Reliable Data Delivery Protocol (RDDP) William Anderson MEI Technologies Inc.

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Reliable Data DeliveryProtocol(RDDP) William
AndersonMEI Technologies Inc.

• 2006 MAPLD International Conference
• Washington, D.C.
• September 25, 2006

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Reliable Data Delivery Protocol (RDDP)
Introduction

• Purpose
• Provide a means of ensuring correct packet
  delivery from source to destination by
• Acknowledgement from receiver
• Selective Retransmit based on ACK timeout
• Used over SpaceWire (SpW)
• Minimize packet overhead
• Be generic in nature
• Developed to use Protocol ID (PID) standardized
  by ECSS-E-50-11
• Permanent Protocol ID request pending
• Developed by Geostationary Environmental
  Satellite (GOES) -R series project
• Protocol developed to meet project data loss
  requirement

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RDDP Modes

• Nominal Mode
• Reliable Delivery Acknowledge (ACK) every good
  packet
• Urgent Message Mode
• No ACKS No Retransmits, fire and forget

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How It Works

• The protocol provides multiple virtual channels
  multiplexed
• over a single SpaceWire connection.
• Each virtual channel is independent of all other
  channels.
• Channels should have allocated buffer space, and
  parameters
• set for each channel.
• After ACK timeout, selective retransmit can
  occur.

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How It WorksTransmitter

• XMTR establishes link by sending a RESET to the
  receiver
• RCVR never sends RESET, XMTR never receives RESET
• XMTR may send up to Window Size packets ahead of
  last ACK
• After ACK timeout, retransmit up to Max Retries
  number of times
• After Max Retries is exhausted, notify host and
  quit. Host may issue RESET

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How It WorksReceiver

• Receiver sends ACK for every error free packet
• No EOP, no CRC error, valid header
• Receiver orders Reliable Delivery packets and
  eliminates duplicates
• Receiver does not close or RESET a channel
• Receiver may wait forever to receive opening
  RESET or next valid packet

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RDDP Features

• 2-Dword header.
• Programmable parameters sliding window size,
  timeouts, and retries.
• 8 Bit CRC.

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SpaceWire Protocol Identifier
Logical Address
Protocol ID
Rest of Packet
EOP
Logical Address and Protocol ID
Logical Address
Protocol ID
Rest of Packet
EOP
Path Address
Path Address and Protocol ID
Slide from SpaceWire RMAP Protocol, Steve
Parkes, University of Dundee
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RDDPPacket Format
First byte transmitted
Destination Logical Address
Protocol ID
Source Logical Address
Packet Control
Packet Length (MSB)
Packet Length (LSB)
Channel Number
Sequence Number
Data
Data
Data
Data
Data
Data
Data
Data
Data
GRDDP Packet CRC
EOP
Last byte transmitted
Data length is 0 to 6553 bytes Bits in
Packet Control User Defined / Packet Type 0 0
0 0 Packet (expect ACK) 0 0 0 1
Acknowledgement (ACK) 0 0 1 0
Reset Command 0 0 1 1 Urgent
Message (No ACK)
MSB
LSB
MSB
LSB
User defined
Packet Type
4 bits
4 bits
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RDDPABI Data Model

• Imager Science Data

GRDDP Header
CCSDS Source Packet 1
CCSDS Source Packet 2
CCSDS Source Packet 3
CCSDS Source Packet 4
CCSDS Source Packet 5
CCSDS Source Packet 6
CCSDS Source Packet 7
GRDDP Packet CRC
EOP
CCSDS Source Packet 8
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Definitions (1)

• Logical Address - defined in the SpaceWire
  standard
• Identifies the destination of the packet
• Range of 32 to 255 decimal
• Used by SpW router look-up table to associate an
  output port number
• If destination is unknown than default value of
  254 used
• May or may not be used for routing purposes
• Node may reject or accept packet with logical
  address 254
• Path Address
• Identifies PATH to destination
• May be physical or logical (range is 1..253)
• Specifies the SLA to route packet
• Will NEED to be deleted by intermediate routers
  so that only destination logical address remains
  when delivered to protocol destination
• Destination Logical Address
• Destination virtual channel identifier
• Source Logical Address
• Logical address from which packet was transmitted

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Definitions (2)

• Protocol Identifier (ID)
• Specifies the packet format
• PID requested for RDDP
• Currently in experimental range
• Packet Control
• Packet Type
• Packet to be acknowledged
• Packet not to be acknowledged
• Urgent message
• Acknowledgement Packet
• Reset Command
• User defined
• For example could be a sub-protocol ID used to
  identify different packet cargo types using RDDP
• Packet Length
• 2 bytes
• Used to indicate packet cargo length (bytes)
• May be from 0 to 65535 bytes

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Definitions (3)

• Channel Number
• 1 byte
• Allows sub-addressing within a source destination
  pair (1553)
• Sequence Number
• 1 byte
• Used to associate a packet and acknowledgement
  pair
• Current protocol has a fixed range of 0 to 255
• Data
• 0 to 65535 bytes
• Data to be transferred using RDDP
• CRC
• 8 bit CRC
• Same as ATM (HEC)
• Used to confirm that header and data were
  received correctly

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Sliding WindowThe RDDP Utilizes Selective
Retransmit

• The sliding window allows users to improve
  bandwidth
• efficiency.
• -- Gets around send and wait for ACK.
• -- Window size, timeouts, and number of
  retries can
• be tuned for maximum efficiency
• --- Window size should be half sequence
  number.
• Allows reordering packets if received out of
  sequence.
• Detects duplicate packets.

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Nominal OperationNo Errors Fast ACKs
Source
Destination
Packet n1
ACK n1
Tx Window advances 1 (may send next new packet)
Packet n2
ACK n2
Tx Window advances 1 (may send next new packet)
. .
. .
Packet n8
ACK n8
Tx Window advances 1 (may send next new packet)
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Nominal OperationNo Errors Burst Packets or
Slow ACKs
Source
Destination
Packet 1
Packet 2
Packet 3
Packet 4
ACK 1
Tx Window advances 1
ACK 2
Tx Window advances 1
ACK 3
Tx Window advances 1
ACK 4
Tx Window advances 1
Transmitter can send up to window size number of
packets before having to wait to receive an ACK
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Nominal Operation ACK Error, Ex. 1
Source
Destination
Packet 1

• Ex. window size 4
• Tx window may only be advanced by number of
  contiguous ACKed packet received from start of Tx
  window
• Tx window must wait to send packets until ACK 1
  received

ACK 1
Packet 2
ACK 2
Packet 3
ACK 3
Packet 4
ACK 4
Time-Out
Resend Packet 1
Rx Window discards duplicate packet 1 The next
packet for window entry 1 will be Sequence 5
with new data packet content
ACK 1
Tx Window advances 4 (may now send 4 new packets)
Next New Packet
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GOES-R Reliable Data DeliveryProtocol - Platforms

• The GOES-R RDDP is now running on 3 hardware
  configurations
• Development and testing has been SWTS to SWTS and
  SWTS to BAE ASIC
• FPGA based SpaceWire Test Set (SWTS)
• NASA SpW core
• Windows PCI workstation
• BAE Systems SpW ASIC integrated onto commercial
  PC board
• NASA SpW core
• PCI Windows workstation
• BAE Systems SpW ASIC integrated onto flight board
  (ITT/ABI Rev A.)
• cPCI form factor
• Uses RAD750 over cPCI
• VxWorks

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GOES-R Reliable Data DeliveryProtocol - SWTS

• The SWTS is a COTS card with FPGA image modified
  for GOES-R.

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SPACEWIRE ASIC Block DiagramBAE Systems
SRAM SDRAM EEPROM
64
32
64
OCB Master
OCB Slave
OCB Master
PCI
RIF
Spacewire Router and Links
9 HP masters 6 HP slaves 1 LP master 6 LP slaves
Spacewire I/F
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GOES-R Reliable Data DeliveryProtocol ASIC
Test Card
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GOES-R Reliable Data DeliveryProtocol ITT/ABI
cPCI Card

• The ITT/ABI BAE ASIC proto flight with RAD750 and
  connected to SWTS workstations.

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RDDP Team
Bill Anderson GOES-R CDH Lead Engineer Craig
Bearer GOES-R CDH Engineer Software Marco
Figueiredo GOES-R Senior Hardware Engineer Eric
Lynum GOES-R Electrical Design Engineer Dan May
GOES-R Test Engineer Glenn Rakow GSFC
SpaceWire Consultant Jeffrey A. Kronenwetter
GOES-R ABI System Engineer Alexander Krimchansky
GOES-R Systems Manager