
IWE8, V3.4
PXB 4219E, PXB 4220E, PXB 4221E
Operational Description
Data Sheet
66
2003-01-20
Figure 17
Reassembly Buffer Initialization: Negative CDV at Start Up
If the first cell has maximum negative CDV there will be “starv_ini” + 1 octets left in the
Reassembly Buffer when the following cell arrives with maximum negative CDV. In case
the following cell arrives with maximum positive CDV it will be “starv_ini” + 1 plus the
amount of data to be transmitted in the expectation interval. Just after cell arrival the
filling level of the Reassembly Buffer is at its maximum:
[6]
The delay introduced by the Reassembly Buffer is:
[7]
Structured Data Transfer:
After activation of a channel both SAR Receiver and Framer Transmit Interface start
operation. As long as no reassembled cell in P format is accepted the Reassembly Buffer
it is considered to be in underflow condition and starvation octets are passed to the
Framer Transmit Interface.
After that, “starv_ini” + 1 starvation octets are given to the Framer Transmit Interface.
Then, the transmitter reads as many octets from the Reassembly Buffer as indicated by
the pointer field. For each octet one starvation octet is given to the Framer Transmit
Interface. The next octet to be read from the Reassembly Buffer is the “ATM Start of
Structure” (The octet where the AAL1 pointer field points at).
Reassembly Buffer
Filling Level [octets]
buff_lsize
Time
T
0
T
0
+T
T
0
+T-CDV
T
0
+2*T
0
4
Time
Framer
Interf.
T
S
: (starv_ini + 1) * 125μs / N
T: Average cell distance
Starvation octets
Data octets
T
0
+CDV+T
S
T
0
: First cell arrival time (theoretical)
Example: part_fill = 16 octets; N = 16
1st cell has max. neg. CDV = 15,625μs
2nd cell has max. pos. CDV = -15,625μs
T
0
+CDV
T
0
+2*T+CDV
Reassembly Buffer neg CDV
bufflsize
partfill
starvini
1
partfill
4
CDV
×
N
125
μ
s
--------------
×
+
=
+
+
+
≥
delay
starvini
-----------------------------------------
125
μ
s
×
N
=