S/UNI®-8x155 ASSP Telecom Standard Product Data Sheet
Released
Figure 6 Packet Over SONET/SDH Frame Format
Flag
Packet (PPP or other)
POS Frame
FCS
Flag
Flag
In the event of a FIFO overflow caused by the FIFO being full while a packet is being received,
the packet is marked with an error so it can be discarded by the system. Subsequent bytes
associated with this now aborted frame are discarded. Reception of POS data resumes when a
Start of Packet is encountered and the FIFO level is below the programmable Reception
Initialization Level (RIL[7:0]).
10.7.4 Byte Destuffing
The byte destuffing algorithm searches the Control Escape character (0x7D). These characters,
listed in Table 3, are added for transparency in the transmit direction and must be removed to
recover the user data. When the Control Escape character is encountered, it is removed and the
following data byte is XORed with 0x20. Therefore, any escaped data byte will be processed
properly by the S/UNI-8x155.
Table 3 HDLC Byte Sequences
Data Value
Sequence
0x7D 0x5E
0x7D 0x5D
0x7D 0x7E
0x7E (Flag Sequence)
0x7D (Control Escape)
HDLC Aborted Packet
10.7.5 FCS Check
The FCS Generator performs a CRC-16.ISO-3309 or CRC-32 calculation on the whole POS
frame, after byte destuffing and data descrambling scrambling. A parallel implementation of the
CRC polynomial is used. The CRC algorithm for the frame checking sequence (FCS) field is
either a CRC-16.ISO-3309 or CRC-32 function. The CRC-16.ISO-3309 is two bytes in size and
5
12
16
has a generating polynomial g(x) = 1 + x + x + x . The CRC-32 is four bytes in size and
2
4
5
7
8
10
11
12
16
has a generating polynomial g(x) = 1 + x + x + x + x + x + x + x + x + x + x
+
22
23
26
32
x
+ x + x + x . The first FCS bit transmitted is the coefficient of the highest term. .
Packets with FCS errors are marked as such and should be discarded by the system.
Proprietary and Confidential to PMC-Sierra, Inc., and for its customers’ internal use.
Document No.: PMC- 2010299, Issue 2
78
PMC [ PMC-SIERRA, INC ]
