MT92210 Datasheet, PDF (111/175 Pages) Zarlink Semiconductor Inc – 1023 Channel Voice Over IP Processor

Data Sheet
MT92210
In RTP, the HDLC Address LUT Structure contains a pointer to a TX Connection Structure, as well as a TI
(Timestamp Insert) bit. When this bit is ‘1’, this chip will insert its own timestamp, adding the one contained in the
HDLC packet to the final timestamp. When ‘0’, the timestamp in the HDLC packet will be used as-is.
The format of the RTP HDLC Address LUT Structure is the following:
b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
+0
TX Connection Structure Base [20:5] for Address = 0
+2
0 TI
+4
TX Connection Structure Base [20:5] for Address = 1
+6
0 TI
+(N-2)*4+0
+(N-2)*4+2
+(N-1)*4+0
+(N-1)*4+2
TX Connection Structure Base [20:5] for Address = N-2
0 TI
TX Connection Structure Base [20:5] for Address = N-1
0 TI
Figure 63 - HDLC Address LUT (RTP)
Field
TX Connection Structure
Base for Address
TI
N
Description
Base address of the TX Connection Structure that will be used to send HDLC
packets with the address shown. When this field is 0000h, the address is deemed
invalid and the packet is discarded.
Time Stamp Insert. When ‘0’, the time stamp will be inserted in the packet as it is
received in the HDLC packet. When ‘1’, the time stamp in the HDLC packet will be
treated as an offset from the current bus time stamp.
Number of HDLC addresses supported as defined by Add Range in the HDLC
Stream to HDLC Address LUT Structure.
Table 42 - Fields and Description
10.2 TX TDM Data Formats
When interfacing with external compression or silence suppression agents in xxPCM, the MT92210 uses special
data formats that allow it to pass more than payload information over the H.110 bus. When receiving ADPCM data,
the position of the highest ‘1’ in the data sample indicates the type of compression used: in this way, all ADPCM
compression types can be encoded within a single payload byte. In addition, the 00h code is used to indicate a
suppression decision. All of this information is coded within an 8-bit sample. The ADCPM sample may also be
contained in the high bits of the byte: in this case, the decoding is reversed, the position of the lowest ‘1’ in the data
sample indicates the compression type.
However, when the received data is ADPCM and silence suppression is being performed, the MT92210 is
incapable of extracting the energy level of the silence from the ADPCM samples. Therefore, the magnitude of the
original PCM value must be transmitted somehow to the MT92210. This is done on an associated stream, so a
single sample of an xxPCM channel now occupies 2 H.110 TSSTs.
When the compression type can be PCM or ADPCM, then an extra indication is necessary to indicate this
compression type. Because the magnitude of the original PCM value is 7 bits, there is a single free bit left on the
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