MT92210 Zarlink Semiconductor, MT92210 Datasheet - Page 93

• Manufacturer Part Number: MT92210
• Description: 1023 Channel Voice Over ip (VoIP) Processor
• Manufacturer: Zarlink Semiconductor

Data Sheet
8.2
In xxPCM, packet loss and adjustment can be performed by using the timestamps of the received packets. If the LE
(Loss Enable) bit is set, the module will perform packet loss/misinsertion compensation by adjusting its pointer by
the number of TDM frames that have elapsed. This is very useful when performing silence suppression, where the
loss of packets is not only accepted but expected. In practice, Loss Enable should always be set except in UDP,
where there is no timestamp to measure time with. The Last Packet Remote Timestamp, as well as the current
timestamp of the packet, are used for this purpose in RTP.
The remaining fields in the xxPCM RX Channel structure are mostly used for error reporting and monitoring. AR
(Always Report) and SR (Slip Report) each indicate whether or not an error of the given type will cause an error
structure to be generated. Note that if an error structure is generated, all errors that occurred on that packet will be
reported, regardless of their Enable bit.
The extension structure contains a 16-bit Received Packet count and a 32-bit Received Octet Count. These have
the same definition as those in the disassembly structure (i.e. count UDP payload), but since all packets that are
treated by this structure are valid UDP/RTP packets, they will all be included in the counts. It is important that the
size of the payload in each packet be a multiple of the number of bearers present on the connection: if not, the BL2
bit (Bad Packet Length 2) in the RX error report structure will be flagged.
Finally, at the very end of the structure, are a certain number of Circular Buffer Base Addresses that indicate, for
each channel in the connection, where is the circular buffer associated to it. These addresses point to 256 byte
boundaries, which is the smallest allowed size for any RX circular buffer. The buffers can be between 256 bytes
and 4K bytes in size, as indicated by the Buffer Size field.
xxPCM channels can receive CN packets in addition to normal packets filled with voice payload. Two types of CN
packets can be received: single-byte, “white” packets that indicate only an energy level, and multi-byte, “spectral”
packets containing both an energy level and spectral information.
RX xxPCM channel structures can generate clock recovery pulses to the clock recovery module to indicate the
arrival of packets. The MT92210 allows 2 redundant clock recovery circuits to run simultaneously, so the extension
structures contain 2 bits, clock recovery A and clock recovery B, which the structure used to generate pulses. When
it generates packet arrival pulses to the clock recovery module, the disassembly process also sends it the
timestamp and the sequence number of the current packet (if RTP is being used). This will more accurately allow
the clock recovery process to reconstruct the relationship between mclk and the packet arrival rate.
UDP Payload
Length
Previous RTP
Sequence Number
This RTP
Sequence Number
Local Bus Time
Stamp
Field
xxPCM Treatment
This field contains the length of the UDP payload of the received packet that caused this
structure to be generated. If the UDP Payload is longer than 255 bytes, this field will be
saturated at value 255.
RTP Sequence number of the second last packet that was received.
RTP Sequence number of the last packet that was received.
Local Bus Time Stamp present at the time of reception of the packet that caused this
report structure to be generated.
Table 31 - Fields and Description (continued)
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Description
MT92210
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