org.cometd.server.ext
Class TimesyncExtension

java.lang.Object
  extended by org.cometd.server.ext.TimesyncExtension
All Implemented Interfaces:
BayeuxServer.Extension

public class TimesyncExtension
extends java.lang.Object
implements BayeuxServer.Extension

Timesync extension (server side). With each handshake or connect, the extension sends timestamps within the ext field like: {ext:{timesync:{tc:12345567890,l:23,o:4567},...},...} where:

A cometd server that supports timesync, can respond with an ext field like: {ext:{timesync:{tc:12345567890,ts:1234567900,p:123,a:3},...},...} where:

The relationship between tc, ts, o & l on the server is given by ts=tc+o+l (the time the server received the message is the client time plus the offset plus the network lag). Thus the accuracy of the o and l settings can be determined with a=tc+o+l-ts.

When the client has received the response, it can make a more accurate estimate of the lag as l2=(now-tc-p)/2 (assuming symmetric lag). A new offset can then be calculated with the relationship on the client that ts=tc+o2+l2, thus o2=ts-tc-l2.

Since the client also receives the a value calculated on the server, it should be possible to analyse this and compensate for some asymmetry in the lag. But the current client does not do this.


Constructor Summary
TimesyncExtension()
           
 
Method Summary
 int getAccuracyTarget()
          timesync responses are not set if the measured accuracy is less than the accuracyTarget.
 boolean rcv(ServerSession from, ServerMessage.Mutable message)
           
 boolean rcvMeta(ServerSession from, ServerMessage.Mutable message)
           
 boolean send(ServerMessage.Mutable message)
           
 boolean sendMeta(ServerSession to, ServerMessage.Mutable message)
           
 void setAccuracyTarget(int target)
          timesync responses are not set if the measured accuracy is less than the accuracyTarget.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

TimesyncExtension

public TimesyncExtension()
Method Detail

getAccuracyTarget

public int getAccuracyTarget()
timesync responses are not set if the measured accuracy is less than the accuracyTarget.

Returns:
accuracy target in ms (default 25ms)

setAccuracyTarget

public void setAccuracyTarget(int target)
timesync responses are not set if the measured accuracy is less than the accuracyTarget.

Parameters:
target - accuracy target in ms

rcv

public boolean rcv(ServerSession from,
                   ServerMessage.Mutable message)
Specified by:
rcv in interface BayeuxServer.Extension

rcvMeta

public boolean rcvMeta(ServerSession from,
                       ServerMessage.Mutable message)
Specified by:
rcvMeta in interface BayeuxServer.Extension

send

public boolean send(ServerMessage.Mutable message)
Specified by:
send in interface BayeuxServer.Extension

sendMeta

public boolean sendMeta(ServerSession to,
                        ServerMessage.Mutable message)
Specified by:
sendMeta in interface BayeuxServer.Extension


Copyright © 2010 Dojo Foundation. All Rights Reserved.