In 2012, an effort started to design a communication backbone that would allow all MBARI assets to communicate easily across the organization. Much work has been done in computer science in the areas of message based systems over the years and this is an exploration of how those systems can make communications across MBARI assets much easier and more pervasive.

Communication/Messaging Systems

Technologies

• LCM
  • White Paper on LCM
  • Detailed Technical Paper
• MOOS
• Player
• AMQP
  • RabbitMQ
• ZeroMQ

Comparison

Feature/Framework	LCM	MOOS	Player	RabbitMQ	ZeroMQ	Carmen (IPC)	JAUS	ROS	RDS	DDS	Apache Kafka	MQTT
Target App	Real-time systems	Robotic Vehicles (Under water mostly)	Robot control			Robot control		Robotics Development	Robotics
Transport	UDP Multicast	TCP	TCP			TCP	UDP	Shared Memory TCP (most common) UDP Spread	Mulitple SOAP XML/RPC
Communications Model(s)	pub/sub(push)	pub/sub (pull)	pub/sub(pull)			pub/sub (push)	routed message	pub/sub service oriented	service
Messages Duplicated?	N	Y	Y			Y	Y	Y	Y
Type safe?	Y	N	N			N	N	N	Y
Marshalling Technique	Automatice	Manual - Free form ASCII	XDR (automatic for C)	Manual		Partial - users must keep an ASCII description of types in sync with a C construct	Manual	Automatic - Type specification language similar to C	Automatic
Server/ Central Hub?	N	Y	Y	Y		Y	N
Pros	Tools for introspection and analysis of the messaging traffic and the messages themselves
Cons			If subscriber can't keep up with publisher, TCP buffers can fill hurting performance			Keeping ASCII/struct in sync for marshalling is error prone due to machines having different word sizes	Small subspace is available for user-defined types Messages limited to 4096 bytes Each node has to have globally unique ID	little endian, so big endian systems supported	More difficult to inject previously recorded data
Platforms	C Java Python MATLAB C++ (compatible) Objective-C (compatible)	C++	C C++ Java Tcl Python			C Java	C	C++ Python	.NET

Marshalling

Technologies

1. Protocol Buffers
2. LCM
3. Avro
4. Thrift
5. MessagePack

Comparisons

1. Protocol Buffers, Avro, Thrift & MessagePack

LCM_Technical_Paper.pdf (application/pdf)
LCM_White_Paper.pdf (application/pdf)