org.javagroups.protocols
Class UNICAST

java.lang.Object
  extended byorg.javagroups.stack.Protocol
      extended byorg.javagroups.protocols.UNICAST
All Implemented Interfaces:
AckSenderWindow.RetransmitCommand

public class UNICAST
extends Protocol
implements AckSenderWindow.RetransmitCommand

Reliable unicast layer. Uses acknowledgement scheme similar to TCP to provide lossless transmission of unicast messages (for reliable multicast see NAKACK layer). When a message is sent to a peer for the first time, we add the pair to the hashtable (peer address is the key). All messages sent to that peer will be added to hashtable.peer_addr.sent_msgs. When we receive a message from a peer for the first time, another entry will be created and added to the hashtable (unless already existing). Msgs will then be added to hashtable.peer_addr.received_msgs.

This layer is used to reliably transmit point-to-point messages, that is, either messages sent to a single receiver (vs. messages multicast to a group) or for example replies to a multicast message. The sender uses an AckSenderWindow which retransmits messages for which it hasn't received an ACK, the receiver uses AckReceiverWindow which keeps track of the lowest seqno received so far, and keeps messages in order.

Messages in both AckSenderWindows and AckReceiverWindows will be removed. A message will be removed from AckSenderWindow when an ACK has been received for it and messages will be removed from AckReceiverWindow whenever a message is received: the new message is added and then we try to remove as many messages as possible (until we stop at a gap, or there are no more messages).

Author:
Bela Ban

Nested Class Summary
static class UNICAST.UnicastHeader
           
 
Field Summary
 
Fields inherited from class org.javagroups.stack.Protocol
down_handler, down_prot, down_queue, down_thread, observer, props, stack, up_handler, up_prot, up_queue, up_thread
 
Constructor Summary
UNICAST()
           
 
Method Summary
 void down(Event evt)
          An event is to be sent down the stack.
 java.lang.String getName()
          All protocol names have to be unique !
 void retransmit(long seqno, Message msg)
          Called by AckSenderWindow to resend messages for which no ACK has been received yet
 boolean setProperties(java.util.Properties props)
          Configures the protocol initially.
 void start()
          This method is called on a Channel.connect(String).
 void stop()
          This method is called on a Channel.disconnect().
 void up(Event evt)
          An event was received from the layer below.
 
Methods inherited from class org.javagroups.stack.Protocol
destroy, getDownProtocol, getDownQueue, getProperties, getUpProtocol, getUpQueue, init, passDown, passUp, providedDownServices, providedUpServices, receiveDownEvent, receiveUpEvent, requiredDownServices, requiredUpServices, setDownProtocol, setObserver, setPropertiesInternal, setProtocolStack, setUpProtocol, startDownHandler, startUpHandler, stopInternal
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

UNICAST

public UNICAST()
Method Detail

getName

public java.lang.String getName()
All protocol names have to be unique !

Specified by:
getName in class Protocol

setProperties

public boolean setProperties(java.util.Properties props)
Description copied from class: Protocol
Configures the protocol initially. A configuration string consists of name=value items, separated by a ';' (semicolon), e.g.:
 "loopback=false;unicast_inport=4444"
 

Overrides:
setProperties in class Protocol

start

public void start()
           throws java.lang.Exception
Description copied from class: Protocol
This method is called on a Channel.connect(String). Starts work. Protocols are connected and queues are ready to receive events. Will be called from bottom to top. This call will replace the START and START_OK events.

Overrides:
start in class Protocol
Throws:
java.lang.Exception - Thrown if protocol cannot be started successfully. This will cause the ProtocolStack to fail, so Channel.connect(String) will throw an exception

stop

public void stop()
Description copied from class: Protocol
This method is called on a Channel.disconnect(). Stops work (e.g. by closing multicast socket). Will be called from top to bottom. This means that at the time of the method invocation the neighbor protocol below is still working. This method will replace the STOP, STOP_OK, CLEANUP and CLEANUP_OK events. The ProtocolStack guarantees that when this method is called all messages in the down queue will have been flushed

Overrides:
stop in class Protocol

up

public void up(Event evt)
Description copied from class: Protocol
An event was received from the layer below. Usually the current layer will want to examine the event type and - depending on its type - perform some computation (e.g. removing headers from a MSG event type, or updating the internal membership list when receiving a VIEW_CHANGE event). Finally the event is either a) discarded, or b) an event is sent down the stack using passDown() or c) the event (or another event) is sent up the stack using passUp().

Overrides:
up in class Protocol

down

public void down(Event evt)
Description copied from class: Protocol
An event is to be sent down the stack. The layer may want to examine its type and perform some action on it, depending on the event's type. If the event is a message MSG, then the layer may need to add a header to it (or do nothing at all) before sending it down the stack using passDown(). In case of a GET_ADDRESS event (which tries to retrieve the stack's address from one of the bottom layers), the layer may need to send a new response event back up the stack using passUp().

Overrides:
down in class Protocol

retransmit

public void retransmit(long seqno,
                       Message msg)
Called by AckSenderWindow to resend messages for which no ACK has been received yet

Specified by:
retransmit in interface AckSenderWindow.RetransmitCommand


Copyright © 2001,2002 www.javagroups.com . All Rights Reserved.