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2.0 Architecture Overview
2.4 Automated Reassembly Engine
RS8234
Datasheet for RS8234 xBR ServiceSAR
N8234DS1B
(which increases with longer Tx FIFO depth) and PCI latency protection (which
decreases with shorter Tx FIFO depth).
The RS8234 provides a method to segment traffic from a fixed PCI address
(or Virtual FIFO). This is intended for circuit-based CBR traffic such as voice
channel(s).
The RS8234 reports segmentation status to the host on one of a set of 32 inde-
pendent parallel segmentation status queues. The RS8234 writes segmentation
status queue entries on either PDU boundaries or buffer boundaries, selectable on
a per-VCC basis. PDU boundary status reporting is called Message Mode, while
buffer status reporting is called Streaming Mode.
2.4 Automated Reassembly Engine
The reassembly coprocessor processes cells received from the ATM Physical
Interface block. The coprocessor extracts the AAL SDU payload from the
received cell stream and reassembles this information into buffers supplied by the
Host system.
Each active reassembly channel is specified as a single entry in the Reassem-
bly VCC Table located in SAR shared memory. One Rsm VCC Table entry
defines the negotiated or contracted characteristics of the reassembly traffic for a
particular channel. Each table entry is initialized by the Host during system ini-
tialization, or on-the-fly. The SAR uses the Rsm VCC Table to store temporary
information to assist the reassembly process. An initialized Reassembly VCC
Table entry effectively establishes a connection on which the RS8234 can reas-
semble data.
Using a dynamic Channel Directory lookup method, the RS8234 reassembles
up to 64 k VCCs simultaneously at a rate up to 200 Mbits/sec on simplex connec-
tions and 155 Mbits/sec on full duplex connections. The Channel Directory
mechanism allows flexible preallocation of resources and provides deterministic
channel identification over the full UNI or NNI Virtual Path Identifier/Virtual
Channel Identifier (VPI/VCI) address space. The total number of VCCs sup-
ported is limited by the memory allocated to the Rsm VCC Table and the Channel
Directory.
The reassembly coprocessor extracts the AAL SDU payload from the received
cell stream and reassembles this information into system buffers allocated per-
VCC. The RS8234 supports AAL5, AAL3/4 and AAL0 reassembly, as well as
52-octet Raw Cell mode.
For AAL5, the reassembly coprocessor extracts and checks all PDU protocol
overhead.
For AAL3/4, the reassembly coprocessor performs all error detection and
checking procedures incorporated in AAL3/4, and reassembles SDUs based on
Message ID (MID).
The RS8234 provides two methods of terminating an AAL0 PDU: Payload
Type Identifier (PTI) termination (wherein the PTI bit in the cell header is moni-
tored for the End of Message [EOM] cell indication), and Cell Count termination
(wherein the RS8234 terminates the PDU when a user-defined number of cells
have been received on that channel). The AAL0 PDU termination method is
selectable on a per-VCC basis.