PXB4219 Datasheet, PDF (68/290 Pages) Infineon Technologies AG – IWE8 Interworking Element for 8 E1/T1 Lines

PXB4219 / PXB4220 / PXB4221
Operational Description
As the transmission of the reassembled cell stream is delayed by “starv_ini”+1 octets,
there will be “starv_ini”+1 octets of the previous cell left in the Reassembly Buffer if the
following cell arrives without CDV.
If the maximum positive CDV is the same as the maximum negative CDV the expectation
interval has a length of 2 x CDV. Assuming N octets of data are transmitted within one
frame period of 125µs the amount of data transmitted in this interval is:
∆ = 2 × CDV × -1---2--N-5---_µ----s
[4]
The worst case for buffer underflow is given if the first cell has maximum positive CDV.
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
Starvation octets
Data octets
T₀+T
T₀+T+CDV
T₀: First cell arrival time (theoretical)
T_S: (starv_ini + 1) * 125µs / N
T: Average cell distance
T₀+2*T
T₀+2*T-CDV
Figure 16 Reassembly Buffer Initialization: positive CDV at Start Up
Time
Time
In this case the amount of starvation octets inserted after receipt of the first cell has to
be bigger than the amount of data transmitted during the expectation interval. 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 × CDV × -1---2--N-5---_µ----s – 1 ≥ 0
[5]
The worst case for buffer overflow is given if the first cell has maximum negative CDV
and then any cell with maximum negative CDV is followed by a cell with maximum
positive CDV.
Data Sheet
68
2002-05-06