Unified CM and CME Connectivity

There are two primary ways to connect Cisco Unified CM systems and CME's between sites, that is H.323 or SIP. The primary focus in the SRND seems to be on the H.323 model which is deployed using either a Cisco Unified Border Element (CUBE) or what's called a via-zone gatekeeper. The important thing to note between CUCM and CME is that H.450 is used with CME for supplementary services but not with CUCM which can turn into dropped calls over a PSTN due to compatibility issues. I believe CUBE or a via-zone gatekeeper is used to mitigate these issues and act as the middle man. SRND is a pretty high-level document so a lot of things I read aren't going to really explain the reasons why or how. That's what's the CCNP: Voice books should provide for me...hopefully.

Gatekeeper Redundancy

There seems to be two different options for gatekeeper design, clustering and directory gatekeeper (DGK). It looks as if the preferred method is clustering gatekeepers together rather than creating a DGK. Using gatekeeper clustering, you configure a local gatekeeper at each site but then you make redundant alternate connection other sites. This allows for the gatekeeper to provide primary call routing for the main site along with providing alternate call routing for other locations connected to it and vice versa.

DGK depends on the Hot Standby Router Protocol (HSRP) or by configuring multiple DGK's in your environment. I'm still trying to wrap my head around how this particular way works a little more.

Call Processing Overview

I'm on part 2 of the Unified CM SRND guide, it's a good 400 pages long so it's going to take me a while to finish this section. The last few days I went through 40 pages or so reading up on a high-level over view regarding the best ways to deploy Call Manager 8.x along with providing scalability, resiliency, and high speed performance. This is for all three flavors of Cisco Unified Communications:

Cisco Unified Communications Manager (CUCM)
Cisco Unified Communcations Manager Business Edition (CMBE)
Cisco Unified Communications Express (CME)

Unified CM Clustering over the WAN

I went over yet another Cisco VoIP deployment model which involves configuring a CM cluster that is spread over multiple remote sites. So there is a subscriber and maybe a backup subscriber (depending on resiliency needed) at each site that is to be involved with the CM Cluster. With that you provide either local fail over or remote fail over. Local fail over provides the most resilience sense it implies that there's a subscriber and backup subscriber at each site. Remote fail over provides more flexibility since you are failing over to another remote sites CM subscriber server essentially instead of failing over to your own local subscriber. This model only requires one subscriber as well.

I also reviewed the section that discusses virtualization of all of these different deployment models using Unified Computing System (UCS) which is just all of the Cisco VoIP products deployed on a VMware system using Fibre Channel over Ethernet (FCoE) as the media for communication between them all.

Intercompany Media Engine Architecture

I had a quick study session this morning reading up more on a new feature to me called Cisco Intercompany Media Engine. I went over the call processing and how it uses IME compatible ASA's and Unified CM's to learn and place calls between enterprises. Along with our to fail over to PSTN in case of connectivity or latency issues. It's a pretty neat technology but I'm curious as to how many enterprises implement this solution currently.

Multisite Distributed VoIP Deployment

I briefly went over the Multisite Distributed VoIP Deployment section in the SRND Guide. It has very similar attributes and requirements as the centralized model except it is a lot more versatile due to having a call processing cluster at each site. That eliminates the need to depend on the WAN or whatever media of inter-site connectivity for calls as much. I also began reading about the Cisco Intercompany Media Engine which seems to dynamically interconnect different enterprise organization phone numbers and create a network similar to how internet was when it was first created. Instead of just IP services, the network is used to connect Unified Communications within all the Enterprises. There's a lot more to learn about this technology and I may be off a little bit with my understanding of it at this point in time.

VoIP Site Based Design Models

I spent sometime this morning reading through the various VoIP deployment models and how to implement high availability with each model while trying to get over this cold I currently have. So far I only went through the Campus model and the model that shows centralized call processing with multiple sites. In my current work environment we currently use the latter which is a centralized site that provides all the call processing which is then distributed to our multiple remote call centers. We're working on converting this into a more highly available solution which is a distributed model.

I plan on reading up on the other site based design guides that shows the distributed model along with a few others. I'm starting to see that there are multiple ways to provide redundancy using tools such as SRST (Survivable Remote Site Telephony), Distributed Communications Manager Express (CME), and many others.