This week I am taking some time out from my schedule to catch up and do a bit of training. I am also taking a look at the new Cisco 8.x SRND as well as the new Cisco interoperability document on using the CUBE with OCS 2007 R2.
Cisco Unified Border Element and OCS 2007 R2 Interoperability Document
Get the document here.
There are some really good things about this documents that are well worth checking out but there also a few items to be aware of such as support from Microsoft for the IOS version and some of the CUCM setup used. The current Microsoft supported IOS version can be found here. If you are currently using the CUBE to do interoperability between OCS and CUCUM this offers some new commands in the IOS code (15.1.1T) that will help overcome some previously encountered issues . In saying that direct SIP to CUCM 7.1 is also supported by Microsoft so using the CUBE is not a requirement for interoperability.
First stop is a comment on page 5. “Some Microsoft Client endpoints require RTCP packets. If RTCP packets are not generated by all endpoints, additional features of the Cisco Unified Border Element can be used to resolve this issue. Contact your Cisco sales engineer for information.” If you read down the page, 5 bullet points down you get a better understanding about what they are talking about. Basically if you stop sending RTCP packets to Communicator or the conferencing service, they will hang up after 30 seconds under certain circumstances which are explained in the document. This behaviour has been seen with Cisco IP phones and Unity when they stop sending RTCP. Cisco have a work around for Unity with ISR's acting as MGCP gateways as well, so its an issue they have had to deal within their own ecosystem and not just with OCS.
There is one more point worthy of a mention in this first part of the document. The last bullet in this section talks about early media negotiation and ringback not working. It does not require a CUBE to solve this issue but having the IOS command suggested as a fix does simplify things if you have a CUBE deployed. This issue can be solved using a MSPL script on the front ends of your OCS deployment. Doug Lawty wrote a great blog post on this sometime ago if you’re experiencing this issue. For the CUBE, Cisco are recommending using the command “voice-class sip block 183 sdp present” on dial peers. This only allows 180 SIP ringing messages towards CUCM.
After skipping through the OCS configuration (beaware the screenshots showing the dialplan is not using Microsoft recommended E.164 best practices) on page 46 you get to the IOS configuration which is pretty helpful. If you are using an earlier version of Cisco UCM prior to 7.1 you may have to experiment a little with some of these commands to see if they work as expected.
The last half of the document is screen shots from CUCM configuration. Looking over the SIP trunk portion, one point to be aware of is this document does not show MTP as required selected. Now, for the SIP endpoints registered with CUCM this is not going to be an issue but for first generation Cisco SCCP IP phones this could cause a problem. 7940’s and 7960’s to be clear. Just something to keep in mind when you follow this document if you run into issues. With that you may also need to do some MTP planning which can be also run on the CUBE which is in flow though mode. The media is going to run through the CUBE regardless if the MTP is hosted there or not.
The last couple of areas worth mentioning is Appendix A which talks about earlier versions OF CUCM and removing the + sign and transcoding G.711 to G.729. Appendix A is handy if you plan to do it this way rather than remove the + at the mediation server itself. So again you do not need to use the CUBE to fix this issue. Then finally the transcoding section is handy if you implemented G.729 in areas of your Cisco network.
So overall this looks and feels like a lot of preceding documents Cisco have done on OCS integration. Something’s have provided a handy fix and other parts of the document are there for the sake of showing how it’s done with a sceenshot. Don't expect an in-depth analysis and I think you will be okay. Of course the main part of the document is the IOS configuration so its worth a look if for nothing else than that.