Added transmission end signalling – SP5WWP

docs/application_layer.rst

@@ -74,10 +74,13 @@ value is extracted from the NONCE field, as the 96 most significant
 bits of it. The highest 16 bits of the counter are the remaining 16
 bits of the NONCE field. FN field value is then used as the
 counter. The 16 bit frame counter and 40 ms frames can provide for
-over 43 minutes of streaming without rolling over the counter. This
+over 20 minutes of streaming without rolling over the counter [#fn_roll]_. This
 method adapts 16-bit counter to the standard 32-bit CTR for the
 encryption. FN counter always start from 0 (zero).
 
+.. [#fn_roll] The effective capacity of the counter is 15 bits, as the
+              MSB is used for transmission end signalling
+
 The nonce value should be generated with a hardware random number
 generator or any other method of generating non-repeating
 values. Nonce values must be used only once. It is obvious that with a

docs/data_link_layer.rst

@@ -137,6 +137,10 @@ Subsequent frames
      - 4 bits
      - Flushing bits for the convolutional encoder that don't carry any information
 
+The most significant bit in the FN counter is used for transmission
+end signalling. When transmitting the last frame, it shall be set to 1
+(one).
+
 Superframes
 ~~~~~~~~~~~