PSB50505EV13GXT Lantiq, PSB50505EV13GXT Datasheet - Page 52

• Manufacturer Part Number: PSB50505EV13GXT
• Manufacturer: Lantiq

Specifications of PSB50505EV13GXT

• Lead Free Status / RoHS Status: Supplier Unconfirmed

4.3
This function implements the Convergency Sublayer for Structured Data Transfer (SDT)
and Unstructured Data Transfer as well as the Segmentation Sublayer for AAL type 1 as
described in ITU-T recommendation I.363.1 [31]. The structure of AAL1 SAR-PDU is
shown in
The Octet Receive Processing block is responsible for:
• Segmentation port decorrelation
• Segmentation
• SN/SNP generation
• SDT pointer generation
• RTS value insertion
• Statistics counter event generation
• Write to Segmentation Buffer
The Cell Receive Processing block is responsible for:
• Read cells from Segmentation Buffer
• Padding of partially filled cells
4.3.1
4.3.1.1
In synchronous systems, the microprocessor may activate a number of channels
consecutively, in phase with the segmentation period of a particular channel, causing a
large number of cells to be generated within the same 125 µs period. This would result
in a large number of cells residing in the Output Queue and increase the Cell Delay
Variation (CDV).
To avoid this, a decorrelation circuit has been implemented in the “Octet Receive
processing” (OR), that inserts a random waiting period between activation of a channel
and start of cell segmentation. This feature can be activated by setting bit “dcor” in the
“AAL Receive Reference Slot” of the channel in RAM1. Otherwise segmentation is
started as soon as the channel has been activated by the microprocessor (field
“channel_mode”)
The decorrelation circuit consists of a free-running 5-bit counter at a frequency of F
3360 (7.5 KHz if F
“dcor_random_nr”) and a comparator. Each time an octet for this channel is received the
counter is compared with the random value. Only when both values are equal,
segmentation is started.
When using the decorrelation circuit make sure that the random number is written to the
“dcor_random_nr” field of the “AAL Receive Reference Slot” before activating the
channel with “channel_mode”
Data Sheet
Chapter
AAL Segmentation Functions
Operation
Segmentation Port Decorrelation
12.
CLOCK
= 25 MHz) a register containing a random number (bits
52
PXB 4219E, PXB 4220E, PXB 4221E
Operational Description
IWE8, V3.4
2003-01-20
CLOCK
/