[ENet-discuss] peer->roundTripTime

[intripoon]

Hi!

I know about that. Actually, my program doesn't do much more than servicing
enet, sending a packet once per second and print out the rtt every 5
seconds.

What I do is get the system time in microseconds by using the
PerformanceCounter, put that value in a packet and send it to the other
peer, which again gets the system time in microseconds using the
PerformanceCounterr. The difference is about 300 microseconds, averaged over
a few interations. So it actually takes about 300 microseconds to send a
packet from one peer to another on the same pc, in two different processes.
At the same time, the rtt returned by enet is 7 milliseconds, telling me the
averaged time for a packet transmission is 3500 microseconds. Factor 10
off?!?

I didn't know of http://enet.bespin.org until Bjorn's post. Googleing for
enet results in the cubrik page for me. However, I downloaded the 1.0 from
the bespin page and it is probably newer because some files are larger than
in my previous version. The issue described above is the same in both
versions though.

The reason why I'm curious about it is because I planed to use the rtt value
to correct time differences between the peers. But a 6.5 ms error on
localhost is too much for my application. I could send packets containing
timestamps between the peers and calculate the rtt and the time correction
myself. However, that'ld require to send additional packets. The possibility
to use all packets sent to calculate the rtt has to be done in enet's layer
- or I would have to introduce another layer on top of enet adding the
required information to each packet. But all this is already done in enet,
but for some reason it seems to be quite unprecise. Any idea why?

Best regards
	Marc


-----Ursprüngliche Nachricht-----
Von: enet-discuss-bounces at cubik.org [mailto:enet-discuss-bounces at cubik.org]
Im Auftrag von Lee Salzman
Gesendet: Mittwoch, 27. Dezember 2006 17:37
An: Discussion of the ENet library
Betreff: Re: [ENet-discuss] peer->roundTripTime

Remember, ENet does pretty much all work in enet_host_service(). So if 
you aren't constantly servicing the host, then the frequency at which 
you call it is going to have a small effect on RTTs. It's never been a 
big deal in so far as what ENet's designed for.

Lee

intripoon wrote:
> Hi !
> 
> I wonder about the peer->roundTripTime value. Between every pc in my local
> network, all peers have a roundTripTime of 7 to each other, no matter what
I
> do. Shouldn't that be value be smaller? Even on one pc having two
processes
> connecting to each other by enet peers, that value is 7. I also tried
> sending a high performance counter value from one process to the other to
> check if it really takes 3.5 ms to send a packet - but it doesn't.
> 
> Somewhere I read, the rtt value is computed by comparing the time of a
> reliably sent packet and it's returning ack packet. Do maybe ack packets
get
> delayed for some reason? Maybe waiting for more possible ack packets to be
> sent? Maybe something like that explains the 7 ms?
> 
> Is there a way to configure enet to return a more correct value in this
> case?
> 
> I'm not quite sure which version of enet I'm using. Is there a version
> string somewhere? It's not too old though.
> 
> Best regards
> 	Marc
> 
> _______________________________________________
> ENet-discuss mailing list
> ENet-discuss at cubik.org
> http://lists.cubik.org/mailman/listinfo/enet-discuss
> 

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