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SRST operation on MGCP GW w/ PRI?

Arthur Luke
Level 1
Level 1

This is a general design question, as I don't have the ability to test at the moment. Question is whether or not I would drop all active calls in the scenario where a remote site is using a 29XX gateway with an ISDN PRI for all inbound / outbound calls, configured with ccm-manager fallback-mgcp?

I know the D-channel is backhauled to CallManager with an MGCP gateway, and in previous years, the only thing that was survivable during the fallback in the event of a WAN outage was FXO and T1 CAS. Has this changed recently?

5 Replies 5

Anas Abueideh
Level 9
Level 9

Hi,

PRI is supported for MGCP GW in SRST mode. We have implemeted it several times.

HTH

Anas

please rate if it is helpful

s_mcnally
Level 1
Level 1

I just tested this feature recently, I can confirm that calls that were in place before the SRST event will remain up. 

This is a general design question, as I don't have the ability to test at the moment. Question is whether or not I would drop all active calls in the scenario where a remote site is using a 29XX gateway with an ISDN PRI for all inbound / outbound calls, configured with ccm-manager fallback-mgcp?

In the event of a WAN failure all active MGCP calls are dropped.MGCP does not preserves calls during WAN failure or when failing over to SRST. MGCP preserves calls only during failover from Primary CUCM (due to service crash or whatever reason) to Secondary CUCM. MGCP does not support call preserve in WAN link failure scenario.

H323 and SIP will both support preservation of calls during the failover in both scenarios - during the WAN link failure as well as during the failover from primary to secondary CUCM. Though you will need to configure h323 to preserve calls in failover scenario (this feature was added around IOS12.4(9) T). But as already said SIP and H323 will provide call preservation support in both failover scenarios.

Terry

Paul McGurn
Level 6
Level 6

In a scenario where the SRST router is the same gateway that the PRI is installed on, and the IP phones retain IP connectivity to that gateway, the calls won't drop.  If the phones or gateway lose connectivity to CUCM, all the signaling will fail (they won't be able to end those active calls easily, but audio shouldn't drop.  We had this happen a couple weeks ago in one of our branch sites.  Their active calls stayed active, but their phones' signaling went haywire and required phone resets in some cases in order to get the electronic hookswitch functionality to behave again.

If the PRI/gateway loses connectivity to the IP phone side of things, you'll likely lose the calls.

The below table compares the SIP, MGCP and H323 features. Clearly mentions MGCP call preservation not supported in case of PRI WAN link failure. MGCP will support call preservation only for Analog or CAS T1/E1. Just copy pasted the relevant sections.

http://www.cisco.com/en/US/prod/collateral/routers/ps259/product_data_sheet0900aecd8057f2e0.pdf

SIP

MGCP

H.323

Feature

Benefits

Y

Y

Y

Cisco Unified Communications Manager failover redundancy

When the unified communications router loses contact with the primary Cisco Unified Communications Manager, the gateway uses the next available Cisco Unified Communications Manager.

Y

Y

Y7

Cisco Unified Communications Manager call preservation during failover

Existing calls are preserved during a failover to the next available Cisco Unified Communications Manager. Calls are also preserved upon restoration of the primary host Cisco Unified Communications Manager.

Y

Y

Y

SRST and gateway fallback

When contact with the Cisco Unified Communications Manager cluster is lost, SRST provides basic call handling for the IP phones. Gateway fallback provides support for PSTN telephony interfaces on the branch-office router for the duration of the loss.

Y

N

Y7

Call preservation for existing BRI and PRI calls during gateway fallback and recovery

Existing calls are preserved during a loss of connection to the Cisco Unified Communications Manager cluster and gateway fallback. Calls are also preserved upon restoration of the Cisco Unified Communications Manager connection.

Y

Y

Y7

Call preservation for existing T1/E1 (CAS) and analog calls during gateway fallback and recovery

Existing calls are preserved during a loss of connection to the Cisco Unified Communications Manager cluster and gateway fallback. Calls are also preserved upon restoration of the Cisco Unified Communications Manager connection.

There are lot of threads here – on this as well.

https://supportforums.cisco.com/docs/DOC-3048

https://supportforums.cisco.com/thread/2044723

Terry

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