PEB2085 SIEMENS [Siemens Semiconductor Group], PEB2085 Datasheet - Page 123

• Manufacturer Part Number: PEB2085
• Description: ISDN SubscribernAccess Controller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

Q921: Invalid Frames and Frame Abortion
Paragraphs 2.9 and 2.10 of the Q.921 deal with Invalid Frames and Frame Abortion. In the
following the original text is given.
Q.921 § 2.9: Invalid Frames
An invalid frame is a frame which:
Invalid frames shall be discarded without notification to the sender. No action is taken as the
result of that frame.
Q.921 § 2.10: Frame Abort
Receipt of seven or more contiguous 1 bits shall be interpreted as an abort and the data link
layer shall ignore the frame currently being received.
Reaction of the ISAC-S
A frame is supposed to be unbounded according to § 5.8.5 if the byte counter RBCH, RBCL
after RPF or RME exceeds 528.
Semiconductor Group
a) is not properly bounded by two flags, or
b) has fewer than 6 octets between flags or frames that contain sequence numbers, or
c) does not consist of an integral number of octets prior to zero bit insertion or following zero
d) contains a frame check sequence error, or
e) contains a single octet address field, or
f) contains a service access point identifier (see § 3.3.3) which is not supported by the
a) A frame which does not start with a flag is discarded in the ISAC-S. A frame which does
or, if it was an I or U-frame
b) The frame is discarded by the ISAC-S if
c) An S-frame is discarded. In the own-receiver-busy state I-frames are discarded.
d) In case of an -S frame,
bit extraction, or
receiver.
not end with a flag is one, that is aborted, i.e. if § 2.9b does not apply then the ISAC-S
– discards the frame, if it was an S-frame
– generates an ISTA: RME (or RPFs and a RME) and
– puts RSTA: RAB = 1 after the RME-Interrupt RAB = 1.
with U-frames or undefined frames
with I-frames
with S-frames
For U-frames with a content between 4 and 5 octets exclusively or for I-frames between
5 and 6 octets exclusively an ISTA: RME interrupt is generated and afterwards the RSTA:
CRC is set to 0.
For an I-frame in the normal state and U frames, after several possible RPF interrupts and
the final RME interrupt, the bit RSTA: CRC is set to 0 in this case.
-U and I-frames
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it contains less or equal to 4 octets or
it contains less or equal to 5 octets
it contains less than 6 octets.
the frame is discarded
RSTA: CRC is set to "0" in this case.
Functional Description