Private:psim

This page documents the development of a discrete event simulator for P2P video streaming applications. This simulator captures important features of data-driven video streaming systems. In particular, it is designed to evaluate: (i) the performance of various segment scheduling algorithms; (ii) the potential of network coding in multi-layer P2P video streaming systems.

Class Diagrams

• use long for time/offset in msec, which has a rollover time 24.85 days

class Layer { // video layer, we divide each layer into fixed size blocks, we keep track of
                    // block size and no blocks here
    int layer; // layer number it belongs to, set to zero for nonscalable frame
    int blockSize; // blocks are fixed size, in bytes
    int noBlocks; // how many block here
    int dataSize; // aggregate size of all blocks
}

class Frame { // video frame, read from trace file
    int no; // serial number
    long deadlineOffset; // deadline offset compared to the start of the video, in msec
    int totalSize; // total frame size in bytes, including all layers
}

class Segment { // packetized frames
    int no; // serial number
    Vector<Frame> frames; // reference to included frame
    int totalSize; // aggregate size in bytes
    Hashtable<Integer, Layer> layers; // reference to layers of this frame, key is the layer id
    long getDeadline(); // returns the worst case deadline of this segment (first frame?)
}

class Video { // a media file, shared by a group of peers
    String filename; // video trace file path and name
    Hashtable<int, Frame> frameTrace; // frames read from the trace file
    Hashtable<int, Segment> segmentTrace; // segments generated by the prepareSegments(...)
    void prepareSegments(int noFrame); // packetize frames into segment, 
        // noFrame indicates how many frames should we put in one segment; 
        // we might implement other packtization schemes later.
}

Interface Node { // a network node, currently can be either a tracker or a peer
}
                        
class Tracker implement Node { // holds a set of groups/videos
    Vector<Group> groups; // all the video groups
    void addPeer(Group group, Peer peer); // insert a peer into a video group
}

class Peer implement Node { // represent a running peer
    int id; // sequential peer id
    int ingressBW; // incoming bandwidth in bps
    int egressBW; // outgoing bandwidth in bps
    Hashtable<Video, Vector<Connection>> senders; // peers that we may send requests to 
    Hashtable<Video, Vector<Connection>> receivers; // peers that we may send data to 
    Connection tracker; // control connection to the tracker
    Hashtable<Video, VideoBufMap> vBufMaps; // points to the video-level buffer map
    void start(Video video); // start downloading a video 
    void stop(Video video); // stop downloading
}

class Group { // peers that have downloaded or want to download a Video
    Video video; // media shared among peers
    Vector<Peer> peers; // peers in this group
    Vector<Peer> join(Peer peer); // adding a new peer into this group, and return a list of senders
    void leave(Peer peer); // removing a peer from this group
}

class Connection { // end to end network link between two peers
    Peer peer1; // one end
    Peer peer2; // the other
    long delay; // transmission delay in msec
    int e2eBW; // end-to-end bandwidth in bps
    int estimateRate; // estimated rate (maybe historical)
}

class VideoBufMap {
    Hashtable<Integer, SegBufMap> sBufMaps; // points to segment bufmap
}

class SegBufMap {
    Hashtable<Integer, LayerBufMap> lBufMaps; // points to layer bufmap
}

class LayerBufMap {
    boolean avail; // availability bit for this (video, segment, layer) tuple
    NCBuf ncBuf; // network coding structure
}

class NCBuf {
    boolean servCapibility; // Serving capability of each segment
                                      // show whether this segment is capable of serving other peers(applicable in NC)
    int noCodedBl; //  No. of encoded blocks for this (video,segment,layer)
    BufferedMatrix matrix; // coefficients and their corresponding encoded blocks up to now
}

class BufferedMatrix{ // save coefficients and their corresponding encoded blocks up to now
    Vector<Vector<Integer>> coef; // coefficients of the corresponding encoded blocks
    Vector <Integer>encodedValue; // encoded blocks
    Vector<Integer> decode(); // perform decoding process and return the original blocks of a segment
    void encode(); // perform encoding process on blocks of a segment
    
}

class SysParam{ // system parameters that can be changed in each iteration of the simulation
    float portionServ; // after receiving this portion of coded blocks out of total number of blocks, the segment is capable  
                              // of serving to others [in case of network coding]
    long skipSec; // time duration which is skipped from the current playback point for a new joined peer [in case of 
                        // network coding]
}
    
// XXX TODO XXX

class SlidingWindow{ // the sliding window which contains all the segments that the receiver is interested currently
                                  // set it to a fixed size, for example 1 minute of videos
                                    // the receiver first inform all its neighbors which part of the video it is interested currently,
                                    // then its neighbors will send their bitmap of that part to the receiver for scheduling
  int startOffset;         //the offset of the starting segment compared with the start of the video
  int endOffset;           // the offset of the ending segment compared with the start of the video
  double slidingWindowSize(); //get the size of the sliding window
}

class exchangeWindow{ // the exchange window is the front part of the sliding window. 
                                       //The unavailable segments in exchange window will be requested by the peer
                                       //usually we set it to a fixed size, for example, 10 seconds of video
                                       // the field of this class is similar to that of the SlidingWindow class
  int startOffset;
  int endOffset;
  void move();           // move the exchange window forward afte a scheduling period and do a next scheduling 
  double getSlidingWindowSize()
}

interface Scheduler{ // any class wants to do scheduling should implement this interface
  void schedule() throws simException; // the scheduling period is specified in the specific scheduling algorithm class
}

class resultItem{ //this class records a scheduling item
   int peerID;
   int segID;
   long startTime; //start time of the peer to transmit this segment
}

class SchedulingResult{                // this class is used to record scheduling results and do some statistics, 
                                                      // for example, calculate the average delivery rate
  Vector<resultItem> item;    // result item: <peerID, segID, startTime> (we may write this vector to a log file later)
  long runningTime;                  //running time of the algorithm
  long deliveryRatio;                 //Average delivery ratio

  double getDeliveryRatio();  //get the actual  average delivery ratio
  double getRunningTime(); //get the running time 
}

class SEFF implements Scheduler{ // the Serial Earliest Finish-time First scheduling algorithm
  SchedulingResult result;                 // create a schedulingResult object to store the result
  
  void schedule();                                   //implement the Scheduler interface
  void writeResult(SchedulingResult);  //write scheduling result to the result object of one scheduling period
                                                              //including calculating the average delivery ratio and running time
}

class LRF implements Scheduler{ // the Local Rarest First algorithm
  SchedulingResult result;                 // create a schedulingResult object to store the result
  
  void schedule();                                   //implement the Scheduler interface
  void writeResult(SchedulingResult);  //write scheduling result to the result object of one scheduling period
                                                              //including calculating the average delivery ratio and running time
}



class RndGen { // common random number/event generators, to deal with
                       // 1. event: add new receiver for a group/video
                       // 2. event: remove a receiver from a group/video
                       // 3. number: peer's bandwidth
}

class SimException {

}

Interface EventHandler {
    void handle() throws SimException; // callback function
}

class Event {
    long time; // when this event happens
    Node src; // which peer generates this event
    Node dst; // whom is destinate of this event 
    Vector<EventHandler> handlers; //process an event and update states accordingly
    int type; // enum, see below
    // 1. connectSent: peer 1 makes a connection to peer 2, and add each other into neighbors
    // 2. connectArrived: the connect message is received by the peer 2
    // 3. acceptSent: the potential sender reply with an accept message
    // 4. acceptArrived: the accept message arrives at the connection originator
    // 5. requestSent: a receiver sends a high-priority request message to a sender
    // 6. requestArrived: a request message gets to a sender
    // 7. dataSent: a sender sends a data segment
    // 8. dataArrived: a data segment arrives to a receiver
    // 9. joinSent: a join message to the tracker
    // 10. joinArrived: a join message reaches the tracker
    // 11. responseSent: a response message sent by the tracker
    // 12. responseArrived: a response message reaches the receiver
   
    // 13. scheduleStarted: a scheduling period started.
     //14. bimapSyncSent: the receiver inform all its neighbors what part of the video it is interested currently
                                           in order to get a small bitmap from them to do scheduleing, this message is sent
                                            when the receiver: jumps to view another part of the video or a new neighbor joins. 
     //15. bitmapSyncArrived: the sender receives the bitmap Synchronization information

    //commet: how should we do when a scheduling period expires? 
    //There are two situations: 1. all scheduled segments arrived; 2. some segments are still in transmission.

    void addHandler(Interface EventHandler); // add an additional event handler
    void rmvHandler(Interface EventHandler); // remove an additional event handler
}

class EventQueue {
    SortedMap<Long, Event> queue; // events sorted on its time
    void dispatch(Event event); // sequentially invoke even handlers 
}

class Simulator {
    long simTime; // elapsed simulation time in msec
    EventQueue events; // pending events that will be processed
    void dispatchEvent(); // forever loop to process the next event
}



Some comments:
*
  

Performance metrics for scheduling

Here are some performance metrics:

1. Average delivery ratio: number of on-time scheduled segments over total number of segments to be scheduled
2. Load balance among senders
3. Initial buffering time
4. Time and space complexity of the scheduling algorithm