[asterisk-users] Real trunk group w/ DAHDI

[Kevin P. Fleming]

On 01/15/2012 08:14 PM, Louis Carreiro wrote:
> 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
> originator)
> 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
> octets
> *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 channels.
> 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.

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.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
Jabber: kfleming at digium.com | SIP: kpfleming at digium.com | Skype: kpfleming
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at www.digium.com & www.asterisk.org