Real trunk group w/ DAHDI

Home » Asterisk Users » Real trunk group w/ DAHDI
Asterisk Users 2 Comments

Hey all!

I’ve been banging my head against the wall for a while (almost 18 hours
today alone) with this one… I migrated our incomming T1’s from the Option
11 to our Asterisk box this morning. We have 1 local T1 and 2 long distance
T1’s. The local T1 went over with out a hitch. The problem is with my 2
long distance T1’s. The switch on the other end is a DMS250 I’m told so I
set Asterisk to DMS100 and got the timing, framing, etc all set. Well, the
D channels came up so thats good. I started getting dropped calls every
once in a while. I did a debug on the spans and saw the following:

PRI Span: 3
PRI Span: 3 < Protocol Discriminator: Q.931 (8) len=40
PRI Span: 3 < TEI=0 Call Ref: len= 2 (reference 857/0x359) (Sent from
PRI Span: 3 < Message Type: SETUP (5)
PRI Span: 3 < [04 03 80 90 a2]
PRI Span: 3 < Bearer Capability (len= 5) [ Ext: 1 Q.931 Std: 0 Info
transfer capability: Speech (0)
PRI Span: 3 < Ext: 1 Trans mode/rate: 64kbps,
circuit-mode (16)
PRI Span: 3 < User information layer 1:
u-Law (34)
PRI Span: 3 < [18 04 e9 80 83 08]
PRI Span: 3 < Channel ID (len= 6) [ Ext: 1 IntID: Explicit Other(PRI)
Spare: 0 Exclusive Dchan: 0
PRI Span: 3 < ChanSel: As indicated in following
*PRI Span: 3 < Ext: 1 DS1 Identifier: 0
*PRI Span: 3 < Ext: 1 Coding: 0 Number Specified
Channel Type: 3
PRI Span: 3 < Ext: 0 Channel: 8 Type: CPE]
PRI Span: 3 < [20 02 00 e2]
PRI Span: 3 < Network-Specific Facilities (len= 2) [ Toll Free MEGACOM ]
PRI Span: 3 < [6c 0c 21 83 37 32 37 34 30 33 34 30 37 34]
PRI Span: 3 < Calling Number (len=14) [ Ext: 0 TON: National Number (2)
NPI: ISDN/Telephony Numbering Plan (E.164/E.163) (1)

The key part is the “*Ext: 1 DS1 Identifier: 0*” part. That’s when calls
fail. Right now, all calls are coming in on span 3 and want to talk to
Identifier 0 (span 2). If a call comes in on span 2 and requests “*Ext: 1
DS1 Identifier: 1*”, it fails. I called Verizon and asked them what was
going on. Turns out, its configured as a trunk group. The tech mentioned
that I need to figure out how to set my identifiers on the group and I
should be good to go. I’ve done a ton of research about chan_dahdi.conf and
dahdi-channels.conf and I think the answer is trunk groups.

I tried configuring a trunkgroup and set the primary dch to 24 and the bdch
to 72 and then then spanmap’ed span 2 and 3 into group 1 (e.g. 2,1,0 and
3,1,1) but I don’t see anything when I do a “dahdi show channels” or a “pri
show spans” or a “pri show channels”, not even the channels not in the
group. If I delete the trunkgroup, all three commands return all the

I’m just curious if I’m going down the right path with trunkgroups for this
or if there is something else to take care of the DS1 Identifier issue.

Thanks in advance everyone!


2 thoughts on - Real trunk group w/ DAHDI

  • So another quick look… when a sucessful call comes in it goes to DS1
    Identifier 0… the Asterisk CLI shows the following:

  • You are, but your configuration attempt doesn’t make much sense; it
    sounds like you created an invalid configuration, and when chan_dahdi
    attempted to load it, it dropped the whole thing (and you should have
    seen errors on the console/logs).

    You have three physical spans:

    span 1 is channels 1-24, and is your local group.
    span 2 is channels 25-48, and is your first span of the LD group.
    span 3 is channels 49-72, and is your second span of the LD group.

    If you want to setup NFAS for this configuration, you’d do this:

    * Create a trunkgroup, with channel 48 as the primary D-channel, and
    channel 72 as a backup D-channel (if that’s how your NFAS group is
    configured… many NFAS groups only have one D-channel).

    * ‘spanmap’ span 2 into that trunkgroup as logical span 1.
    * ‘spanmap’ span 3 into that trunkgroup as logical span 2.

    To keep your configuration consistent, you can also configure your first
    span as a trunkgroup, even though it only has one span in it:

    * Create a trunkgroup with channel 24 as the primary D-channel, and no
    backup D-channels.

    * ‘spanmap’ span 1 into that trunkgroup as logical span 1.

    The trunkgroup numbers you assign really aren’t important, as long as
    they are unique; they are never communicated over the ISDN signaling,
    only the logical span numbers are.