doc/src/library/user.xfm

.if false
==================================================================================
	Copyright (c) 2019 Nokia
	Copyright (c) 2018-2019 AT&T Intellectual Property.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
==================================================================================
.fi

.if false
	Mnemonic:	user.xfm
	Abstract:	This is the main module for the base RMR user documentation.
	Date:		30 July 2019
	Author:		E. Scott Daniels
.fi

.** setup will do the right thing with the index configuration
.dv index_snare_file index_snatch.im
.im ./setup.im

.** func is a bit odd; if punct needs to be added, it must be supplied as the second
.** parm because we add () to the first. E.g. &func(foo_bar:.) will add a parm
.**
.dv func .ix force ${1} ^:  ^&cw(${1}()$2 )

.dv mtsid message type and subscription ID
.dv Mtsid Message type and subscription ID
.dv mt message type
.dv Mt Message type
.dv mts message types

.dv textfont Helvetica
.dv textsize 10p
.hn off


.gv e XFM_PASS pass
.if &pass 2 =
	.** two pass mode -- pull in variables captured during pass 1 for forward references
	.im p1var_setup.ca
.fi

.** vars picked up by front_junk as it's a generic module
.dv doc_title RIC Message Router -- RMR
.dv doc_subtitle User's Manual

.if pfm
	.** add licence,  a title page, and talbe of contents
	.im front_junk.im 
.ei
	.** for text based things, nothing more than license
	.im license.im
.fi

.if pfm
	.pn on noline center f=%d 0
.fi

&mult_space( 5 )
.st 18
&center_start
.sf &bold_font
&doc_title
.br
.st 12
&doc_subtitle
&center_end
.sf &textfont
&mult_space( 2 )
.st &textsize

&h1(Overview)
The RIC Message Router (a.k.a. RMR) is a thin library which provides a latency sensitive application with the ability
to send and receive messages with other RMR based applications.
The library provides the following major features:

&half_space
&indent
&beg_list( &lic1 )
	&li Routing and endpoint selection is based on &ital(message type.)
	&half_space

	&li Application is insulated from the underlying transport mechanism and/or protocols.
	&half_space

	&li Message distribution (round robin or fanout) is selectable by message type.
	&half_space

	&li Route management updates are received and processed asynchronously and without overt
		application involvement.
&end_list
&uindent

&space
&h2(Purpose)
RMR's main purpose is to provide an application with the ability to send and receive messages to/from other
peer applications with minimal effort on the application's part.
To achieve this, RMR manages manages all endpoint information, connections, and routing information necessary
to establish and maintain communication.
From the application's point of view, all that is required to send a message is to allocate (via RMR) a message
buffer, add the payload data, and set the message type.
To receive a message, the application needs only to invoke the receive function; when a message
arrives a message buffer will be returned as the function result.


&h2(Message Routing)
Applications are required to place a message type into a message before sending, and may optionally add a
subscription ID when appropriate.
The combination of message type, and subscription ID are refered to as the &ital(message key,)
and is used to match an entry in a routing table which provides the possible endpoints expecting
to receive messages with the matching key.

&h3(Round Robin Delivery)
An endpoint from RMR's perspective is an application to which RMR may establish a connection, and expect to
send messages with one or more defined message keys.
Each entry in the route table consists of one or more endpoint groups, called round robin groups.
When a message matches a specific entry, the entry's  groups are used to select the destination of the message.
A message is sent once to each group, with messages being &ital(balanced) across the endpoints of a group
via round robin selection.
Care should be taken when defining multiple groups for a message type as there is extra overhead required
and thus the overall message latency is somewhat reduced.

&h3(Routing Table Updates)
Route table information is made available  to RMR a static file (loaded once), or by updates sent from a
separate route manager application.
If a static table is provided, it is loaded during RMR initialisation and will remain in use until
an external process connects and delivers a route table update (often referred to as a dynamic update).
Dynamic updates are listened for in a separate process thread and applied automatically; the application does not
need to allow for, or trigger, updates.

&h2(Latency And Throughput)
While providing insulation from the underlying message transport mechanics, RMR must also do so in such a
manner that message latency and throughput are not impacted.
In general, the RMR induced overhead, incurred due to the process of selecting an endpoint for each message,
is minimal and should not impact the overall latency or throughput of the application.
This impact has been measured with test applications running on the same physical host and the average
latency through RMR for a message was on the order of 0.02 milliseconds.

&space
As an application's throughput increases, it becomes easy for the application to overrun the underlying
transport mechanism (e.g. NNG), consume all available TCP transmit buffers, or otherwise find itself
in a situation where a send might not immediately complete.
RMR offers different &ital(modes) which allow the application to manage these states based on the
overall needs of the application.
These modes are discussed in the &ital(Configuration) section of this document.


.** snarf in the major sections (to avoid one huge source document and maybe to promote reuse)
.im general_use.im
.im advanced_use.im
.im failures.im
.im config.im


.if tfm
	.** show all column/foot notes
	.cn showend
	&mult_space( 3 )
.fi



.dv qr_appendix A
.pa
.im api_qref.im

.dv mbuf_appendix B
.pa
.im mbuf.im

.dv gloss_appendix C
.pa
.im glossary.im

.dv code_appendix D
.pa
.im code_appendix.im

.** if pfm and index was setup, include it now
.if index_here
	.st 8p
	&index_here
	.st &textsize
.fi
.pa

.** capture all interesting variables to be used as forward references during pass 2
.ca expand start p1var_setup.ca
	.** pass 1 variable settings -- do NOT commit to repo

	.dv qr_appendix &qr_appendix
	.dv mbuf_appendix &mbuf_appendix
	.dv gloss_appendix &gloss_appendix
	.dv code_appendix &code_appendix
.ca end

.qu
glossary:
context
endpoint
mt/sid
NNG
push back
route table