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New Contributor II

Configuration question - trunk cost & Backup path

so I have several CPE's with the configuration below. What I need to know is, will this "failover" as the previous engineer expected it to with this cost setup? should T03 and T02's costs be reversed?

NOTE - this is a primary TRUNK and a backup TRUNK to SBC's on my network, and a PRI to the premise:

!

voice trunk T01 type sip

  description "to primary SBC"

  sip-server primary x.x.x.x

  codec-list "High Bit Rate" both

!

voice trunk T02 type isdn

  description "PRI to Customer PBX"

  resource-selection circular descending

  connect isdn-group 1

  no early-cut-through

  rtp delay-mode adaptive

!

voice trunk T03 type sip

  description "to backup SBC"

  sip-server primary y.y.y.y

  codec-list "High Bit Rate" both

!

!

voice grouped-trunk PRI

  trunk T02

  accept $ cost 100

!

!

voice grouped-trunk SIP

  trunk T01

  accept $ cost 0

!

!

voice grouped-trunk BACKUP

  trunk T03

  accept $ cost 200

!

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7 Replies
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Valued Contributor
Valued Contributor

Re: Configuration question - trunk cost & Backup path

Hello,

If both trunk T01 and T03 have the same settings you may want to consolidate them into one trunk.

voice trunk T01 type sip

  description "to primary SBC"

  sip-server primary x.x.x.x

  sip-server secondary y.y.y.y

  sip-server rollover service-unavailable-or-timeout

  codec-list "High Bit Rate" both

You can see more configuration examples here https://supportforums.adtran.com/docs/DOC-4388.

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Honored Contributor
Honored Contributor

Re: Configuration question - trunk cost & Backup path

This will work for outbound calls in most cases. It depends on the failure mode of trunk T01. If it is completely unreachable, unregistered, or returns a SIP code of a hard failure such as 503 then the call will go out T03. If the carrier on T01 accepts the call and misroutes it, gives dead air, or plays an intercept recording then the call won't be re-tried.

For inbound calls, it's very difficult to achieve any kind of redundancy in real time for a given number.

In cases where there are more than one carrier involved, I would get a bit more sophisticated than merely "accept $ cost" in grouped-trunk configuration. If one carrier sends random calls to you either maliciously or erroneously, you don't want to send those out another carrier (and get billed for them by the outgoing carrier).

* For your PBX, don't use "$" but program the actual numbers that are routed to the PBX. If these are in blocks, there are regular-expression-like shortcuts for entering them.

* For your carrier trunks, set up SABR so that one trunk can't send calls to the other.

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Valued Contributor
Valued Contributor

Re: Configuration question - trunk cost & Backup path

When using "sip-server secondary" the trunk will accept inbound calls from both the primary and secondary sip servers.

If the purpose of the two sip servers is fail over, "sip-server secondary" will be a good option.

It eliminates the need for a new trunk which in turn eliminates the need for SABR routing.

This will keep the config a lot less complicated.

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Honored Contributor
Honored Contributor

Re: Configuration question - trunk cost & Backup path

unified wrote:

When using "sip-server secondary" the trunk will accept inbound calls from both the primary and secondary sip servers.

If the purpose of the two sip servers is fail over, "sip-server secondary" will be a good option.

The problem with inbound failover isn't getting the TA900 to accept calls from a second provider. It's getting the PSTN and SS7 network to port the numbers to the backup provider on-the-fly in the event of a failure (and then back again).

If both your primary and backup SIP servers are from the same provider, then that provider can obviously route inbound calls to the secondary, but that isn't real redundancy as you're relying on a single provider and a significant outage within that carrier is going to kill your inbound calls. Sure, you can configure your device to accept inbound calls from multiple providers, but getting the rest of the world to send your calls to the backup provider is a much different story. It's a bit easier with toll-free numbers that the carrier routes to a POTS number but still far from automatic.

I still recommend SABR any time you've got two different carriers coming in to a box. You really don't want to accidentally provide transit between two carriers. It can get ugly and expensive.

Valued Contributor
Valued Contributor

Re: Configuration question - trunk cost & Backup path

Based upon the original question it seems that this is a CPE being connected back to a primary and secondary SBC.

There is no mention of there being two different providers.

If there are then as jayh​ said, SABR would be the solution.

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New Contributor II

Re: Configuration question - trunk cost & Backup path

this is correct. 1 carrier, 2 separate IP's.

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Honored Contributor
Honored Contributor

Re: Configuration question - trunk cost & Backup path

OK, then yes you can just configure the IPs as primary and backup SIP servers on the same trunk.

Ask your provider if they use SRV records for SIP. If so, you can use their hostname instead of IP addresses as the SIP server and configure your Adtran device as if it was a single non-redundant provider. Failover will take place silently in the background. This is by far the simplest and most elegant way do do it, and avoids reconfiguration on your part in the future if the provider changes their redundancy scheme.