Scaling the Data Distribution Service to Global Networks

Angelo Corsaro, Ph.D.
PrismTech
angelo.corsaro@prismtech.com

Sara Tucci-Piergiovanni, Ph.D.
University of Rome “La Sapienza”
sara.tucci@dis.uniroma1.it

OpenSplice DDS
Delivering Performance, Openness, and Freedom

Scaling the Data Distribution
Service to Global Networks

State of the Art
Scaling DDS to Global Networks
Agenda

Extensions to the Standard
Concluding Remarks

Addressing Data Distribution Challenges
DDS is standard designed to address the data-distribution challenges across
The OMG DDS Standard a wide class of Defense and Aerospace Applications
‣ Introduced in 2004 to address the Data
Distribution challenges faced by a wide
class of Defense and Aerospace
Applications

Proprietary Information - Distribution without Expressed Written Permission is Prohibited.
‣ 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.

© 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?


Challenges
DDS 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

Challenges

Publisher Publisher

B B
Subscriber Subscriber

m m
A F A F

Publisher J Publisher
D C J
X Z

K
E
K
Subscriber Y
Subscriber
DDS-1
Publisher

Wan


Challenges

Publisher A Publisher

B B
Subscriber Subscriber

m m
A F A F

Publisher J Publisher
D C J
X Z

K
E
K
Subscriber Y
Subscriber
DDS-1
Publisher

Wan


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)


Architecture for Internet Scale DDS

‣ DDS-Level Routers will be introduced that H 1,1,h

establish a Peer-to-Peer overlay that N2,5 R N1,1 H 1,1,1
relays DDS data over the WAN SN
R
H 1,1,0
‣ The Router provides a single access point for H 2,1,m

deciding what to expose to the external world SN
H 1,0,k
‣ The Router can perform Topic Transformation, etc. SN
‣ A Network of Super-Nodes is used for
R
N2,0 H 1,0,1 N1,0
ensuring: H 2,0,i H 1,0,0 R
R N2,4
‣ Scalable (Global) Discovery R SN
‣ Subscription Management (when crossing the N2,1
boundaries of a System) SN H 2,1,n

‣ Support for establishing communication between
Pub and Sub (perhaps via STUNT to circumvent N2,2 R R N2,3
H 2,1,j
NAT/FIREWALL issues)

H 2,1,k H 2,1,h

DDS Router
‣ DDS Router communicates with the
local DDS Domain by Multicast Ni
R
‣ DDS Router are configured with the
set of topics to be exposed along with
potential transformations
‣ Router2Router communication is

R N
carried on by RTPS over TCP (since k

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
‣ Topic, Subscription and Publication are propagated to Super Nodes
‣ Information available into super nodes ensure that local reader/writer will be properly matched


DDS Super-Nodes (SN)
‣ Super-Nodes store all the “discovery information”
‣ List of Topics available in the system R
SN
‣ Associations between Topics and Router role (e.g. Pub or SN
R
Sub)

‣ A distributed protocol is used to replicated data,
SN
eventually, on all replicas
SN
‣ Router keep a list of well-known Super-Nodes to
bootstrap discovery R

R

‣ NOTE: Super-Nodes can also be used to support
the implementation of STUNT-like protocols to
facilitate NAT/Firewall trespassing

How it Works
{P(A),S(B),P(C)} {S(B), S(D),P(E)}

DDS R1 SN1 SN4 R4 DDS

SN2 SN3

{S(A),P(B),P(C)} R2 R3 {S(A),P(D),S(E)}

DDS DDS


How it Works
{P(A),S(B),P(C)} R1-{P(A),S(B),P(C)} {S(B), S(D),P(E)}

R4-{S(B), S(D),P(E)}

SN2 SN3 R3-{S(A),P(D),S(E)}
R2-{S(A),P(B),P(C)}

{S(A),P(B),P(C)} R2 R3 {S(A),P(D),S(E)}

DDS DDS


How it Works
{P(A),S(B),P(C)} {S(B), S(D),P(E)}

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)}

SN2 SN3

{S(A),P(B),P(C)} R2 R3 {S(A),P(D),S(E)}

DDS DDS


How it Works
{P(A),S(B),P(C)} {S(B), S(D),P(E)}

{P(A)} R1-{P(A),S(B),P(C)}
R2-{S(A),P(B),P(C)}
{P(A)} R3-{S(A),P(D),P(E)} {P(E)}
R4-{S(B), S(D),S(E)}

SN2 SN3

{P(B)} {P(D)}
{S(A),P(B),P(C)} {P(B)} R3 {S(A),P(D),S(E)}
R2

DDS DDS


How it Works
{P(A),S(B),P(C)} {S(B), S(D),P(E)}

DDS A R1 SN1 SN4 R4 DDS
{P(A)} R1-{P(A),S(B),P(C)}
R2-{S(A),P(B),P(C)}
{P(A)} R3-{S(A),P(D),P(E)} {P(E)}
R4-{S(B), S(D),S(E)}

SN2 SN3

{P(B)} {P(D)}
{S(A),P(B),P(C)} {P(B)} R3 {S(A),P(D),S(E)}
R2
A A
A

DDS DDS


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


Discovery Extension
1‣ A new Discovery Protocol should be R
added that allows to discover 1 SN
SN
relevant information (Topics, R
2
Subscriptions, Publications) via the

Super-Nodes SN
SN
2‣ A new protocol to be used between
Super-Nodes should also be R
standardized!
R


DDSI/RTPS Protocol xTensions
DDSI/RTPS Should be extended DDS R1 SN1 SN4 R4 DDS
to include:
SN2 SN3

‣ Support for TCP/IP
‣Offloading reliability from DDSI to TCP R2 R3

whenever possible DDS DDS

‣ Compression


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.


Scaling the Data Distribution Service to Global Networks

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