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PBX failure Tracing..!!

xtam1
Beginner
Beginner

Dear All,

Kindly I have the following questions regarding the below setup,

VoIP GW1---Backup PRI[to PBX using PSTN]

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Leased Line

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VoIP GW2

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PRI

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PBX----Backup PRI[from VoIP GW1 via PSTN]

1- Let's say that the Leased line between GW1 & GW2 fails so the calls will flow via the backup PRI.

2- If the VoIP GW2 fails so it's going to be the same as in the previous case.

# My question is:

What if the PRI link between VoIP GW2 & the PBX fails or what if the PBX itself failed.. How will the VoIP GW1 detect this case and switch to the backup PRI?!!

The diagram will be the same if the PRI Link between the VoIP GW2 & PBX Fails, but in case of PBX failure actually the diagram will be as

follow:

VoIP GW1

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Backup PRI[to BackupPBX using PSTN]

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Backup PBX

VoIP GW1 is Cisco 2650XM

VoIP GW2 is Cisco 3745

Regards,

Tamer Bayomy

6 REPLIES 6

dragos.stroescu
Beginner
Beginner

Hello,

You must use the hunting mechanism built into the CISCO routers.

First you construct two dial peers in GW1 (one VoIP lower preference to GW2 and the second POTS pointing to the back-up PSTN link).

After that you configure the global option "voice hunt ..." with tens of cause codes as options which means: if on the first VoIP call the return disconnect cause code is .... then hunt to next dial-peer available which is the POTS one (higher preference).

See next the router oyions in lates IOS:

CCM-EXPRESS(config)#voice hunt ?

<1-180> Call disconnect cause code

access-info-discard access info discarded (43)

all continue hunt for all disconnect cause codes

b-cap-not-implemented bearer capability not implemented (65)

b-cap-restrict restricted digital info bc only (70)

b-cap-unauthorized bearer capability not authorized (57)

b-cap-unavail bearer capability not available (58)

call-awarded call awarded (7)

............................

Thanks Dragos, i started reading regarding the keyworks that you provide me, but it seems very confusing so i started to post the diagram of my case but the system gave me error while uploading so i'll send it to you just if you don't mind..

Regards,

Tamer

Thanks Dragos, i started reading regarding the keyworks that you provide me, but it seems very confusing so i started to post the diagram of my case but the system gave me error while uploading so i'll send it to you just if you don't mind..

Regards,

Tamer

Tamer,

The things are not so complicate. First you'll have to test each failure scenario at the remote end and "see" what is the failure code the GW1 is receiving.

For example if GW2 is down the H323 setup will timeout based on:

voice service voip

h323

h225 timeout setup 10 <- this timer

after that the router will go for the next dial-peer matching the called number.

Another example is the remote link between GW2 and PBX is down, then you will have to debug the calls and see WHAT "disconnect reason - cause code" you'll get back (for example you can get "no circuit" cause code).

For those specific cause codes for each failure scenario you should enable the hunting on GW1 (e.g. "voice hunt no-circuit") so the router will search for another dial-peer WITHOUT sending you the disconnect.

Tip. You can enable "voice hunt all" and basically the GW1 will go on the second dial-peer via PSTN for ANY unsuccesfull attept to get to GW2.

Good luck

dragos.stroescu
Beginner
Beginner

One more Tamer,

All scenarios are OK based on previous explanations just take care to the "PBX Failure" scenario!

To access the second (redundant) PBX you will probably have to "call" a different phone no. as in the middle is the PSTN.

There are two options here:

- either the PSTN SP is able to provide 2 E1's one active (main PBX) one standby (second PBX) or;

- you should use two different dial-peers pointing to PSTN on which you will change the destination number with translations (translation-profile) to be able to call the second PBX.

Thanks Dragos, you have been more than helpfull..

Regards,

Tamer Bayomy

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