n n n n Classroom area network (e. g. “legacy classroom”) Press conferences, media events Conventions and trade shows Disaster recovery sites Recruiting events Schools Voting. . . 16

Portable Networks (2 of 2) 17

Developing Regions n n Wi. Fi is an economical solution for Internet deployment in developing regions Eric Brewer, UC Berkeley n n TIER project: Technology and Infrastructure for Emerging Regions http: //tier. cs. berkeley. edu Health care, vision care, education, agricultural and economic information, … 18

The Bad n n n Wireless is a Broadcast Technology Your Network is My Network Wireless Users are Naïve Vulnerability of Personal Data WEP is Useless 19

Wireless: Broadcast Technology n n n Broadcast means “shared channel” All stations see all transmissions In normal use, stations simply ignore and discard frame transmissions that are not addressed to them In malicious use, stations can easily capture copies of all packet traffic seen using “promiscuous mode” Transmission range not easily limited (signals can pass through walls!) 20

Your Network is My Network 21

Wireless “War Driving” n n See wardriving. com Hobbyists charting wireless LANs good? evil? fun? profit? ) (for 22

Vulnerable Home Users 23

WEP: Wired Equivalent Privacy n WEP weaknesses well-documented: n n n “Your Wireless Network Has No Clothes” [Arbaugh, Shankar, and Wan 2001] “(In)Security of the WEP Algorithm” [Borisov, Goldberg, and Wagner 2001] [Fluhrer, Mantin, and Shamir 2001] show weaknesses in key scheduling algorithms Can determine WEP key in 15 minutes! Tools available on Internet (e. g. Air. Snort) 802. 11 i should improve the situation 24

The Ugly n n n Inefficiencies of IEEE 802. 11 b WLANs TCP over Wireless Networks Wireless TCP Fairness Issues TCP over Mobile Ad Hoc Networks The Wireless “Bad Apple” Phenomenon 25

Main Example: TCP n The Transmission Control Protocol (TCP) is the protocol that sends your data reliably n n Used for email, Web, ftp, telnet, … Makes sure that data is received correctly: right data, right order, exactly once Detects and recovers from any problems that occur at the IP network layer Mechanisms for reliable data transfer: n sequence numbers, ACKs, flow control, timers, retransmissions, congestion control. . . 26

Example 1: Wi. Fi Inefficiency n n n For an 11 Mbps IEEE 802. 11 b WLAN, the achievable effective throughput at the user-level is about 5. 2 Mbps Assumes single user, bulk data transfer, fast laptop, no collisions, no errors Theoretical maximum is about 60% Practical configurations rarely achieve more than about 50% efficiency Similar observations apply for 802. 11 a/g 27

Example 2: TCP over Wireless n Wireless TCP Performance Problems Low capacity, high error rate Wireless Access Wired Internet Hard to distinguish losses here from losses here High capacity, low error rate 28

Example 2: TCP over Wireless n Solution: “wireless-aware TCP” (I-TCP, Proxy. TCP, Snoop-TCP, split connections. . . ) The assumption “Loss = Congestion” no longer applies 29

Example 3: Fairness Issues n D Wireless TCP Fairness Problems DATA ACK Wireless Bottleneck Wired Internet AP U DATA ACK Loss of ACK = Loss of DATA 30

Example 4: TCP over Ad Hoc n Mobile “ad hoc” networking John Carey 31

Example 4: TCP over Ad Hoc n Mobile “ad hoc” networking John Carey 32

Example 4: TCP over Ad Hoc n Mobile “ad hoc” networking John Carey 33

Example 4: TCP over Ad Hoc n Mobile “ad hoc” networking John Carey 34

Example 4: TCP over Ad Hoc n n Problem: TCP vs Dynamic ad hoc routing Node movement can disrupt the IP routing path at any time, disrupting TCP connection Yet another way to lose packets!!! Route discovery delays are unpredictable n n can vary from 10 ms to 5 s or more [Gupta 2004] Possible solutions: n n n Explicit Loss Notification (ELN) [Balakrishnan et al. 1998] Wireless loss inference techniques [Liu et al. 2003] Fast TCP handoffs [Tan et al. 1999] 35

Example 5: Wireless Streaming Wireless Sniffer 36

Example 5: Cont’d “bad apple” phenomenon Wireless Sniffer 37

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The “Bad Apple” Phenomenon n What? One user with poor or transient wireless connectivity in the WLAN disrupts performance for everyone!!! Why? Shared broadcast WLAN; lots of MAC-layer retransmissions; FIFO server queue; Head of Line (HOL) blocking Solutions? n n n Disable MAC-layer retransmissions (yuck!) Multiple queues and packet scheduling Station-based adaptation [Cao et al. 2006] 39

Summary and Conclusions n Wireless Internet is wonderful! n n n Wireless Internet is scary n n n Affordable, convenient, and easy to use Widely available, useful, exciting, and fun Security risks, naïve users, vulnerable data “Wireless Security” is an oxymoron Wireless Internet ain’t perfect n n Slow, inefficient, inconsistent, and unfair Subtle and unique performance anomalies 40

The End n For more information: n n n Credits: n n n Email: carey@cpsc. ucalgary. ca Web URL: www. cpsc. ucalgary. ca/~carey Guangwei Bai, Jean Cao, Mingwei Gong, Abhinav Gupta, Tianbo Kuang, Hongxia Sun, Ian Wormsbecker, Qian Wu The rest of my i. CORE research team Questions? 41