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 Post subject: Use of openl2tp with high-latency connections
PostPosted: Wed Jun 20, 2012 4:48 pm 

Joined: Wed Jun 20, 2012 4:33 pm
Posts: 1
Hi,
I managed it to get openl2tp working (just openlt2pd with pppd):
PC with Client -> DSL internet connection -> Server
It works great at full speed (10MBit).
But I have another mobile internet connection (10MBit) that suffers of a high latency (nearly 1 second). Same setup, same machines but different internet connection.
PC with Client -> mobile internet connection with high latency -> Server

If I download a large file via ppp connection I do not reach 10 MBit but not more than 2 MBit average. It is pending between 200 kBit and 5 MBit. After about 10 seconds it is usually at its highest speed, then it slows down. Pure internet connection without tunnel is always at full speed.

Without being an UDP transmission expert, this is what I suppose:
Server begins sending at full speed, then it slows down because some packet acks come too late or something like this and he thinks the connection is not as fast as supposed at beginning.
So I think the reason is the high ping of my connection. Can anyone tell me if there is a usual practice on dealing this?
I already tried to find the section of throtteling the sending speed in code to debug but didn´t find yet.

Would be great if someone could help me on this issue.
Martin

Edit: I missed something - I think with multiple downloads the sum of avg. speed is higher than single downloads (same server, same file).


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 Post subject: Re: Use of openl2tp with high-latency connections
PostPosted: Mon Jul 16, 2012 9:01 am 
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Joined: Sun Jul 27, 2008 1:39 pm
Posts: 122
martin.g wrote:
Hi,
I managed it to get openl2tp working (just openlt2pd with pppd):
PC with Client -> DSL internet connection -> Server
It works great at full speed (10MBit).
But I have another mobile internet connection (10MBit) that suffers of a high latency (nearly 1 second). Same setup, same machines but different internet connection.
PC with Client -> mobile internet connection with high latency -> Server

If I download a large file via ppp connection I do not reach 10 MBit but not more than 2 MBit average. It is pending between 200 kBit and 5 MBit. After about 10 seconds it is usually at its highest speed, then it slows down. Pure internet connection without tunnel is always at full speed.

Without being an UDP transmission expert, this is what I suppose:
Server begins sending at full speed, then it slows down because some packet acks come too late or something like this and he thinks the connection is not as fast as supposed at beginning.
So I think the reason is the high ping of my connection. Can anyone tell me if there is a usual practice on dealing this?
I already tried to find the section of throtteling the sending speed in code to debug but didn´t find yet.

Would be great if someone could help me on this issue.
Martin

Edit: I missed something - I think with multiple downloads the sum of avg. speed is higher than single downloads (same server, same file).

If the network is unreliable, L2TP will rely on the sender to retransmit.
Read up about Linux Traffic Control and try to configure your ppp interface using iptables/tc to limit bandwodth. The pppd ppp-up and ppp-down scripts might be useful to apply traffic control commands when your interface(s) are created and deleted.


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