Using video endpoints in the Cisco CallManager system is, from the perspective of a user, as easy as placing a telephone call. Video terminals can be either H.323- or SCCP-controlled and are able to communicate with each other regardless of the protocol controlling the device. All video devices use the same dial plan as all other devices in the Cisco CallManager system. For Cisco CallManager, video devices are treated like voice devices, with the same configuration options. For the Cisco VT Camera, the same DN as the associated IP Phone is used. There is no additional number to remember to be able to reach someone over the video system. The video signaling is transparent to the user, and the devices negotiate their video capabilities, such as codec, format, and bit rate used for the video call, with no additional user action.
Cisco CallManager Involvement in Video Calls
A video telephony call can be established between any two video-enabled endpoints. If one of the endpoints is not video-enabled, the call is set up as a normal voice call. When both endpoints are video-enabled, Cisco CallManager signals the voice and video capabilities to both endpoints, as shown in Figure 28-1, and the endpoints directly build two RTP streams, one for voice and one for video. Call control for video calls operates the same way as the call control that governs voice calls.
Figure 28-1. CallManager Video Involvement
The term "video call" is sometimes confused with the term "videoconferencing." A videoconference is a video call with at least three participants.
For videoconferences in the Cisco CallManager system, extra hardware is required. The device that mixes the video streams is an MCU.
Video Call Flow
The typical video call includes two RTP streams in each direction. A basic video call includes two unidirectional RTP streams for voice and two unidirectional RTP streams for video. The call can include these stream types:
In the example shown in Figure 28-2, the video-enabled endpoints report their video and audio capabilities to Cisco CallManager. Cisco CallManager now treats the endpoints simply as video phone devices. When a call is placed or received between two video-enabled devices, Cisco CallManager signals for both audio and video streams. First the audio capabilities, such as audio codec information and audio bit rate, are signaled and negotiated, and then the audio stream is set up. After the audio stream is set up, the video capabilities, such as video codec information and video channel bit rate, are negotiated, and the devices exchange their video streams separately from the audio. In this example, the video call has four RTP streamstwo unidirectional RTP streams for voice and two unidirectional RTP streams for video transmission.
Figure 28-2. Video Call Flows
Video Codecs Supported by Cisco CallManager
Cisco CallManager supports several standard video codecs and a Cisco proprietary video codec. H.263 is a video codec specified by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) as a low-bit-rate encoding solution for videoconferencing. It was first designed to be used in H.324-based systems (PSTN and other circuit-switched network video environments) but has since found use in these other solutions as well:
H.263 was developed as an evolutionary improvement based on experience with H.261, the previous ITU-T standard for video compression, and the Moving Picture Experts Group-1 (MPEG-1) and Moving Picture Experts Group-2 (MPEG-2) standards. The first version of H.263 was completed in 1995, and it provided a suitable replacement for H.261 at all bit rates. H.263 was further enhanced in H.263 version 2 (H.263v2, also known as H.263+ or H.263 1998) and H.263 version 3 (H.263v3, also known as H.263++ or H.263 2000).
The next enhanced codec specified by the ITU-T after H.263 is the H.264 standard. Because H.264 provides a significant improvement in capability beyond H.263, the H.263 standard is now considered primarily a legacy design (although this is a recent development). Most new videoconferencing products include H.261, H.263, and H.264 capabilities.
The video codecs supported by Cisco CallManager Release 4.1 include H.261, H.263, and H.264. These codecs exhibit the parameters and typical values listed in Table 28-1.
Video call speed
128 kbps, 384 kbps, 768 kbps, and 1.544 Mbps
15 frames per second (fps)
The Cisco Wideband codec is a proprietary codec that is a fixed-bit-rate codec and runs on a PC that is linked to a phone. It enables the PC to associate with a call that the phone receives and can only be used by the Cisco VT Camera.
Video Protocols Supported in Cisco CallManager
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
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
Configuring Alarms and Traces
Using Additional Management and Monitoring Tools
Part VIII: Appendix
Appendix A. Answers to Review Questions