scaling the data distribution service to global networks
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Angelo Corsaro, Ph.D.PrismTech
angelo.corsaro@prismtech.com
Delivering Performance, Openness, and Freedom
OpenSplice DDS
Sara Tucci-Piergiovanni, Ph.D.University of Rome “La Sapienza”
sara.tucci@dis.uniroma1.it
Scaling the Data Distribution Service to Global Networks
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State of the Art
Scaling DDS to Global Networks
Extensions to the Standard
Concluding Remarks
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© 2009, PrismTech. All Rights Reserved
Addressing Data Distribution Challenges
The OMG DDS Standard‣ Introduced in 2004 to address the Data
Distribution challenges faced by a wide class of Defense and Aerospace Applications
‣ Key requirement for the standard were its ability to deliver very high performance while seamlessly scaling from embedded to ultra-large-scale deployments
‣ Today recommended by key administration worldwide and widely adopted across several different application domains, such as, Automated Trading, Simulations, SCADA, Telemetry, etc.
DDS is standard designed to address the data-distribution challenges across a wide class of Defense and Aerospace Applications
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© 2009, PrismTech. All Rights Reserved
Addressing Data Distribution Challenges
‣ DDS is swiftly being adopted as the standard for providing System of Systems with ubiquitous and access to tactical data
‣ DDS deployments on WAN and sizable MAN have also proven it fitness with Metropolitan/Wide Area Networks
So... Why I am doing this presentation?
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ChallengesDDS presents today some limitations with respect to addressing large scale geographical deployments, these are:
Discovery
‣ Standard Discovery Protocol Requires Multicast
‣ Scalability
‣ Limited Control over Topics Visibility, e.g., choosing what to expose to the external world
Communication
‣ Standard Communication Protocol Relies on UDP
‣ No Support for Compression
‣ Difficult NAT/Firewall traversal
‣ Sub-Optimal Data Distribution for WAN Scenario (limited exploitation of multicast)
‣ Scalability
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© 2009, PrismTech. All Rights Reserved
Challenges
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© 2009, PrismTech. All Rights Reserved
Challenges
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State of the Art
Scaling DDS to Global Networks
Extensions to the Standard
Concluding Remarks
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© 2009, PrismTech. All Rights Reserved
Looking at Internet Apps.
When looking at a solutions for extending DDS applicability to Internet Scale Systems, we can’t ignore architectures adopted by very successful Internet Applications.
‣ P2P application like KaZaa have shown to scale very well and to support millions of users while effectively managing millions of subjects
‣ Application like Skype are connecting millions of people and managing in real-time they presence (discovery)
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© 2009, PrismTech. All Rights Reserved
Architecture for Internet Scale DDS
‣ DDS-Level Routers will be introduced that establish a Peer-to-Peer overlay that relays DDS data over the WAN‣ The Router provides a single access point for
deciding what to expose to the external world
‣ The Router can perform Topic Transformation, etc.
‣ A Network of Super-Nodes is used for ensuring:‣ Scalable (Global) Discovery
‣ Subscription Management (when crossing the boundaries of a System)
‣ Support for establishing communication between Pub and Sub (perhaps via STUNT to circumvent NAT/FIREWALL issues)
N1,0
N1,1
N2,0
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N2,2 N
2,3
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H1,0,0
H1,0,1
H1,0,k
H1,1,h
H1,1,0
H1,1,1
H2,0,i
H 2,1,j
H 2,1,k H2,1,h
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H 2,1,m
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© 2009, PrismTech. All Rights Reserved
DDS Router‣ DDS Router communicates with the
local DDS Domain by Multicast
‣ DDS Router are configured with the set of topics to be exposed along with potential transformations
‣ Router2Router communication is carried on by RTPS over TCP (since TCP has been tuned over years to work fine in WAN
‣ If required the Router takes care of compressing Data
‣ DDS Router Runs a “variation” or DDSI/RTPS
Nk
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‣ Topic, Subscription and Publication are propagated to Super Nodes
‣ Information available into super nodes ensure that local reader/writer will be properly matched
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DDS Super-Nodes (SN)
‣ Super-Nodes store all the “discovery information” ‣ List of Topics available in the system
‣Associations between Topics and Router role (e.g. Pub or Sub)
‣ A distributed protocol is used to replicated data, eventually, on all replicas
‣ Router keep a list of well-known Super-Nodes to bootstrap discovery
‣ NOTE: Super-Nodes can also be used to support the implementation of STUNT-like protocols to facilitate NAT/Firewall trespassing
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How it Works
DDS
R3
DDSR4
DDS
R2
SN1 SN4
SN2 SN3
DDS R1
{P(A),S(B),P(C)}
{S(A),P(B),P(C)} {S(A),P(D),S(E)}
{S(B), S(D),P(E)}
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© 2009, PrismTech. All Rights Reserved
How it Works
DDS
R3
DDSR4
DDS
R2
SN1 SN4
SN2 SN3
DDS R1
R1-{P(A),S(B),P(C)}
R2-{S(A),P(B),P(C)}
R3-{S(A),P(D),S(E)}
R4-{S(B), S(D),P(E)}
{P(A),S(B),P(C)}
{S(A),P(B),P(C)} {S(A),P(D),S(E)}
{S(B), S(D),P(E)}
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How it Works
DDS
R3
DDSR4
DDS
R2
SN1 SN4
SN2 SN3
DDS R1
R1-{P(A),S(B),P(C)}R2-{S(A),P(B),P(C)}R3-{S(A),P(D),P(E)}R4-{S(B), S(D),S(E)}
{P(A),S(B),P(C)}
{S(A),P(B),P(C)} {S(A),P(D),S(E)}
{S(B), S(D),P(E)}
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© 2009, PrismTech. All Rights Reserved
How it Works
DDS
R3
DDSR4
DDS
R2
SN1 SN4
SN2 SN3
DDS R1
R1-{P(A),S(B),P(C)}R2-{S(A),P(B),P(C)}R3-{S(A),P(D),P(E)}R4-{S(B), S(D),S(E)}
{P(A),S(B),P(C)}
{S(A),P(B),P(C)} {S(A),P(D),S(E)}
{S(B), S(D),P(E)}
{P(A)}
{P(A)}
{P(B)}
{P(B)}
{P(D)}
{P(E)}
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How it Works
DDS
R3
DDSR4
DDS
R2
SN1 SN4
SN2 SN3
DDS R1
R1-{P(A),S(B),P(C)}R2-{S(A),P(B),P(C)}R3-{S(A),P(D),P(E)}R4-{S(B), S(D),S(E)}
{P(A),S(B),P(C)}
{S(A),P(B),P(C)} {S(A),P(D),S(E)}
{S(B), S(D),P(E)}
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AAA AAA
{P(A)}
{P(A)}
{P(B)}
{P(B)}
{P(D)}
{P(E)}
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State of the Art
Scaling DDS to Global Networks
Extensions to the Standard
Concluding Remarks
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© 2009, PrismTech. All Rights Reserved
Extension to the DDS Standard
‣What described in the previous slides can easily be implemented in an interoperable manner, exploiting the pre-designed extension points present in the DDS Standard
‣Areas of extension include:
‣Discovery
‣DDSI/RTPS
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© 2009, PrismTech. All Rights Reserved
Discovery Extension
‣ A new Discovery Protocol should be added that allows to discover relevant information (Topics, Subscriptions, Publications) via the Super-Nodes
‣ A new protocol to be used between Super-Nodes should also be standardized!
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© 2009, PrismTech. All Rights Reserved
DDSI/RTPS Protocol xTensions
DDSI/RTPS Should be extended to include:
‣Support for TCP/IP ‣Offloading reliability from DDSI to TCP
whenever possible
‣Compression
DDS
R3
DDSR4
DDS
R2
SN1 SN4
SN2 SN3
DDS R1
Age
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State of the Art
Scaling DDS to Global Networks
Extensions to the Standard
Concluding Remarks
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© 2009, PrismTech. All Rights Reserved
Concluding Remarks‣ The DDS Standard includes today some known
limitation when trying to address Ultra-Large-Scale Systems
‣ These limitation mostly impact its scalability and efficiency
‣ The good news is that exploiting available extension points in the standard it is possible to extend the DDS Architectural Style to scale to Ultra-Large-Scale Systems
‣ The Router/Super-Nodes approach builds over years of experience in the domain of Internet Scale applications, such as, KaZaa, Skype, etc.
‣ Thus, PrismTech will work toward update of the DDS Spec to include these extension points.
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