Cisco IPT (voice) multi-site design - local vs. LD calls

Posted on 2011-03-04
Medium Priority
Last Modified: 2012-06-21
I have some fairly basic design questions regarding Cisco IP telephony deployment "best/common" practices.  

Let's consider a simple multi-site design - centralized call control (Communications Manager) at HQ/head-end, with multiple, small remote offices. Don't worry about bandwidth between sites or any other capacity issues - this is really focused on PSTN access, and local vs. long-distance.  Each remote site has less than 20 users. I would consider a "standard" deployment in this case to include a local voice gateway at each site, just to support the minimum number of FXO ports for 911 and SRST access during failover.  So, maybe we put a 4x FXO card in each remote site router.  So, my questions, in this deployment, and using best practices:

1) Is the local voice gateway configured to handle all local PSTN calls? Meaning, if someone at remote site X calls the pizza joint across the street, will the local gateway handle that call (which seems logical)? But if that's so, then that office could only handle as many local concurrent calls as they have local analog trunks, correct?

2) Conversely, if all PSTN traffic was defaulted through the central site, then a "local" call would traverse over the WAN back to the central site, then become a long distance call back to the pizza joint across the street.

So, looking for "best practices" here - is it recommended to provision as many FXO/analog trunk connections at each remote site for concurrency of local calls?   I've seen a LOT of designs in the company I'm currently with where they provision the bare minimum at each remote location, just to handle 911.

Thanks, folks.
Question by:cfan73
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Expert Comment

ID: 35042578
Hi There


FXO on the remote sites is not a best practice you are going to have lots of issues in future. I recomend to upgrade them to 2x BRI ISDN and that will give you 4 local concurrent calls.

If you are going to centralize the outbound calls then you can use the local gateway as MGCP or H323 to route the local calls to the local gateway via route group (standard local group) and device pool to minimize complex configurations.

You can also route emergency numbers to the local gateway via route group (standard local group) and device pool which is recomended as a best practice and easy configuration otherwise you need CER which is not cheap .

I hope that helps.


Author Comment

ID: 35044479
Thanks for the response - a couple clarification questions if I may:

1) Why are FXO modules not a good choice at the remote sites?  Let's say, a single 4-port FXO module in the voice gateway vs. the 2x BRI you mentioned?

2) Regardless of which method you use, is this the "best practice" and most commonly-implemented design... provisioning as many local ports at each remote sites based on the number of concurrent PSTN calls they'll place (vs. centralizing PSTN access at the HQ, for example)?

Thanks again!

Expert Comment

ID: 35045822

FXO is well known for issues like Discconect tones complex configuration. I'm not saying that is not going to work but BRI or PRI are preferred for business lines. The price for BRI and FXO lines is the same.

Regardless of which method you use, is this the "best practice"?

That all depend on how many users you have in the cluster. if more than 500 then Centralized will cut cost. If below 500 you should use the local ISDN for all the calls and centralize the CUCM only.

Many organizations now implement the centralized solution for the outbound and Inbound calls however you still need the local lines for SRST which they can also be used to route emergancy and local calls.

By centriliazing  the LD and international  calls you can use SIP which is grwoing very fast this days and use local BRI or PRI ISDN for SRST. Many organizations love this solution because you can get great bundles with SIP specialy if you have high volume of calls.


LVL 79

Accepted Solution

lrmoore earned 2000 total points
ID: 35046944
1) You can design the call flow any way you want, but if it is a long distance charge to call Joe's Pizza using the HQ' PRI, then yes, you want to route local calls through the local PSTN. And yes, you are limited to the physical number of analog circuits that you have. We do recommend POTS lines for SRST and for local 911 calls, but a fractional PRI might be a better choice is there are going to be lots of inbound/outbound calls. It all depends on what those 20 employees do. If they sit at a desk and make/take calls all day, or if they are, say bank tellers that wait on customers all day with little phone usage, you have different patterns.
Bottom line is that you need to understand the phone usage at the remote sites and understand the costs associated with consolidating calls at a main site vs routing local calls to local gateways. I see nothing wrong with FXO modules and rarely ever have issues with them, at least not in the USA.

2) yes. You have to work with the telco provider. It may end up less $ in the long run if you have an expanded local calling area, or only $0.02/minute long distance charges, and just keep a couple of analog pots lines at a remote site for true emergency use only.

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