Download Introduction GOALS: APPROACH:

Introduction
GOALS:
 To improve the Quality of Service (QoS)
for the JBI platform and endpoints
JBI Client Pub
..
.
 E.g., latency, fault tolerance, scalability,
graceful degradation
 Includes QoS of interactions JBIendpoint
JBI Client Pub
APPROACH:
 Build on QoS-aware middleware
JBI Client Sub
 Examined Java Message Service (JMS)
and Real-Time Java (e.g., RTSJ)
..
.
JBI Server (s)
(Using DDS)
 Currently using OMG Data Distribution
Service (DDS)
JBI Client Sub
Original Proposed JBI/DDS Architecture
 Questions/Challenges:
Processing an Information Object (IO)
 Can important pieces of JBI be implemented with DDS?
 DDS does not include centralized brokering
 DDS does not include archival data (a limit to queries)
Broker #1 in each JBI
Server is servicing clients
subscribing to ImageInfo
objects
1. JBI Client 1 publishes an
ImageInfo object
 Can better QoS properties be attained with DDS?
Note: DDS QoS parameters useful such as Deadline, Reliability,
Latency Budget, Resource Limits, etc.
JBI Client 1
(publisher)
IOType: ImageInfo
2. PubCatcher converts XML to
C++ binary and sends a
DDS publication to local
brokers and other JBI
server’s PubCatchers
1
Introduction of New Information Object Type
2
Pub
Catcher
Pub
Catcher
2
XML
Schema
Parse XML Schema
3. PubCatcher on JBI Server 2
sends a DDS publication to
brokers on its local DDS
Domain
3
Broker
#1
Broker
#2
4. JBI Client 4’s predicate
doesn’t match
Broker
#1
Broker
#2
4
New IO Type
Generate IDL (Interface Definition
Language) structure
Predicate
Match
JBI
Server 1
Compile into DDScompatible C++ code
Generate XML to
C++ conversion code
6. Disseminator forwards
publication to JBI Client 3
Predicate
Mismatch
5
Disseminator (s)
JBI
Server 2
5. Broker converts back to XML
to send to Disseminator
Disseminator (s)
6
JBI Client 2
(subscriber)
IOType: SARInfo
JBI Client 3
(subscriber)
IOType: ImageInfo
JBI Client 4
(subscriber)
IOType: ImageInfo
Legend
XML
C++ binary
Generate C++ to
XML conversion code
 Bandwidth Savings: Transmitting C++ binary data rather
than XML
Compile
 Brokering Savings: Parse an IO once and do most predicate
Generated
object code
evaluation in DDS
JBI/DDS Architecture Implementation
 Completed work: Demonstrate feasibility of proposed architecture
 Difficulties
 IDL generation from supported XML schemas
 Security – dynamic code generation
 Prototype of XML IO conversion
 Aggressive application of DDS
 DDS predicate generation from supported XPath predicates
 Potential next steps:
 Interim experiment:
 The 100X JBI uses “JBI Connectors” to connect multiple 100X servers
 Automate generation of XML IO conversion code
 Apply DDS in a less aggressive manner
 Automate compilation of generated source code
 See right panel
 Dynamically load generated code
 Evaluate expressability of XML schema and XPath predicates, as used
by JBI, when converted to IDL and DDS predicates
The 100X JBI Connector
The DDS/JBI Connector
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Executes alongside 100X JBI servers
Connects multiple 100X JBI servers
Candidate scheme for integration
TAO DDS is utilized between JBI servers
The DDS code is transparent to the JBI servers
and JBI clients
Above: Three 100X JBI servers and their connectors.
Above: Three 100X JBI servers and DDS/JBI connectors.
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TAO DDS
Currently supports five of the 22 QoS policies defined
in the DDS specification
History/Durability
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–
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Whether samples are discarded by DDS after
being sent to all known subscribers or if a certain
number of samples is kept to send to late-joining
subscribers
Verified with a three-node configuration
experiment to allow a new Connector or a
restarted Connector to get a snapshot of the past
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•
Liveliness
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Supports the Automatic setting, which indicates that
DDS should periodically poll participants at a
configurable interval
When an SSH tunnel is broken or a DDS/JBI
Connector exits, the DDS components on the nodes
are notified within the lease duration. Notification is
also given to the DDS components when the
DDS/JBI Connector which was previously not
reachable is again reachable (the SSH tunnel is
restored and/or the DDS/JBI Connector restarts).
One major issue identified: there is no mechanism
within the current JBI with which the DDS/JBI
Connector can communicate to indicate liveliness
information. That is, the DDS/JBI Connector has no
way of notifying the JBI that a node has gone down
or reappeared.
Providing QoS-enabled dissemination between multiple
JBI servers and compression of JBI IOs
The dashed connections between the DDS/JBI
Connectors and the DCPSInfoRepo are part of the TAO
DDS architecture
All JBI IO types are represented with just one DDS
message type and, currently, one DDS topic.
Performance results (latency) were obtained for the
100X Connector, the DDS/JBI Connector with
compression, and the DDS/JBI Connector without
compression
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Reliability and Resource Limits:
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Message type of approximately one kilobyte in size
Most of the latency can be attributed to network
communication time for both the 100X and DDS/JBI
Connector and not to the overhead of the connectors
Only the use of TCP transports with Reliability as
Reliable ensured message delivery. Other settings
resulted in samples being dropped in cases of heavy
load for tests (or error message indicating that the
maximum blocking time has been exceeded).
Later renamed to OpenDDS