41.4.5 PagePool/WebTraf

The class PagePool/WebTraf is a standalone Web traffic modle that utilizes PagePool framework. However, this class has nothing to do with the HttpApp classes. Because we are only interested in using it to study Web traffic pattern here, and do not want to be bothered with the burden of transmitting HTTP headers, etc. It has the following two major data structures. Details can be found in ns/webcache/webtraf.cc and ns/webcache/webtraf.h, the architecture WebTraf model is also loosely described in [10], Section 2.4, paragraph 3-4 and the appendix A.1.

• WebTrafSession - a class that models Web user session. It is defined as follows:

  class WebTrafSession : public TimerHandler {
  	public:   
  	        WebTrafSession(WebTrafPool *mgr, Node *src, int np, int id) : rvInterPage_(NULL),
  	        rvPageSize_(NULL), rvInterObj_(NULL), rvObjSize_(NULL), mgr_(mgr), src_(src), 
  	        nPage_(np), curPage_(0), donePage_(0), id_(id), interPageOption_(1) {} 
  	        virtual ~WebTrafSession();
  
  	        // Queried by individual pages/objects
  	        inline RandomVariable*& interPage() { return rvInterPage_; }
  	        inline RandomVariable*& pageSize() { return rvPageSize_; }
  	        inline RandomVariable*& interObj() { return rvInterObj_; }
  	        inline RandomVariable*& objSize() { return rvObjSize_; }
  		
  	        void donePage(void* ClntData); // all the pages within this
  	                                       // session have  been sent
  	        void launchReq(void* ClntData, int obj, int size);
  	        inline int id() const { return id_; }
  	        inline WebTrafPool* mgr() { return mgr_; }
  	 private:
  	        virtual void expire(Event *e = 0); // Lanuch request for a page
  	        virtual void handle(Event *e); // schedule the timer for next page
  
  	        RandomVariable *rvInterPage_, *rvPageSize_, *rvInterObj_, *rvObjSize_;
  	        WebTrafPool* mgr_;
  	        Node* src_;  // One Web client (source of request) per session
  	        nt nPage_; // number of pages per session
  	        int curPage_; // number of pages that have been sent
  	        int id_; // page ID
  	        int interPageOption_;
  }
  

• WebPage - a class that models Web Page. It is defined as follows:

  class WebPage : public TimerHandler {
  	public:
  	        WebPage(int id, WebTrafSession* sess, int nObj, Node* dst) :
  	                id_(id), sess_(sess), nObj_(nObj), curObj_(0),
  	                doneObj_(0), dst_(dst) {}
  	        virtual ~WebPage() {}
  	        inline void start() { // Call expire() and schedule the next one if needed     
  	        void doneObject() { // All the objects within this page have been sent
  	        inline int id() const { return id_; }
  	        Node* dst() { return dst_; }
  	        inline int curObj() const { return curObj_; }
  	        inline int doneObj() const { return doneObj_; }
  	private:  
  	        virtual void expire(Event* = 0) { // Launch request for an object
  	        virtual void handle(Event *e) { // schedule the timer for the next object
  	        int id_; // object ID
  	        WebTrafSession* sess_; // the session that requested this page
  	        int nObj_; // number of object in this page
  	        int curObj_ ; // number of object that have been sent
  	        Node* dst_; //  server that this page has been requested from
  }
  

Following is a list of related OTcl methods to the WebTraf class. rX set-num-session number-of-session & set the total number of sessions in the WebTraf pool.
set-num-server number-of-server & set the total number of servers.
set-num-client number-of-client & set the total number clients.
set-interPageOption option & There are two ways to interpret inter-page time: One is the time between the start of two consecutive page downloads by the same user, and the other is the time between the end of previous page download and the start of the following page by the same user. $option can be set to either 0 or 1 (default is 1). When $option is set to 1, the second interpretation is used for "inter-page" time. The first interpratation is adopted when $option is set to 0. Note the resulted traffic volume using the first interpretation is much higher than the second interpretation.
doneObj webpage & all the objects in $webpage have been sent.
set-server id node & set $node as server $id.
set-client id node & set $node as client $id.
recycle tcp sink & Recycle a TCP source/sink pair.
create-session session-index pages-per-sess &
launch-time inter-page-rv page-size-rv &
inter-obj-rv obj-size-rv & Create a Web session. $session-index is the sesson index. $pages-per-sess is the total number of pages per session. $launch-time is session starting time. $inter-page-rv is the random variable that generates page inter-arrival time. $page-size-rv is the random variable that generates number of objects per page. $inter-obj-rv is the random variable that generates object inter-arrival time. $obj-size-rv is the random variable that generates object size.

The example script is available at ns/tcl/ex/web-traffic.tcl (also see ns/tcl/ex/large-scale-web-traffic.tcl for use of a large-scale web traffic simulation)