VP306 datasheet(18/85 Pages) MITEL

18 / 85 page

VP305/6

DRAFT - PRELIMINARY DATA

The duplication or disclosure of data contained on this sheet is subject to the restrictions

on the title page of this document.

1.5.

The Reed Solomon block.

In the Transmission system, the MPEG2 message packet is encoded using the Reed Solomon

RS(204,188, T=8) shortened code. This converts the 188 byte data packet into a Reed Solomon

encoded block containing 204 bytes. The 16 check bytes allow the decoding system to search the

packet for errors and correct up to eight bytes containing errors. If there are more than eight bytes

containing errors, the packet is flagged as containing uncorrectable errors by pulling the BKERR

pin low and setting the TEI bit in the second byte of the packet header, see figure 21 on page 68.

The number of blocks containing uncorrectable errors may be read from the RS UBC register

which is reset to zero each time it is read. The 16 check bytes are discarded before the data

packet is passed on to the Energy Dispersal block.

Sync byte

187 bytes

16 check bytes

Reed Solomon encoded block.

Sync byte

187 bytes

MPEG2 transport packet.

1.6.

The Energy Dispersal (descrambler) block.

Before Reed Solomon encoding in the transmission system, the MPEG2 data stream is

randomised using the configuration shown in figure 11 below. This is a Pseudo Random Binary

Sequence (PRBS) generator, with the polynomial:

1 + X14 + X15

The PRBS registers are loaded with the initialisation sequence as shown, at the start of the first

transport packet in a group of eight packets. This point is indicated by the inverted sync byte

B8hex. The normal sync. byte is 47hex. The data starting with the first byte after the sync. byte is

randomised. (The sync. bytes themselves are not randomised).

In the decoder, the process of de-randomising or de scrambling the data is exactly the same as

described above.

12 13

000

Initialisation sequence

XOR

Fig. 11. Energy dispersal conceptual diagram.

VP306 Datasheet(PDF) 18 Page - Mitel Networks Corporation