The Future of Broadband Wireless (and the role of “awareness” in wireless Internet performance)
Carey Williamson iCORE Professor Department of Computer Science University of Calgary
October 16, 2002 1
Introduction
r It is an exciting time to be an Internet
researcher (or even a user!) r The last 10 years of Internet development have brought many advances:
m m m m m m
World Wide Web (WWW) Media streaming applications “Wi-Fi” wireless LANs Mobile computing E-Commerce, mobile commerce Pervasive/ubiquitous computing
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The Wireless Web
r The emergence and convergence of these
technologies enable the “wireless Web”
m m m
the wireless classroom the wireless workplace the wireless home
r Holy grail: “anything, anytime, anywhere”
access to information (when we want it, of course!) r My iCORE mandate: design, build, test, and evaluate wireless Web infrastructures
October 16, 2002 4
Clarification
“Wireless Communications”
(the enabler)
“Wireless Internet”
(the value-added service)
October 16, 2002
=
5
Internet Protocol Stack
r Application: supporting network
m
applications and end-user services
FTP, SMTP, HTTP, DNS, NTP
Application
r Transport: end to end data transfer m TCP, UDP r Network: routing of datagrams
Transport
Network
from source to destination
m
IPv4, IPv6, BGP, RIP, routing protocols
Data Link
Physical
r Data Link: hop by hop frames,
m
channel access, flow/error control
PPP, Ethernet, IEEE 802.11b
001101011...
r Physical: raw transmission of bits
October 16, 2002 6
Pieces of the Puzzle
r Portable computing devices: no problem
r
r r r
(cell phones, PDAs, notebooks, laptops…) Wireless access: not much of a problem (BlueTooth, IEEE 802.11, 802.11b, “WiFi”, 802.11a, Pringles…) Security: still an issue, but being addressed Services: the next big growth area??? Performance transparency: providing an end-user experience that is hopefully no worse than that in traditional wired Internet desktop environments (my focus)
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October 16, 2002
Research Theme
r Existing layered Internet protocol stack
does not lend itself well to providing optimal performance for diversity of service demands and environments r Who should bend: users or protocols? r Explore the role of “awareness” in Internet protocol performance r Identify tradeoffs, evaluate performance
October 16, 2002
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Talk Overview
r Introduction
r Background m Emerging Wireless Trends and Technologies m The Future of Broadband Wireless
r The Role of “Awareness”
m m m
TCP 101 Motivating Examples Our Work on CATNIP
r Concluding Remarks
October 16, 2002 9
Brief History: Cellular/Wireless
r First Generation (1G): analog
(cellular voice, AMPS, RTMS, TACS, 1980’s)
r Second Generation (2G): digital
(IS-64, GSM, ISM-95, 8-32 kbps, 1990’s) 2.5G You are here (always on, UMTS, 334 kbps-2 Mbps, 2000’s)
r Third Generation (3G): broadband multimedia
October 16, 2002
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Some Interesting Reading
r Brave New Unwired World (BNUW),
by Alex Lightman and William Rojas
r In a nutshell, the authors argue that:
m
m
2.5G is dead
3G is a waste of time (and money)
m 4G
is EVERYTHING!!!
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October 16, 2002
Another Lightman Opinion
r “the success of a technology in the
marketplace is inversely proportional to the amount of hype associated with that technology prior to its release”
Examples:
ISDN BlueTooth 3G
Examples:
Internet, Web, napster, WiFi
October 16, 2002
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What is 4G then?
r Culmination of wireless Internet revolution r Convergence of key emerging technologies:
Image Generation
802.11b
Storage technology Semiconductors
GPS Wearable Computers New Interfaces WIDs
IP-based Networks Satellite Backhaul NWs Molecular Engineering Wireless Services
October 16, 2002
Microprocessors Antenna Arrays RF elements
NanoTech Quantum
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Some Challenges/Opportunities
r Ultra low-power processors:
m
pg 108: “could change the entire industry…”
r Services: m pg 76: “extension of the Internet to mobile devices…whole new range of Internet services…personalized, location-sensitive content…previously impossible or impractical”
r Awareness: m pg 221: “Location/context-aware applications… can determine and react to current physical computing context of mobile users… altering information presented to users accordingly”
October 16, 2002 14
The Future?
r Service-centric economy
r Significant shifting of economic power
r The “winner” is likely to be either Japan
(iMODE, DoCoMo) or China (Internet growth, wireless growth) r Reasons:
m
m
cooperation, encouragement, support from government on a national scale strategic alliances within and across industries
October 16, 2002
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Talk Overview
r Introduction
r Background m Emerging Wireless Trends and Technologies m The Future of Broadband Wireless
r The Role of “Awareness”
m m m
TCP 101 Motivating Examples Our Work on CATNIP
r Concluding Remarks
October 16, 2002 16
My iCORE Research Team
r Martin Arlitt: Web performance,
r r r r
r
workload characterization Transport Qian Wu: TCP, ns-2 simulation Guangwei Bai: network traffic Network measurement and modeling Tianbo Kuang: wireless measurements, Data Link video compression, streaming media Nayden Markatchev: technical support Physical Grad Students: Mingwei Gong, Yujian Li, Kehinde Oladosu, Fang Xiao, Andreas Hirt, Abhinav Gupta, Gwen Houtzager
October 16, 2002
Application
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Internet Protocol Stack
r Application: supporting network
m
applications and end-user services
FTP, SMTP, HTTP, DNS, NTP
Application
r Transport: end to end data transfer m TCP, UDP r Network: routing of datagrams
Transport
Network
from source to destination
m
IPv4, IPv6, BGP, RIP, routing protocols
Data Link
Physical
r Data Link: hop by hop frames,
m
channel access, flow/error control
PPP, Ethernet, IEEE 802.11b
001101011...
r Physical: raw transmission of bits
October 16, 2002 18
Viewpoint
r “Layered design is good;
layered implementation is bad” -Anon. r Good:
m m
unifying framework for describing protocols modularity, black-boxes, “plug and play” functionality, well-defined interfaces (good SE)
r Bad: m increases overhead (interface boundaries) m compromises performance (ignorance)
October 16, 2002
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Research Theme
r Existing layered Internet protocol stack
does not lend itself well to providing optimal performance for diversity of service demands and environments r Who should bend: users or protocols? r Explore the role of “awareness” in Internet protocol performance r Identify tradeoffs, evaluate performance
October 16, 2002
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Tutorial: TCP 101
r The Transmission Control Protocol (TCP) is r r r r
the protocol that sends your data reliably 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: sequence numbers, acknowledgements, timers, retransmissions, flow control...
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October 16, 2002
TCP 101 (Cont’d)
r TCP is a connection-oriented protocol
SYN SYN/ACK GET URL ACK
YOUR DATA HERE
FIN ACK
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FIN/ACK
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TCP 101 (Cont’d)
r TCP slow-start and congestion avoidance
ACK
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TCP 101 (Cont’d)
r TCP slow-start and congestion avoidance
ACK
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TCP 101 (Cont’d)
r TCP slow-start and congestion avoidance
ACK
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TCP 101 (Cont’d)
r This (exponential growth) “slow start”
process continues until either of the following happens:
m
m
packet loss: after a brief recovery phase, you enter a (linear growth) “congestion avoidance” phase based on slow-start threshold found all done: terminate connection and go home
October 16, 2002
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Simple Observation
r Consider a big file transfer download:
m
brief startup period to estimate network bandwidth; most time spent sending data at the “right rate”; small added penalty for lost packet(s)
r Consider a typical Web document transfer: m median size about 6 KB, mean about 10 KB m most time is spent in startup period; as soon as you find out the network capacity, you’re done! m if you lose a packet or two, it hurts a lot!!!
October 16, 2002 27
The Problem (Restated)
r TCP doesn’t realize this dichotomy between
optimizing throughput (the classic file transfer model) versus optimizing transfer time (the Web document download model)
r Wouldn’t it be nice if it did?
(i.e., how much data it was sending, and over what type of network)
r Some research starting to explore this...
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Motivating Example #1
r Wireless TCP Performance Problems
Low capacity, high error rate
Wireless Access
Wired Internet
High capacity, low error rate
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Motivating Example #1
r Solution: “wireless-aware TCP” (I-TCP,
ProxyTCP, Snoop-TCP, ...)
October 16, 2002
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Motivating Example #2
r Multi-hop “ad hoc” networking
Janelle
October 16, 2002
Carey
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Motivating Example #2
r Multi-hop “ad hoc” networking
Janelle
Yannis
October 16, 2002
Carey
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Motivating Example #2
r Multi-hop “ad hoc” networking
Janelle
Yannis
October 16, 2002
Carey
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Motivating Example #2
r Multi-hop “ad hoc” networking
Janelle
Yannis
October 16, 2002
Carey
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Motivating Example #2
r Two interesting subproblems:
m
Dynamic ad hoc routing: node movement can disrupt the IP routing path at any time, disrupting TCP connection; yet another way to lose packets!!!; possible solution: Explicit Loss Notification (ELN)
TCP flow control: the bursty nature of TCP packet transmissions can create contention for the shared wireless channel among forwarding nodes; possible solution: rate-based flow control
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m
October 16, 2002
Example of Our Work
r Context-Aware Transport/Network
Internet Protocol (CATNIP)
r Motivation: “Like kittens, TCP connections
are born with their eyes shut” - CLW 2002
r Research Question: How much better could
TCP perform if it knew what it was trying to accomplish (e.g., Web document transfer)?
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October 16, 2002
Some Key Observations (I think)
r Not all packet losses are created equal
r TCP sources have relatively little control r IP routers have all the power!!!
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Tutorial: TCP 201
r There is a beautiful way to plot and
visualize the dynamics of TCP behaviour r Called a “TCP Sequence Number Plot” r Plot packet events (data and acks) as points in 2-D space, with time on the horizontal axis, and sequence number on the vertical axis
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SeqNum
Key: X Data Packet + Ack Packet
+ X + X + X + X + X + X + X
+ + + +
X X X X X + X X + +
Time
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TCP 201 (Cont’d)
r What happens when a packet loss occurs? r Quiz Time... m Consider a 14-packet Web document m For simplicity, consider only a single packet loss
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SeqNum
Key: X Data Packet + Ack Packet
+ X + X + X + X + X + X + + + +
?
X X X X X + X X + +
Time
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SeqNum
Key: X Data Packet + Ack Packet
+ X + X + X + X + X + X + + + +
X
+
X X X X X + X X + +
Time
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SeqNum
Key: X Data Packet + Ack Packet
X X X X X X X X + X X + + + + + +
?
X X X + + +
Time
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SeqNum
Key: X Data Packet + Ack Packet
X X X X X X
+
X +++ + + +
X X X X X + X X + +
+ + + +
Time
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SeqNum
Key: X Data Packet + Ack Packet
?
X + X
+
Time
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SeqNum
Key: X Data Packet + Ack Packet X X X X X X X X X + X + ++ + X + + + + + +
Time
October 16, 2002 46
TCP 201 (Cont’d)
r Main observation:
m
“Not all packet losses are created equal”
r Losses early in the transfer have a huge
adverse impact on the transfer latency r Losses near the end of the transfer always cost at least a retransmit timeout r Losses in the middle may or may not hurt, depending on congestion window size at the time of the loss
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The TCP Transfer “Pain Profile”
Relative Transfer Time
1
SeqNum of the Single Lost Packet
N
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Design of CATNIP
• Can we make the TCP/IP protocols “smarter” about the specific job they are trying to do? Yes. Convey application-layer context information to the TCP and IP layers
Application
Document Size Transport Packet Priority
October 16, 2002
Network
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Design of CATNIP (Cont’d)
• Q: What could a TCP source do differently? • A: If it knew how much data it had to send, and how far along it was already, then maybe… Rate-Based Pacing of the Last Window (RBPLW)
Early Congestion Avoidance (ECA)
Selective Packet Marking (SPM): Use the reserved high-order bit in the TCP header to convey packet priority information (high priority for the really crucial packets)
October 16, 2002
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Design of CATNIP (Cont’d)
• Q: What could an IP router do differently? • A: If it knew which packets were the “painful” ones to lose, then the router could… CATNIP-Good: give them preferential treatment, and avoid throwing them away (if possible) when congested
CATNIP-Bad: throw them away
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Simulation Evaluation
• Network model:
Client 1 Server 1
1.5 Mbps, 5 ms
Client 2
Server 2
RouterS
RouterC
Client 99 Client 100
Server 10
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Simulation Evaluation (Cont’d)
• Web workload model: 100 clients, 10 different Web pages Use empirically-observed distribution to determine the size, and the number of embedded images
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Simulation Evaluation (Cont’d)
• Factors and Levels:
F a cto r TC P IP L ev els R en o , R B P LW , E C A , E C A +R B P LW , S P M D ro p Tail, R E D , C A TN IP -G o o d , C A TN IP -B ad , C A TN IP -R E D
• Performance metrics: transfer time for each Web page packet loss ratio
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Simulation Results for DropTail Routers
Reno/ RBPLW Reno
Mean and Standard Deviation of Transfer Times
ECA
ECA/RBPLW
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Simulation Results for CATNIP-Good Routers
Mean and Standard Deviation of Transfer Times
Reno/DropTail
SPM/Good
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Observations
r Sources have relatively little control
r IP routers have all the power
r Adding context-awareness at the IP
routers improves both mean and standard deviation of Web page transfer times r SPM and CATNIP-Good provide most of the benefit r Advantages of CATNIP are most prominent at low levels of IP packet loss (1-5%)
October 16, 2002 57
Summary
r There seem to be performance advantages
to bending the rules regarding the Internet protocol stack layered model r The general notion of “awareness” needs to explored in a variety of contexts
m
wireless networks, ad hoc routing, TCP/IP, Web caching, mobile computing, adaptive applications, …
r Many exciting issues to explore!!
October 16, 2002 58
The Next Steps
r Putting it all together: Web + Wireless r Wireless Internet Performance Lab (UofC) r Experimental Laboratory for Internet
Systems and Applications (UofS/UofC,CFI)
r Research Collaborations: m UofC, UofS, UofA, TRLabs, CS/ECE m Nortel? HP? Cisco? Agilent? Telus Mobility?
October 16, 2002 59
The End: Question Time!
r For more information: m Email: carey@cpsc.ucalgary.ca m URL: www.cpsc.ucalgary.ca/~carey
r Many thanks to my research team and the
TeleSim Research Group at the U of C r Special thanks to iCORE, NSERC, CFI, andTelus Mobility
October 16, 2002
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