Welcome to the first article on the series “Demystifying CCNA Voice”. We will be dealing with CCNA Voice certification topics and discuss them on an easy-to-learn approach.

Before we discuss the pieces of Unified Communications, first we need to understand what Unified Communications is. This term was coined in the mid-90’s but was not widely used until a few years back when companies like Cisco began developing more technologies in this market.

Unified communications is basically the integration of real-time communication services such as IP telephony, video, web conferencing, presence, instant messaging and other widely used media. Integration basically means making several components interoperate or work as one solution. Most common example of integration of UC is between CUCM (Cisco Unified Communications Manager), a call processing system and Cisco Unity Connection (CUC) which provides voicemail services.

Now that we have the basic understanding of Unified Communications, it’s time for us to discuss each of the layers and components that comprise the Cisco Unified Communication solutions. The first figure below illustrates the layers and the core components for each layer. The second figure shows an example where the components are located in a voice network.

Figure 1 – Cisco Unified Communications Voice Infrastructure

Figure 2 – Sample of a Voice Network from Cisco.com


This layer consists of routers, switches, voice gateways and security appliances like firewalls. The primary function of the infrastructure layer is to carry data, voice and video between all network devices and applications. Infrastructure layer would also provide, high availability, management, administration, QoS and security to all devices. I would say that this layer glues the pieces together. Infrastructure is always the core of any network based service or application. This is why knowledge of routing and switching is a prerequisite for the CCNA-Voice. Cisco recommends passing the CCENT exam to able to obtain the CCNA-Voice certification.

Let’s discuss a few details on the components that belong to the infrastructure layer.

Routers – the norm for any organization is to have multiple branches. These branches communicate data using routers which are connected to a WAN network. Routers are responsible for carrying the data through the shortest and fastest path possible. High availability features in routers and routing designs provide multiple paths from one destination to another. Routers also provide QoS (Quality of Service) in a Unified Communications environment. QoS ensures that delay and jitter sensitive traffic like voice packets are prioritized and sent first in the event of network congestion.

Switches – Ethernet is a common interface in any of the IP devices nowadays. It is the handoff of just about almost all of the network or IP-based devices. Cisco IP Phones are connected to switches and the switches that are normally being used are POE (Power over Ethernet) capable. PoE means that the Cisco IP Phones are powered through the Ethernet port on the switch and will not require any power adaptor. Cisco 2960, 3560, 3750, 4500 and 6500 series switches support POE. The servers hosting CUCM and other services are also connected to the switches.

Voice Gateways – a voice gateway is a router that is connected to the PSTN (Public Switched Telephone Network) that is either traditional analog, digital or PBX (private branch exchange). Voice gateways’ function is to enable communication between the enterprise voice network and the outside world telephony systems.

Applications like CUCME (Cisco Unified Communications Manager Express) and Cisco Unity Connection Express are installed in voice gateways.

The Cisco routers that are used as voice gateways are the ISRs (Integrated Services Routers) which include Cisco 1800, 1900, 2800, 2900, 3900 and 4451X series.

Security Devices – Security devices like Cisco ASA 5500 can prevent any unauthorized network connections being made to the call control servers that can impact performance and availability. It can also provide voice and video encryptions services to prevent any eavesdropping on the network. For telecommuters and remote users, the ASA can provide VPN services that will allow them to connect to the corporate network and UC services.

Call Control

The call control layer is what processes the calls, controls the devices or endpoint applications, administers the dial plan and features to the endpoints. Included here are CUCM, CUCME and CUCM BE (Business Edition). This layer also connects the endpoints to the services available in the Cisco Unified Communications environment.

In layman’s terms I would say that this is the brain of the whole UC network. Endpoints like IP phones and softphones’ functionalities or features mostly rely on the call control devices. For example, a phone will understand that it needs to sound a specific ringtone when there is an incoming call, knows that it needs to provide a dial tone when the handset is lifted and knows which number to dial if the speed dial buttons are pressed. The reason for this is that the call control device like the CUCM tells the phone what to do through some signalling protocol like SIP and SCCP. Moreover, call control devices allow the phones to connect to a specific service through providing URLs of the service.

When administering dial-plans, the call control layer tells the endpoints how to reach the other endpoints. Likewise, call control devices also communicate with the voice gateways when a call to the PSTN is made. Common protocols used for voice gateway signalling are H.323 and MGCP (Media Gateway Control Protocol) but SIP is slowly getting into the picture.

Let’s move on and discuss some details on the call control systems.

Cisco Unified Communications Manager (CUCM) – This, I would say, is the most important application used for centralized call processing. Meaning, the phones can register to the CUCM regardless of their physical location. Most people still call this “call manager” as it was its original name and I guess because it’s a lot easier to say. Originally, this ran on MS Windows Server platform using HP or IBM Servers. Starting version 5.0, Linux was the platform that this application ran on. Cisco introduced the MCS (Media Convergence Servers) as an addition to the supported servers. With the gaining popularity of the cloud, this can now run as a virtual server usually on Cisco UCS (Unified Computing Servers).

CUCM can be run in a cluster. By definition, a cluster is a group of devices that share the same function and database. A CUCM cluster is composed of a publisher, subscribers, TFTP servers and media resource servers. A normal cluster can manage up to 60,000 phones using 20 servers which are composed of one publisher, eight subscribers (four primary and four secondary), two TFTP servers and up to nine media resource servers. Normally, a CUCM cluster resides in one location but some voice network designs require them to be in different locations. This is called Clustering over WAN (CoW) and is usually implemented within a single metropolitan area or sites with high speed links as this setup requires less than 80ms return trip time to work properly.

A publisher is a device where the administration of the CUCM is done like adding phones, users and dial plans. The configuration in the publisher is propagated to the servers called “subscribers” in the cluster. However, in the event of publisher failure, none of the subscribers will take the publisher role. It needs to be restored so the administration can be done once again. CUCM administration is done through browser based GUI.

The endpoints like IP phones can register to any of the publisher or subscriber depending on the configuration. The IP phones can be configured to register up to three CUCM servers. This is done one at a time and in particular order for redundancy purposes. The list of three CUCM servers is known as the CM Group.

TFTP servers are where the phones’ configurations are saved. In most implementations, the CUCM servers themselves are configured as TFTP servers but third party TFTP servers can also be used. Media resource servers perform media processing functions like transcoding and streaming audio for music on hold.

Cisco Unified Communications Manager Business Edition (CUCM BE) – This has close to full functionality of the CUCM, however this can only support up to 1000 users. Cisco recommends this for midsize businesses. This is a standalone product and cannot be clustered. Cisco Unity Connection is included in the CUCM BE product package and resides in one physical server.

Cisco Unified Communications Manager Express (CUCME) – This is also commonly known as CME or “call manager express”. As the word “express” implies, CUCME can be considered a “lite” version of CUCM. This application is installed in voice gateways (ISR routers) and provides some of the basic features of the CUCM. CUCME can support up to 450 phones depending on the router used.

CUCME is used by small and big organizations. Smaller organizations use CUCME as the local call processing system which would mean the CUCME should be residing in the same site as the phone. Each of the companies’ sites will have its own CUCME router. For calls to be made from one site to another, CUCME’s are configured with dial peers. It’s like telling the routers that if it sees a number is dialled, route to the IP address, specified in order, is done to make the call. Below is an example of a dial-peer configuration.

	dial-peer voice 1 pots
 	destination-pattern 555....
 	port 1/0:1

	dial-peer voice 2 voip
 	destination-pattern 555....
 	session target ipv4:

For bigger organizations, CUCME is mostly used for phone redundancy, a feature commonly referred to as SRST (Survivable Remote Site Telephony). SRST can be standalone without CUCME, however most implementations use CUCME with SRST. When the branch site loses its connection to the CUCM due to a WAN failure, the phones registers instead to the CUCME and will be able to make and receive calls through the PSTN network. Not all features supported by CUCM work in CUCME.

CUCME can be managed through CLI or GUI by using CCP (Cisco Configuration Professional) web based application.


Applications can reside anywhere in the network, provided through IP. This doesn’t rely on call control functions and the physical voice-processing infrastructure. Examples of this are Unity Connection, Unity Express, Unified Presence, and Unified Customer Contact Solutions.

For the CCNA Voice, we will be discussing the first three listed.

Cisco Unity Connection (CUC) – is a voicemail application that also provides auto attendant and IVR services. Its predecessor was called Unity and ran on MS Windows. Cisco Unity Connection now runs on Linux and is usually integrated with CUCM. This can also be integrated with MS Exchange like accessing your exchange calendars or even sending your voicemails through email. Currently supports up to 20,000 users per server. Administration is done through GUI.

Cisco Unity Express (CUE) – has similar functions like the Cisco Unity Connection. Like the CUCME, this resides inside a router through an AIM (Application Integration Module) or through an SM (Services Module). Currently supports up to 250 users. CUE administration can be done through CLI or GUI.

Cisco Unified Presence Server (CUPS) – basically provides “presence” or status of the user similar to what you see in well-known instant messengers. (Busy, Away, Online, etc.) This can be integrated on just about any component of the UC like CUCM, Unity and IP Phones. Additionally, this provides Instant Messaging services so endpoint applications like CUPC (Cisco Unified Personal Communicator) can send instant messages. This is managed through GUI.


These are devices or applications end users use. This can be IP Phones and applications like CIPC and CUPC.

IP Phones – Cisco phones can run either SCCP or SIP protocol. 7937G, 7975G and 7931G are only few examples of the models of Cisco IP Phones. The 9900 series are phones that are video capable. 7926G, 7925G, 7925G-EX and 7921G are Cisco wireless IP Phones.

CIPC (Cisco IP Communicator) – is a Windows based Cisco softphone. It enables voice and video calls from a desktop or a laptop computer using a standard USB headset. This software is mostly used by people who work from home, supporting a contact center or those who are doing business travels.

CUPC (Cisco Unified Personal Communicator) – is an all in one software solution that includes, voice, HD video, presence and instant messaging.

We have covered all the core pieces of Cisco Unified Communications. In the next articles, we will be discussing more in detail how these pieces work and how to configure them. I hope that this article has sparked your interest to pursue your CCNA Voice certification. See you in the next article.