Aruna Balasubramanian Brian Neil Levine Arun Venkataramani University of Massachusetts, Amherst Enhancing Interactive Web Applications in Hybrid Networks 1

Motivation Mobile users increasingly want to access network applications on the go Cost Technologies Application support 3G Opportunistic WiFi 2

Our work How can we support a broader class of interactive applications using opportunistic WiFi access? Internet 1. Mobile-to- Infrastructure contacts 2. Mobile-to-Mobile contacts 3

Application design space Disconnection duration with AP Connection duration with AP ~1s~60s~3600s ~1s ~3600s ~60s VoIP Interactive Web? Web browsing, Web search Delay Tolerant , bulk transfer m2m contacts useful m2i contacts useful ??? 4

Outline How can opportunistic mobile-to-Infrastructure (m2i) contacts be used to support web search? Can performance be improved by simultaneously leveraging mobile-to-mobile (m2m) contacts? What is the performance of web search using opportunistic WiFi access? 5

Web search process Retrieving…. 6

Challenges: Intermittent connectivity Retrieving…. 7

Thedu: Adapting Web search for intermittently connected networks 1. Use aggressive prefetching web pages to convert interactive process to transactional 2. Prioritize prefetched web pages during bandwidth limited connection 8

Internet 1. Aggressive prefetching Thedu Proxy 9

1. Aggressive prefetching Queries from mobile node Store query Interface Google, Yahoo, Live, Ask, …. Google, Yahoo, Live, Ask, …. Snippets Prefetch Prioritized web pages Prioritized web pages Web pages returned to mobile node Related work Use prefetching to improve availability[Coda91, Jiang98, Chandra01] Proxy-based to mask disconnections [Seth06,Ott06] 10

2. Prioritizing useful web pages How many of these web pages are useful? How many web pages to prefetch? How to compare web pages from different queries? 11

How many to prefetch and how many web pages are useful?  80% users are interested in top 20 web pages  Thedu: Only prefetch webpages for top 20 url snippets  For some queries (homepage), there is only a single useful response  E.g., query “mobicom 2008” likely needs one response “  Thedu: Identify homepage queries and send only one relevant web response 12

Homepage versus Non-homepage queries Mobicom MobiCom 2008, the 14th Annual International Conference on Mobile, ACM Mobicom 2008 Mobicom MobiCom 2008, the 14th Annual International Conference on Mobile, ACM Mobicom 2008 Oil prices summer Residential natural gas prices over the same period are projected to, EIA - Short-Term Energy Outlook Oil prices summer Residential natural gas prices over the same period are projected to, EIA - Short-Term Energy Outlook 13

Thedu’s query-type classifier HomepageNon Homepage Query terms occur in URLQuery is in question form All query terms occur in title or snippet Top URL is wikipedia Less than 3 wordsLength greater than 3 words URL is root Thedu’s query-type classifier accuracy: 88% 14

How to compare web pages from different queries? Today’s search engine rank web page for a single query using relevance scores Scores not comparable across queries Queries q1, q2 q1 q2 Thedu’s query normalization technique … … … Thedu: Aggressive prefetching 1.Prefetch top 20 URLs for each query 2. Identify home page queries and return only 1 relevant web page in expectation 3.Prioritize the remaining web pages across queries by normalizing relevance scores Thedu: Aggressive prefetching 1.Prefetch top 20 URLs for each query 2. Identify home page queries and return only 1 relevant web page in expectation 3.Prioritize the remaining web pages across queries by normalizing relevance scores 15

Outline How can intermittent mobile-to-Internet (m2i) connectivity be used to support web search? Can performance be improved by simultaneously leveraging mobile-to-mobile (m2m) contacts? What is the performance of web search using opportunistic WiFi access? 16

Leveraging opportunistic m2m contacts Internet When useful? When meeting opportunities are skewed Why useful? Because of decreasing marginal utility of web pages 17

Should nodes download their own web pages or route for others? Thedu uses utility-based routing. W X Y y1y2 … x1x2 … w1w2 … w1w2 … x1x2w3y1 Sorted according to utility 18

Utility computation: IR meets networking Goal: Maximize number of relevant responses delivered within a deadline Utility of routing X or Y’s web page P(web page is relevant) x P(W can deliver the web page to destination within deadline) Utility of downloading own web page P(web page is relevant) x P(web page will NOT be delivered to W within deadline if the opportunity is missed) W X Y 19

m2m routing between mobile nodes Deliver web pages destined to peer Route other web pages using similar utility-based routing Exploit query locality by caching popular web pages W X Thedu leverages m2m contacts 1. Using a utility-driven routing protocol 2. Exploiting caching Thedu leverages m2m contacts 1. Using a utility-driven routing protocol 2. Exploiting caching 20

Outline Can intermittent mobile-to-Internet (m2i) connectivity be used to support web search? Can performance be improved by simultaneously leveraging mobile-to-mobile (m2m) contacts? How does Thedu perform in practice? 21

Evaluation goals Does Thedu improve performance of web search for opportunistic WiFi networks? Is there a benefit for leveraging m2m contacts? Evaluation based on deployment of Thedu on DieselNet testbed and trace-driven simulations 22

Evaluation tools: Networking and IR DieselNet Testbed at UMass Search engine 10 GB web collection, Large user study 23

DieselNet: Both m2i and m2m contacts m2m meeting m2i meeting 24

Web search deployment results Relevant Web pages delivered 25

Delay in receiving relevant web page 26

Effect of m2i meeting frequency on web search performance Deployment: March, 2007 Trace-driven: Nov,

Leveraging m2m contacts On DieselNet, leveraging m2m contacts provide little benefit Ratio of m2i versus m2m contacts is 20:1 Our analytical model confirms result Leveraging m2m routing is useful only if AP density is low 28

Leveraging m2m contacts: Sparse AP Leveraging m2m contacts provides throughput benefit, but not delay does not improve performance of interactive applications, even in sparse AP scenarios 29

Conclusions Thedu enables interactive web search application for intermittently connected networks Leveraging m2m contacts only provides throughput benefits and only when AP density is low Deployment of Thedu on DieselNet shows 3 times improvement in number of relevant web pages trace.cs.umass.edu 30