doc/src/library/glossary.im

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&h1(Appendix  &gloss_appendix -- Glossary)

Many terms in networking can be interpreted with multiple meanings, and several terms used
in this document are RMR specific.
The following definitions are the meanings of terms used within this document and should
help the reader to understand the intent of meaning.

&beg_dlist( &1.0i Helvetica-bold )
&term(application) A programme which uses RMR to send and/or receive messages to/from another RMR based application.

&term(Critical error)	An error that RMR has encountered which will prevent further successful processing by
			RMR. Critical errors usually indicate that the application should abort.

&term(Endpoint) An RMR based application that is defined as being capable of receiving one or more types of messages
			(as defined by a &ital(message key.) .sm )

&term(Environment variable) A key/value pair which is set externally to the application, but which is available
			to the application (and referenced libraries) through the &cw(getenv) system call. Environment variables
			are the main method of communicating information such as port numbers to RMR.

&term(Error) An abnormal condition that RMR has encountered, but will not affect the overall processing by RMR,
			but may impact certain aspects such as the ability to communicate with a specific endpoint. 
			Errors generally indicate that something, usually external to RMR, must be addressed.

&term(Host name) The name of the host as returned by the &cw(gethostbyname) system call. In a containerised 
			environment this might be the container or service name depending on how the container is started.
			From RMR's point of view, a host name can be used to resolve an &ital(endpoint) definition in 
			a &ital(route table.)

&term(IP)	Internet protocol. A low level transmission protocol which governs the transmission of datagrams
			across network boundaries.

&term(Listen socket) A &ital(TCP) socket used to await incoming connection requests. Listen sockets are defined
			by an interface and port number combination where the port number is unique for the interface.

&term(Message) A series of bytes transmitted from the application to another RMR based application. A message
			is comprised of RMR specific data (a header), and application data (a payload).

&term(Message buffer) A data structure used to describe a message which is to be sent or has been received.
			The message buffer includes the payload length, message type, message source, and other information.

&term(Messgae type) A signed integer (0-32000) which identifies the type of message being transmitted, and is 
			one of the two components of a &ital(routing key.) See &ital(Subscription ID.)

&term(Payload) The portion of a message which holds the user data to be transmitted to the remote &ital(endpoint.)
			The payload contents are completely application defined.

&term(RMR context) A set of information which defines the current state of the underlying transport connections that
			RMR is managing. The application will be give a context reference (pointer) that is supplied to most
			RMR functions as the first parameter.

&term(Round robin) The method of selecting an &ital(endpoint) from a list such that all &ital(endpoints) are selected
			before starting at the head of the list.

&term(Route table) A series of "rules" which define the possible &ital(endpoints) for each &ital(message key.)

&term(Route table manager) An application responsible for building a &ital(route table) and then distributing it to
			all applicable RMR based applications.

&term(Routing) The process of selecting an &ital(endpoint) which will be the recipient of a message.

&term(Routing key) A combination of &ital(message type) and &ital(subscription ID) which RMR uses to select the 
			destination &ital(endpoint) when sending a message.

&term(Source) The sender of a message. 


&term(Subscription ID) A signed integer value (0-32000) which identifies the subscription characteristic of a message.
			It is used in conjunction with the &ital(message type) to determine the &ital(routing key.)

&term(Target) The &ital(endpoint) selected to receive a message.

&term(TCP)	Transmission Control Protocol. A connection based internet protocol which provides for
			lossless packet transportation, usually over IP.

&term(Thread)	Also called a &ital(process thread, or pthread.)  This is a lightweight process which executes in concurrently with
			the application and shares the same address space. 
			RMR uses threads to manage asynchronous functions such as route table updates.

&Term(Trace information)  An optional portion of the message buffer that the application may populate with data
			that allows for tracing the progress of the transaction or application activity across components.
			RMR makes no use of this data.

&term(Transaction ID) A fixed number of bytes in the &ital(message buffer) which the application may populate with 
			information related to the transaction. RMR makes use of the transaction ID for matching response messages
			with the &c(rmr_call) function is used to send a message.

&term(Transient failure) An error state that is believed to be short lived and that the operation, if retried by the 
			application, might be successful. C programmers will recognise this as &cw(EAGAIN.)
			
&term(Warning) A warning occurs when RMR has encountered something that it believes isn't correct, but has a defined
			work round.  

&term(Wormhole) A direct connection managed by RMR between the user application and a remote, RMR based, application.
&end_dlist

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