Nicholas Allen wrote a post detailing the different throttling parameters for a service:
- MaxConcurrentCalls limits the number of service calls (messages) that the service will have processing at one time. You may get less than this maximum number if the concurrency or instancing behavior of your service does not allow processing multiple messages.
- MaxConcurrentSessions limits the number of persistent connections (sessionful channels) that the service will accept messages from at one time. Again, you need a minimum level of concurrency in your service for this to become an issue.
- MaxConcurrentInstances limits the number of copies of the service (instance contexts) that can exist. This is only interesting if your service is permitted to have multiple instances.