28236-DSH-001-B Datasheet, PDF (49/443 Pages) M/A-COM Technology Solutions, Inc. – ATM ServiceSAR Plus with xBR Traffic Management

CN8236
ATM ServiceSAR Plus with xBR Traffic Management
2.0 Architecture Overview
2.4 Automated Reassembly Engine
The CN8236 provides the user with generous per-channel control of the
reassembly process, including the following:
• Assignment of priorities for reassembly buffer return processing.
• Cell filtering on inactive channels.
• Mechanisms to establish per-VCC firewalling by allocating buffer credits
on a per-channel basis. (This limits the possibility of one VCC consuming
all of the memory resources.)
• Per-VCC activation and control of a background hardware time-out
function where the user selects one of eight programmable time-out
periods. (The background function then automatically detects partially
reassembled PDUs and reports this status to the host so that these buffers
can be recovered and re-allocated.)
• Per-VCC monitoring of the length of the reassembled PDU, with status
reporting if the length exceeds a set maximum length for that channel.
The CN8236 implements an early packet discard feature to enable discarding
of complete or partial CPCS-PDUs based upon service discard attributes or error
conditions. The early packet discard function halts reassembly of the CPCS-PDU
marked for discard until the next Beginning of Message (BOM) cell and/or the
error condition has cleared. The SAR writes a status queue entry with the
appropriate status flags set, which indicate the reason for the discard. This
function can be enabled for the following conditions:
• Frame Relay discard based on the frame’s DE setting and the channel
exceeding a user-defined priority threshold.
• CLP packet discard based on the received cell’s CLP bit setting and
exceeding channel priority threshold.
• LANE-LECID packet discard on ELAN channels, which implements echo
suppression on multicast data frames.
• Early packet discard on AAL5 channels when the reassembled PDU length
exceeds the user-defined maximum PDU length for that VCC.
• Early packet discard on channels encountering a free buffer queue empty
(underflow) condition (meaning there are no available buffers in the free
buffer queue that channel is assigned to).
• Early packet discard on PDUs when a DMA Incoming FIFO buffer full
condition occurs.
• Early packet discard on channels encountering a reassembly status queue
full (overflow) condition.
• Early packet discard on AAL3/4 channels with these MIB errors: ST_ERR
(Segment Type error), SN_ERR (Sequence Number error), and LI_ERR
(SAR-PDU Length error).
The system designer can set the reassembly status reporting for any channel to
either Message Mode or Streaming Mode. In Message Mode, a status entry is
written only when the last buffer in a message completes reassembly. In
Streaming Mode, a status entry is written for each buffer as it completes
reassembly.
28236-DSH-001-B
Mindspeed Technologies™
2-15