If you're not familiar with how least-cost/failover routing works in Lync, please refer to my post on the subject in my Lync Enterprise Voice Best Practices series.
With version 9.0 of the Lync Dialing Rule Optimizer, Lync administrators now have the option to create least-cost/failover routing between all sites that have been deployed using the Optimizer (or at least follows the same naming conventions used by the Optimizer).
When the Optimizer-generated script detects multiple Lync sites, it will prompt the user if they want to apply least-cost/failover routing to the voice policy being generated. If the user allows it, the Optimizer will add PSTN usages for all the other sites to the new voice policies. This assumes the existing PSTN usages are named with the country abbreviation first, and ends with either Local, National, International etc in any of the languages currently supported by the Optimizer as in the following examples: UK-Leeds-113-Local, IT-Rome-06-Nazionali.
The output can be best summarized by way of example. Assume a company has Lync Enterprise Voice deployed in the following locations:
After running the Optimizer script against all sites, the PSTN usages for the Toronto International user voice policy would look like this (you might want to sit down for this):
The Optimizer will group PSTN usages from the same country near the top, using the assumption that most of the calls will be made to in-country locations and that the fewer PSTN usages the system needs to evaluate for each call, the better.
The ordering is such that least-cost routing and failover routing will occur. PSTN usages from other countries will be placed lower in the list while still providing least-cost and failover routing for all calls. If there are multiple Lync sites out-of-country, the ordering of PSTN usages within the National and International usages will be somewhat random. Administrators should review the PSTN ordering to make sure it suits their needs.
It is assumed that premium numbers can only be dialed from in-country locations, so out-of-country premium PSTN usages are not assigned. Also, only the local service PSTN usage is assigned for similar reasons.
All calls will use the least-cost route where possible. If a route assigned to a specific usage is unavailable, calls will use a route in another site, again keeping the call in-country if possible.
With the inclusion of least-cost/failover routing in the Lync Optimizer, administrators now have a tool that can completely build the Enterprise Voice environment for even the largest enterprise-level Lync deployment.
As always, feedback is greatly appreciated. Let me know if you come across any issues with functionality or scalability as I haven't tested if there is a limit to the number of PSTN usages that can be assigned to a voice policy.