october 16, 2002 1 the future of broadband wireless (and the role of “awareness” in wireless...
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October 16, 2002 1
The Future of Broadband Wireless
(and the role of “awareness” inwireless Internet performance)
Carey WilliamsoniCORE Professor
Department of Computer ScienceUniversity of Calgary
October 16, 2002 2
Introduction
It is an exciting time to be an Internet researcher (or even a user!)
The last 10 years of Internet development have brought many advances: World Wide Web (WWW) Media streaming applications “Wi-Fi” wireless LANs Mobile computing E-Commerce, mobile commerce Pervasive/ubiquitous computing
October 16, 2002 3
October 16, 2002 4
The Wireless Web
The emergence and convergence of these technologies enable the “wireless Web” the wireless classroom the wireless workplace the wireless home
Holy grail: “anything, anytime, anywhere” access to information (when we want it, of course!)
My iCORE mandate: design, build, test, and evaluate wireless Web infrastructures
October 16, 2002 5
Clarification
“Wireless Communications”
“Wireless Internet”=
(the enabler)
(the value-added service)
October 16, 2002 6
Internet Protocol Stack Application: supporting network
applications and end-user services FTP, SMTP, HTTP, DNS, NTP
Transport: end to end data transfer TCP, UDP
Network: routing of datagrams from source to destination IPv4, IPv6, BGP, RIP, routing protocols
Data Link: hop by hop frames, channel access, flow/error control PPP, Ethernet, IEEE 802.11b
Physical: raw transmission of bits
Application
Transport
Network
Data Link
Physical
001101011...
October 16, 2002 7
Pieces of the Puzzle Portable computing devices: no problem
(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)
October 16, 2002 8
Research Theme
Existing layered Internet protocol stack does not lend itself well to providing optimal performance for diversity of service demands and environments
Who should bend: users or protocols? Explore the role of “awareness” in
Internet protocol performance Identify tradeoffs, evaluate performance
October 16, 2002 9
Talk Overview
Introduction Background
Emerging Wireless Trends and Technologies The Future of Broadband Wireless
The Role of “Awareness” TCP 101 Motivating Examples Our Work on CATNIP
Concluding Remarks
October 16, 2002 10
Brief History: Cellular/Wireless
First Generation (1G): analog (cellular voice, AMPS, RTMS, TACS, 1980’s)
Second Generation (2G): digital (IS-64, GSM, ISM-95, 8-32 kbps, 1990’s)
Third Generation (3G): broadband multimedia (always on, UMTS, 334 kbps-2 Mbps, 2000’s)
2.5G You are here
October 16, 2002 11
Some Interesting Reading
Brave New Unwired World (BNUW), by Alex Lightman and William Rojas
In a nutshell, the authors argue that:2.5G is dead
3G is a waste of time (and money)
4G is EVERYTHING!!!
October 16, 2002 12
Another Lightman Opinion
“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:ISDNBlueTooth3G
Examples:Internet,Web,napster,WiFi
October 16, 2002 13
What is 4G then? Culmination of wireless Internet revolution Convergence of key emerging technologies:
IP-based Networks
Satellite
Wireless Services
Semiconductors
MicroprocessorsWIDsNew Interfaces
Wearable Computers
NanoTechMolecular Engineering
Backhaul NWs RF elements
Storage technologyImage Generation
Quantum
Antenna Arrays
GPS
802.11b
October 16, 2002 14
Some Challenges/Opportunities Ultra low-power processors:
pg 108: “could change the entire industry…” Services:
pg 76: “extension of the Internet to mobile devices…whole new range of Internet services…personalized, location-sensitive content…previously impossible or impractical”
Awareness: 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 15
The Future?
Service-centric economy Significant shifting of economic power The “winner” is likely to be either Japan
(iMODE, DoCoMo) or China (Internet growth, wireless growth)
Reasons: cooperation, encouragement, support from
government on a national scale strategic alliances within and across
industries
October 16, 2002 16
Talk Overview
Introduction Background
Emerging Wireless Trends and Technologies The Future of Broadband Wireless
The Role of “Awareness” TCP 101 Motivating Examples Our Work on CATNIP
Concluding Remarks
October 16, 2002 17
My iCORE Research Team
Martin Arlitt: Web performance, workload characterization
Qian Wu: TCP, ns-2 simulation Guangwei Bai: network traffic
measurement and modeling Tianbo Kuang: wireless measurements,
video compression, streaming media Nayden Markatchev: technical support Grad Students: Mingwei Gong, Yujian Li,
Kehinde Oladosu, Fang Xiao, Andreas Hirt, Abhinav Gupta, Gwen Houtzager
Application
Transport
Network
Data Link
Physical
October 16, 2002 18
Internet Protocol Stack Application: supporting network
applications and end-user services FTP, SMTP, HTTP, DNS, NTP
Transport: end to end data transfer TCP, UDP
Network: routing of datagrams from source to destination IPv4, IPv6, BGP, RIP, routing protocols
Data Link: hop by hop frames, channel access, flow/error control PPP, Ethernet, IEEE 802.11b
Physical: raw transmission of bits
Application
Transport
Network
Data Link
Physical
001101011...
October 16, 2002 19
Viewpoint
“Layered design is good; layered implementation is bad” -Anon.
Good: unifying framework for describing protocols modularity, black-boxes, “plug and play”
functionality, well-defined interfaces (good SE)
Bad: increases overhead (interface boundaries) compromises performance (ignorance)
October 16, 2002 20
Research Theme
Existing layered Internet protocol stack does not lend itself well to providing optimal performance for diversity of service demands and environments
Who should bend: users or protocols? Explore the role of “awareness” in
Internet protocol performance Identify tradeoffs, evaluate performance
October 16, 2002 21
Tutorial: TCP 101
The Transmission Control Protocol (TCP) is 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...
October 16, 2002 22
TCP 101 (Cont’d)
TCP is a connection-oriented protocol
SYNSYN/ACK
ACKGET URL
YOUR DATA HERE
FIN FIN/ACKACK
October 16, 2002 23
TCP 101 (Cont’d)
TCP slow-start and congestion avoidance
ACK
October 16, 2002 24
TCP 101 (Cont’d)
TCP slow-start and congestion avoidance
ACK
October 16, 2002 25
TCP 101 (Cont’d)
TCP slow-start and congestion avoidance
ACK
October 16, 2002 26
TCP 101 (Cont’d)
This (exponential growth) “slow start” process continues until either of the following happens: 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 27
Simple Observation
Consider a big file transfer download: brief startup period to estimate network
bandwidth; most time spent sending data at the “right rate”; small added penalty for lost packet(s)
Consider a typical Web document transfer: median size about 6 KB, mean about 10 KB most time is spent in startup period; as soon as
you find out the network capacity, you’re done! if you lose a packet or two, it hurts a lot!!!
October 16, 2002 28
The Problem (Restated)
TCP doesn’t realize this dichotomy between optimizing throughput (the classic file transfer model) versus optimizing transfer time (the Web document download model)
Wouldn’t it be nice if it did? (i.e., how much data it was sending, and over what type of network)
Some research starting to explore this...
October 16, 2002 29
Motivating Example #1
Wireless TCP Performance Problems
Wired Internet
WirelessAccess
Highcapacity,lowerrorrate
Low capacity,high error rate
October 16, 2002 30
Motivating Example #1
Solution: “wireless-aware TCP” (I-TCP, ProxyTCP, Snoop-TCP, ...)
October 16, 2002 31
Motivating Example #2
Multi-hop “ad hoc” networking
Carey
Janelle
October 16, 2002 32
Motivating Example #2
Multi-hop “ad hoc” networking
Carey
Janelle
Yannis
October 16, 2002 33
Motivating Example #2
Multi-hop “ad hoc” networking
Carey
Janelle
Yannis
October 16, 2002 34
Motivating Example #2
Multi-hop “ad hoc” networking
Carey
Janelle
Yannis
October 16, 2002 35
Motivating Example #2
Two interesting subproblems: 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
October 16, 2002 36
Example of Our Work
Context-Aware Transport/Network Internet Protocol (CATNIP)
Motivation: “Like kittens, TCP connections are born with their eyes shut” - CLW 2002
Research Question: How much better could TCP perform if it knew what it was trying to accomplish (e.g., Web document transfer)?
October 16, 2002 37
Some Key Observations (I think)
Not all packet losses are created equal
TCP sources have relatively little control
IP routers have all the power!!!
October 16, 2002 38
Tutorial: TCP 201
There is a beautiful way to plot and visualize the dynamics of TCP behaviour
Called a “TCP Sequence Number Plot” 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
October 16, 2002 39
Time
Seq
Num
X +
Key: X Data Packet + Ack Packet X
XXXX
XXXX
XX
XX
++
++++
+
++++
++
October 16, 2002 40
TCP 201 (Cont’d)
What happens when a packet loss occurs?
Quiz Time... Consider a 14-packet Web document For simplicity, consider only a single packet
loss
October 16, 2002 41
Time
Seq
Num
X +
Key: X Data Packet + Ack Packet X
XXXX
XXXX
XX
X
++
++++
+
+++
++
?
October 16, 2002 42
Time
Seq
Num
X +
Key: X Data Packet + Ack Packet X
XXXX
XXXX
XX
X
++
++++
+
+++
++
X +
October 16, 2002 43
Time
Seq
Num
X +
Key: X Data Packet + Ack Packet X
XXX
XXXX
XX
XX
++
++++
+
++
?
October 16, 2002 44
Time
Seq
Num
X +
Key: X Data Packet + Ack Packet X
XXX
XXXX
XX
XX
++
++++
+
+++++
X
+
October 16, 2002 45
Time
Seq
Num
X +
Key: X Data Packet + Ack Packet
X +?
October 16, 2002 46
Time
Seq
Num
X +
Key: X Data Packet + Ack Packet
XX
X + ++
XXXX +
+++
X
XX +
+
+
October 16, 2002 47
TCP 201 (Cont’d)
Main observation: “Not all packet losses are created equal”
Losses early in the transfer have a huge adverse impact on the transfer latency
Losses near the end of the transfer always cost at least a retransmit timeout
Losses in the middle may or may not hurt, depending on congestion window size at the time of the loss
October 16, 2002 48
The TCP Transfer “Pain Profile”
SeqNum of the Single Lost Packet1 N
Rel
ativ
e T
rans
fer
Tim
e
October 16, 2002 49
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
Network
Transport
Application
Document Size
Packet Priority
October 16, 2002 50
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 51
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
October 16, 2002 52
Simulation Evaluation
• Network model:
Client 100
Server 1
Server 2
Server 10
Client 1
Client 2
Client 99
1.5 Mbps, 5 ms
10 Mbps, 5 ms 10
Mbp
s, 5 m
s
10 M
bps,
5 m
s 10 Mbps, 5 m
s
RouterS RouterC
October 16, 2002 53
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
October 16, 2002 54
Simulation Evaluation (Cont’d)
• Factors and Levels:Factor Levels
TCP IP
Reno, RBPLW, ECA, ECA+RBPLW, SPM DropTail, RED, CATNIP-Good, CATNIP-Bad, CATNIP-RED
• Performance metrics:
transfer time for each Web page
packet loss ratio
October 16, 2002 55
Simulation Results for DropTail Routers
Reno/ RBPLWReno
ECA
ECA/RBPLW
Mean and Standard Deviation of Transfer Times
October 16, 2002 56
Simulation Results for CATNIP-Good Routers
Mean and Standard Deviation of Transfer Times Reno/DropTail
SPM/Good
October 16, 2002 57
Observations
Sources have relatively little control IP routers have all the power Adding context-awareness at the IP
routers improves both mean and standard deviation of Web page transfer times
SPM and CATNIP-Good provide most of the benefit
Advantages of CATNIP are most prominent at low levels of IP packet loss (1-5%)
October 16, 2002 58
Summary
There seem to be performance advantages to bending the rules regarding the Internet protocol stack layered model
The general notion of “awareness” needs to explored in a variety of contexts wireless networks, ad hoc routing, TCP/IP,
Web caching, mobile computing, adaptive applications, …
Many exciting issues to explore!!
October 16, 2002 59
The Next Steps
Putting it all together: Web + Wireless
Wireless Internet Performance Lab (UofC)
Experimental Laboratory for Internet Systems and Applications (UofS/UofC,CFI)
Research Collaborations: UofC, UofS, UofA, TRLabs, CS/ECE Nortel? HP? Cisco? Agilent? Telus Mobility?
October 16, 2002 60
The End: Question Time!
For more information: Email: [email protected] URL: www.cpsc.ucalgary.ca/~carey
Many thanks to my research team and the TeleSim Research Group at the U of C
Special thanks to iCORE, NSERC, CFI, andTelus Mobility