The latest strategy / best practice for telepresence deployment is to register all the endpoints to UCM instead of VCS, and using Expressway C and E for B2B calls. There are several feature gaps, for endpoints register to UCM and VCS, one of the most common ask is IP dialling. In an ideal world we can make calls and receive calls with SIP URI, but there are still quite a lot of endpoints / users in the field using IP address dialling to make calls. I have read a very good post from UC Guerrilla and I have tested option 1 which works quite well in my lab environment. (My lab environment: UCM 10.5 + Expressway 8.2)
For the end user who wants to make outgoing IP address dialling, they can make a call to URI firstname.lastname@example.org where a.b.c.d is the IP address.
On UCM, you need to define the SIP route pattern beforehand.
Then what I need to do is to simply add a transform on the Expressway-C to remove the "ip@" suffix. You also need to have a search rule to route the IP address to Expressway E then to the DNS Zone. Try to make a call using IP dialling now!