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Reliable Data Delivery Protocol (RDDP) William Anderson MEI Technologies Inc. 2006 MAPLD International Conference Washington, D.C. September 25, 2006. Reliable Data Delivery Protocol (RDDP) Introduction. Purpose

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reliable data delivery protocol rddp william anderson mei technologies inc

Reliable Data DeliveryProtocol(RDDP)William AndersonMEI Technologies Inc.

2006 MAPLD International Conference

Washington, D.C.

September 25, 2006

reliable data delivery protocol rddp introduction
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
rddp modes
RDDP Modes
  • Nominal Mode
    • Reliable Delivery – Acknowledge (ACK) every good packet
  • Urgent Message Mode
    • No ACKS & No Retransmits, fire and forget
how it works
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.
how it works transmitter
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 WindowSize packets ahead of last ACK
  • After ACK timeout, retransmit up to MaxRetries number of times
  • After MaxRetries is exhausted, notify host and quit. Host may issue RESET
how it works receiver
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
rddp features
RDDP Features
  • 2-Dword header.
  • Programmable parameters – sliding window size, timeouts, and retries.
  • 8 Bit CRC.
spacewire protocol identifier
SpaceWire Protocol Identifier*

Logical

Address

Protocol ID

Rest of Packet

EOP

Logical Address and Protocol ID

Path

Address

Logical

Address

Protocol ID

Rest of Packet

EOP

Path Address and Protocol ID

* Slide from SpaceWire RMAP Protocol, Steve Parkes, University of Dundee

rddp packet format
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

rddp abi data model
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

CCSDS Source Packet 8

GRDDP Packet CRC

EOP

definitions 1
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
    • May be used to send back acknowledgements
definitions 2
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
definitions 3
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
sliding window the rddp utilizes selective retransmit
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.
nominal operation no errors fast acks
Nominal OperationNo Errors – Fast ACKs

Source

Destination

Packet n+1

ACK n+1

Tx Window advances 1

(may send next new packet)

Packet n+2

ACK n+2

Tx Window advances 1

(may send next new packet)

.

.

.

.

Packet n+8

ACK n+8

Tx Window advances 1

(may send next new packet)

nominal operation no errors burst packets or slow acks
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

nominal operation ack error ex 1

Source

Destination

Nominal Operation – ACK Error, Ex. 1

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

goes r reliable data delivery protocol platforms
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
goes r reliable data delivery protocol swts
GOES-R Reliable Data DeliveryProtocol - SWTS
  • The SWTS is a COTS card with FPGA image modified for GOES-R.
spacewire asic block diagram bae systems

External Memory I/F

Clocks/Reset

DMA

PLL

SRAM

16K bytes

MCTL

SRAM

16K bytes

EMC

CAT

OCB Master

OCB Slave

OCB Master

OCB Master

OCB Slave

OCB Slave

OCB Slave

OCB Slave

OCB Slave

64

64

32

64

64

64

64

64

32

OCB Connection Medium

32

32

64

64

64

64

32

64

64

32

OCB Master

OCB Slave

OCB Master

OCB Master

OCB Slave

OCB Master

OCB Slave

OCB Slave

OCB Slave

OCB Master

JTAG Slave (JTAG)

PCI

MISC

UART

RIF

FIFO

FIFO

FIFO

FIFO

PCI 2.2

PCI 2.2

PID’s

UART

JTAG

Reused

New or Modified

SPACEWIRE ASIC Block DiagramBAE Systems

SRAM

SDRAM

EEPROM

64

64

32

OCB Master

OCB Master

OCB Slave

PCI

RIF

Spacewire

Router

and Links

9 HP masters

6 HP slaves

1 LP master

6 LP slaves

Spacewire I/F

goes r reliable data delivery protocol itt abi cpci card
GOES-R Reliable Data DeliveryProtocol – ITT/ABI cPCI Card
  • The ITT/ABI BAE ASIC proto flight with RAD750 and connected to SWTS workstations.
rddp team
RDDP Team

Bill Anderson – GOES-R C&DH Lead Engineer

Craig Bearer – GOES-R C&DH 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