doc/src/library/user.xfm

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==================================================================================
	Copyright (c) 2019-2020 Nokia
	Copyright (c) 2018-2020 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.
==================================================================================
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	Mnemonic:	user.xfm
	Abstract:	This is the main module for the base RMR user documentation.
	Date:		30 July 2019
	Author:		E. Scott Daniels
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.** vars picked up by front_junk or gen_title as it's a generic module
.dv doc_title RIC Message Router -- RMR
.dv doc_subtitle User's Guide
.dv orig_date 30 July 2019
.** must reverse titles when generating rst to disambiguate in the doc list
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.** setup will do the right thing with the index configuration
.dv index_snare_file index_snatch.im
.im ./setup.im

.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

.** --------------------------------------------------------------------------------------

&line_len( &line_size )
&h1(Overview)

The RIC Message Router (RMR) is a library for peer-to-peer
communication.  Applications use the library to send and receive
messages where the message routing and endpoint selection is based on
the message type rather than DNS host name-IP port combinations.
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 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 increased.

&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 initialization
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


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	.** show all column/foot notes
	&h1(Notes)
	.cn showend
	&mult_space( 3 )
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.dv qr_appendix A
.pa
.if "&ot" "rst" =
&h1(Appendix &qr_appendix -- Quick Reference)
	Please refer to the RMR manual pages on the Read the Docs site
	&space
	https://docs.o-ran-sc.org/projects/o-ran-sc-ric-plt-lib-rmr/en/latest/index.html
.ei
	.im api_qref.im
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.dv mbuf_appendix B
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.im mbuf.im

.dv gloss_appendix C
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.im glossary.im

.dv code_appendix D
.pa
.im code_appendix.im

.** if pfm and index was setup, include it now
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.** 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