<!--{{{-->
<link rel='alternate' type='application/rss+xml' title='RSS' href='index.xml' />
<!--}}}-->
Background: #fff
Foreground: #000
PrimaryPale: #8cf
PrimaryLight: #18f
PrimaryMid: #04b
PrimaryDark: #014
SecondaryPale: #ffc
SecondaryLight: #fe8
SecondaryMid: #db4
SecondaryDark: #841
TertiaryPale: #eee
TertiaryLight: #ccc
TertiaryMid: #999
TertiaryDark: #666
Error: #f88
/*{{{*/
body {background:[[ColorPalette::Background]]; color:[[ColorPalette::Foreground]];}

a {color:[[ColorPalette::PrimaryMid]];}
a:hover {background-color:[[ColorPalette::PrimaryMid]]; color:[[ColorPalette::Background]];}
a img {border:0;}

h1,h2,h3,h4,h5,h6 {color:[[ColorPalette::SecondaryDark]]; background:transparent;}
h1 {border-bottom:2px solid [[ColorPalette::TertiaryLight]];}
h2,h3 {border-bottom:1px solid [[ColorPalette::TertiaryLight]];}

.button {color:[[ColorPalette::PrimaryDark]]; border:1px solid [[ColorPalette::Background]];}
.button:hover {color:[[ColorPalette::PrimaryDark]]; background:[[ColorPalette::SecondaryLight]]; border-color:[[ColorPalette::SecondaryMid]];}
.button:active {color:[[ColorPalette::Background]]; background:[[ColorPalette::SecondaryMid]]; border:1px solid [[ColorPalette::SecondaryDark]];}

.header {background:[[ColorPalette::PrimaryMid]];}
.headerShadow {color:[[ColorPalette::Foreground]];}
.headerShadow a {font-weight:normal; color:[[ColorPalette::Foreground]];}
.headerForeground {color:[[ColorPalette::Background]];}
.headerForeground a {font-weight:normal; color:[[ColorPalette::PrimaryPale]];}

.tabSelected{color:[[ColorPalette::PrimaryDark]];
	background:[[ColorPalette::TertiaryPale]];
	border-left:1px solid [[ColorPalette::TertiaryLight]];
	border-top:1px solid [[ColorPalette::TertiaryLight]];
	border-right:1px solid [[ColorPalette::TertiaryLight]];
}
.tabUnselected {color:[[ColorPalette::Background]]; background:[[ColorPalette::TertiaryMid]];}
.tabContents {color:[[ColorPalette::PrimaryDark]]; background:[[ColorPalette::TertiaryPale]]; border:1px solid [[ColorPalette::TertiaryLight]];}
.tabContents .button {border:0;}

#sidebar {}
#sidebarOptions input {border:1px solid [[ColorPalette::PrimaryMid]];}
#sidebarOptions .sliderPanel {background:[[ColorPalette::PrimaryPale]];}
#sidebarOptions .sliderPanel a {border:none;color:[[ColorPalette::PrimaryMid]];}
#sidebarOptions .sliderPanel a:hover {color:[[ColorPalette::Background]]; background:[[ColorPalette::PrimaryMid]];}
#sidebarOptions .sliderPanel a:active {color:[[ColorPalette::PrimaryMid]]; background:[[ColorPalette::Background]];}

.wizard {background:[[ColorPalette::PrimaryPale]]; border:1px solid [[ColorPalette::PrimaryMid]];}
.wizard h1 {color:[[ColorPalette::PrimaryDark]]; border:none;}
.wizard h2 {color:[[ColorPalette::Foreground]]; border:none;}
.wizardStep {background:[[ColorPalette::Background]]; color:[[ColorPalette::Foreground]];
	border:1px solid [[ColorPalette::PrimaryMid]];}
.wizardStep.wizardStepDone {background:[[ColorPalette::TertiaryLight]];}
.wizardFooter {background:[[ColorPalette::PrimaryPale]];}
.wizardFooter .status {background:[[ColorPalette::PrimaryDark]]; color:[[ColorPalette::Background]];}
.wizard .button {color:[[ColorPalette::Foreground]]; background:[[ColorPalette::SecondaryLight]]; border: 1px solid;
	border-color:[[ColorPalette::SecondaryPale]] [[ColorPalette::SecondaryDark]] [[ColorPalette::SecondaryDark]] [[ColorPalette::SecondaryPale]];}
.wizard .button:hover {color:[[ColorPalette::Foreground]]; background:[[ColorPalette::Background]];}
.wizard .button:active {color:[[ColorPalette::Background]]; background:[[ColorPalette::Foreground]]; border: 1px solid;
	border-color:[[ColorPalette::PrimaryDark]] [[ColorPalette::PrimaryPale]] [[ColorPalette::PrimaryPale]] [[ColorPalette::PrimaryDark]];}

.wizard .notChanged {background:transparent;}
.wizard .changedLocally {background:#80ff80;}
.wizard .changedServer {background:#8080ff;}
.wizard .changedBoth {background:#ff8080;}
.wizard .notFound {background:#ffff80;}
.wizard .putToServer {background:#ff80ff;}
.wizard .gotFromServer {background:#80ffff;}

#messageArea {border:1px solid [[ColorPalette::SecondaryMid]]; background:[[ColorPalette::SecondaryLight]]; color:[[ColorPalette::Foreground]];}
#messageArea .button {color:[[ColorPalette::PrimaryMid]]; background:[[ColorPalette::SecondaryPale]]; border:none;}

.popupTiddler {background:[[ColorPalette::TertiaryPale]]; border:2px solid [[ColorPalette::TertiaryMid]];}

.popup {background:[[ColorPalette::TertiaryPale]]; color:[[ColorPalette::TertiaryDark]]; border-left:1px solid [[ColorPalette::TertiaryMid]]; border-top:1px solid [[ColorPalette::TertiaryMid]]; border-right:2px solid [[ColorPalette::TertiaryDark]]; border-bottom:2px solid [[ColorPalette::TertiaryDark]];}
.popup hr {color:[[ColorPalette::PrimaryDark]]; background:[[ColorPalette::PrimaryDark]]; border-bottom:1px;}
.popup li.disabled {color:[[ColorPalette::TertiaryMid]];}
.popup li a, .popup li a:visited {color:[[ColorPalette::Foreground]]; border: none;}
.popup li a:hover {background:[[ColorPalette::SecondaryLight]]; color:[[ColorPalette::Foreground]]; border: none;}
.popup li a:active {background:[[ColorPalette::SecondaryPale]]; color:[[ColorPalette::Foreground]]; border: none;}
.popupHighlight {background:[[ColorPalette::Background]]; color:[[ColorPalette::Foreground]];}
.listBreak div {border-bottom:1px solid [[ColorPalette::TertiaryDark]];}

.tiddler .defaultCommand {font-weight:bold;}

.shadow .title {color:[[ColorPalette::TertiaryDark]];}

.title {color:[[ColorPalette::SecondaryDark]];}
.subtitle {color:[[ColorPalette::TertiaryDark]];}

.toolbar {color:[[ColorPalette::PrimaryMid]];}
.toolbar a {color:[[ColorPalette::TertiaryLight]];}
.selected .toolbar a {color:[[ColorPalette::TertiaryMid]];}
.selected .toolbar a:hover {color:[[ColorPalette::Foreground]];}

.tagging, .tagged {border:1px solid [[ColorPalette::TertiaryPale]]; background-color:[[ColorPalette::TertiaryPale]];}
.selected .tagging, .selected .tagged {background-color:[[ColorPalette::TertiaryLight]]; border:1px solid [[ColorPalette::TertiaryMid]];}
.tagging .listTitle, .tagged .listTitle {color:[[ColorPalette::PrimaryDark]];}
.tagging .button, .tagged .button {border:none;}

.footer {color:[[ColorPalette::TertiaryLight]];}
.selected .footer {color:[[ColorPalette::TertiaryMid]];}

.sparkline {background:[[ColorPalette::PrimaryPale]]; border:0;}
.sparktick {background:[[ColorPalette::PrimaryDark]];}

.error, .errorButton {color:[[ColorPalette::Foreground]]; background:[[ColorPalette::Error]];}
.warning {color:[[ColorPalette::Foreground]]; background:[[ColorPalette::SecondaryPale]];}
.lowlight {background:[[ColorPalette::TertiaryLight]];}

.zoomer {background:none; color:[[ColorPalette::TertiaryMid]]; border:3px solid [[ColorPalette::TertiaryMid]];}

.imageLink, #displayArea .imageLink {background:transparent;}

.annotation {background:[[ColorPalette::SecondaryLight]]; color:[[ColorPalette::Foreground]]; border:2px solid [[ColorPalette::SecondaryMid]];}

.viewer .listTitle {list-style-type:none; margin-left:-2em;}
.viewer .button {border:1px solid [[ColorPalette::SecondaryMid]];}
.viewer blockquote {border-left:3px solid [[ColorPalette::TertiaryDark]];}

.viewer table, table.twtable {border:2px solid [[ColorPalette::TertiaryDark]];}
.viewer th, .viewer thead td, .twtable th, .twtable thead td {background:[[ColorPalette::SecondaryMid]]; border:1px solid [[ColorPalette::TertiaryDark]]; color:[[ColorPalette::Background]];}
.viewer td, .viewer tr, .twtable td, .twtable tr {border:1px solid [[ColorPalette::TertiaryDark]];}

.viewer pre {border:1px solid [[ColorPalette::SecondaryLight]]; background:[[ColorPalette::SecondaryPale]];}
.viewer code {color:[[ColorPalette::SecondaryDark]];}
.viewer hr {border:0; border-top:dashed 1px [[ColorPalette::TertiaryDark]]; color:[[ColorPalette::TertiaryDark]];}

.highlight, .marked {background:[[ColorPalette::SecondaryLight]];}

.editor input {border:1px solid [[ColorPalette::PrimaryMid]];}
.editor textarea {border:1px solid [[ColorPalette::PrimaryMid]]; width:100%;}
.editorFooter {color:[[ColorPalette::TertiaryMid]];}

#backstageArea {background:[[ColorPalette::Foreground]]; color:[[ColorPalette::TertiaryMid]];}
#backstageArea a {background:[[ColorPalette::Foreground]]; color:[[ColorPalette::Background]]; border:none;}
#backstageArea a:hover {background:[[ColorPalette::SecondaryLight]]; color:[[ColorPalette::Foreground]]; }
#backstageArea a.backstageSelTab {background:[[ColorPalette::Background]]; color:[[ColorPalette::Foreground]];}
#backstageButton a {background:none; color:[[ColorPalette::Background]]; border:none;}
#backstageButton a:hover {background:[[ColorPalette::Foreground]]; color:[[ColorPalette::Background]]; border:none;}
#backstagePanel {background:[[ColorPalette::Background]]; border-color: [[ColorPalette::Background]] [[ColorPalette::TertiaryDark]] [[ColorPalette::TertiaryDark]] [[ColorPalette::TertiaryDark]];}
.backstagePanelFooter .button {border:none; color:[[ColorPalette::Background]];}
.backstagePanelFooter .button:hover {color:[[ColorPalette::Foreground]];}
#backstageCloak {background:[[ColorPalette::Foreground]]; opacity:0.6; filter:'alpha(opacity=60)';}
/*}}}*/
/*{{{*/
* html .tiddler {height:1%;}

body {font-size:.75em; font-family:arial,helvetica; margin:0; padding:0;}

h1,h2,h3,h4,h5,h6 {font-weight:bold; text-decoration:none;}
h1,h2,h3 {padding-bottom:1px; margin-top:1.2em;margin-bottom:0.3em;}
h4,h5,h6 {margin-top:1em;}
h1 {font-size:1.35em;}
h2 {font-size:1.25em;}
h3 {font-size:1.1em;}
h4 {font-size:1em;}
h5 {font-size:.9em;}

hr {height:1px;}

a {text-decoration:none;}

dt {font-weight:bold;}

ol {list-style-type:decimal;}
ol ol {list-style-type:lower-alpha;}
ol ol ol {list-style-type:lower-roman;}
ol ol ol ol {list-style-type:decimal;}
ol ol ol ol ol {list-style-type:lower-alpha;}
ol ol ol ol ol ol {list-style-type:lower-roman;}
ol ol ol ol ol ol ol {list-style-type:decimal;}

.txtOptionInput {width:11em;}

#contentWrapper .chkOptionInput {border:0;}

.externalLink {text-decoration:underline;}

.indent {margin-left:3em;}
.outdent {margin-left:3em; text-indent:-3em;}
code.escaped {white-space:nowrap;}

.tiddlyLinkExisting {font-weight:bold;}
.tiddlyLinkNonExisting {font-style:italic;}

/* the 'a' is required for IE, otherwise it renders the whole tiddler in bold */
a.tiddlyLinkNonExisting.shadow {font-weight:bold;}

#mainMenu .tiddlyLinkExisting,
	#mainMenu .tiddlyLinkNonExisting,
	#sidebarTabs .tiddlyLinkNonExisting {font-weight:normal; font-style:normal;}
#sidebarTabs .tiddlyLinkExisting {font-weight:bold; font-style:normal;}

.header {position:relative;}
.header a:hover {background:transparent;}
.headerShadow {position:relative; padding:4.5em 0 1em 1em; left:-1px; top:-1px;}
.headerForeground {position:absolute; padding:4.5em 0 1em 1em; left:0px; top:0px;}

.siteTitle {font-size:3em;}
.siteSubtitle {font-size:1.2em;}

#mainMenu {position:absolute; left:0; width:10em; text-align:right; line-height:1.6em; padding:1.5em 0.5em 0.5em 0.5em; font-size:1.1em;}

#sidebar {position:absolute; right:3px; width:16em; font-size:.9em;}
#sidebarOptions {padding-top:0.3em;}
#sidebarOptions a {margin:0 0.2em; padding:0.2em 0.3em; display:block;}
#sidebarOptions input {margin:0.4em 0.5em;}
#sidebarOptions .sliderPanel {margin-left:1em; padding:0.5em; font-size:.85em;}
#sidebarOptions .sliderPanel a {font-weight:bold; display:inline; padding:0;}
#sidebarOptions .sliderPanel input {margin:0 0 0.3em 0;}
#sidebarTabs .tabContents {width:15em; overflow:hidden;}

.wizard {padding:0.1em 1em 0 2em;}
.wizard h1 {font-size:2em; font-weight:bold; background:none; padding:0; margin:0.4em 0 0.2em;}
.wizard h2 {font-size:1.2em; font-weight:bold; background:none; padding:0; margin:0.4em 0 0.2em;}
.wizardStep {padding:1em 1em 1em 1em;}
.wizard .button {margin:0.5em 0 0; font-size:1.2em;}
.wizardFooter {padding:0.8em 0.4em 0.8em 0;}
.wizardFooter .status {padding:0 0.4em; margin-left:1em;}
.wizard .button {padding:0.1em 0.2em;}

#messageArea {position:fixed; top:2em; right:0; margin:0.5em; padding:0.5em; z-index:2000; _position:absolute;}
.messageToolbar {display:block; text-align:right; padding:0.2em;}
#messageArea a {text-decoration:underline;}

.tiddlerPopupButton {padding:0.2em;}
.popupTiddler {position: absolute; z-index:300; padding:1em; margin:0;}

.popup {position:absolute; z-index:300; font-size:.9em; padding:0; list-style:none; margin:0;}
.popup .popupMessage {padding:0.4em;}
.popup hr {display:block; height:1px; width:auto; padding:0; margin:0.2em 0;}
.popup li.disabled {padding:0.4em;}
.popup li a {display:block; padding:0.4em; font-weight:normal; cursor:pointer;}
.listBreak {font-size:1px; line-height:1px;}
.listBreak div {margin:2px 0;}

.tabset {padding:1em 0 0 0.5em;}
.tab {margin:0 0 0 0.25em; padding:2px;}
.tabContents {padding:0.5em;}
.tabContents ul, .tabContents ol {margin:0; padding:0;}
.txtMainTab .tabContents li {list-style:none;}
.tabContents li.listLink { margin-left:.75em;}

#contentWrapper {display:block;}
#splashScreen {display:none;}

#displayArea {margin:1em 17em 0 14em;}

.toolbar {text-align:right; font-size:.9em;}

.tiddler {padding:1em 1em 0;}

.missing .viewer,.missing .title {font-style:italic;}

.title {font-size:1.6em; font-weight:bold;}

.missing .subtitle {display:none;}
.subtitle {font-size:1.1em;}

.tiddler .button {padding:0.2em 0.4em;}

.tagging {margin:0.5em 0.5em 0.5em 0; float:left; display:none;}
.isTag .tagging {display:block;}
.tagged {margin:0.5em; float:right;}
.tagging, .tagged {font-size:0.9em; padding:0.25em;}
.tagging ul, .tagged ul {list-style:none; margin:0.25em; padding:0;}
.tagClear {clear:both;}

.footer {font-size:.9em;}
.footer li {display:inline;}

.annotation {padding:0.5em; margin:0.5em;}

* html .viewer pre {width:99%; padding:0 0 1em 0;}
.viewer {line-height:1.4em; padding-top:0.5em;}
.viewer .button {margin:0 0.25em; padding:0 0.25em;}
.viewer blockquote {line-height:1.5em; padding-left:0.8em;margin-left:2.5em;}
.viewer ul, .viewer ol {margin-left:0.5em; padding-left:1.5em;}

.viewer table, table.twtable {border-collapse:collapse; margin:0.8em 1.0em;}
.viewer th, .viewer td, .viewer tr,.viewer caption,.twtable th, .twtable td, .twtable tr,.twtable caption {padding:3px;}
table.listView {font-size:0.85em; margin:0.8em 1.0em;}
table.listView th, table.listView td, table.listView tr {padding:0px 3px 0px 3px;}

.viewer pre {padding:0.5em; margin-left:0.5em; font-size:1.2em; line-height:1.4em; overflow:auto;}
.viewer code {font-size:1.2em; line-height:1.4em;}

.editor {font-size:1.1em;}
.editor input, .editor textarea {display:block; width:100%; font:inherit;}
.editorFooter {padding:0.25em 0; font-size:.9em;}
.editorFooter .button {padding-top:0px; padding-bottom:0px;}

.fieldsetFix {border:0; padding:0; margin:1px 0px;}

.sparkline {line-height:1em;}
.sparktick {outline:0;}

.zoomer {font-size:1.1em; position:absolute; overflow:hidden;}
.zoomer div {padding:1em;}

* html #backstage {width:99%;}
* html #backstageArea {width:99%;}
#backstageArea {display:none; position:relative; overflow: hidden; z-index:150; padding:0.3em 0.5em;}
#backstageToolbar {position:relative;}
#backstageArea a {font-weight:bold; margin-left:0.5em; padding:0.3em 0.5em;}
#backstageButton {display:none; position:absolute; z-index:175; top:0; right:0;}
#backstageButton a {padding:0.1em 0.4em; margin:0.1em;}
#backstage {position:relative; width:100%; z-index:50;}
#backstagePanel {display:none; z-index:100; position:absolute; width:90%; margin-left:3em; padding:1em;}
.backstagePanelFooter {padding-top:0.2em; float:right;}
.backstagePanelFooter a {padding:0.2em 0.4em;}
#backstageCloak {display:none; z-index:20; position:absolute; width:100%; height:100px;}

.whenBackstage {display:none;}
.backstageVisible .whenBackstage {display:block;}
/*}}}*/
/***
StyleSheet for use when a translation requires any css style changes.
This StyleSheet can be used directly by languages such as Chinese, Japanese and Korean which need larger font sizes.
***/
/*{{{*/
body {font-size:0.8em;}
#sidebarOptions {font-size:1.05em;}
#sidebarOptions a {font-style:normal;}
#sidebarOptions .sliderPanel {font-size:0.95em;}
.subtitle {font-size:0.8em;}
.viewer table.listView {font-size:0.95em;}
/*}}}*/
/*{{{*/
@media print {
#mainMenu, #sidebar, #messageArea, .toolbar, #backstageButton, #backstageArea {display: none !important;}
#displayArea {margin: 1em 1em 0em;}
noscript {display:none;} /* Fixes a feature in Firefox 1.5.0.2 where print preview displays the noscript content */
}
/*}}}*/
<!--{{{-->
<div class='header' macro='gradient vert [[ColorPalette::PrimaryLight]] [[ColorPalette::PrimaryMid]]'>
<div class='headerShadow'>
<span class='siteTitle' refresh='content' tiddler='SiteTitle'></span>&nbsp;
<span class='siteSubtitle' refresh='content' tiddler='SiteSubtitle'></span>
</div>
<div class='headerForeground'>
<span class='siteTitle' refresh='content' tiddler='SiteTitle'></span>&nbsp;
<span class='siteSubtitle' refresh='content' tiddler='SiteSubtitle'></span>
</div>
</div>
<div id='mainMenu' refresh='content' tiddler='MainMenu'></div>
<div id='sidebar'>
<div id='sidebarOptions' refresh='content' tiddler='SideBarOptions'></div>
<div id='sidebarTabs' refresh='content' force='true' tiddler='SideBarTabs'></div>
</div>
<div id='displayArea'>
<div id='messageArea'></div>
<div id='tiddlerDisplay'></div>
</div>
<!--}}}-->
<!--{{{-->
<div class='toolbar' macro='toolbar [[ToolbarCommands::ViewToolbar]]'></div>
<div class='title' macro='view title'></div>
<div class='subtitle'><span macro='view modifier link'></span>, <span macro='view modified date'></span> (<span macro='message views.wikified.createdPrompt'></span> <span macro='view created date'></span>)</div>
<div class='tagging' macro='tagging'></div>
<div class='tagged' macro='tags'></div>
<div class='viewer' macro='view text wikified'></div>
<div class='tagClear'></div>
<!--}}}-->
<!--{{{-->
<div class='toolbar' macro='toolbar [[ToolbarCommands::EditToolbar]]'></div>
<div class='title' macro='view title'></div>
<div class='editor' macro='edit title'></div>
<div macro='annotations'></div>
<div class='editor' macro='edit text'></div>
<div class='editor' macro='edit tags'></div><div class='editorFooter'><span macro='message views.editor.tagPrompt'></span><span macro='tagChooser excludeLists'></span></div>
<!--}}}-->
To get started with this blank [[TiddlyWiki]], you'll need to modify the following tiddlers:
* [[SiteTitle]] & [[SiteSubtitle]]: The title and subtitle of the site, as shown above (after saving, they will also appear in the browser title bar)
* [[MainMenu]]: The menu (usually on the left)
* [[DefaultTiddlers]]: Contains the names of the tiddlers that you want to appear when the TiddlyWiki is opened
You'll also need to enter your username for signing your edits: <<option txtUserName>>
These [[InterfaceOptions]] for customising [[TiddlyWiki]] are saved in your browser

Your username for signing your edits. Write it as a [[WikiWord]] (eg [[JoeBloggs]])

<<option txtUserName>>
<<option chkSaveBackups>> [[SaveBackups]]
<<option chkAutoSave>> [[AutoSave]]
<<option chkRegExpSearch>> [[RegExpSearch]]
<<option chkCaseSensitiveSearch>> [[CaseSensitiveSearch]]
<<option chkAnimate>> [[EnableAnimations]]

----
Also see [[AdvancedOptions]]
<<importTiddlers>>
{{classDiagram{[img[images/class.png]]}}}
Background: #fff
Foreground: #000
PrimaryPale: #eee
PrimaryLight: #ccc
PrimaryMid: #600
PrimaryDark: #600
SecondaryPale: #eee
SecondaryLight: #ccc
SecondaryMid: #999
SecondaryDark: #666
TertiaryPale: #eee
TertiaryLight: #ccc
TertiaryMid: #999
TertiaryDark: #666
Error: #f88
As with other transports, dynamic configuration is provided by the ACE Service Configurator Framework. A svc.conf file should be created which contains the following:
{{{
dynamic OpenDDS_DCPS_Multicast_Service Service_Object * OpenDDS_Multicast:_make_MulticastLoader()
}}}
The transport may then be loaded at runtime by passing the following arguments:
{{{
-ORBSvcConf svc.conf
}}}
Alternately, the transport may be statically loaded by including the {{{dds/DCPS/transport/multicast/Multicast.h}}} header (implies static linking):
{{{
#ifdef ACE_AS_STATIC_LIBS
# include <dds/DCPS/transport/multicast/Multicast.h>
#endif
}}}
A number of additional transport configuration options are available:
{{{
# Enables IPv6 default group address selection.
# The default value is: 0 (disabled).
default_to_ipv6=0

# The offset used to determine default port numbers; this value
# will be added to the transport ID for the actual port number.
# The default value is: 49400.
port_offset=49400

# The multicast group to join to send/receive data.
# The default value is:
#   224.0.0.128:<port> (IPv4), or
#    [FF01::80]:<port> (IPv6)
group_address=224.0.0.128:49401

# Enables reliable communication. This option will eventually
# be deprecated.
# The default value is: 1 (enabled).
reliable=1

# The exponential base used during handshake retries; smaller
# values yield shorter delays between attempts (reliable only).
# The default value is: 2.0.
syn_backoff=2.0

# The minimum number of milliseconds to wait between handshake
# attempts during association (reliable only).
# The default value is: 250.
syn_interval=250

# The maximum number of milliseconds to wait before giving up
# on a handshake response during association (reliable only).
# The default value is: 30000 (30 seconds).
syn_timeout=30000

# The number of datagrams to retain in order to service repair
# requests (reliable only).
# The default value is: 32.
nak_depth=32

# The minimum number of milliseconds to wait between repair
# requests (reliable only).
# The default value is: 500.
nak_interval=500

# The maximum number of milliseconds to wait before giving up
# on a repair response (reliable only).
# The default value is: 30000 (30 seconds).
nak_timeout=30000

# Set the time-to-live value.
# The default value isL 1 (local subnet)
ttl=1
}}}
Default examples of these files are provided under: {{{$DDS_ROOT/dds/DCPS/transport/multicast/}}}.
[[Overview]]
[[Class Diagram]]
[[Reliability]]
[[Configuration]]
[[Known Issues]]
[[Future Tasks]]
NAK requests currently contain individual ranges; performance testing should be done to determine if collapsing ranges into a single sample would yield better performance for the entire multicast group in a lossy network.

An FEC mechanism should be introduced to reduce repair requests and to provide an additional source from which to detect reception gaps.

{{{MULTICAST_SYNACK}}} responses should be predicated on association status to prevent potential denial of service attacks (not currently supported by the ETF).
The current implementation supports //at most// one DDS domain per multicast group.

A given participant may only have a single multicast {{{TransportImpl}}} attached per multicast group; if you wish to send and receive samples on the same multicast group in the same process, independent {{{DomainParticipant}}}s must be used.

{{{TRANSPORT_PRIORITY}}} is not directly supported. This is partially due to routing restrictions placed on default group addresses as the selection heuristic assigns from the link-local range. Setting the TOS would provide little to no benefit for non-default group addresses at the cost of additional resources and complexity managing n-ary associations by priority key.

Reliability must be configured via the {{{reliable}}} transport configuration option. The ETF currently multiplexes best-effort and reliable samples across the same {{{DataLink}}} which effectively disables autonegotiation of reliability between peers at the transport level.

The current implementation provides no rate limiting or flow control; it is possible to overrun the receive buffer which can lead to unrecoverable data loss even if reliability is enabled. Users should either implement their own rate limiting for excessive rates, increase the {{{nak_depth}}} configuration option, and/or increase the OS receive buffer size if needed. {{{nak_depth}}} should not exceed {{{16383}}} (2^^14^^-1) due to limits imposed by {{{OpenDDS::DCPS::SequenceNumber}}} comparisons (see: {{{$DDS_ROOT/dds/DCPS/Definitions.h}}}).

The current implementation relies on {{{LIVELINESS}}} to periodically send application-level heartbeat messages to aid in detecting reception gaps. If {{{AUTOMATIC_LIVELINESS_QOS}}} (the default) is not used, peers may not detect these gaps in a timely manner leading to unrecoverable data loss.

The current implementation relies on the transport reactor being derived from {{{ACE_Select_Reactor}}}; this ensures a single thread may be active when sending/receiving data. If the transport reactor implementation is changed, additional locks must be introduced to protect critical sections.
[[Overview]]
[[Class Diagram]]
[[Reliability]]
[[Configuration]]
[[Known Issues]]
[[Future Tasks]]
OpenDDS is an open source C++ implementation of the Object Management Group (OMG) Data Distribution Service (DDS). OpenDDS also supports Java bindings through JNI and can be included with JBoss (ESB) frameworks by means of a JMS wrapper. OpenDDS leverages the ADAPTIVE Communication Environment (ACE) to provide a cross platform environment.

OpenDDS is supported by [[Object Computing, Inc.|http://www.ociweb.com/]]
Starting with the OpenDDS 2.1 release, a new IP multicast transport is available which replaces the {{{SimpleMcast}}} and {{{ReliableMulticast}}} transports. The source for the {{{multicast}}} transport is available under the general OpenDDS license and may be found under: {{{$DDS_ROOT/dds/DCPS/transport/multicast/}}}.

What follows is a detailed description of the design, configuration, known issues, and potential enhancements for the {{{multicast}}} transport:

Unlike other transports, a single {{{DataLink}}} is maintained for each {{{TransportImpl}}} instance. Multicast reservations are also formed between participants rather than individual publications and subscriptions via a transport-specific session layer. This allows any number of associations  belonging to the same pair of participants to re-use an existing {{{MulticastSession}}}, thereby reducing the amount of resources needed in multicast intensive environments. Another departure is unified support for best-effort and reliable delivery based on transport configuration. Delivery-specific behavior is abstracted by each concrete {{{MulticastSession}}} implementation, which allows for the same set of transport strategies to be used regardless of delivery mode.

Two delivery modes are supported: best-effort and reliable.
* Best-effort delivery imposes the least amount of overhead as data is exchanged between peers, however it does not provide any guarantee of delivery. Data may be lost due to unresponsive or unreachable peers or received in duplicate (see: {{{OpenDDS::DCPS::BestEffortSession}}}).
* Reliable delivery provides for guaranteed delivery of data to associated peers with no duplication at the cost of additional processing and bandwidth (see: {{{OpenDDS::DCPS::ReliableSession}}}).
When a new reservation is made, a remote and local peer identifier is assigned based on the participant ID of the associated entities. These values are used to uniquely identify each side of a given {{{MulticastSession}}} within the multicast group. The Extensible Transport Framework (ETF) will always designate the publishing side of the association as being active. Multicast datagrams will always assign the local peer ID to the source field of the transport header (see: {{{OpenDDS::DCPS::TransportHeader}}}).

The {{{multicast}}} transport may be configured and attached similarly to other transport implementations:
{{{
OpenDDS::DCPS::TransportImpl_rch transport_impl =
  TheTransportFactory->create_transport_impl(OpenDDS::DCPS::DEFAULT_MULTICAST_ID,
                                             OpenDDS::DCPS::AUTO_CONFIG);

OpenDDS::DCPS::AttachStatus status = transport_impl->attach(...);
if (status != OpenDDS::DCPS::ATTACH_OK) {
  exit(EXIT_FAILURE);
}
}}}
MPC base projects are also provided for linking against the {{{OpenDDS_Multicast}}} library:
{{{
project : dcps_multicast {
}
}}}
and:
{{{
project : dcpsexe_with_multicast {
}
}}}
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Reliable delivery is achieved through two primary mechanisms:
* 2-way peer handshaking (SYN/SYN+ACK)
* Negative acknowledgment of missing data (NAK/NAK+ACK)
For the purpose of examining the interactions between reliable peers, it helps to narrow the view of the multicast group to two specific peers: active and passive. The active peer is the publishing side of the {{{MulticastSession}}}. The passive peer will be the remote peer associated with the session when it was created. It is important to remember that control data will be exchanged among all peers within the multicast group, however disinterested peers will discard payloads which are not addressed to them directly.

DCPS control samples were chosen in lieu of more traditional ~PDUs for the exchange of control data between peers; this allowed the transport to leverage existing functionality at the cost of a slightly increased payload size.
!!SYN/SYN+ACK
[<img[images/handshake.png]]
The active peer initiates a handshake by sending a {{{MULTICAST_SYN}}} control sample to the passive peer at periodic intervals bounded by a timeout to ensure delivery. An exponential backoff is observed based on the number of retries.

Upon receiving the {{{MULTICAST_SYN}}} control sample, the passive peer records the current transport sequence value for the active peer and responds with a {{{MULTICAST_SYNACK}}} control sample. This sequence number establishes a value from which reception gaps may be identified in the future.

If the active peer receives a {{{MULTICAST_SYNACK}}} control sample, it will then notify the ETF that the association is complete, which will in turn trigger a communication status change in the DCPS layer. In the event a {{{MULTICAST_SYNACK}}} control sample is not received, an error will be logged.
!!NAK/NAK+ACK
[>img[images/repair.png]]
As each datagram is delivered to the {{{ReliableSession}}}, the transport sequence value is scored against a special container which identifies reception gaps (see: {{{OpenDDS::DCPS::DisjointSequence}}}). Periodically, a watchdog executes and will age off any outstanding repair requests which have not been fulfilled by resetting the sequence low-water mark and logging an error. Once outstanding requests have been purged, the watchdog will then check for reception gaps.  In the event a new (or existing) reception gap is identified, the {{{ReliableSession}}} records the current interval and the high-water mark for the transport sequence. It will then issue {{{MULTICAST_NAK}}} control samples to active peers from which it is missing data. Passive peers perform NAK suppression based on all repair requests destined for the same active peer. If previous requests have been sent, a passive peer will temporarily elide previously requested ranges for the current interval. This interval is randomized to prevent potential collisions among similarly associated peers.

If the active peer receives a {{{MULTICAST_NAK}}} control sample it will examine its send buffer for the missing datagram. If the datagram is no longer available, it sends a {{{MULTICAST_NAKACK}}} control sample to the entire multicast group to suppress further repair requests. If the datagram is still available, it resends the missing data to the entire multicast group.

If the passive peer receives a {{{MULTICAST_NAKACK}}} control sample, it will behave just as if the repair request has aged off, suppressing further repair requests and logging an error.
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