Cisco UC – Unified Communications Arquitecture

By | 07/05/2014

UC Architecture

Infrastructure Layer:

  • Components: Switches, Routers and voice gateways
  • Carries data, voice and video between devices and applications

Call Control Layer:

  • CUCM, CUCM Express or CUCM Business Edition
  • CUBE – Cisco Unified Border Element (Session Border Controller)
  • SRST – Survivable Remote Site Telephony
  • Provides call processing, device control, dial plan admin

Appplication Layer:

  • Cisco Unity, Contact Center, Cisco Unified Presence (enables Jabber), Cisco Webex Meeting Centre
  • Support for standard protocols: TAPI. JTAPO, SOAP, H.323, MGCP, SIP

Endpoint Layer:

  • IP Phone, Softphone
  • Support for SCCP, H.323, MGCP and SIP


  • Cisco Unified Attendant Console


Jabber architecture:

cisco jabber architecture

CUCM Architecture

Based on a unique Publisher with Read/Write access to the DB and N Subscribers with Read access only. It’s not possible to promoto a Subscriber to a Publisher so the Publisher node should be very well protected with backups.

Software (since version 5)

  • Custom Hardened Red Hat Linux
  • IBM IDS Database – Informix
  • Legacy: Versions previous to 4.x were based on Windows Server + MSSQL.


Managed in the Cisco Prime License Manager (Same server that the CUCM)

  • Device-based licensing
    • Basic – 1 device per user
    • Enhanced – 2 devices per user
    • Premium – unlimited devices per user
  • User-based licensing


  • MCS – Media Convergence Server or Third Party server platforms approved by Cisco
  • Since version 8, CUCM was optionally virtualized or hosted in a dedicated server.
  • From version 10, all the Cisco Boxes (CUCM Publisher, Subscriber, Unity,…) are always virtualized

C Series

Rackable servers. Are usually packaged with the Business Edition 6000 product. It’s a special bundle with 2 cluster servers capacity, supporting up to 8VMs each and with ESXi software on them.

Up to 1000 users and 40 sites (1HQ + 39 brances)

Legacy: Buesiness Edition 5000 (BE5000) was a bundle of  a CUCM + Unity in a MCS 7825.

B Series

It’s a blade hardware that support up to 30.000 users. Maximum of 20 servers but only 8 of them can process telephony.

It’s expected that each Subscriber hosts 7500 phone devices and only 4 subscribers are actively used. The other 4 subscribers are kept as backup.

To telephony redundancy models: 1:1 (1 active, 1 passive) and 2:1 (1 passive for each 2 active)

  • Up to 1000 phones
    • 1 Publisher (TFTP)
    • 1 Subscriber (First for telephony processing)
  • Up to 7500 phones — Redundancy 1:1
    • 1 Publisher + TFTP – No processing telephony
    • 1 Subscriber with 7500 phones
    • 1 backup subscriber
  • Up to 15.000 phones
    • 1 Publisher + TFTP – No processing telephony
    • 2 Subscriber with 7500 phones each
    • 1:1 2 Subscriber for backup
    • 2:1 1 Subscriber for backup
  • Up to 30.000 phones
    • 1 Publisher + TFTP – No processing telephony
    • 4 Subscriber with 7500 phones each
    • 1:1 redundancy – 4 subscribers for backup
    • 2:1 redundancy – 2 subscribers for backup

When using the 2:1 redundancy level,  there is a save when using physical servers. It doesn’t make sense when using virtual machines. If the 2 subscribers are down, the backup subscriber won’t be able to support 15000 phones.

There is a “Megacluster” option that supports up to 80.000 users.

Deployment Models

Single site

All services (CUCM, Gateways) and phones are in the same site.

Codecs: High bandwidth codecs can be used: G711, G722. No transcoding needed.

Dial plan: Centralized. Simple configuration for emergency numbers (112).

Multisite – Centralized call processing

This is the most common model. CUCM, GW and other services are kept in a central site (HQ, DC). Remote sites or branches connect to the central sites through the WAN network to register to the phones and get access to PSTN. Infrastructure is managed centrally and it’s not required to setup servers in the branches.

Dial plan: Centralized, but use of regions and locale configurations.

Codecs: BW is limited. It will require CAC (Call Adminission Control), G729 and transcoding

SRSTs may be required – Branches routers can be used as a gateway to provide telephony backup services when WAN is down. It’s like a backup small call manager express. SRST will require a license and also a DSP to connect to the PSTN network. If DSP is not available, SRST also makes sense just to keep the internal phone working when the WAN is down.

Multisite – Distributed call processing

Two big sites, each one with one telephony cluster (Publisher + Subscribers). The two  CUCM systems are interconnected with a Trunk through a IP-WAN network that will require a high bandwidth.

Central gatekeeper is required to implement Call Admission Control.

It’s the most complicated scenario.

Cluster over WAN

Publisher in one site and subscriber in the second site. They require a WAN link with high bandwidh and a maximum delay of 40 ms.

Phones register to the local site subscriber but they can also register in the remote subscriber in case of local failure..

There is only one management point.


Contact Center


  • Contact Center Express (CCX)
  • Contact Center Enterprise (CCE)

It requires a Voice Gateway to control the voice flows and CUCM for call control and agent users.


  • Intelligent contact routing
  • Call treatment
  • Network to desktop computer telephony integration
  • Multi-channel contact management
  • Precision routing  (Agents attributes and competences)
  • Script editor
  • Dashboards, reports
  • Remote agent support


  • Contact Center Management Portal (CCMP) – Management of agents, contacts, equipment, audio
  • Queue Manager – call treatment, caller options, static announcements, music, dynamic announcements
  • Intelligence Center – Reports and Dashboards

Desktop options:

  • Finesse – think clients desktop based on browser
  • Cisco Agent Desktop (CAD) – software client, not in development anymore
  • CTI Toolkit Desktop (CTI – Computer Telephony Integration)
  • Cisco Unified IP Phone Agent
  • CRM Integrated desktop
    • It’s not possible to combine Finesse agents with CAD agents.

Recording methods:

  • Computer between the phone and the network to capture the traffic
  • Network based – Fork the media. Requires a built-in bridge in the media termination.
  • Server based – using SPAN ports

CCX Licensing

There are 3 license versions: Standard, Enhanced and Premium.

It requires per concurrent user licenses, but they can’t be mixed. All licenses should be standard or premium or enhanced.

Standard license doesn’t support Desktop Client Agent

The license is bound to the MAC address. Migrating the CCX to another machine requires to “re-host the license”. This can be done contacting


Video – Designing and Deploying Cisco Contact Centre Express

CAD vs Finesse

Finesse site

CCX Script Repository



Unity is the dedicated box of the Unified Communications that manager Voice Mails, AutoAttendants and IVRs. It has some minor and very limited Contact Center functions regarding prompts

Message Waiting Indicator – MWI – Red light on the phone to indicate there are messages. Some times it loses sync and needs to be refreshed.


Gateway, Gatekeeper, CUBE and SRST

The Gateway is the component of the Unified Communications system that will link the IP Telephony with the PSTN network. They are routers with special VWIC cards depending on the type of link with PSTN network that will be used (BRI, PRI, ISDN,…). Gateways will also need the PVDM card to transform between codecs.

CUBE (Cisco Unified Border Element) is the SBC (Session Border Controller) that allows the link between different UC systems through SIP trunks. It’s needed if the ISP provides a SIP trunk instead of a PSTN connection. It’s also based on Cisco routers.

SRST is also another component based on Cisco routers that will allow basic call manager functionality for remote sites when they lose connectivity to the CUCM. It can be build in the same gateway or it can be a separated box.

H323 Gatekeeper is also based on Cisco routers and it’s the component that can be used as a central dial plan when there are several CUCM clusters in the Enterprise domain. That will save the full-mesh connection configuration between CUCMs. It also provide scalability and Call Admission Control in a central way. As a disadvantage, it’s a single point of failure, although HSRP, secondary gatekeepers and GUP clusters can be used to mitigate this problem.