Re: [B.A.T.M.A.N.] Latency Related Problem

Re: [B.A.T.M.A.N.] Latency Related Problem

[Marek Lindner]

Hi,

> I am using batman-adv for my project. I have configured my network in
> following topology,
> 
> 
> NODE 1 (STA|AP) ------ NODE 2 (STA|AP) ------ NODE 3 (STA|AP) ------
> 
> I am getting very high latency if I ping NODE 2 or NODE 3 from NODE 1. Ping
> latency is approx 100ms.
> 
> I am getting the normal delay ( 1ms) if I ping the Nodes without
> batman-adv.
>
> I have also tested with "batctl ping" and getting the same issue.

can you please provide packet dumps (tcpdump or wireshark) of the different 
traffic types flowing through your network ?

Which batman-adv version are you using ?

Cheers,
Marek

Re: [B.A.T.M.A.N.] Latency Related Problem

[Marek Lindner]

Hi,

you don't like the mailing list ? Why do you keep mailing me privately ? this 
is the last time I respond to mails you send to me privately concerning 
batman-adv. Use the mailing list!

On Tuesday, January 08, 2013 19:36:45 you wrote:
> I am not comparing the ping between two nodes.
> 
> I am just concerned about the ping latency between nodes.
> 
> As per my experiment, I am getting 100ms delay between one hop(SPK3
> –to-SPK2) and 200 ms delay between two hops (SPK3-to-SPK1) and so on.
> 
> Even 100ms delay seems a lot, some applications may not work properly.
> 
> Is there any delay (buffer) involved in local packet delivery from  bat0 to
> local mesh interfaces (wlan0)?

yes, there is standard wifi buffering. Consider this:

ping time from node1 to node2: ~100ms
ping time from node2 to node3: ~100ms

=> ping time from node1 to node3: ~200ms

The delays simply add up because wifi is a shared medium. The node in the 
middle can only forward the packet while it does not receive. That is due to 
how wifi works and has nothing to do with batman-adv.

If you wish to mitigate the delay you should not use a shared medium. For 
example using multiple wifi cards on different channels is a solution.

Cheers,
Marek

Re: [B.A.T.M.A.N.] Latency Related Problem

[NicoEchániz]

On 01/08/2013 09:52 AM, Marek Lindner wrote:
> 
> Hi,
> 
> you don't like the mailing list ? Why do you keep mailing me privately ? this 
> is the last time I respond to mails you send to me privately concerning 
> batman-adv. Use the mailing list!
> 
> On Tuesday, January 08, 2013 19:36:45 you wrote:
>> I am not comparing the ping between two nodes.
>>
>> I am just concerned about the ping latency between nodes.
>>
>> As per my experiment, I am getting 100ms delay between one hop(SPK3
>> –to-SPK2) and 200 ms delay between two hops (SPK3-to-SPK1) and so on.
>>
>> Even 100ms delay seems a lot, some applications may not work properly.
>>
>> Is there any delay (buffer) involved in local packet delivery from  bat0 to
>> local mesh interfaces (wlan0)?
> 
> yes, there is standard wifi buffering. Consider this:
> 
> ping time from node1 to node2: ~100ms
> ping time from node2 to node3: ~100ms
> 
> => ping time from node1 to node3: ~200ms
> 
> The delays simply add up because wifi is a shared medium. The node in the 
> middle can only forward the packet while it does not receive. That is due to 
> how wifi works and has nothing to do with batman-adv.
> 
> If you wish to mitigate the delay you should not use a shared medium. For 
> example using multiple wifi cards on different channels is a solution.


There must be some other problem involved here. We have very good ping
times with batman advanced in working networks as well as test setups.
See this article for example:

http://blog.altermundi.net/article/multiple-hop-mesh-performance-with-multi-band-dual/