// log / record ....        if (super.reportWriter_ != null)        {            super.write("");            super.write("receive incoming, " + pkt + ", delay, " + nextTime);            super.write("break this packet into, " + numPackets);        }        // break a large packet into smaller ones that fit into MTU        // by making null or empty packets except for the last one        for (int i = 0; i < numPackets - 1; i++)        {            NetPacket np = new NetPacket(null, pkt.getID(), MTU, tag,                                         pkt.getSrcID(), pkt.getDestID(),                                         pkt.getNetServiceType(),i+1,numPackets);            np.setLast(id);            super.write("enqueing, " + np);            sched.enque(np);  // put the packet into the scheduler        }        // put the actual packet into the last one and resize it accordingly        pkt.setLast(id);        pkt.setSize(pkt.getSize() - MTU * (numPackets - 1));        super.write("enqueing, " + pkt);        sched.enque(pkt);  // put the packet into the scheduler    }    /**     * Gets the link's name for a given id     * @param destID    a destination id     * @return the link's man     * @pre destID > 0     * @post $none     */    private synchronized String getLinkName(int destID)    {        String destName = GridSim.getEntityName(destID);        String linkName = null;        //directly connected        if (hostTable.containsValue(destName)) {            linkName = (String)linkTable.get(destName);        }        else        {            // need to forward to another router            Object[] data = (Object[]) forwardTable.get(destName);            String router = (String) data[0];            linkName = (String) linkTable.get(router);        }        return linkName;    }    /**     * Returns the Scheduler associated with a packet.     *     * @param np NetPacket for which the associated scheduler is to be returned     * @return the packet's scheduler or <tt>null</tt> if the packet is empty     * @pre np != null     * @post $none     */    public PacketScheduler getScheduler(Packet np)    {        if (np == null) {            return null;        }        String destName = GridSim.getEntityName( np.getDestID() );        return getScheduler(destName);    }    /**     * Returns the Scheduler that the router would use to reach a particular     * destination. This can be used to set weigths, priorities etc. as the     * case may be on the Scheduler     *     * @param dest id of the destination for which the Scheduler is required.     * @return the destination's packet scheduler     * @pre dest > 0     * @post $none     */    public PacketScheduler getScheduler(int dest)    {        if (dest < 0) {            return null;        }        String destName = GridSim.getEntityName(dest);        return getScheduler(destName);    }    /**     * Returns the Scheduler that the router would use to reach a particular     * destination. This can be used to set weigths, priorities etc. as the     * case may be on the Scheduler     *     * @param dest Name of the destination for which the Scheduler is required.     * @return destination's packet scheduler or <tt>null</tt> if destination     *         name is invalid.     * @pre dest != null     * @post $none     */    public PacketScheduler getScheduler(String dest)    {        if (dest == null || dest.length() == 0) {            return null;        }        PacketScheduler sched = null;        try        {            if ( hostTable.containsValue(dest) )            {                String linkName = (String) linkTable.get(dest);                sched = (PacketScheduler) schedTable.get(linkName);            }            else            {                // need to forward to another router                Object[] data = (Object[]) forwardTable.get(dest);                // in case the forwarding table is incomplete                if (data == null) {                    return null;                }                String router = (String) data[0];                String linkName = (String) linkTable.get(router);                sched = (PacketScheduler) schedTable.get(linkName);            }        }        catch (Exception e) {            sched = null;        }        return sched;    }    /**     * Processes internal event     * @param ev    a Sim_event object     * @pre ev != null     * @post $none     */    private synchronized void processInternalEvent(Sim_event ev)    {        PacketScheduler sched = (PacketScheduler) ev.get_data();        dequeue(sched);    }    /**     * Dequeue a packet from the scheduler and sends it to the next     * destination via a link.     * @param sched  the packet scheduler     * @pre sched != null     * @post $none     */    private synchronized void dequeue(PacketScheduler sched)    {        Packet np = sched.deque();        // process ping() packet        if (np instanceof InfoPacket) {            ((InfoPacket) np).addExitTime( GridSim.clock() );        }        super.write("dequeuing, " + np);        // must distinguish between normal and junk packet        int tag = GridSimTags.PKT_FORWARD;        if (np.getTag() == GridSimTags.JUNK_PKT) {            tag = GridSimTags.JUNK_PKT;        }        // sends the packet via the link        String linkName = getLinkName( np.getDestID() );        super.sim_schedule(GridSim.getEntityId(linkName),                           GridSimTags.SCHEDULE_NOW, tag, np);        // process the next packet in the scheduler        if ( !sched.isEmpty() )        {            double nextTime = (np.getSize() * BITS) / sched.getBaudRate();            sendInternalEvent(nextTime, sched);        }    }    /**     * Sends an internal event to itself     * @param time  the delay time period     * @param data  the data to be sent     * @return <tt>true</tt> if it is successful, <tt>false</tt> otherwise     * @pre time >= 0     * @post $none     */    private synchronized boolean sendInternalEvent(double time, Object data)    {        if (time < 0.0) {            return false;        }        super.sim_schedule(id, time, GridSimTags.INSIGNIFICANT, data);        return true;    }    /**     * Prints this router's routing table in a nice-formatted layout     * @pre $none     * @post $none     */    public synchronized void printRoutingTable()    {        synchronized (System.out)        {            System.out.println();            System.out.println("--- Routing Table for " +                               super.get_name() + " ---");            for (Enumeration e = hostTable.keys(); e.hasMoreElements(); )            {                String link = (String) e.nextElement();                System.out.println(hostTable.get(link) + "\t\t" + link);            }            for (Enumeration e = forwardTable.keys(); e.hasMoreElements(); )            {                String host = (String)e.nextElement();                Object[] data = (Object[])forwardTable.get(host);                String nextHop = (String)data[0];                System.out.println(host + "\t\t" + nextHop);            }            System.out.println("-------------------------------------");            System.out.println();        }    }    //----------- ADVERTISING FUNCTIONS --------------//    /**     * All hosts connected to this router are advertised to adjacent routers     * @pre $none     * @post $none     */    protected synchronized void advertiseHosts()    {        Collection hosts = hostTable.values(); // who to advertise        Enumeration routers = routerTable.elements();        while ( routers.hasMoreElements() )        {            RIPAdPack ad = new RIPAdPack(super.get_name(), hosts);            String router = (String) routers.nextElement();            super.write("advertise to router, " + router);            sim_schedule(Sim_system.get_entity_id(router),                         GridSimTags.SCHEDULE_NOW, GridSimTags.ROUTER_AD, ad);        }        super.sim_pause(5);   // wait for 5 secs to gather the results    }    /**     * When an ad is recieved, the forwarding table is updated. After that we     * need to propogate this ad along all links except the incoming one.     * {@link #forwardAd(RIPAdPack)} is used for that     * @param ev  a Sim_event object     * @pre ev != null     * @post $none     */    private synchronized void receiveAd(Sim_event ev)    {        super.write("receive router ad from, "+GridSim.getEntityName(ev.get_src()));        // what to do when an ad is received        RIPAdPack ad = (RIPAdPack)ev.get_data();        // prevent count-to-infinity        if (ad.getHopCount() > 15) {            return;        }        String sender = ad.getSender();        Iterator it = ad.getHosts().iterator();        while ( it.hasNext() )        {            String host = (String) it.next();            if ( host.equals(super.get_name()) ) {                continue;            }            if (hostTable.containsValue(host)) { // direct connection                continue;            }            if (forwardTable.containsKey(host))            {                Object[] data = (Object[])forwardTable.get(host);                int hop = ((Integer)data[1]).intValue();                if ((hop) > ad.getHopCount())                {                    Object[] toPut = { sender, new Integer(ad.getHopCount()) };                    forwardTable.put(host, toPut);                }            }            else            {                Object[] toPut = { sender, new Integer(ad.getHopCount()) };                forwardTable.put(host, toPut);            }        }        forwardAd(ad);    }    /**     * Received ads should be forwarded along all links except the incoming     * one. Also need to change id to onself     *     * @param ad    a RIPAdPack object     * @pre ad != null     * @post $none     */    private synchronized void forwardAd(RIPAdPack ad)    {        String sender = ad.getSender();        ad.incrementHopCount();        RIPAdPack newad = new RIPAdPack(super.get_name(),ad.getHosts());        newad.setHopCount(ad.getHopCount());        Enumeration routers = routerTable.elements();        while ( routers.hasMoreElements() )        {            String router = (String)routers.nextElement();            if (!router.equals(sender))            {                sim_schedule(Sim_system.get_entity_id(router),                      GridSimTags.SCHEDULE_NOW, GridSimTags.ROUTER_AD, newad);            }        }    }} // end class