WCDTV IPTV Middleware Bedienungsanleitung PDF herunterladen (Seite 6)

Figure 1: Visual Display of HDMI Initialization Sequence

The source will then send its public key (AKSV) and read the sink’s public key (BKSV). In addition, speciﬁc timing

requirements have to be met. For example, the source has to allow at least 100 milliseconds after writing the

AKSV to the sink device before reading the Ro value [5]. The rst part of HDCP authentication is completed

successfully when the source reads the Ro’ value from the sink device and it matches the Ro value cal-

culated by the source. If there is a mismatch between Ro of the source and Ro’ of the display device, the

source will repeat the rst part of HDCP authentication [5]. The characteristic ashing seen in interopera-

bility problems is the HDMI source sending the 30 frames of unencrypted video. The HDMI source will then

set the Encryption Enable and begin encrypting the content [5]. The source will continue to monitor encryption

status using a periodic read of the Ri value.

When there is a repeater device involved in an installation, the initialization sequence and HDCP authentication

is much more complex. The source has to ensure that all of the devices downstream from the repeater device are

HDCP-compliant. The ﬁrst part of the HDCP authentication process is the same, but the repeater device has to

incorporate the public keys of all of the downstream devices into one register [5]. The repeater device has a maxi-

mum amount of time in which to collect the keys from the downstream devices, and some repeaters can handle

only a limited number of downstream devices [5]. If the repeater is able to handle all of the devices, it will calculate

a V’ value using the public keys of those devices. The source will calculate a similar V value with the same public

keys. The two values will be compared, and if they match, the authentication is successful [5].

HDCP’s purpose is to prevent users from accessing high deﬁnition content during transmission from a source

device to a sink device (i.e. from a set-top box to a TV). Each HDCP-capable device has 40 keys, and HDCP allows

sources, sinks, and repeaters to be connected in a tree-shaped topology with up to seven levels and 127 devices

[1]. HDCP can sometimes cause handshaking problems in which devices cannot establish a connection, especially

with older high-deﬁnition displays. Problems are almost always in the source device, according to HDMI LLC, and

tend to arise in one major area of implementation. Sources have to support a function called “authenticate

forever,” which in layman’s terms means the source must consistently send a signal inquiring whether its HDMI

input is selected, even while another input is in use [2]. If a source device times out and stops inquiring, an HDCP

authentication failure will most likely result.

Figure 2: Visualizing Hot Plug Detect

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WCDTV IPTV Middleware Bedienungsanleitung Seite 6