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120 lines
3.3 KiB
Java
120 lines
3.3 KiB
Java
// ABPSender.java
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package protocol; // protocol package
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import java.util.Enumeration; // enumeration
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import java.util.Vector; // vector (list)
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import support.*; // protocol entity support
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/**
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This is the class for the alternating bit protocol sender.
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@author Iain A. Robin, Kenneth J. Turner
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@version 1.0 (1st September 1999, IAR): initial version
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<br/> 1.4 (9th March 2006, KJT): updated for JDK 1.5
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<br/> 1.5 (27th July 2010, KJT): minor tidying
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*/
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public class ABPSender implements ProtocolEntity, Timeouts {
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private PDU pduBeingSent;
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private PDU pduReceived;
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private ProtocolEntity peer;
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private Medium medium;
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private String name;
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private boolean timerEnabled;
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private Vector<ProtocolEvent> entityEvents; // events from entity
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public ABPSender(Medium m, String name) {
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this.name = name;
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medium = m;
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initialise();
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}
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public String getName() {
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return(name);
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}
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public Vector<String> getServices() {
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Vector<String> list = new Vector<String>();
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if (pduReceived != null && pduReceived.type.equals("ACK")) {
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list.addElement("Send DATA(" + pduReceived.seq + ")");
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timerEnabled = false;
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}
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if (timerEnabled)
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list.addElement("Timeout - presume loss of message and resend");
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return(list);
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}
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public boolean hasTimer(String type) {
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return(true);
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}
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/** Increment PDU sequence number (0 or 1 only in ABP protocol) */
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private int inc(int seq) {
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return(1 - seq);
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}
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public void initialise() {
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// dummy initial data PDU
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pduBeingSent = new PDU("DATA", 1);
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pduBeingSent.setSource(this);
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// dummy initial ack PDU
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pduReceived = new PDU("ACK", 0);
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timerEnabled = false;
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entityEvents = new Vector<ProtocolEvent>(); // empty medium events
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}
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public Vector<ProtocolEvent> performService(String s) {
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Vector<ProtocolEvent> events = new Vector<ProtocolEvent>();
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if (s.startsWith("Send DATA")) {
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// PDU seq number delimited by brackets:
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int startIndex = s.indexOf( '(' ) + 1;
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int endIndex = s.indexOf( ')' );
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int seq = Integer.parseInt(s.substring(startIndex, endIndex));
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transmitPDU(new PDU("DATA", seq), peer);
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events.addElement(
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new ProtocolEvent(ProtocolEvent.TRANSMIT, pduBeingSent));
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}
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if (s.startsWith("Timeout")) {
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transmitPDU(pduBeingSent, peer);
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events.addElement(
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new ProtocolEvent(ProtocolEvent.TIMEOUT, pduBeingSent));
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}
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for (Enumeration e = entityEvents.elements(); // get medium events
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e.hasMoreElements(); )
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events.addElement( // add medium event
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(ProtocolEvent) e.nextElement());
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return(events);
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}
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public Vector<ProtocolEvent> receivePDU(PDU pdu) {
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pduReceived = pdu;
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return(new Vector<ProtocolEvent>());
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}
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public void setPeer(ProtocolEntity peer) {
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this.peer = peer;
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}
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/**
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Set the timer for a specified PDU.
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@param pdu PDU
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@param enabled whether the timer is enabled
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*/
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public void setTimer(PDU pdu, boolean enabled) {
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timerEnabled = enabled;
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}
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public void transmitPDU(PDU pdu, ProtocolEntity dest) {
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pdu.setSource(this);
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pdu.setDestination(dest);
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pduBeingSent = pdu;
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entityEvents = medium.receivePDU(pdu); // medium receives PDU
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pduReceived = null;
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timerEnabled = false;
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}
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}
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