Crestron DM-RX1-1G Specifications download pdf (Page 10)

Crestron DigitalMedia™ Design Guide

6 Check website (www.crestron.com) for product availability

HDCP

HDCP encryption is another complicating factor in HDMI installations. The HDCP system has two parts:

1. Authenticates HDCP devices to make sure they are authorized to receive the content

2. Encrypts the content to prevent interception during transmission

Authentication ensures that all devices receiving the content are licensed and authorized. Only after successful authentication

can the display output the audio and video streams.

HDCP Encrypts Each Individual Segment of an AV Transmission

HDCP Authenticates Each Device via the Source

Devices that re-transmit HDCP content must inform the source of all the downstream connections in the system. Every HDCP

device has a unique ID, known as a KSV (Key Selection Vector), which must be passed to the source. The source must then

verify each device before it transmits content. It is this authentication process that causes the 5-10 second switch times

in HDMI devices.

DigitalMedia solves this “blank screen” issue by using a technology called QuickSwitch HD™. In a standard HDMI switcher,

each display is authenticated dynamically when video is routed to it. With DigitalMedia, the authentication process takes place

as displays are added. During initialization, sources are authenticated with each display through the DigitalMedia system

before any audio or video is routed. By doing this, each switch can occur instantly.

Unfortunately, all sources have a hard limit on the number of displays that can be connected, due to a limit in the number

of KSVs they will accept. The HDCP specification allows for up to 127 devices, but sources usually support far fewer. Many

support fewer than ten devices, and for at least one popular cable box in the field, it’s only one. If a repeater presents a source

with too many KSVs, the source stops transmitting content. Unfortunately, KSV limits are not an advertised feature. Clients

won’t even realize they have a problem until they try to route a given source an extra repeater or display. Audio and video

drops out inexplicably in all connected rooms, typically without so much as an error message.

Again, a solution is needed that allows installers to make intelligent design decisions. During commissioning, the DigitalMedia

system tests the KSV limits of each source, and sets appropriate limits on the switch. It will bring any problem areas to the

attention of the installer, to be solved before becoming end user issues.

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Crestron DM-RX1-1G Specifications Page 10