The Cisco TelePresence 65-inch displays and cameras natively support 1080p and 720p resolutions and use digital media interfaces to connect to the codecs. This ensures the integrity of the video signal from end to end, eliminating the need for any digital and analog conversion.
Inside the Cisco TelePresence codec, an onboard array of Digital Signal Processors (DSP) encode the digital video signal from the cameras into Real-Time Transport Protocol (RTP) packets using the H.264 encoding and compression standard.
The quality of the video enjoyed by the meeting participants is a function of three variables:
- Resolution (the number of pixels within an image)
- Frame rate (how often pixels are redrawn on the display)
- Degree of compression applied to the original video signal
Video Resolution
The 1080p resolution provides the highest quality video image currently available on the market, supplying a resolution of 1920 x 1080 and 2,074,000 pixels per frame. The 720p resolution provides a resolution of 1280 x 720 and 922,000 pixels per frame. Compared with today’s DVD standard video with a resolution of 720 x 480 and 346,000 pixels per frame, you can see the dramatic increase in resolution and pixel count. Figure 1 illustrates the difference between these three resolutions.
Frame Rate
The frame rate of the displayed video directly corresponds to how motion within the video is perceived by the participants. To maintain excellent motion handling, the Cisco TelePresence system encodes and displays video at 30 frames per second (30fps) at all times. In addition, the cameras and displays use progressive-scan technology to refresh the pixels within the video signal faster than with traditional television and video conferencing equipment that use an interlaced refresh format.
Compression
Note that 1080p video uncompressed is delivered at approximately 1.5Gbps. The Cisco TelePresence codecs must take this native video received from the cameras and compress it to a more feasible amount of bandwidth in as little time as possible. As mentioned previously, the codec achieves this by using an array of Digital Signal Processors (DSP) to compress the original 1.5-Gbps video from each camera down to under 4Mbps (per camera), representing a compression ratio of over 99 percent, which is done in under 90ms. The customer is provided with some amount of control over how much compression is applied. However, For each of the two resolution formats supported (1080p and 720p), the Cisco TelePresence codec supports three quality levels. Each quality level is really a function of the degree of compression applied with each quality level requiring a different amount bandwidth. For simplicity, these three levels are referred to as good, better, and best. The best quality level has the least amount of compression applied and, therefore, requires the most bandwidth, while the good quality level has the most amount of compression applied and requires the least amount of bandwidth.
Providing two resolutions and three quality levels within each resolution provides flexibility when deploying Cisco TelePresence. More importantly, it allows the Cisco TelePresence codec to automatically adapt to adverse network conditions by lowering the quality level and resolution to deal with packet loss.
Considering the three variables of resolution, frame rate, and the degree of compression applied, Table 1 illustrates the different quality settings supported by the Cisco TelePresence codec and the requisite bandwidth required for each quality setting.
1080p | 720p | |||||
|---|---|---|---|---|---|---|
Quality Level | Best | Better | Good | Best | Better | Good |
Frame Rate | 30 | 30 | 30 | 30 | 30 | 30 |
Bandwidth | 4Mbps | 3.5Mbps | 3Mbps | 2.25Mbps | 1.5Mbps | 1Mbps |
These bandwidth values apply per camera. Therefore, a CTS-3000 or CTS-3200 that has three cameras and three displays, running at 1080p resolution at the best quality level, requires 12Mbps of video bandwidth, whereas a CTS-1000 or CTS-500 requires 4Mbps of video bandwidth.
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