Recently in the TechNet Forums I have seen a number of questions regarding using simultaneous ringing from CUCM or OCS to ring both a Cisco IP phone and Microsoft Communicator at the same time. Not to get this confused with dual call forking which this is not, I plan to use the term dual ringing devices. The Nortel CS1000 is the only OIP certified PBX that is capable of dual call forking. Cisco and Microsoft can both dual ring devices using different but similar methods . Due to this not being true dual call forking which has feedback mechanisms to avoid call loops the configuration between OCS and CUCM does not. Which means if configured incorrectly could cause some significant issues.
I don’t want to go in to the actual configuration but want to give some tips on what can help when doing this type of configuration and deciding if its right for your organization.
Tip 1. Where are my incoming PSTN DID’s terminating? Most likely calls from the PSTN may be the most critical. So having both devices ring when this occurs will be something you want. If you do not have both systems with direct PSTN access the best place to do dual ringing devices will be the system that is configured for the gateway that is terminating PSTN calls.
Tip 2. Choose one system that will do the dual ringing devices and live with it. Take the good with the bad and pick one system that will be configured to ring both endpoints. This falls into keeping it simple to avoid call loops.
Tips 3. Make sure you let users know what will work and what wont. Depending on where you ring from sometimes both devices will ring and sometimes it won’t but all incoming PSTN calls will, as an example.
Tip 4. If it’s not the right fit for an organization don’t do it because you can. For large enterprises this could be just too much work to keep a track of. Some people have it, some don’t, we have it on this cluster and not one that etc, etc. All in all it ends in much confusion and may be some mistakes which can leave a bad taste in a user’s mouth. So evaluate the value of doing this before committing to rolling it out everywhere.
Tip 5. Make this a server side configuration don’t leave it in the hands of your users. There are a couple of options to make this server side only configuration and if you plan on doing this it would be my recommendation to make it server side rather than user configured.
I hope these tips help in making the right choices for your organization.