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<h2><a href="https://wiki.asterisk.org/wiki/display/TOP/Basic+Routing+Service+Design">Basic Routing Service Design</a></h2>
<h4>Page <b>edited</b> by <a href="https://wiki.asterisk.org/wiki/display/~khunt">Ken Hunt</a>
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<h3><a name="BasicRoutingServiceDesign-Overview"></a>Overview</h3>
<p>The Routing Service provides a central facility for looking up Endpoint interfaces. The Channel Services dynamically register and deregister their own EndpointLocator interface with the Routing Service, along with one or more regular expressions which describe which destinations are managed by a given EndpointLocator interface. The Routing Service acts as an aggregator for all of the Channel-specific EndpointLocators, so any component in the system which needs to lookup an endpoint need only refer to the Routing Service. </p>
<p>The Routing Service also provides the capability to route Session objects, by looking up a requested destination endpoint, creating a new session for the destination, and causing a Bridge to be created to connect the two sessions. </p>
<p>This page describes the design of a Basic Routing Service which incorporates a script engine. Various users / deployments are expected to require very specific Routing needs, so custom implementations of Routing Service implementations could become common. The Script Engine acts as a simple example of a means to support custom extensions withing a component, and is an alternative to the Extension Point mechanisms described on <a href="/wiki/display/TOP/Extension+Points+and+Hooks" title="Extension Points and Hooks">Extension Points and Hooks</a>.</p>
<h3><a name="BasicRoutingServiceDesign-ClassStructure"></a>Class Structure</h3>
<p>The basic structure of the Routing Service component is shown in Figure 1 below. Notes on the class structure:</p>
<ol>
<li>The administrative interfaces are separate to allow controlled access to the administrative functionality.</li>
<li>The Administrative interfaces are implemented by a totally distinct object, so that a reference to the LocatorRegistry interface can't be simply cast to a RoutingServiceAdmin interface.</li>
<li>The lookup operation (of EndpointLocator interface) and the setPolicy operation (of the RoutingServiceAdmin interface) will be forwarded to a Lua Script Processor. The administrative operation setPolicy will have a no-op default operation, but could be altered (via scripting) to deny lookups for a variety of reasons, such as time of day, etc.</li>
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<h3><a name="BasicRoutingServiceDesign-Operation"></a>Operation</h3>
<p>EndpointLocator implementations are registered with the Routing Service via their respective Channel Service. The Channel Service locates the Routing Service via the system Service Locator, as shown in Figure 2. The Service Locator's location is set via configuration / deployment for most all Asterisk SCF components. </p>
<p>At some point during the Channel Service startup, the ChannelService acquires a reference to the RoutingService in order to provide the RoutingService with its EndpointLocator interface. When it does, the ChannelService provides a sequence of regular expressions that define the ranges (or other patterns) of destination ids that are managed by the channel. </p>
<p>When devices outside of the Asterisk SCF system register with the ChannelService after the ChannelService has initialized, the ChannelService can (if needed) update the device IDs associated with it's EndpointLocator by calling SetEndpointLocatorDeviceIds with a new set of regular expressions. </p>
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<p>Figure 3 shows the Routing Service routing a Session. A client Channel Service calls routeSession() of the SessionRouter interface published by the Basic Routing Service. The Routing Service calls lookup() on itself, which identifies the applicable ChannelService. It then uses the EndpointLocator registered by the destination's ChannelService to get a reference to the Endpoint. If this succeeds, the Routing Service creates a new Session via the destination endpoint's interface. </p>
<p>The Bridge Service is accessed (via the Service Locator - not shown), and a Bridge object is created to bridge the calling and destination Session objects. </p>
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<h3><a name="BasicRoutingServiceDesign-PublishedEvents"></a>Published Events</h3>
<p>As seen in RoutingServiceIf.ice, the following events are published by the Routing Service component.</p>
<div class="code panel" style="border-style: solid;border-width: 1px;"><div class="codeHeader panelHeader" style="border-bottom-width: 1px;border-bottom-style: solid;"><b>From RoutingServiceIf.ice</b></div><div class="codeContent panelContent">
<pre class="theme: Confluence; brush: java; gutter: false">module Hydra
{
module RoutingService
{
...
module Event
{
enum OperationResult
{
SUCCCESS,
FAILED
};
// Interface for IceStorm topic named "::hydra::routing::event"
interface RoutingEvents
{
void LookupEvent(string deviceId, OperationResult result);
void AddEndpointLocatorEvent(string channelId, StringSeq deviceIdRangeList, OperationResult result);
void RemoveEndpointLocatorEvent(string channelId, OperationResult result);
void SetEndpointLocatorDeviceIds(string channelId, StringSeq deviceIdRangeList, OperationResult result);
void ClearEndpointLocatorsEvent();
void LoadRoutingTableEvent(string tableId, OperationResult result);
void SaveRoutingTable(string tableId, OperationResult result);
};
};
};
};</pre>
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<h3><a name="BasicRoutingServiceDesign-Itemstoberesolved"></a>Items to be resolved</h3>
<ul>
<li>Failover - The failover design needs to be incorporated into this component.</li>
<li>I haven't put much thought into how we protect access to the Administrative interface.</li>
</ul>
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