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set tmp [new RandomVariable/Exponential]$tmp set avg_ 5$pgp ranvar-age $tmp;## Page age generator;## average page age;## Create a server and link it to the cen-;## Create a cache;## Create a client;## Poisson process as request sequence;## average request interval;## simulation start time;## simulation end timeset server [new Http/Server $ns $node(s)]tral page pool$server set-page-generator $pgp$server log $logset cache [new Http/Cache $ns $node(e)]$cache log $logset client [new Http/Client $ns $node(c)]set tmp [new RandomVariable/Exponential]$tmp set avg_ 5$client set-interval-generator $tmp$client set-page-generator $pgp$client log $logset startTime 1set finishTime 50$ns at $startTime "start-connection"$ns at $finishTime "finish"Then we define a procedure which will be called after simulation starts. The procedure will setup connections among all Httpobjects.proc start-connection {} {global ns server cache client$client connect $cache$cache connect $server$client start-session $cache $server}At the end, the usual closing:proc finish {} {global ns log$ns flush-traceflush $logclose $logexit 0}$ns runThis script is also available at ns/tcl/ex/simple-webcache.tcl. Examining its output http.log, one will find that the resultof the absense cache consistency algorithm results in a lot of stale hits. This can be easily remedied by replacing “newHttp/Cache” line with: set cache [new Http/Cache/TTL $ns $node(e)]. For more complicated cache consistencyalgorithm examples, see ns/tcl/test/test-suite-webcache.tcl.356