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: carey@cpsc.ucalgary.ca 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