DDS vs AMQP

OpenSplice DDS
Delivering Performance, Openness, and Freedom

Angelo Corsaro, Ph.D.
Chief Technology Officer

DDS vs. AMQP
OMG DDS SIG Co-Chair
angelo.corsaro@prismtech.com

Agenda

‣Genesis
‣Technology Comparison
‣Code Examples
‣Concluding Remarks

OpenSplice DDS

Historical
Perspectives

Genesis
DDS AMQP

‣ Emerged from Aerospace and Defense ‣ Emerged from the Financial Market
to address the data distribution from the desire of freeing users from
requirement of a large class of mission- proprietary and non-interoperable
critical systems messaging systems
‣ Evolved to address on-the-wire ‣ Evolved into an effort to deﬁne a
interoperability and provide the generic enterprise messaging standard
ubiquitous data-bus for mission-critical
System-of-Systems

Standardization Organization
DDS AMQP

‣ DDS is an Object Management Group ‣ AMQP is standardized by the AMQP
(OMG) Standard Working Group
‣ The OMG is a an international, open ‣ The AMQP Working Group is a non-
membership, not-for-profit computer profit organization with a free
industry consortium since 1989 membership based on interest and
‣ OMG is an ISO PAS submitter, able to merit
submit our specifications directly into
ISO’s fast-track adoption process.

Standard Evolution

DDS v1.0 DDS v1.1 DDS v1.2 DDSI v2.0 DDSI v2.1 DDS-XTopics
Dec Dec Jan Apr Jan March

2004 2005 2006 2007 2008 2009 2010

Jun Nov Dec

AMQP v0-8 AMQP v0-9-1 AMQP v1-0 draft
???
Dec
AMQP v0-10
AMQP v0-9

Scope of Standardization
Application
Application
Object/Relational Mapping

Data Local Reconstruction Layer (DLRL)

DDS v1.2
Content
Ownership Durability
Subscription
API (?) Minimum Proﬁle

Data Centric Publish/Subscribe (DCPS)

DDSI v2.1
AMQP v1-0
Advanced Message Queuing Protocol Real-Time Publish/Subscribe Protocol

Interoperability Wire Protocol DDS Interoperability Wire Protocol

TCP/IP UDP/IP

OpenSplice DDS

Technology
Comparison

Which Versions?

In the reminder of this presentation I’ll compare DDS v1.2 / DDSI v2.1 with AMQP v1-0

OpenSplice DDS

Messages vs. Topics

AMQP v1-0 Messages

‣ AMQP is a standard protocol for messaging
‣ As such AMQP the unit of information that
can be sent or received is a message.
‣ An AMQP message encapsulate the “Bare
Message”, provided by the application, within
an annotated message

[Source AMQP speciﬁcation v1-0]

DDS Topics
{Circle, Square, Triangle}
Topic
‣ Unit of information exchanged between
Publisher and Subscribers.
‣ An association between a unique name, a
type and a QoS setting {ShapeType} {...}

Topic Type.
struct ShapeType {
‣ Type describing the data associated with one long x;
or more Topics long y;
‣ A Topic type can have a key represented by an long shapesize;
string color;
arbitrary number of attributes };
‣ Expressed in IDL #pragma keylist ShapeType color

© 2009, PrismTech. All Rights Reserved

Topic/Instances/Samples Recap.
Topics Instances

Samples

ti tj tnow time

OpenSplice DDS

Node/Links vs. Reader/Writers

AMQP v1-0 Conceptual Model
‣ An AMQP Network consists of Nodes and Links
‣ A Node is a named source and/or sink of Messages. A Message is created at a
(Producer) Node, and may travel along links, via other nodes until it reaches a
terminating (Consumer) Node.
‣ A Link is a unidirectional route between nodes along which messages may travel. Links
may have entry criteria (Filters) which restrict which messages may travel along them.
The link lifetime is tied to the lifetime of the source and destination nodes.

m m
Link
m

Node Node

Destructive Links

Destructive Links consume the message from the originating source.

Destructive Link Destructive Link Destructive Link
m m m m

Node 1 Node 2 Node 1 Node 2 Node 1 Node 2

Time

Non-Destructive Links

Non-Destructive Links don’t consume messages from the source node.

Non-Destructive Non-Destructive
Link Link
m m m m m

Node 1 Node 2 Node 1 Node 2 Node 1 Node 2

Time

Filtered Links
Links can have associated ﬁlters that allow to predicate on the messages that might
traverse. Filter can be based on the non opaque portion of the message.

Link Link m

{color = red} {color = red} m

m m Node Node
m
m m
m

Node Link Node Link m
{color = green} {color = green}
m

Node Node
Time

Anatomy of a DDS Application

Topic
Topic
Topic
Samples
Samples
Instances Samples
Instances
Instances
1
1
21 62
21 62
1
1
22 62
22 62
1
1
23 63
23 63
DataReader
DataReader 2 20 61 2 19 60
DataReader
DataReader 2 20 61 2 19 60 DataWriter
DataWriter
DataReader
DataReader 3 25 70 3 25 71
25 3 25 74 3
3
26 77
26 77
DataWriter
DataWriter
struct ShapeType { 3 25 70 3 25 71
25 3 25 74
long x;
long y;
long shapesize;
string color;
};
#pragma keylist ShapeType color

Destructive/Non-Destructive Links can be paralleled with the DDS read/take semantics

Content Filtering
X0 X1
X0 <= X <= X1
‣ DDS allows to specify content-
filtered Topics for which a subset
of SQL92 is used to express the
filter condition
Y0
‣ Content filters can be applied on
the entire content of the Topic Type Y0 <= Y <= Y1

‣ Content filters are applied by DDS
Y1
each time a new sample is
produced/delivered


Local Queries
‣ A subset of SQL92 can be used for performing queries X0

‣ Queries are
performed under Circle Topic
user control and Y0
color x y shapesize Y0
provide a result that red 57 62 50
depends on the blue 90 85 50
Y0 <= Y <= Y1
current snapshot of yellow 30 25 50
the system, e.g.,
samples currently x > 25 AND y < 55 Y1
available
color x y shapesize
yellow 30 25 50


OpenSplice DDS

Deployment Model

AMQP v1-0 Deployment Model

‣ Nodes within the AMQP network
exist within Containers
‣ A container is a physical or logical
process to which network
connections can be established


DDS Deployment Model
‣ DDS is based around the concept
of a fully distributed Global Data
Publisher Subscriber
Space (GDS)
Global Data Space
‣ Publishers and Subscribers can
join and leave the GDS at any time
Subscriber
‣ Publishers and Subscribers Publisher Brokers
express their intent to produce/
consume specific type of data,
e.g., Topics
Subscriber
‣ Data flows from Publisher to Publisher

Subscribers DDS


Domains and Partitions
Domain

Domain
‣ A Domain is one instance of the DDS
Global Data Space
‣ DDS entities always belong to a specific
domain
Partition
‣ A partition is a scoping mechanism
provided by DDS organize a domain DDS
Global Data Space
Partition


OpenSplice DDS

Communication Model

Sessions

‣ A Session is a named interaction

between two containers providing
for a pair of reliable ordered
command streams (one in each
direction)
‣ Links between nodes in different
containers are created on a
session
‣ Containers and Sessions form an
underlay network, nodes and links
an overlay network atop them

Sessions & Commands
‣ Sessions are a transport for commands
‣ Commands are the atomic units of work of the AMQP transport protocol
Commands are used to create links between nodes in the source and destination
containers, to transfer message data, and to issue and revoke credit
‣ In general an AMQP session will be carried over some form of network layer, thus
commands sent on a session are asynchronous.


Transport Model
m m
Link
m

Node Node

Links Links
Session Session
Links Links
Session Transport Connection (TCP/IP) Session
Links Links
Session Session


Topic
Topic
Topic
Samples
Samples
Instances Samples
Instances
Instances
1
1
21 62
21 62
1
1
22 62
22 62
1
1
23 63
23 63
DataReader
DataReader 2 20 61 2 19 60
DataReader
DataWriter
DataReader
DataReader 3 25 70 3 25 71
25 3 25 74 3
3
26 77
26 77
DataWriter
DataWriter
25 3 25 74
long x;
long y;
long shapesize;
string color;
};



Topic
Topic
Topic
Samples
Samples
Instances Samples
Instances
Instances
1
1
21 62
21 62
1
1
22 62
22 62
1
1
23 63
23 63
DataReader
DataReader 2 20 61 2 19 60
DataReader
DataWriter
DataReader
DataReader 3 25 70 3 25 71
25 3 25 74 3
3
26 77
26 77
DataWriter
DataWriter
25 3 25 74
long x;
long y;
Arrows long shapesize;
string color;
show };
structural
relationship
s, not data- Subscriber Publisher
ﬂows Partition



Topic
Topic
Topic
Samples
Samples
Instances Samples
Instances
Instances
1
1
21 62
21 62
1
1
22 62
22 62
1
1
23 63
23 63
DataReader
DataReader 2 20 61 2 19 60
DataReader
DataWriter
DataReader
DataReader 3 25 70 3 25 71
25 3 25 74 3
3
26 77
26 77
DataWriter
DataWriter
25 3 25 74
long x;
long y;
long shapesize;
Arrows string color;
};
show #pragma keylist ShapeType color
structural
relationship
s, not data- Subscriber Publisher
ﬂows Partition

Domain Participant

Domain

Transport Model
Readers
Writers Writers

Subscriber
Publisher

Publisher
Readers Readers
Writers Writers Writers Writers

Domain

Subscriber
Publisher

Publisher

Subscriber
Publisher

Publisher
Participant

Domain
Domain
Participant UDP (Unicast/MCast)
Participant

Domain Domain
Participant Participant

Subscriber

Subscriber
Subscriber

Subscriber
Publisher

Publisher
Readers Readers Readers Readers
Writers Writers

OpenSplice DDS

Type System

AMQP Type System

‣ AMQP deﬁnes a type-system
that is used to encode messages
and controls sent as part of the
protocol
‣ This type system can be also
used to encode application data


Primitive Types

DDS Type System
boolean long
octet unsigned long
char long long
wchar unsigned long
long

‣ DDS supports the definition of types based on a subset of short
unsigned short
float
double
the IDL specification language. long double

‣ This type system is used internally by DDS and is also Constructed Types Example

available to user for defining topic types enum enum Dimension { 1D, 2D, 3D, 4D };

Template Type Example
string<length = UNBOUNDED> string s1;
string<32> s2; struct Coord1D { long x;};
struct Coord2D { long x; long y; };
wstring<length = UNBOUNDED> wstring ws1;
struct struct Coord3D { long x; long y; long
wstring<64> ws2;
z; };
struct Coord4D { long x; long y; long z,
unsigned long long t;};
sequence<T,length = UNBOUNDED> sequence<octet> oseq;
sequence<octet, 1024> oseq1k;

sequence<MyType> mtseq; union Coord switch (Dimension) {
sequence<MyType, 10> mtseq10; case 1D:
Coord1D c1d;
case 2D:
Coord2D c2d;
union
case 3D:
Coord3D c3d;
fixed<digits,scale> fixed<5,2> fp; //d1d2d3.d4d5 case 4D:
Coord4D c4d;
};

OpenSplice DDS

Putting it all Together

DDS AMQP

‣ A generic DDS application is a self-formed ‣ A generic AMQP application is a graph of
federation reads and writes topics over the nodes connected by links over which travel
Global Data Space application provided messages
‣ Communication is hidden to the applications ‣ The link-related trafﬁc is managed by
which is provided with a read/write sematics sessions which in turns communicate via a
transport connection.
‣ UDP Unicast and Multicast are available for
DDS v1.2, DDSI v2.1 ‣ The only transport currently available for
AMQP v1-0 is TCP

AMQP v1-0 StatusDDS AMQP

‣ Addressing Scheme. Does not define a standard
‣ Data Centricity. DDS is about data and it is fair global addressing scheme, this will be part of v1-1
to say that data takes life in DDS, thanks to the ‣ Transport Protocol. Currently only supports
support for keys, lifecycle management, etc. TCP, but UDP and SCTP will be added in future
‣ Transport Protocol. Currently supports UDP revisions of the spec
(Unicast and Multicast). TCP will be supported in ‣ Broker Management. A SIG is working on
upcoming revisions of the standard. However, defining an API for Broker Management, today,
there is nothing that prevents DDS today to use each implementation has its own way
TCP as a transport ‣ Topology Configuration. The Broker topology
‣ Topology Configuration. Topology is dynamically can be configured via management tools, yet the
discovered by DDS via its standard discovery spec does not explicitly supports automatic
protocol propagation of queue subscriptions (some
product do)

OpenSplice DDS

Code Examples

Setting-up Subscriptions
DDS AMQP
std::string exchange = "amq.topic";

dds::Topic<Track> track("TrackTopic"); // Connect to the broker
dds::Topic<TrackClass> track_class("TrackClassTopic"); Connection connection;
connection.open(host, port);
dds::DataReader<Track> tDR(track);
dds::DataReader<TrackClass> tcDR(track_class); // Create a session
Session session = connection.newSession();

// Decrlare a queue
session.queueDeclare(arg::queue=queue,
arg::exclusive=true,
arg::autoDelete=true);

struct Track { struct TrackClass { // Set-up routes
short id; short id; session.exchangeBind(arg::exchange=exchange,
long x; Classification cls; arg::queue="Track",
long y; string descr; arg::bindingKey="Track.#");
}; }; session.exchangeBind(arg::exchange=exchange,
#pragma keylist Track id #pragma keylist TrackClass id arg::queue="TrackClass",
arg::bindingKey="TrackClass.#");

Writing Data
DDS AMQP
dds::DataWriter<Track> tDW(track); Track t = { 101, 140, 200 };
dds::DataWriter<TrackClass> tcDW(track_class); Message message;

Track t = { 101, 140, 200 }; message.getDeliveryProperties().setRoutingKey("Track.Radar101");
tDW(t);
std::stringstream message_data;
TrackClass tc = { 101, FRIENDLY, “Some descr.”}; data << t.id << “ “ << t.x << “ “ << t.y;
tcDW.write(tc);
message.setData(message_data.str());
async(session).messageTransfer(arg::content=message,
arg::destination="amq.topic");

Reading Data
DDS AMQP

std::vector<Track> data; void Listener::received(Message& message) {
std::vector<SampleInfo> info; std::string data = message.getData();
Track t;
tDR.read(data, info); // Parse the string to extract the data
string_to_track(data, t);
}

OpenSplice DDS

Summing Up

Concluding Remarks
DDS AMQP

‣ DDS provides the abstraction of a Global ‣ AMQP is provides as basic abstraction that
Data Space, a ubiquitous, universal and fully of messages and message routing.
distributed data cache. ‣ AMQP standardized the wire-protocol and
‣ DDS makes user data a ﬁrst class citizen uses this standard to achieve API
‣ DDS provides a standard API as well as an independence
interoperable Wire-Protocol

DDS and AMQP are very interesting technologies, which at some point might work in synergy.
OpenSplice DDS could be using AMQP as one of its wire-protocols. The DDS API over AMQP could be
standardize...

Online Resources

http://www.opensplice.com/
http://www.slideshare.net/angelo.corsaro
emailto:opensplicedds@prismtech.com

http://bit.ly/1Sreg http://twitter.com/acorsaro/

http://opensplice.blogspot.com
http://www.youtube.com/OpenSpliceTube


DDS vs AMQP

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