What's the best way to configure two PRI interfaces in a single trunk group?

[Anonymous]

I'm preparing to install the device between the carrier and the customer's PBX. Currently two PRI circuits connect to their PBX directly. Both PRI circuits have a D-channel (FAS) and they're provisioned as one logical trunk group. The carrier-side B-channel hunt order is linear ascending from PRI1 channel 1 to PRI2 channel 23 (46 total). PBX B-channel hunt order is linear descending in the opposite direction.

It's important that the hunt from TA900e toward telco is descending between the circuits as well as their B-channels (PRI2 then PRI1).

I plan to wire interfaces as follows:

TA PRI 0/1 - Telco PRI1

TA PRI 0/2 - Telco PRI2

TA PRI 0/3 - PBX PRI1

TA PRI 0/4 - PBX PRI2

My question:

Should I configure two isdn-groups and connect each to two PRI interfaces? This would require only two voice trunks (one for telco and one for PBX). For example:

!

isdn-group 1

  connect pri 1

  connect pri 2

!

!

isdn-group 2

  connect pri 4

  connect pri 3

!

-OR-

Should I create four voice trunks and simply use trunk groups to combine them at that level for call routing? For example:

!

voice trunk T01 type isdn

  description "Telco1"

  resource-selection linear descending

  connect isdn-group 1

!

voice trunk T02 type isdn

  description "Telco2"

  resource-selection linear descending

  connect isdn-group 2

!

voice trunk T03 type isdn

  description "PBX1"

  resource-selection linear ascending

  connect isdn-group 3

!

voice trunk T04 type isdn

  description "PBX2"

  resource-selection linear ascending

  connect isdn-group 4

!

!

voice grouped-trunk TELCO

  trunk T01

  trunk T02

!

!

voice grouped-trunk PBX

  trunk T04

  trunk T03

!

Does it matter, really? I want to make sure the linear B-channel hunt order begins with lowest channel on first PRI (telco) and highest channel on second PRI (PBX), but not sure if either approach (or both approaches) provide a way to order the respective circuits in this way.

A third approach would be four separate trunk groups.  I'm confident we can use accept/cost values to control the hunt order between circuits in each direction.

What's the most efficient or elegant way to configure this?

[Anonymous · Accepted solution]

A support engineer from ADTRAN provided the following guidance:

I would recommend the first option in grouping your PRI's such as the following:

!

isdn-group 1

  connect pri 1

  connect pri 2

!

!

isdn-group 2

  connect pri 4

  connect pri 3

!

This will avoid any call loops (therefore bypassing the need to run Source Ani Based Routing (SABR)).

I would like to point out, though, that PRI to PRI is not a supported application.  So while it can be configured, if there are any issues with the operational capacity of the configuration, we will be unable to assist in configuration changes or troubleshooting.  If you have the option of running PRI from your carrier and then SIP to your PBX (or vice versa), it would be recommended to take that course.

Further clarification was given:

The order that the PRIs are connected will determine how the channels are allocated.  This can be somewhat manipulated by changing the 'resource-selection' command which is detailed on page 4,668 of our AOS Command Reference Guide located at the following URL:

AOS Version R13.6.0 Command Reference Guide - https://supportforums.adtran.com/docs/DOC-2011

Perhaps this will be helpful.  Thanks,  adtran-support​!

Cheers,

Chris