
PEB 20560
Functional Block Description
Semiconductor Group
2-39
2003-08
2.1.2.5.3
Control Channel Delay
Depending on the selected system configuration different delays between the activation
of the control channel and the corresponding D-channel response occur.
Beware of Arbiter Locking!
In the state “l(fā)imited selection”, the D-channel arbiter sends the “blocked” information to
the terminal from which the last HDLC-frame was received. Since the “blocked”
information reaches the terminal with several IOM-frames delay
t
CCDD
(e.g. after
5
×
125
μ
s) the terminal may already have started sending a second HDLC-frame. On
reception of the “blocked” information the terminal immediately aborts this frame.
Since the abort sequence of the second frame reaches the ELIC with several frames
delay
t
DCDU
, the full selection counter value must be set so that the D-channel arbiter
re-enters the state “full selection” only after the abort sequence of the second frame has
reached the ELIC.
If the D-channel arbiter re-enters the “full selection” state (in which it again sends an
“available” information to the terminal) before the abort sequence has reached the ELIC,
it would mistake a ‘0’ of the second frame as the start of a new frame. When the delayed
abort sequence arrives at the ELIC, the D-channel arbiter would then switch back to the
state “l(fā)imited selection” and re-block the terminal. Thus the D-channel arbiter would
toggle between sending “available” and “blocked” information to the terminal, forever
aborting the terminal’s frame. The arbiter would have locked.
Table 2-12 Control Channel Delay Examples
Number of Frames (= 125
μ
s)
Blocked
→
Available
min.
max.
4
8
System
Configuration
Circuit Chain
Available
→
Blocked
min.
4
max.
8
U
PN
line card -
- U
PN
phone
U
PN
line card -
- S
0
adapter -
- S
0
phone
ELIC
+
OCTAT-P
+
ISAC-P TE
ELIC
+
OCTAT-P
+
ISAC-P
TE
+
SBCX
+
ISAC-S
ELIC
+
OCTAT-P
+
ISAC-P TE
+
ISAC-P TE
+
ISAC-P TE
ELIC + QUAT-S +
ISAC-S TE
9
13
5
9
U
PN
line card -
- U
PN
adapter -
- U
PN
phone
9
13
9
13
S
0
line card
- S
0
phone
4
8
4
8