MT92220BG Zarlink Semiconductor, MT92220BG Datasheet - Page 118

• Manufacturer Part Number: MT92220BG
• Description: Description = 1023 Channel Voice Over IP/AAL2 Processor ;; Package Type = Epbga ;; No. Of Pins = 608
• Manufacturer: Zarlink Semiconductor

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9.4
The MT92220's PDV monitoring writes packets within a PDV window, minimizing delay while trying to avoid slips.
To do this, it writes packets based on their remote timestamp: a packet's position in the circular buffer is decided by
its RTP timestamp or AAL2 UUI. This allows compensation for packet loss and misinsertion.
Because some profiles in both AAL2 and RTP use varying-length packets (the term varying-length here refers to
changing number of samples per packet, not length in bytes; compressed packets are converted to a number of
samples before PDV monitoring is applied to them), changing packets lengths will show up as PDV on the network.
To compensate for this, the xxPCM channel structure contains a Max Expected Payload Size in Samples field. Any
variation in packet length up to this size will be compensated for. Setting this field to too large a value will insert
delay; setting this field to too small a value will allow the changing length to show up as PDV. If the value is not
known with certainty, a smaller value is usually better.
The default mode of the PDV monitoring system allows a PDV window of length Maximum Used Samples in
Circular Buffer. (Note: the Max Expected Payload Size in Samples - 1 must be added to Maximum Used Samples in
Circular Buffer to get a window of the desired size. As an example, if the Max Expected Payload Size in Samples is
160 and the desired PDV window is 10 ms (80 samples) long, then Maximum Used Samples in Circular Buffer
should be set to 239 (80 + (160-1)).
RPM
RSx
SL
BL2
PLX
BL4
BL3
XD
RX xxPCM Channel
Structure Address
Samples Lost
Remote Time Stamp
Local Bus Time Stamp
Packet Delay Variation (PDV) Monitoring
Field
Table 47 - Fields and Description (continued)
Reset PDV Monitoring Completed. When this bit is set, the RPM bit in the RX
xxPCM Channel Structure has been cleared by hardware and a new PDV
monitoring period has been started.
Reset Total Slip Offset Delta Completed. When this bit is set, the Total Slip
Offset Delta has been reset in the Common PDV Absorption structure.
Samples lost. When set, the Samples Lost[31:0] field is non-zero, meaning that
one or many samples have been lost between packets.
Bad Packet Length 2. When set, the number of “payload bytes” * 8 was not
divisible “Number of channels” * “Number of bits per sample”. Packets affected
by this error will be discarded.
Packet Longer than Expected. The number of samples in the received packet
exceeded the “Max Expected Payload Size in Samples” field of the RX xxPCM
Channel Structure,
Bad Packet Length 4. The number of samples in the received packet exceeded
2047 frames.
Bad Packet Length 3. The number of samples in the received packet was 0
frames.
Extreme Delay. When ‘1’, extreme delay has been detected in the Extended
PDV monitoring structure.
Base address of the RX xxPCM Channel Structure that generated this report
structure.
Number of samples lost due to packet loss as detected by the difference
between remote time stamps in two consecutive packets.
Remote time stamp of the packet received that cause the generation of this
report structure.
Local Bus Time Stamp present at the time of reception of the packet that
caused this report structure to be generated.
Zarlink Semiconductor Inc.
Description