ClearOne Digital Media - Manual (Page 30)

Another complicating factor with many HDMI connected multi-
source / multi-display systems is HDCP encryption.
There are two parts to HDCP, which must be discussed to better understand why solving the
EDID problem alone does not guarantee reliable interconnection in advanced systems using
HDMI. The first is HDCP authentication and the second is HDCP encryption to prevent
interception during transmission. Using HDCP authentication ensures all devices receiving
content over the HDMI link are licensed and authorized. Only after successful authentication
may the display output audio and video streams received from the HDMI link.
Every HDMI device contains a unique ID known as KSV (Key Selection Vector), which must
be passed to the source. Devices that re-transmit HDCP content will inform the source
of all downstream connections in the system. The source must then verify each device
before it transmits content. It is this authentication process that frequently causes delays
when switching between devices as the source and display(s) must negotiate their KSV’s to
ensure content is only delivered to authorized devices.
The HDMI standard imposes a hard limit on the number of displays that can be connected.
Due to a limit in the number of KSVs available, the HDCP specification calls for only up
to 127 devices. However sources usually support considerable less than 127 and in
fact most consumer products only support ten devices at most. What this means is if a
repeater presents a source with too many KSVs, the source will cease transmitting content.
Unfortunately for the AV professional KSV limits are not an advertised feature as HDMI was
really designed for point to point communications where even ten KSVs was thought to be
“more than enough” by the manufacturer of the HDMI silicon chipsets.
When KSV values are exceeded, the viewer will not realize a problem until they try to route
an additional source to an extra display and audio / video begins to drop out inexplicably.
To make matters worse, this can occur without so much as an error message.
ClearOne’s StreamNet solution solves these problems because of the innovative application
of encoders and decoders in its architecture. Since every source in a StreamNet system is
connected to what is known as an encoder, the source is able to easily negotiate EDID and
KSV values with the connected encoder, keeping the original design intent of HDMI’s point
to point architecture intact. In the case of StreamNet decoders, these devices connect to
each display and in-turn are able to easily return the EDID and KSV information an HDMI
connected source requires. The StreamNet solution also informs the user of potential HDCP
limits and issues, for example if you try to connect to a source that has already exceeded its
KSV limit, we will instruct you on screen or on the touch panel of your options, and how to
remedy the issue. Since we store all information on each unit, we can also switch sources
very quickly, greatly improving the overall user experience.
pg 30 StreamNet Digital Media and System Design Reference Guide
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Digital File Security and DRM