Download Architectures for Disruption Tolerant Networking Implementation for

Architectures for Delay/Disruption
Tolerant Networking Implementations
for Space
Authors
Unnikrishnan E, Ravichandran V, Sudhakar S, Subramanya Udupa,
(Indian Space Research Organization-ISRO, India)
Overview
Introduction to DTN
DTN architecture
Underlying protocols
Study on DTN2 reference implementation
Architectural components
Design models for flight implementation
Hardware implementation using VHDL
Embedded processor based implementation
Software implementation on SBC
Conclusion
DTN Introduction
DTN protocol objective is to integrate networks of different
communication characteristics, called regional networks, for
seamless operation
Eg. regional network: mobile network, sensor network, space
network, terrestrial networks like Internet, etc.
Communication characteristics of a network include
•
•
•
•
connectivity (disruption or intermittency)
path delay (long)
error rate BER or packet loss (high)
data rate (asymmetric)
The underlying protocols are optimized for its characteristic
for each network
Applications are made transparent to the above communication
characteristics of individual networks for inter regional
operation.
A typical DTN scenario
DTN GATEWAY
A
Region Network B
(Satellite Network)
DTN GATEWAY
B
C
B
Network C
(Internet)
Region Network A
(Sensor Network)
Node C2
(user)
NodeA1
(user)
An illustrative diagram of DTN network
How DTN works
Transport layer is terminated when there is a
network partition (disruption /delay)
A store and forward message switching mechanism
is embedded in the network architecture
Messages are stored in a persistent storage in this
new architecture when networks are partitioned
A new overlay protocol, called Bundle layer, is
introduced above transport layer
Bundles are moved towards destination for delivery
on opportunistic and scheduled contacts
DTN Architecture
Application Layer
Application Layer
Bundle layer
Region Specific
Layers
Region Specific
Layers
Region Specific
Layers
Region Specific
Layers
Application
Application
Bundle layer
Transport (TCP)
Transport
Network ( IP)
Network
Data link
Data Link
Physical
Physical
Internet layers
DTN layers
Persistent storage
Network specific
layers
Protocol Features
Store and forward message switching
Reliability and custody transfer
Time stamp and time synchronization
Routing and Forwarding
Fragmentation and reassembly
Congestion control
Security
Bundle Block Format
Bundle Processing control flags
0 -- Bundle is a fragment.
1 -- Application data unit is an administrative record.
2 -- Bundle must not be fragmented.
3 -- Custody transfer is requested.
4 -- Destination endpoint is a singleton.
5 -- Acknowledgement by application is requested.
6 -- Reserved for future use.
Bits in positions 7 through 13 are used to
indicate the bundle's class of service.
Bit positions 8 &7 as follows:
00 = bulk, 01 = normal, 10 = expedited,
11 is reserved for future use.
14 -- Request reporting of bundle reception.
15 -- Request reporting of custody acceptance.
16 -- Request reporting of bundle forwarding.
17 -- Request reporting of bundle delivery.
18 -- Request reporting of bundle deletion.
19 -- Reserved for future use.
Administrative records
Administrative record types :
Bundle status report.
Custody signal.
Bundle status report:
Reporting node received bundle.
Reporting node accepted custody of bundle
Reporting node forwarded the bundle
Reporting node delivered the bundle
Reporting node deleted the bundle.
Custody signal:
Redundant reception
Depleted storage.
Destination endpoint ID unintelligible.
No known route to destination
No timely contact with next route
Block unintelligible.
Evaluation of DTN2 reference
implementation
Configured and evaluated reference
implementation DTN2 on a Linux test bed
Simulated DTN operation for a typical
configuration of a ground node, orbiter and a rover
on the test bed
Simulated command file delivery to rover and
telemetry reception at ground for intermittently
connected links (LAN)
Proved the concept of DTN operation over
disrupted link where other protocols fail to operate
Contact Graph based routing was configured
DTN simulation test bed
Simulated as
Ground node
PC
DTN Node-1
Simulated as
Orbiter
link 1
PC
Simulated as
Rover
link 2
DTN Node-2
PC
DTN Node-3
telemetry
file
command
file
LAN
Links are
disrupted using
test scripts
received
command
file
Contact graphs are maintained
at each node with scheduled
connectivity
DTN simulation test bed
DTN prototype on FPGA
(hardware implementation)
Specification (scaled down)
EID is singleton (only unicast is supported)
Storage – 4 memory blocks
DTN Timer resolution - 1ms
Priority levels – 3
Life time of bundle – 10 minutes
Bundle size – 1024 bytes (primary block 64 bytes + 4 bytes
payload block + 956 bytes payload ADU)
SDNV encoding / decoding
Contact graph based routing
Security (not addressed)
Test setup for prototype validation
Test setup of DTN prototype implementations on FPFA
Hardware Xilinx vertex-4 FPGA XC4VFX60
Software ISE Design Suite 13.4, ModelSim SE 6.4
Coding Language – VHDL
System frequency – 4MHz
Simulation test done
Major VHDL modules
DTN Node
UART TX/RX
UART RX
SDNV encode &
Bundle formation
Persistent
storage
Forward Module
SDNV and
block decoding
UART
TX
Extract
ADU
Top bundle protocol module
Top transmitter module
Top receiver module
Administrative record
Persistent storage
Header formation
Payload block formation
RAM modules
SDNV encoding
SDNV decoding
Clock generation
UART module (testing with I/O data)
DTN prototype hardware-software
implementation
Core8051soft core
RAM
PROM
(component )
(component )
FPGA (Xilinx)
•
•
•
Core8051, an Intel compatible 8 bit
microcontroller, executes all ASM51
instructions with RISC like design
System frequency 12MHz
Coding language –VHDL
Libero IDE 9.0, ModelSim SE 6.5d
Open Keil uVision 3
H/W Xilinx vertex4 FPGA XC4VFX60
Core8051 is chosen as an embedded processor platform to prove the concept
DTN basic modules ‘hex code’ is loaded on PROM to validate the platform
DTN modules are tested independently to port to the target
Software Design approach
Bundle Protocol Server
Bundle Protocol Agent
Contacts
Registration
Commands
Application Agent
Convergence
Naming
Routing
Utilities
Convergence layer
Top level package level design
Bundle Protocol Sequence Diagram
Design approaches
Standard defines a DTN Node as
•
•
•
•
•
Single process running on a general purpose computer
Thread in a process
An object in an object oriented system
A special purpose hardware device
....
Monolithic hardware
design
(collection of
hardware modules)
Embedded
processor
OS (optional)
OS
Processor
H/W
software modules
software modules
Hardware implementation
Hardware software
implementation
Software implementation
Comparison of different DTN design
architectures
Hardware based
design
Hardware- software
design
Software based design
No processor chip or
A processor is embedded
software component in the in FPGA
design
Higher reliability
Reliability of software
component to be
addressed
Fast realization of a flight Faster realization as
worthy implementation
protocol features are
with minimum features
implemented as software
Difficult to provide all
Easy to provide more
features due to complexity features
Design is based on a
general purpose processor
Not possible to
accommodate changes
Most flexible to changes
as a software
implementation
Flexible to accommodate
changes as it is limited to
software modifications
Reliability of a fully
software system
Software testing and
qualification takes longer
time with more features
Most easy to provide all
the features
DTN Application envisaged
DTN /BP
DTN/BP
LTP
Prox-1
TM /TC
APPLN
DTN/BP
Orbiter
Prox-1
Lander
DTN /BP
TCP/IP
LTP
TM /TC
DTN/BP
AX.25
APPLN
rover
DTN/BP
APPLN
DTN/BP
AX.25
planetary surface
Ground
station
APPLN
DTN/BP
TCP/IP
MCC
Earth
Protocol stack diagram for envisaged space DTN network
Conclusion
Results of the study on DTN-2 reference implementation
are promising for its usage on a disconnected network.
For DTN for space a highly reliable and light weight
version of the protocol suit is required.
Different design approaches are compared and efforts for
prototyping were summarized
Protocol implementations need to undergo sufficient
testing on simulators for all possible end to end scenarios
More simulations at ground are required for introducing
dynamic routing of bundles for a large network
CCSDS standards on the DTN protocols help the space
agencies to deploy an interoperable network for future
References
1. Rationale, Scenarios, and Requirements for DTN in Space Informational Report CCSDS
734.0 G-1August 2010
2. CCSDS Bundle Protocol Specification Recommended Standard CCSDS 734.2 B-1
September 2015
3. RFC 5050 Bundle Protocol Specification ,Network Working Group Category:
Experimental 2007
4. RFC 4838 Delay-Tolerant Networking Architecture, Network Working Group Category:
Informational 2007
5. Solar System Internetwork Architecture Informational Report CCSDS 730.1 G-1July 2014
6. Report of the Interagency Operations Advisory Group Space Internetworking Strategy
Group Recommendations on a Strategy for Space Internetworking July 2008
7. Licklider Transport Protocol (LTP) for CCSDS 734.1 B-1 May 2015
8. Proximity-1 Space Link Protocol— Data Link Layer CCSDS 211.0-B-5 December 2013
9. “Design of DTN for Interplanetary Communication” ,M Tech Thesis, Samreen Fiza ,
Project work done at TMD/DSG/CDA/ISAC 2013-14
10. “Design of a Platform for embedded applications using 8051 IP core”, M Tech Thesis,
Pranam Amin, Project work done at TMD/CDEG/CDA/ISAC 2014-15
11. “Design and Modeling of DTN Bundling Protocol”, Deepak N A, Unnikrishnan E, et al
International Conference on Modeling and Simulation August 2007
Thank you
Acknowledgement to
Dr. M Annadurai, Director ISRO, Satellite Centre