3.1.1.4 Proximity Detection
In proximity detection, the transmitter and receiver exchange messages in an attempt to determine the latency between them. If the latency is low enough (less than 7 milliseconds), the receiver is considered near the transmitter. The transmitter transfers licenses only to receivers that are near.
The proximity detection procedure is considered a part of the overall registration procedure. It is always performed after the registration response message is handled by the receiver. Proximity detection MUST be initiated after the successful completion of the registration procedure and after each revalidation procedure. The proximity detection procedure MUST have successfully completed before license retrieval can occur.
The following diagram illustrates proximity detection, which is part of the registration procedure:

Figure 5: Proximity Detection Flow
The following table describes elements of the preceding diagram.
|
Value |
Description |
|---|---|
|
Session ID |
128-bit random session ID. |
|
Seq |
8-bit incremental sequence number. |
|
Nonce |
128-bit random value. |
|
{Nonce}KCE |
Nonce encrypted using the content encryption key. |
The format of the proximity detection messages is defined in section 2.1.1.4.2.