sime

Class Router

java.lang.Object

sime.NetworkElement

sime.Router

public class Router
extends NetworkElement

This class is a simple simulation of a network router. It is expressly crafted to "route" TCP packets. What it does it to enforce that no more packets are let pass through than what the bottleneck resource capacity allows.

The bottleneck resource that we study using this router is the memory space, which determines the maximum possible queue length (the queuing capacity). If more packets arrive than the queue (buffer) can hold, the excess packets are discarded.

The router needs help from the simulator environment to know about the progression of time. The simulation clock ticking is signaled by invocation of the method send(NetworkElement, Packet). Every time this method is called, the router performs the work allowed within the elapsed time. Currently, this means that the router will hand over the queued packets in packetBuffer to their outgoing links (outputPorts).

Note that this class defines an inner class for output ports (see Router.OutputPort).

Author:

Ivan Marsic

See Also:

Simulator

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected class	Router.OutputPort Inner class for router's output ports.

Field Summary

Fields

Modifier and Type	Field and Description
private int	bufferCapacity The router buffer capacity, in bytes.
private int	currentBufferOccupancy Current occupancy of the router memory is obtained as a sum of the packet lengths for all packets currently queued in the router memory packetBuffer.
protected java.util.HashMap<NetworkElement,Link>	forwardingTable Router's forwarding table maps the destination node (found in the Packet header) to the outgoing link.
protected java.util.HashMap<Link,Router.OutputPort>	outputPorts Output ports associated with the router's links.
private java.util.ArrayList<Packet>	packetBuffer Router memory for buffered/queued packets.

Fields inherited from class sime.NetworkElement

lastTimeProcessCalled, name, simulator

Constructor Summary

Constructors

Constructor and Description
Router(Simulator simulator_, java.lang.String name_, int bufferSize_) Constructor.

Method Summary

Methods

Modifier and Type	Method and Description
void	addForwardingTableEntry(NetworkElement node_, Link outgoingLink_) Adds another entry into the router's forwarding table.
int	getMaxBufferSize() Accessor for retrieving the packet buffering capacity of this router.
void	handle(NetworkElement source_, Packet receivedPacket_) Buffers the incoming packet in the router memory.
void	process(int mode_) When this method is called, it is a signal to the router to transmit packets on their corresponding outgoing links, if there are any packets buffered in the router memory. Only the caller knows when sufficient amount of time has elapsed and when it should call this method.
void	send(NetworkElement dummySource_, Packet dummyPacket_) Currently does nothing.

Methods inherited from class sime.NetworkElement

getName, getSimulator

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

bufferCapacity

private int bufferCapacity

The router buffer capacity, in bytes. If more packets arrive than the currently available buffer space allows for queuing (currentBufferOccupancy), the excess packets will be discarded.

currentBufferOccupancy

private int currentBufferOccupancy

Current occupancy of the router memory is obtained as a sum of the packet lengths for all packets currently queued in the router memory packetBuffer.

forwardingTable

protected java.util.HashMap<NetworkElement,Link> forwardingTable

Router's forwarding table maps the destination node (found in the Packet header) to the outgoing link.

outputPorts

protected java.util.HashMap<Link,Router.OutputPort> outputPorts

Output ports associated with the router's links.

packetBuffer

private java.util.ArrayList<Packet> packetBuffer

Router memory for buffered/queued packets. Buffer capacity is represented by bufferCapacity. Current memory occupancy is represented by currentBufferOccupancy.

Constructor Detail

Router

public Router(Simulator simulator_,
      java.lang.String name_,
      int bufferSize_)

Constructor.

Parameters:

simulator_ - the runtime environment

name_ - the name given to this router

bufferSize_ - the given buffer size for the router's memory (in bytes).

Method Detail

addForwardingTableEntry

public void addForwardingTableEntry(NetworkElement node_,
                           Link outgoingLink_)

Adds another entry into the router's forwarding table.

Parameters:

node_ - the network node (hash-table key) with which the specified outgoing link is to be associated

outgoingLink_ - the outgoing link to be associated with the specified network node

getMaxBufferSize

public int getMaxBufferSize()

Accessor for retrieving the packet buffering capacity of this router. (Note that we ignore the packet header, i.e., it does not count towards the router's memory occupancy.)

Returns:

this router's memory capacity [in bytes].

handle

public void handle(NetworkElement source_,
          Packet receivedPacket_)

Buffers the incoming packet in the router memory. If the bufferCapacity memory capacity is exceeded, the input packet will be discarded.

Specified by:

handle in class NetworkElement

Parameters:

source_ - the immediate source of the arrived packet

receivedPacket_ - the packet that arrived on an incoming link

See Also:

Router.OutputPort.handleIncomingPacket(NetworkElement, Packet), NetworkElement.handle(NetworkElement, sime.Packet)

process

public void process(int mode_)

When this method is called, it is a signal to the router to transmit packets on their corresponding outgoing links, if there are any packets buffered in the router memory.
Only the caller knows when sufficient amount of time has elapsed and when it should call this method.

Specified by:

process in class NetworkElement

Parameters:

mode_ - the processing mode, currently not used and ignored

See Also:

Router.OutputPort.transmitPackets(), Simulator.run(java.nio.ByteBuffer, int)

send

public void send(NetworkElement dummySource_,
        Packet dummyPacket_)

Currently does nothing. The input parameters are simply ignored.
Note that this method may need to be implemented if the router will send route advertisement packets ...

Specified by:

send in class NetworkElement

Parameters:

dummySource_ - [ignored]

dummyPacket_ - [ignored]

See Also:

NetworkElement.send(NetworkElement, Packet)