Which Dahdi/libpri Combo For BRI/PtmP ?

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I need to rebuild a system which has 4 BRI ports and is connected to Point-to-multiPoint lines, in a country where telco often “drop lines for energy savings“.

I’m planning to use latest 11.4.0 asterisk version along with dahdi and libpri (no misdn).

Which version are recommended for Dahdi and Libpri ?

My main requirements are, beside having calls coming in and out:
– keep a meaningful “pri show spans” status (pri show spans outputs Down when the line is down (cable unplugged, no q921 traffic, …))
– avoid sporadic ERROR messages in logs.


5 thoughts on - Which Dahdi/libpri Combo For BRI/PtmP ?

  • I think the dropped D-channel issue should be handled by a very recent DAHDI. If there are still issues file a bug. Don’t know about PtMP.

    Probably the very latest you can find. If the latest stable does not work for you then try an RC of an upcoming version or get master from git.

    Guess you have to test.

    Regards, Patrick

  • I am using ISDN BRI connections for several years now. I have never seen a problem with down states of the D channel. If there is nothing hooked up to the S bus it is very likely that the D channel will be down after a while. When you start the low level driver, the line might still be down. But when you start Asterisk and DAHDI tries to negotiate a TEI
    value, then the line will connect. So far I have never seen a disconnected state on a BRI-P2MP line while Asterisk is running. To be precise, I always observed periodic RR frames (typically every 10
    seconds) when Asterisk is running for apparently idle lines. I have all the docs, but I wasn’t motivate enough so far to read them and learn whether disconnected states are possible with active devices. As I said, any recent version should be fine. Did you have any problems with the line status?


  • 2013/6/6 jg

    I think but I’m far from being certain that PtmP lines are the one concerned by Telco energy savings. If someone could shed some light on this, that would be perfect.

    My case is worse : I didn’t even try to get the docs 😉

    Not exactly but I was thinking about tweaks such as *layer1_presence*=ignore or layer2_persistence=keep_up. I wonder if the later one, didn’t mask current line status.

  • Googling, I found this one-year old thread about the same subject http://thr3ads.net/asterisk-users/2012/06/1950384-Asterisk-10-1.6.1-and-Dahdi-Libpri-compatilities-in-BRI-PtmP

    If my reading and understanding is correct:
    1. Briging layer 1 down is specific to PtmP (PtP is not concerned).
    2. When a line is down, pri show spans shows it as such, and the one way to check this line can be up is to it an outgoing (easy) or incoming (harder)

    A workaround is to use layer2_persistence=keep_up which can be forbidden by Telco, as it will keep the line from entering energy saving mode.

    An other way to deal with this is to completely forget pri show spans in PtmP installation, forget about beautiful RRDTools graphs and learn to supervise systems with log output (“no failure when trying to output a call
    = no problem”).

    Thoughts ?

    2013/6/6 Olivier

  • I don’t see where your problem is. Can you get a pcap trace of the D-channel? There’s not that much, so you could run it overnight.

    You should see the RR frames, maybe a few of SABMEs. I am wondering whether the RR frames will stop at some point. When things need to reinitialize you should see a SABME frame before a SETUP request.