Conference Bridge Resources

A conference bridge is a resource that joins multiple participants into a single call. Depending on the conference bridge you are using, each conference call is limited to a certain number of participants and specific codecs. There is a one-to-one correspondence between media streams that are connected to a conference and participants who are connected. The conference bridge mixes the streams together and creates a unique output stream for each connected party. The output stream for a given party is the composite of the streams from all connected parties minus its own input stream.

Cisco CallManager supports both hardware and software conference bridges. Hardware and software conference bridges can be active at the same time.

Hardware-enabled conferencing provides the ability to support voice conferences using hardware resources. Digital signal processors (DSPs) convert multiple voice over IP (VoIP) packets into streams that are mixed into a single conference call stream. The DSPs support both Meet-Me and ad hoc conferences. Hardware conference devices can provide a mixing of multiple codecs on the same conference call for G.711, G.729, G.723, Global System for Mobile Communication (GSM) Full Rate (FR), and GSM Enhanced Full Rate (EFR). Not all hardware resources support all of these codecs, but they all support at least G.711 and G.729, which are the two codecs supported by all modern Cisco IP Phones.

Software conferences use the resources of Cisco CallManager. A software conference bridge is capable of mixing G.711 audio streams and Cisco Wideband audio streams. Any combination of Wideband or G.711 a-law and mu-law streams can be connected to the same conference.

Conference bridges enable both ad hoc and Meet-Me voice conferencing:

  • Ad hoc conference A user, known as the conference controller, adds participants to a conference by calling the new participant and pressing the Confrn softkey. Alternatively, the conference controller can press the Select softkey and then press the Join softkey to make it an ad hoc conference. Up to 15 established calls can be added to the ad hoc conference (16 total). Only the conference controller can add participants to an ad hoc conference. An ad hoc conference can continue if the conference controller hangs up, but new participants cannot be added. When only two participants remain in conference, the conference terminates and the two remaining participants are reconnected directly as a point-to-point call. This action saves conference resources.
  • Meet-Me conference A user, known as the conference controller, presses the MeetMe button or softkey and establishes the conference. The administrator must configure a directory number (DN) or range of DNs in Cisco CallManager Administration. The conference controller provides the DN to the participants, and at the appointed time, participants dial the DN to join the conference. Participants can leave the conference by hanging up. If the conference controller hangs up, the conference continues if there are least two participants on the bridge.


The Meet-Me conference functionality included with Cisco CallManager is very basic and does not provide scheduling and/or security capabilities. The Cisco Meeting Place or Meeting Place Express software can be used for this functionality.


Conference Bridge Hardware

Table 15-1 identifies the conference bridge types that exist in Cisco CallManager 4.1 Administration. For each conference bridge type, the table lists the supported product or application, the supported codecs, and the maximum number of participants.

Table 15-1. Conference Bridge Hardware

Cisco CallManager Resource Type

Conferences Resource


Max. Participants per Conference

Cisco Conference Bridge


G.711 mu-law, G.711 a-law, G.729 annex A and annex B, and G.723.1

8 per conference, 64 conferences per port adapter

Cisco Conference Bridge Hardware

WS-X6608-T1 WS-X6608-E1

G.711, G.723, G.729, GSM FR, GSM EFR

1 CFB32 users to 10 CFB3 users

For G.711 or G.729a: 256 streams total per module, 32 streams maximum per port

Cisco Conference Bridge Software

Cisco IP Voice Media Streaming App.

G.711, Cisco Wideband

64Ad Hoc


Cisco IOS Conference Bridge


G.711, G.729


Cisco IOS Enhanced Conference Bridge




G.711, G.729, GSM FR, GSM EFR

G.711, G.729, or G723


Cisco Video Conference Bridge (IP/VC-35xx)


Numerous audio and video coding schemes

Varies by platform

Brief descriptions of the conference resources follow:

  • WS-SVC-CMM This conference bridge type, when configured with the ACT port adapter, supports the Cisco Catalyst 6500 Series and Cisco 7600 Series Communication Media Module (CMM). This conference bridge type supports up to eight parties per conference and up to 64 conferences per port adapter. This conference bridge type supports the following codecs: G.711 mu-law, G.711 a-law, G.729 annex A and annex B, and G.723.1. This conference bridge type supports ad hoc conferencing.
  • WS-X6608-T1 and WS-X6608-E1 The WS-X6608-T1 and WS-X6608-E1 provide eight digital T1 or E1 interfaces for public switched telephone network (PSTN) and PBX gateway access, transcoding, and conference bridging. Each one of these eight T1/E1 ports can be used for either WAN/PSTN connectivity or to provision the DSP resources for media resource support, but not both at the same time.
  • Cisco IP Voice Media Streaming Application The Cisco IP Voice Media Streaming Application provides voice media streaming functionality for the Cisco CallManager for use with MTP, conferencing, and MoH. The Cisco IP Voice Media Streaming Application relays messages from the Cisco CallManager to the IP voice media streaming driver. Supporting services using the Cisco CallManager are limited to G.711 only (with the exception of streaming MoH) because the CallManager is not capable of performing transcoding functions.
  • NM-HDV The NM-HDV network modules (NMs) provide conferencing, transcoding, voice termination, and a voice WAN interface card (VWIC) slot, and include the NM-HDV-2E1-60, NM-HDV-2T1-48, NM-HDV-FARM-C36, NM-HDV-FARM-C54, and NM-HDV-FARM-C90. The NM-HDV modules are first generation DSP farms. Much of this functionality has been merged into the NM-HD and NM-HDV2 modules.
  • NM-HD The NM-HD modules include the NM-HD-1V, NM-HD-2V, and NM-HD-2VE. The NM-HD-1V has one video interface card (VIC) slot and supports one analog or BRI VIC. The NM-HD-2V has two VIC slots and supports two analog or BRI VICs (or any combination). The NM-HD-2VE has two VIC slots and supports two analog or BRI VICs or two digital VWICs (or any combination).
  • NM-HDV2 The NM-HDV2 supports up to eight voice channels of analog or BRI voice. The NM-HDV2 supports a VIC/VWIC slot that can be fitted with either digital or analog or BRI voice/WAN interface cards, and supports up to 60 channels of digital voice or four channels of analog voice. The NM-HDV2-1T1/E1 adds support for one built-in T1 or E1 port and supports up to 90 channels of digital voice or 30 channels of digital voice and four channels of analog voice. The NM-HDV2-2T1/E1 adds support for two built-in T1 or E1 ports and supports a maximum of 120 channels of digital voice or 60 channels of digital voice and four channels of analog voice.
  • NM-HD-2VE The NM-HD-2VE supports analog, BRI, T1, E1, voice, and data WANs and up to 48 channels (G.711 codec).
  • IP/VC-3500 Series The Cisco IP/VC 3500 Series Video Multipoint Conference Unit is a dual multimedia bridge that provides videoconferencing. The videoconference bridge provides audio and videoconferencing functions for video Cisco IP Phones, H.323 endpoints, and audio-only Cisco IP Phones with the VT Advantage package. The Cisco IP/VC 3500 Series includes the Cisco IP/VC 3511, the Cisco IP/VC 3521 BRI Videoconferencing Gateway, and the IP/VC 3526 PRI Videoconferencing Gateway. For large or centralized videoconferencing deployments, the scalable, multifunctional IP/VC 3540 Series Videoconferencing System offers the combination of MCUs, a videoconferencing gateway, a rate matching module, and a data collaboration server. Each product in the series supports a number of audio and video codecs (H.261, H.263, H.263++, and H.264); these vary by platform.

Table 15-2 provides additional detail about audio conference bridges.

Table 15-2. Conference Bridge Hardware

Conference Type in Cisco CallManager

Number of Participants and Bridges



For G.711 or G.729a:

  • 256 streams total per module and 32 streams maximum per port.
  • Bridges can range from 10 bridges with 3 participants to 1 bridge with 32 participants.

For all GSM:

  • 192 streams per module and 24 streams per port



CallManager Software (Cisco IP Voice Media Streaming Application)

IP Voice Media Streaming Application on a standalone server:

  • 128 streams.
  • Ad hoc conference bridges can range from 42 bridges with 3 participants to 2 bridges with 64 participants.
  • A Meet-Me conference is 1 bridge with up to 128 participants.

IP Voice Media Streaming Application coresident with Cisco CallManager:

  • 48 streams.
  • Bridges can range from 16 bridges with 3 participants to 1 bridge with 48 participants.


Cisco IOS software

  • 3 bridges per PVDM-12
  • 3, 6, 9, or 15 bridges per NM
  • Maximum of 6 participants per bridge

For information on the PVDM2-8, PVDM2-16, PVDM2-32, PVDM2-48, and PVDM2-64, refer to the "Hardware Resources for MTP, Conferencing, and Transcoding" section of the Cisco IP Telephony Solution Reference Network Design (SRND) for Release 4.1 at:


Enhanced Cisco IOS software

The total number of conference sessions is limited by the capacity of the entire system, the Cisco CallManager, and the codec. Further details can be found in the "Cisco Enhanced Conferencing and Transcoding for Voice Gateway Routers" data sheet at:




The hardware and capacities described in Table 15-2 are accurate at the time of this writing; however, Cisco is continually adding new hardware and making improvements on existing hardware. To ensure accuracy when provisioning your network, refer to the latest CallManager SRND documentation available at


Conference Bridge Hardware CallManager Configuration

You must add hardware-based conference bridges to the Cisco CallManager configuration for the cluster to utilize them. The process of adding conference bridge resources differs, based on the type of conference resources you are adding. As an example, the following steps demonstrate the addition of a WS-X6608 as a DSP farm resource to the Cisco CallManager configuration:

Step 1.

Choose Service > Media Resource > Conference Bridge and then choose Add a New Conference Bridge.

Step 2.

Choose Cisco Conference Bridge Hardware in the Conference Bridge Type field. The Conference Bridge Configuration window shown in Figure 15-1 appears.

Figure 15-1. Cisco Conference Bridge Hardware Configuration


Step 3.

Add the MAC address of the WS-X6608 port that will be used for conferencing.

On the WS-X6608, the port must be pointed toward the Cisco TFTP server to obtain the configuration file and a list of the Cisco CallManager servers within the Cisco IP telephony network to use for registration. Use the set port voice interface command on Cisco Catalyst switches running the Catalyst operating system to point the port toward the Cisco TFTP server (usually the publisher server).

The following example disables Dynamic Host Configuration Protocol (DHCP) on port 3/1 of a 6608 port, assigns an IP address, subnet mask, VLAN number, and default gateway, and points the port to the Cisco TFTP server (in bold):

 set port voice interface 3/1 dhcp disable vlan 15 tftp gateway


Any Cisco CallManager servers in the cluster that have the Voice Media Streaming Application service activated will automatically be listed and used as a software-based conference resource. If you do not want a CallManager server to participate in conference bridge processing (to save resources), you can remove it as a conference bridge server by deleting the CallManager server in the Conference Bridge Configuration window.

Part I: Cisco CallManager Fundamentals

Introduction to Cisco Unified Communications and Cisco Unified CallManager

Cisco Unified CallManager Clustering and Deployment Options

Cisco Unified CallManager Installation and Upgrades

Part II: IPT Devices and Users

Cisco IP Phones and Other User Devices

Configuring Cisco Unified CallManager to Support IP Phones

Cisco IP Telephony Users

Cisco Bulk Administration Tool

Part III: IPT Network Integration and Route Plan

Cisco Catalyst Switches

Configuring Cisco Gateways and Trunks

Cisco Unified CallManager Route Plan Basics

Cisco Unified CallManager Advanced Route Plans

Configuring Hunt Groups and Call Coverage

Implementing Telephony Call Restrictions and Control

Implementing Multiple-Site Deployments

Part IV: VoIP Features

Media Resources

Configuring User Features, Part 1

Configuring User Features, Part 2

Configuring Cisco Unified CallManager Attendant Console

Configuring Cisco IP Manager Assistant

Part V: IPT Security

Securing the Windows Operating System

Securing Cisco Unified CallManager Administration

Preventing Toll Fraud

Hardening the IP Phone

Understanding Cryptographic Fundamentals

Understanding the Public Key Infrastructure

Understanding Cisco IP Telephony Authentication and Encryption Fundamentals

Configuring Cisco IP Telephony Authentication and Encryption

Part VI: IP Video

Introducing IP Video Telephony

Configuring Cisco VT Advantage

Part VII: IPT Management

Introducing Database Tools and Cisco Unified CallManager Serviceability

Monitoring Performance

Configuring Alarms and Traces

Configuring CAR

Using Additional Management and Monitoring Tools

Part VIII: Appendix

Appendix A. Answers to Review Questions


Authorized Self-Study Guide Cisco IP Telephony (CIPT)
Cisco IP Telephony (CIPT) (Authorized Self-Study) (2nd Edition)
ISBN: 158705261X
EAN: 2147483647
Year: 2004
Pages: 329 © 2008-2020.
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