Examples of org.cometd.server.ext.TimesyncExtension

org.cometd.server.ext.TimesyncExtension

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:

tc is the client timestamp in ms since 1970 of when the message was sent.
l is the network lag that the client has calculated.
o is the clock offset that the client has calculated.

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

tc is the client timestamp of when the message was sent,
ts is the server timestamp of when the message was received
p is the poll duration in ms - ie the time the server took before sending the response.
a is the measured accuracy of the calculated offset and lag sent by the client

The relationship between tc, ts, o and 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.


        _processor = new ServerAnnotationProcessor(bayeux, oort, seti);
        _service = new OortChatService();
        _processor.process(_service);


        bayeux.addExtension(new TimesyncExtension());
    }

    }


    @Test
    public void testTimeSync() throws Exception
    {
        final TimesyncExtension extension = new TimesyncExtension();
        extension.setAccuracyTarget(0);
        bayeux.addExtension(extension);


        final BayeuxClient client = newBayeuxClient();
        client.addExtension(new TimesyncClientExtension());


        if (bayeux == null)
            throw new UnavailableException("No BayeuxServer!");


        // Create extensions
        bayeux.addExtension(new TimesyncExtension());
        bayeux.addExtension(new AcknowledgedMessagesExtension());


        // Deny unless granted


        bayeux.createChannelIfAbsent("/**", new ServerChannel.Initializer()

public class CometDTimeSyncExtensionTest extends AbstractCometDTest
{
    @Test
    public void testTimeSync() throws Exception
    {
        bayeuxServer.addExtension(new TimesyncExtension());


        provideTimesyncExtension();


        defineClass(Latch.class);
        evaluateScript("cometd.configure({url: '" + cometdURL + "', logLevel: '" + getLogLevel() + "'});");

Examples of org.cometd.server.ext.TimesyncExtension

Related Classes of org.cometd.server.ext.TimesyncExtension