1 1 2 4 21 4 22 7 221 7 222 9 223 9 3 11 31 12 32 12 33 (Prefetching Parameters)13 34 (Web Traffic Trace)14 35 (Prefetching Time)18 36 (Performance Metrics)19 4 21 41 Prefetchable Object List Generator 22 i
411 HTTP/10 Response Header 24 412 HTTP/11 Request Header 27 413 Squid 29 414 Freshness 32 42 Request Generator 36 5 37 51 37 52 38 53 39 6 41 61 Accuracy41 62 Wasted Bandwidth46 63 Request Saving 47 64 Bandwidth Saving 49 65 Summary51 7 55 [ ] 57 ii
1 1 2 2 3 16 4 17 5 17 6 17 7 18 8 21 9 Prefetchable Object List 23 10 HTTP/10 Response Header 24 11 Cache-Control General Header Field 28 12 30 13 31 14 STALE 32 15 Access Log Format 33 16 Store Log Format 34 17 35 18 40 19 42 iii
20 43 21 44 22 44 23 45 24 Off-peak Periods 47 25 48 26 50 27 Peak Periods 51 iv
1 Cache Summary Statistics 15 2 15 3 16 4 42 5 43 6 45 7 46 8 Off-peak Periods 47 9 48 10 Cache Byte Hit Ratio with and without Prefetching 49 11 Peak Periods 50 12 Performance Mateics 51 13 Peak Periods Off-peak Periods 52 14 Peak Periods 53 v
vi
MCC 9851M08, Sook-Hyang Kim, A Statistical, Batch and Proxy-Initiated Web Prefetching Scheme for Efficient Internet Bandwidth Usage,,, 2000, 60P, Advisor: J Won-Ki Hong, Text in Korean ABSTACT As the number of World-Wide Web (Web) users grows, Web traffic continues to increase at an exponential rate Currently, Web traffic is one of the major components of Internet traffic Also, high bandwidth usage due to Web traffic is observed during peak periods while leaving bandwidth usage idle during off-peak periods One of the solutions to reduce Web traffic and speed up Web access is through the use of Web caching Unfortunately, Web caching has limitations for reducing network bandwidth usage during peak periods In this thesis, we focus our attention on the use of a prefetching algorithm for reducing bandwidth during peak periods by using off-peak period bandwidth We propose a statistical, batch, proxy-side prefetching algorithm that improves cache hit rate while only requiring a small amount of storage We present simulation results based on Web proxy trace and show that this prefetching algorithm can reduce peak time bandwidth using off-peak bandwidth
1 World Wide Web( ),,, [20, 21], (Internet traffic) (Web traffic) (bottleneck) [25, 26] (bandwidth) peak periods, off-peak periods 1 16 subnet 2 (1999 10 15 1999 10 28 ), 2 1 1
2 (156624826 byte) peak periods off-peak periods peak periods 14:00 16:00 18:00 04:00, 12 off-peak periods 04:00 14:00 16:00 18:00 12 1 2 peak periods off-peak periods peak periods off-peak periods, (Web caching) [10], [11, 12], 2
[7, 27, 28] peak peiods off-peak periods, off-peak periods peak periods [4, 5, 11] (caching server) (Web prefethcing) peak periods off-peak periods,, off-peak periods peak periods 2 3 4 5, 6 7 3
4 2 21,, Padmanabhan Mogul [2] (prediction) (prediction algorithm) Griffioen Appletion[13],
hyperlink dependency graph graph A B A B arc (edge) arc A B dependecy graph (Web server traces) trace-driven 45% 2 Wang Crowcroft HotList Manager delay [1] deterministic client-initiated prefetching, Deterministic prefetching Bestavros Server-initiated prefetching [14] D i, D j Bestavros D i time interval T w D j p[i,j] advice Bestavros trace-driven 10% 23% cache miss rate 5
Kroeger, 60% [15] Chinen Yamaguchi Wcol [3, 17] HTML (parsing) - (pre-pushing) Wcol 246 167 281 Jacobson Cao - [18] - (push) (Web access traces) (overhead) (accuracy) - (pre-push scheme) - 10% 18%, (request) 12% Makatos 6
Chronak Top-10 Approach [16, 24] client-proxy-server framework Top-10 (Web server trace), 10% 40%,,, 22,, 221,, 7
Server-initiated prefetching :, hyperlink (pushing) [2, 14, 15], Client-initiated prefetching : (agent) [1, 2, 13] Client-initiated prefetching (Web access pattern) Proxy-initiated prefetching :, [3, 17, 18] 8
222 (statistical prefetching)[5, 8, 9] (deterministic prefetching) [1] Statistical prefetching : (access log) Deterministic prefetching :, 223 (response time) 9
Prefetching for Response Time Reduction :, [2, 5, 13, 16, 18] peak periods Prefetching for Balanced Bandwidth Usage : peak periods off-peak periods Batch prefetching balanced bandwidth usage 10
3 Server-initiated Prefetching Client-initiated Prefetching peak bandwidth usage, (parameter) real-world traffic pattern 16 (subnet) (performance metrics) 11
31??,???? 32?? ( :, 1 )??, (accuracy) prefetchable objects 12
(expiration time) (cache miss)?? 33 (Prefetching Parameters),,,,??,?? Traditional prefetching scheme n 13
?? 100M?? off-peak periods peak periods off-peak periods off-peak periods off-peak periods 35 34 (Web Traffic Trace) real-world traffic pattern 16 (subnet) 1999 10 15 ( ) 10 28 ( ) 2 2 447 (cache object hit rate) 5496% (cache byte hit rate) 3142% (request) 4,077,308 total bytes 502G 291236 bytes 36G 1 14
1 Cache Summary Statistics Number of Client Making Requests 447 Cache Object Hit Rate 5496 % Cache Byte Hit Rate 3142 % Total Number of Objects Requested 4,077,308 Total Bytes to Clients 502 Gbyte 2 (reference count) 7075% 2 2925% 121,883 3 2 (%) 1 86,227 7075 2 16,690 1369 3 6,462 53 4 3,451 283 5 9,053 743 Total 121,883 100 15
3 3 3 total size 1 6812%, 2 3188% total bytes 217227 Mbyte 4 3 (Mbyte) (%) 1 147975 6812 2 31079 1431 3 11820 544 4 7401 341 5 18952 872 Total 217227 100 16
4 5 6 total bytes 5 6 17
35 (Prefetching Time) off-peak periods peak periods off-peak periods off-peak periods off-peak periods off-peak periods off-peak periods off-peak periods 80% (125299861 byte) off-peak peirods off-peak periods 04:00 13:00, peakperiods 13:00 04:00 off-peak periods off-peak periods (04:00 13:00) prefetchable object 7 80% 7 18
36 (Performance Metrics),?? Request Saving : hit Request saving?? Bandwidth Saving : Bandwidth saving peak periods bandwidth usage peak periods peak periods?? Accuracy : accuracy (prefetched object hit rate) (prefetched byte hit rate) total bytes total bytes Accuracy?? Wasted Bandwidth : 19
offpeak periods off-peak periods 20
4 8 Prefetching system Caching Server prefetchable object list Prefetchable Object List Generator accesslog storelog cache Request Generator Caching Server clients request response request response request response Internet 8, Squid[7] Squid freeware, Cobalt Network CacheRaQ[29] Packetstorm Technologies Webspeed[30] Squid Squid 21
Squid transparent Transparent (browser) (data path) [31] configuration default gateway Prefetchable Object List Generator Request Generator (Squid) Squid, Squid request access log, store log squid (accesslog, storelog) Prefetchable Object List Generator prefetchable object list Request Generator off-peak periods prefetchable object list (request) Squid Squid add-on 41 Prefetchable Object List Generator Prefetchable Object List Generator 22
Squid access log store log access log Squid requests store log Prefetch Object List Generator Squid (refresh algorithm) prefetchable object HTTP response message Squid (3 days) [7] 9 prefetchable object list 9 Prefetchable Object List Prefetchable Object List Generator Squid, store log store log HTTP response header HTTP response header HTTP request header Squid 23
411 HTTP/10 Response Header HTTP [22, 23, 33] / (Request/Response), ( : GET, HEAD, POST) TCP,, TCP HTTP method, URI, protocol version,,,,,, HTTP response header HTTP/10 response header 10 Full-Response = Status-Line *(General-Header Response-Header Entity-Header) CRLF [Entity-Body] Status-Line = HTTP-Version Status-Code Reason-Phrase CRLF General-Header = Date Progma Response-Header = Location Server WWW-Authenticate Entity-Header = Allow Content-Encoding Content-Length Content-type Expires Last-Modified extension-header extension-header = HTTP-header 10 HTTP/10 Response Header 24
Full-Response Status-Line HTTP (Status-Code) (Reason-Phrase) CRLF Entity CRLF Status-Code?? 1xx : Informational -?? 2xx : Success -?? 3xx : Redirection -?? 4xx : Client Error -?? 5xx : Server Error - (response message), General-Header, Request-Header, Response-Header, Entity-Header RFC 822 31 [32] 25
General Header Full-Request Full-Response, General Header Date Progma Date Progma / Response Header Status-Line Request-URI Entity-Header Entity-Body,,, (metainformation), entity body Squid HTTP response header?? Date : General Header Date, RFC 822[32] orig-date Date : Wed, 15 Oct 1999 08:12:31 GMT?? Expires : Entity Header Expires, 26
Expires Expires : Mon, 01 Nov 1999 16:00:00 GMT?? Last-Modified : Entity Header Last-Modified Last-Modified Last-Modified : Tue, 14 Oct 1999 12:45:26 GMT 412 HTTP/11 Request Header HTTP/10, URL TCP / / congestion congestion 27
, HTTP/11 [23] HTTP/11, Squid Cache-Control Request Header max-age HTTP/10 HTTP HTTP/11, HTTP/11 General Header Cache-Control Cache-Control (directive) (cache directive) Cache-Control 11 11 cache-response-diective Cache-Control Cache-Control = "Cache-Control" ":" 1#cache-directive cache-directive = cache-request-directive cache-response-directive cache-request-directive = "no-cache" "no-store "max-age" "=" delta-seconds "max-stale" [ "=" delta-seconds ] "min-fresh" "=" delta-seconds "no-transform" "only-if-cached" cache-extension cache-extension = token [ "=" ( token quoted-string ) ] 11 Cache -Control General Header Field 28
cache-request-directive max-age Squid (maximum object age) max-age, max-age max-age Squid CLIENT_MAX_AGE 413 Squid, (expiration time) (cache miss) Squid 13 Squid default value OBJ_DATE OBJ_LASTMOD Expires OBJ_DATE, OBJ_LASTMOD, Expires HTTP Respons Header [22] CLIENT_MAX_AGE HTTP/11 Cache-Control Request Header 29
[23] Squid refresh_pattern CONF_MIN, CONF_PERCENT, CONF_MAX squidconf HTTP Response Header Expires default Expires [7] NOW, OBJ_AGE LM_AGE LM_FACTOR OBJ_AGE LM_AGE 12 OBJ_DATE, Expires, OBJ_LASTMOD millisecond UNIX time ( : Fri Oct 15 04:00:27 1999 GMT = 939927627725) CLIENT_MAX_AGE, OBJ_AGE, LM_AGE, LM_FACTOR second CONF_MAX CONF_MIN minute CONF_PERCENT % OBJ_DATE Expires OBJ_LASTMOD : : : CLIENT_MAX_AGE : OBJ_AGE = NOW - OBJ_DATE (sec) LM_AGE = OBJ_DATE - OBJ_LASTMOD (sec) LM_FACTOR = OBJ_AGE / LM_AGE (sec) CONF_MAX CONF_MIN : 4320 (min, 3 days) : 0 (min) CONF_PERCENT : 02 (20%) 12 30
Is CLIENT_MAX_AGE present in the request? yes Is OBJ_AGE more than CLIENT_MAX_AGE? yes STALE(1) no no Is Expires present in the response? yes Has the object already expired? yes no STALE(2) FRESH no Is OBJ_AGE more than CONF_MAX? yes STALE(3) no Is OBJ_DATE more than OBJ_LASTMOD? yes LM_FACTOR less than the CONF_PERCENT? yes no FRESH STALE(4) no Is OBJ_AGE less than CONF_MIN? yes no FRESH STALE(5) 13 14 STALE 5 Expires, OBJ_DATE, OBJ_LASTMOD, NOW HTTP CLIENT_MAX_AGE 100 sec OBJ_AGE 120 sec OBJ_AGE CLIENT_MAX_AGE STALE (STALE(1)) Expires NOW, (STALE(2)) OBJ_AGE CONF_MAX (STALE(3)) 3 OBJ_DATE OBJ_LASTMOD LM_FACTOR (30%) CONF_PERCENT (20%) (STALE(4)) 31
OBJ_AGE (5760 min) CONF_MIN (0 min) STALE (STALE(5)) STALE(1) CLIENT_MAX_AGE : 100 (sec) OBJ_AGE : 120 (sec) STALE(2) EXPIRES : Fri, 01 Oct 1999 16:00:00 GMT NOW : Sun, 03 Oct 1999 12:01:20 GMT STALE(3) OBJ_AGE : 5760 min (4 days) CONF_MAX :4320 min (3 days) STALE(4) OBJ_LASTMOD : Wed, 29 Sep 1999 16:00:00 GMT OBJ_DATE : Fri, 01 Oct 1999 16:00:00 GMT LM_FACTOR : 30 % CONF_PERCENT : 20 % STALE(5) OBJ_AGE : 5760 min (4 days) CONF_MIN : 0 min 14 STALE 414 Freshness FRESH, STALE STALE squid OBJ_DATE, 32
OBJ_LASTMOD, Expires squid storelog, CONF_MAX, CONF_MIN, CONF_PERCENT squid squidconf CLIENT_MAX_AGE 15 Squid access log, 16 Squid store log 15 Access Log Format?? Time UNIX time milliseconds?? Elapsed (connection)?? Remotehost IP?? Code/Status Code ( : TCP_HIT, TCP_MISS, etc) Status HTTP status code?? Byte?? Method HTTP request Method ( : GET, HEAD, POST)?? URL URL 33
Time Action Status OBJ_DATE OBJ_LASTMOD Expires Type Len Method URL 16 Store Log Format store log Time, Status, Method, URL access log OBJ_DATE, OBJ_LASTMOD, Expires 413?? Action RELASE, SWPIN, SWPOUT RELASE SWAPOUT SWAPIN?? Type, text/html, image/gif?? Len expect-len real-len, expect-len HTTP Content-Length Response Header, real-len NOW, fresh stale access log stale stale Squid NOW 34
NOW? Current Pr efetchngtime? PrefetchingFrequency Current PrefetchingTime : Pr efetchingfrequency : off-peak periods (prefetching frequency) 17 10 15 04 16 04, 17 04 (16 04:00) 10 15 04:00 10 16 04:00 access log store log Last prefetching time Currnt Prefetching time Next prefetching time Input Data (logs) Prefetching Frequency 10/15 4:00 10/16 4:00 10/17 4:00 17 35
42 Request Generator Request generator Prefetchable Obejct List off-peak periods Prefetchable Object List Generator Prefetchable Object List request off-peak periods request HTTP command-line Web client wget [19] crontab off-peak periods Request Generator Off-peak periods off-peak WAN SNMP agent SNMP agent (polling), 36
5 (input parameter) 51 trace-driven CacheRaQ[29] 16 (subnet) Squid (input parameter)?? Logs : 1999 10 15 10 28 2 access log store log?? Off-peak periods : 35 off-peak periods 04:00 13:00 04:00 37
?? : 33 52?? : Squid, 413 NOW 414 52 (Web traffic trace),, (Prefetchable Web Objects) (expiration time) 1, 2, 3, 4, 5 38
off-peak periods 53 18 Prefetchable Object List Generator off-peak periods prefetchable object list performance analyzer prefetchable object list request saving bandwidth saving accracy wasted bandwidth Prefetchable Object List Generator access log store log prefetchable object list 39
Simulation Model accesslog storelog Prefetchable Object List Generator Prefetchable Object List Performance Analyzer Performance Metrics With Prefetching Performance Metrics Without Prefetching 18 Performance Analyzer prefetchable object list access log prefetchable object list access log request saving ( ), bandwidth saving ( ) accuracy (, ) access log wasted bandwidth request saving bandwidth saving accuracy wasted bandwidth 40
6 3 accuracy wasted bandwidth, performance parameter request saving bandwidth saving 61 Accuracy Accuracy 4 10 15 10 28 daily prefetchable object list 10 16 10 29 1 1522% 5 8714% 1 prefetchable object 5064% 1955% linear 41
4 (%) (%) 1 16,274 (5064 %) 2,476 (1955 %) 1522 % 2 5,525 ( 172 %) 2,286 (1805 %) 4138 % 3 3,008 ( 936 %) 1,804 (1424 %) 5996 % 4 1,966 ( 612 %) 1,430 (1129 %) 7276 % 5 5,358 (1668 %) 4,469 (3687 %) 8714 % Total 32,131 (10000 %) 12,665 (10000 %) 3942 % 19 prefetched object hit 20 19 42
20 5 1 868% 5 7264% accuracy 5 (%) (%) 1 545,399,428 (6343%) 47,336,276 (2502%) 868 % 2 154,356,860 (1795%) 56,170,230 ( 297%) 3639 % 3 64,124,072 ( 746%) 25,570,556 (1352%) 3989 % 4 33,972,272 ( 395%) 15,026,692 ( 794%) 4423 % 5 62,024,975 ( 721%) 45,057,416 (2382%) 7264 % Total 859,877,607 (100%) 189,161,170 (100%) 22 % 21 43
22 21 22 6 1, 2, 3, 4 5 44
2 6426% 1 3942%25% 2 461% 1 22% 23 6 1 394 % 22 % 2 643 % 451% 3 765 % 535 % 4 833 % 626 % 5 871 % 726 % 23 45
62 Wasted Bandwidth Wasted bandwidth 7 1 67072 Mbyte (3775043 Mbyte) 178% 2 17265 Mbyte 46% 2 1 4 7 1 67072 M 178 % 2 17265 M 46 % 3 7447 M 20 % 4 3591 M 10 % 5 1697 M 05 % off-peak periods off-peak periods off-peak 796356 Mbyte 1 off-peak 519%, off-peak periods 2 283%, 3 167%, 4 108%, 5 72% 8 off-peak periods 24 46
8 Off-peak Periods Off-peak periods 1 519 % 2 283 % 3 167 % 4 108 % 5 72 % 24 Off-peak Periods 63 Request Saving 9 55%, 1 47
43% 593% 2 353 %, 3 272%, 4 21%, 5 161% 1 2 077% 9 ( ) 55 % ( + ) ( 1 ) 593 % ( + ) ( 2 ) 585 % ( + ) ( 3 ) 577 % ( + ) ( 4 ) 571 % ( + ) ( 5 ) 567 % 25 25 48
64 Bandwidth Saving 10 314%, 1 501%, 2 378 %, 3 227%, 4 159%, 5 119% 1 2 123% 10 ( ) 314 % ( + ) ( 1 ) 364 % ( + ) ( 2 ) 352 % ( + ) ( 3 ) 337 % ( + ) ( 4 ) 330 % ( + ) ( 5 ) 326 % 26 Request saving 49
26 peak periods 11 peak periods 27 11 Peak Periods Peak periods 1 64 % 2 48 % 3 29 % 4 20 % 5 15 % 50
27 Peak Periods 65 Summary 12 Request saving 12 Performance Mateics Bandwidth saving Wasted bandwidth Prefetched object hit rate Accuracy Prefetched byte hit rate 1 430 % 501 % 178 % 394 % 22 % 2 353 % 378 % 46 % 643 % 451% 3 272 % 227 % 20 % 765 % 535 % 4 210 % 159 % 10 % 833 % 626 % 5 162 % 119 % 05 % 871 % 726 % off-peak periods peak periods 51
off-peak periods peak periods 13 13 Peak Periods Off-peak Periods Peak periods off-peak periods 1 64 % 519 % 2 48 % 283 % 3 29 % 167 % 4 20 % 108 % 5 15 % 72 % E p? B s / B w E B B s p w : : ( Mbyte) : ( Mbyte) 1, 2, 3, 4, 5, 52
peak periods peak periods peak periods peak periods 4% peak periods 14 14 Peak Periods B s (Mbyte) B w (Mbyte) E p (Mbyte) Peak periods 1 18916 67072 028 64 % 2 14182 17265 082 48 % 3 8565 7447 115 29 % 4 6008 3591 167 20 % 5 4506 1697 266 15 % 14 peak periods 4% 1, 2 2 082 1 028 2 peak periods 4% 2 53
2 141,824,895 bytes peak periods 54,000 seconds (19 hours) peak periods peak periods = (141824895*8)/54000 = 2052 Kbps 2 peak periods 2052 Kbps 54
7 peak periods, off-peak periods peak periods request saving 353% bandwidth saving 378% 2 6426%, 451% peak bandwidth usage 2052 Kbps peak periods prefetching scheme squid add-on feature 55
Web traffic trace off-peak periods (eg, 20:00~08:00),, real-time prefetchable object list 56
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