PM7311 pmc-sierra, PM7311 Datasheet - Page 76

• Manufacturer Part Number: PM7311
• Description: Freedm 84a1024l Assp Telecom Standard Datasheet
• Manufacturer: pmc-sierra

Proprietary and Confidential to PMC-Sierra, Inc., and for its customers’ internal use.
Document No.: PMC-2021832, Issue 2
For PPP header identification, the HDLC channel number is concatenated with two bits indicating
if the datagram is sequenced, non-sequenced, corrupt, or control. This value is then concatenated
with the COS (0-15) for sequenced, and 0 for non sequenced datagrams to produce an index into
the SSRAM memory. Contained at the memory location is the 14 bit CI.
Unique CI’s must be used for each HDLC channel.
Re-Sequencing Builder
The Re-Sequencing blocks provide the logic and data structures necessary to support the re-
ordering of ingress datagrams. This includes the detection of lost or out of bound datagrams, the
placement of sequences numbers in the correct order, the construction of frames/packets out of
fragments, and the transfer of resequenced/reassembled frames/packets to the ingress queue
manager.
Figure 22 Elements in the Re-sequencing Block
Loss Detection/Out of Bounds Checking
The loss detection block is based on the use of timers. Timers associated with each resequencing
session would be used to detect the lost datagram and advance the resequencing engine. Each
multi-link re-sequencing session has an associated timer. When the multi-link session transitions
from in sequence to out of sequence, a timer is started. This timer is cleared when the session
returns to being in sequence. All timers are periodically polled to detect sessions that have been
out of sequence for an extended period of time.
Size Comparison/Timers
The chunk buffer and re-sequencing structures are shared resources. To ensure that a multi-link
bundle or HDLC channel does not consume more than an allocated amount of resources the
number of bytes in the bundle or channel is compared against a threshold (allocated bytes). If the
threshold is exceeded, the datagram is discarded. The primary reasons for exceeding the threshold
are loss of a link within a multi-link bundle or a number of ML-FR DLCIs losing datagrams. The
first situation would cause the re-sequencing engine to stall on the first lost datagram. Incoming
fragments from other links would then build up and create a backlog of datagrams.
Loss/Out-of-
Sequence
Detection
Channel Size
Comparison
FREEDM 84A1024L ASSP Telecom Standard Product Data Sheet
Resequencing List
Addition
Frame Building Logic
Fragment
Removal
Frame/
Released
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