public class TimesyncExtension extends BayeuxServer.Extension.Adapter
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 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.
BayeuxServer.Extension.Adapter| Modifier and Type | Field and Description |
|---|---|
static java.lang.String |
LAG_ATTRIBUTE |
| Constructor and Description |
|---|
TimesyncExtension() |
| Modifier and Type | Method and Description |
|---|---|
int |
getAccuracyTarget()
timesync responses are not set if the measured accuracy is less than the
accuracyTarget.
|
boolean |
rcvMeta(ServerSession from,
ServerMessage.Mutable message) |
boolean |
sendMeta(ServerSession session,
ServerMessage.Mutable message) |
void |
setAccuracyTarget(int target)
timesync responses are not set if the measured accuracy is less than the
accuracyTarget.
|
rcv, sendpublic static final java.lang.String LAG_ATTRIBUTE
public int getAccuracyTarget()
public void setAccuracyTarget(int target)
target - accuracy target in mspublic boolean rcvMeta(ServerSession from, ServerMessage.Mutable message)
rcvMeta in interface BayeuxServer.ExtensionrcvMeta in class BayeuxServer.Extension.Adapterpublic boolean sendMeta(ServerSession session, ServerMessage.Mutable message)
sendMeta in interface BayeuxServer.ExtensionsendMeta in class BayeuxServer.Extension.AdapterCopyright © 2008–2019 The CometD Project. All rights reserved.