PXB4219 Datasheet, PDF (67/290 Pages) Infineon Technologies AG – IWE8 Interworking Element for 8 E1/T1 Lines

PXB4219 / PXB4220 / PXB4221
Operational Description
4.4.2.3 Initialization of the Reassembly Buffer
Before a channel is activated, the Reassembly Buffer must be configured properly to
compensate Cell Delay Variation (CDV).
In order to avoid buffer underflow due to large cell distances the amount of initial
starvation octets that are passed to the framer interface upon arrival of the first cell needs
to be set. On the other hand this number needs to be as small as possible to avoid
excessive delay. The logical Reassembly Buffer size can be adjusted in order to detect
too small cell distances by Reassembly Buffer overflow.
All parameters are defined in the “AAL Transmit Reference Slot” in RAM3. The amount
of starvation octets given to the framer transmit interface after arrival of the first cell is
defined by “starv_ini”. The contents of the starvation octets can be defined by
“starv_bpslct” and the logical Reassembly Buffer size can be configured with “buff_lsize”.
The following sections give an overview on the Reassembly Buffer operation and
initialization.
Unstructured Data Transfer:
After activation of a channel both SAR Receiver and Framer Transmit Interface start
operation. As long as no reassembled cell is available in the Reassembly Buffer it is
considered to be in underflow condition and starvation octets are passed to the Framer
Transmit Interface.
As soon as the first reassembled cell is available in the Reassembly Buffer the device
starts building up the Reassembly Buffer threshold level. This is done by passing an
additional amount of starvation octets to the framer Transmit Interface
Reassembly Buffer
Filling Level [octets]
buff_lsize
Example:
part_fill = 16 octets
N = 16
no CDV
4
0
Framer
Interf.
T₀
T₀+T_S
T₀+T
Starvation octets
Data octets
T₀: First cell arrival time
T_S: (starv_ini+1) * 125µs / N
T: Average cell distance
Figure 15 Reassembly Buffer Initialization: No CDV
T₀+2*T
Time
Time
Data Sheet
67
2002-05-06