Comparison of communication mechanisms

Of the three communication mechanisms , Parameter server is a data sharing mechanism , Data can be shared between different nodes , Topic communication and service communication transfer data between different nodes , The three are ROS The most basic and widely used communication mechanism in .

Among them , There are some similarities and essential differences between topic communication and service communication , Here we will make a simple comparison between the two :

The implementation process of the two is relatively similar , All involve four elements :

• elements 1: The publisher of the message / client (Publisher/Client)
• elements 2: Subscriber of the message / Server side (Subscriber/Server)
• elements 3: Topic name (Topic/Service)
• elements 4: Data carriers (msg/srv)

Can be summed up as : The two nodes are connected by topic , And use some type of data carrier to realize data transmission .

The realization of the two is also fundamentally different , The specific comparison is as follows :

	Topic( topic of conversation )	Service( service )
Communication mode	Release / subscribe	request / Respond to
Synchronicity	asynchronous	Sync
The underlying protocol	ROSTCP/ROSUDP	ROSTCP/ROSUDP
buffer	Yes	nothing
All the time	weak	strong
Node relationship	Many to many	One to many ( One Server)
Communication data	msg	srv
Use scenarios	Continuous high-frequency data release and reception : radar 、 Odometer	Occasionally call or perform a specific function ： Taking pictures 、 speech recognition