network
access
products
Endstation
ServiceSAR Controller
RS8235
Endstation ATM xBR Service Segmentation
and Reassembly Controller (ServiceSAR)
Conexant’s RS8235 offers endstations all of the xBR
service categories in a highly integrated 3.3V CMOS package.
The RS8235 architecture complements the RS8234 edge SAR
feature set, so that software reuse is maximized. The RS8235
directly connects to Conexant’s RS8251 PHY device for a total
NIC solution.
The RS8235 supports a similar feature set to the RS8234
edge SAR, but in a reduced footprint. System designers can
therefore offer a common traffic control and host interface
to a new market segment.
Integrated Management
The RS8235 complies with ATM Forum specifications UNI 3.1,
T.M. 4.1 and all other relevent standards. The RS8235 provides
integrated traffic management for all service categories, including
constant bit rate (CBR), variable bit rate (VBR1, VBR2, and VBR3),
real-time VBR, unspecified bit rate (UBR), available bit rate (ABR),
guaranteed frame rate (GFR) (guaranteed MCR on UBR VCCs),
and generic flow control (GFC). The xBR traffic management block
automatically schedules each VCC according to user-assigned
parameters to maximize line utilization.
Distinguishing Features
• Fully T.M. 4.1-compliant
• 3.3V/5V low power utilization (< 1 watt)
• 208-pin PQFP
• Commercial temperature
• 4K VCCs
• Software compatible with RS8234
network
access
products
Endstation
ServiceSAR Controller
RS8235
Endstation Architecture
The RS8235’s architecture is designed to minimize and
control host traffic congestion. The host manages the
RS8235 terminal using write-only control and status
queues. The host submits data for transmit by writing
buffer descriptor pointers to one of four transmit queues.
These entries may be thought of as task lists for the
Endstation SAR to perform. In addition, the RS8235 can
perform ATM server functions for up to four clients. The
device’s architecture lessens the control burden on the
host system while minimizing PCI bus utilization, by
eliminating reads across the PCI bus from host control
activities. It also provides control points to manage
congestion, which is critical for ABR.
xBR Cell Scheduler
The cell scheduler rate-shapes all segmentation traffic
according to per-channel parameters. The RS8235
supports eight user-assigned scheduling priorities in
addition to CBR. The user assigns a priority to each
channel and sets the range of available transmission
rates for the scheduler by setting the size of the
dynamic schedule table and the duration of each
scheduling slot in the table. The user can further
control consumption of bandwidth by assigning peak
cell-rate limits to four of those scheduling priorities.
ABR Traffic Management
The ABR flow control manager dynamically
rate-shapes ABR traffic independently per VCC, based
The RS8235 System
The RS8235 consists of five separate coprocessors
(incoming and outgoing DMA, segmentation, reassembly
and xBR traffic manager), each of which maintains state
information in shared, off-chip memory. This memory is
controlled by the SAR through the local bus interface,
which arbitrates access to the bus between the various
coprocessors. These coprocessors, though they run off
the same system clock, operate asynchronously from
each other. Communication between the coprocessors
takes place through on-chip FIFOs or through queues
in local memory.
upon network feedback. One or more ABR templates
are used to govern the behavior of traffic. Both relative
rate (RR) and explicit rate (ER) algorithms are
employed when computing a rate adjustment on
an ABR VCC. Programmable ABR templates allow
rate-shaping policies on groups of VCCs to be tuned
for different network applications. The RS8235
automatically generates and processes all resource
management (RM) cells. The on-chip hardware, coupled
with the user-defined ABR templates, implements all
required source and destination behaviors as defined in
TM4.0. Optional behaviors such as use-it-or-lose-it,
out-of-rate RM cells, host congestion and allowed cell
The RS8235’s on-chip coprocessor blocks are surrounded
by high-performance PCI and UTOPIA ports for glueless
interface to a variety of system components with full
line-rate throughput and low bus occupancy. Figure 1
illustrates these functional blocks.
rate (ACR) monitoring are also supported.
IP Interworking
The VBR-3, CLP0+1 category includes rate-shaping via
the dual leaky bucket GCRA algorithm based on the CLP
bit, which is recommended by the IETF for use with IP
.
Figure 1. RS8235 functional block diagram
Virtual Path Networking
The RS8235 can interleave segmentation of numerous
VCCs (i.e., separate VC channels) as members of one VP
.
VP-based traffic shaping is supported. The entire VP is
scheduled according to one set of traffic parameters.
The PCI interface between the host processor and
the local system is controlled by the RS8235 Hardware
Programming Interface (RS8235HPI), a software driver
for the RS8235, on top of which a system designer can
develop and place proprietary driver software. This
interface allows users to easily port their applications
CBR Tunneling
The user can designate up to four CBR pipes (or tunnels)
in which to transmit multiple CBR channels. This
allows proprietary traffic management schemes to
operate under a pre-allocated CBR bandwidth.
to the RS8235/8251EVM. This software is written in
C, and source code is available under a no-cost
license agreement.
The RS8235/8251EVM also includes documentation,
a full set of design schematics and artwork for the
RS8235/8251EVM ATM Evaluation Module
The RS8235 ATM Evaluation Module (EVM) provides
complete evaluation capability for the RS8235
segmentation and reassembly controller. The
EVM serves as a hardware and software reference
design for development of customer-specific ATM
applications. The RS8235/8251EVM was designed to
provide a rapid prototyping environment to assist
and speed customer development of new ATM
products, thereby reducing product time to market.
RS8235/8251EVM PCI card.
RS8235/8251EVM
(Standard PCI Card Size)
Figure 2 shows a block diagram of the hardware for
the RS8235/8251EVM. The software is described on the
following page.
The RS8235/8251EVM PCI card is specifically
designed to be a full-featured ATM controller based
on Conexant’s RS8251 ATM receiver/transmitter and
the RS8235 Endstation SAR. The PHY interface comes
configured with an optical OC-3 connection for testing
at 155 Mbps.
PCI Bus
Figure 2. RS8235/8251EVM hardware block diagram
What is ATM?
Asynchronous Transfer Mode (ATM) has emerged as the
primary networking technology for next-generation, multi-
service communication networks. ATM-enabled services
benefit the Internet as well as emerging applications in
science, telemedicine and distance learning. Just as the
Internet revolutionized worldwide communications,
RS8235/8251EVM Features
Hardware interface fully compliant with PCI
Benefits
Provides an easy, high-performance hardware
interface to other off-the-shelf PCI products, such
as Ethernet cards or multimedia accelerators.
Full-featured RS8235/8251EVM reference design
provided as a complete ATM UNI which implements
the full functionality of the RS8235 Endstation SAR.
Greatly speeds development of new applications.
Allows the user to develop and port proprietary
software applications atop the software driver
provided with the RS8235/8251EVM.
Assists in product debug state as an ATM load
generator and checker.
Enables high-performance testing.
ATM brings new meaning to high-speed networking.
ATM, which uses a fixed-size packet, or cell, is a transport
protocol capable of providing a homogeneous network
for all traffic types, whether the application is to carry
conventional telephony, video entertainment, or data
traffic over LANs, MANs or WANs.
Hardware reference design
Software reference design
Traffic generation and checking capability
The ITU-T and ANSI selected ATM for Broadband-ISDN.
SONET/SDH, as specified by the ITU, is intended as the
primary transport mechanism for ATM cells in WAN
applications. ATM also plays a key role in next-generation
Optical OC-3 interface
RS8235HPI Features
Software reference design
Benefits
Shortens development time of
customer system-specific ATM applications.
Allows users to utilize only those functions they
want and to incorporate those functions into their
own applications.
Users can establish ABR, CBR, UBR or VBR
connections at VCC setup on each of over
32,000 channels.
Provides detailed examples for control and
management of the RS8235. Significantly
shortens design time.
Enables users to easily port their application to
the RS8235/8251EVM.
Gives users a clear description of how the software
and hardware function.
Offers a layer of abstraction for ease-of-use of
the RS8235HPI primitives. Reference device driver
for VxWorks.
consumer applications for high-speed Internet access and
wireless access. The ADSL Forum and the Universal ADSL
Working Group chose ATM as the network layer protocol
Modular software design
for G.lite and G.DMT ADSL.
Dynamic rate control per virtual channel
ATM physical-layer (ATM-PHY) IC devices adapt ATM cells
to and from transmission rates ranging from 1.544 Mbps
SAR initialization and VCC control
to 2.4 Gbps via a standard system interface called UTOPIA.
ATM-PHY devices perform ATM cell functions (transmission
convergence) such as cell scrambling/descrambling, cell
Well-defined, robust RS8235HPI interface
Well-documented C source code
delineation (HEC), cell header processing, and cell-rate
decoupling as well as rate-specific functions for frame genera-
tion/recovery frame adaptation and clock/data recovery.
RS8235HPI Macro Layer software
RS8235HPI Hardware
Programming Interface
The RS8235 Hardware Programming Interface (HPI)
provides a set of fully-defined software primitives to
interface with an ATM UNI port based on the RS8235
SAR. It serves as an interface point for system software
designed to configure and manage the RS8235-based
UNI without the need for detailed manipulation of hard-
ware-related structures. It thus provides a layer of abstrac-
tion from the hardware for the system designer and user.
• Resource management
• Connection management (including VCC setup
and teardown, and processing status)
• Segmentation/data transmission
• Data reception/reassembly
• Statistics gathering/error reporting
• Diagnostic testing
The RS8235HPI provides a reference implementation of
these critical functions in order to shorten the development
RS8235HPI primitives are used by higher-level application
software (such as network management and device
drivers) to obtain ATM services as required by their upper
protocol layers. These primitives handle SAR resource,
control and status management. The RS8235HPI performs
functions in the following categories:
• RS8235 SAR device initialization
• Memory resource allocation
of a production-quality, customer system specific
ATM application.
The RS8235HPI is implemented in well-documented C
source code, specifically written to be highly portable
across a multiplicity of processors, compilers and
development environments.
RS8235 Endstation SAR
Special Features:
xBR Traffic Management
• TM 4.0 Service Classes
– CBR
– VBR (single, dual and CLP 0+1 leaky buckets)
– Real-time VBR
– ABR
– UBR
– GFC (controlled and uncontrolled flows)
– Guaranteed frame rate (GFR) (guaranteed
MCR on UBR VCCs)
• 8 Levels of priorities (8 + CBR)
• Dynamic per-VCC scheduling
• Multiple programmable ABR templates
(supplied by Conexant or user)
• Scheduler driven by local clock for low-jitter CBR
• Internal RM OAM cell feedback path
• Virtual FIFO rate matching
• Per-VCC MCR and ICR
• Tunneling
– VP tunnels (VCI interleaving on
PDU boundaries)
– CBR tunnels (cells interleaved on UBR
with an aggregate CBR limit)
• Message and streaming status modes
• Variable-length transmit FIFO-CDV-host
latency matching (1 to 9 cells)
• Symmetric Tx and Rx architecture
– Buffer descriptors
– Queues
• User-defined field circulates back to host (32 bits)
• Distributed host or SAR-shared
memory segmentation
• Simultaneous segmentation and reassembly
• Per-PDU control of CLP/PTI (UBR)
• Per-PDU control of AAL5 UU field
• Virtual Tx FIFO (PCI host)
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Message and streaming status modes
Raw cell mode (52 octet)
200 Mbps half duplex
155 Mbps full duplex (with 2-cell PDUs)
Distributed host or SAR-shared
memory reassembly
8 programmable reassembly hardware
time-outs (assignable per VCC)
Global max PDU length for AAL5
Per-VCC buffer firewall (memory usage limit)
Simultaneous reassembly and segmentation
Idle cell filtering
Multi-Queue Reassembly Processing
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4 reassembly queues
4K VCCs maximum **
AAL5 CPCS checking
AAL0
– PTI termination
– Cell count termination
• Early packet discard, based on:
– Receive buffer underflow
– Receive status overflow
– CLP with priority threshold
– AAL5 max PDU length
– Rx FIFO full
– Frame Relay DE with priority threshold
– LECID filtering for echo suppression
– Per-VCC firewalls
• Dynamic channel lookup (NNI or UNI addressing)
– Supports full address space
– Deterministic
– Flexible VCI count per VPI
– Optimized for signaling address assignment
High-Performance Host Architecture
with Buffer Isolation
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Write-only control and status
Read multiple command for data transfer
Up to 4 host clients control and status queues
Physical or logical clients
– Enables peer-to-peer architecture
Descriptor-based buffer chaining
Scatter/gather DMA
Endian neutral
Non-word (byte) aligned host buffer addresses
Automatically detects presence of Tx data
or Rx free buffers
Virtual FIFOs (PCI bursts treated as single address)
Hardware indication of BOM
Allows isolation of system resources
Status queue interrupt delay
Multi-Queue Segmentation Processing
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4 Transmit queues with optional priority levels
4K VCCs maximum **
AAL5 CPCS generation
AAL0 Null CPCS (optional use of PTI for
PDU demarcation)
ATM cell header generation
Raw cell mode (52 octet)
200 Mbps half duplex
155 Mbps full duplex (with 2-cell PDUs)
Designer Toolkit
• Evaluation module (RS8235/8251EVM)
• Reference schematics
• Hardware Programming Interface –
RS8235HPI reference source code (C)
Microcontroller MCU
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