Advanced OCS Dial Plan Part 2: Policy and Phone Usage. How to Alternate Route.
When you look at the OCS dial plan it’s pretty common to try to map what is occurring to the same things that happen in Cisco Unified Communication Manager (CUCM). For those of us that have dealt with both products it’s inevitable that you will try and do this.
OCS is little less granular than CUCM, which I do not mind at all. In my opinion, the dial plan in CUCM can be confusing and difficult to manage in the hands of the inexperienced in large deployments with multiple sites. So to let a bunch of Windows guys loose on a complex dial plan is asking for trouble:-) There are a couple of things that the MSFT engineers have done in OCS which mean they don’t have to be as granular as Cisco as well. The best one is no concept of internal tie trunks. In Cisco terms this is the inter-cluster trunks. This means there is no real need for trunk to trunk transfers or on-net trunking. Thank you MSFT. This doesn’t mean there isn’t a need to alternate route but it just makes it a whole lot simpler.
So let’s take a look at the example. First off a policy is applied directly to the user and dictates what phone usages that a user has access to. It also controls the users access to Simultaneous ringing. In my topology, we have created two copies of each policy, one with simultaneous ring enabled and one without. It really depends on what your current trunk usage is. Every call answered on a off net device generated by this feature consumes two trunk lines or DS0’s, unless of course the original call was internal, then it’s just one. With Sim ring, most users will only publish one number so the chances that your PSTN trunking requirements will increase are highly likely if proliferation of company cell phones in your company is high. Your company policy on call blockage will also play a part as well. So having both types of policies may be required depending on your traffic patterns to control its use.
Phone usage is where the alternate routing begins. A phone usage can contain multiple routes. It is in a specific order which is extremely important. The more specific the route for example 911 the higher in the order you want your phone usage to be. This is the only place in the dial plan where you have good control of the order of route selection so getting the order correct is extremely important. This is also where you can specify alternate routes for call route failures. For instance, if you look at the first two phone usages in my example, I have used to create a backup route for 911. This can also be a handy way to create a more universal route as a backup for local and LD route failures as well. As the example shows, I have a LD alternate for both my LD and local calling routes. Having a final route for calls is certainly a good idea even if receives low usage. Multiple sites can use the same final route so it’s a handy thing to have for route failures and traffic overflow of your primary route.
This example is not going to suit every company. You may want more granular control over separating local and LD, therefore you would need a third policy with only local routes and an alternate route as a backup.
Next week I finish off this series with route configuration. Till then happy alternate routing.