PXB4219 Datasheet, PDF (70/290 Pages) Infineon Technologies AG – IWE8 Interworking Element for 8 E1/T1 Lines

PXB4219 / PXB4220 / PXB4221
Operational Description
Transmit Interface requests the first time-slot octet belonging to the channel in the frame
or the multiframe.
From that moment on, the “ATM Start of Structure” and “Port Start of Structure” are
synchronous and the contents of the Reassembly Buffer are passed to the framer
transmit interface.
The worst case for buffer underflow is given, if the first cell has maximum positive CDV,
the contents of the pointer field is “0” and the “Port Start of Structure” occurs right after
the transmission of “starv_ini” + 1 starvation octets.
Reassembly Buffer
Filling Level [octets]
buff_lsize
Example: part_fill = 16 octets; N = 16
1st cell has max. pos. CDV = 15,625µs
2nd cell has max. neg. CDV = -15,625µs
4
0
Framer
Interf.
T₀ T₀-CDV+T_S
T₀-CDV
T₀+T
T₀+T+CDV
T₀+2*T
T₀+2*T-CDV
Time
Time
Port Start of Structure
ATM Start of Structure
Starvation octets
Data octets
T₀: First cell arrival time (theoretical)
T_S: (starv_ini + 1) * 125µs / N
T: Average cell distance
Figure 18 Reassembly Buffer Initialization for structured CES: positive CDV at
Start Up
In this case the amount of starvation octets inserted after receipt of the first P format cell
has to be bigger than the amount of data transmitted during the expectation interval as
defined in (4). Otherwise the Reassembly Buffer will enter underflow condition at any
time a cell with maximum positive CDV is followed by a cell with maximum negative CDV.
starvini ≥ ∆ – 1 = ^2-----×----1-C--2--D-5----_µ^V----s--×-----N-- – 1 ≥ 0
[8]
The worst case for buffer overflow is given, if the first P format cell has maximum
negative CDV, the contents of the pointer field is at its maximum value Pmax and the
“Port Start of Structure” occurs right before the receipt of that P format cell. In that case
the complete frame needs to be stored in the Reassembly Buffer
If the first cell has maximum negative CDV there will be “starv_ini” + 1 octets left in the
Reassembly Buffer at any time a cell with maximum positive CDV is followed by a cell
Data Sheet
70
2002-05-06