| /* |
| * Copyright 2014 Open Networking Laboratory |
| * |
| * 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. |
| */ |
| |
| /** |
| * Set of abstractions for conveying high-level intents for treatment of |
| * selected network traffic by allowing applications to express the |
| * <em>what</em> rather than the <em>how</em>. This makes such instructions |
| * largely independent of topology and device specifics, thus allowing them to |
| * survive topology mutations. |
| * <p/> |
| * The controller core provides a suite of built-in intents and their compilers |
| * and installers. However, the intent framework is extensible in that it allows |
| * additional intents and their compilers or installers to be added |
| * dynamically at run-time. This allows others to enhance the initial arsenal of |
| * connectivity and policy-based intents available in base controller software. |
| * <p/> |
| * The following diagram depicts the state transition diagram for each top-level intent:<br> |
| * <img src="doc-files/intent-states.png" alt="ONOS intent states"> |
| * <p/> |
| * The controller core accepts the intent specifications and translates them, via a |
| * process referred to as intent compilation, to installable intents, which are |
| * essentially actionable operations on the network environment. |
| * These actions are carried out by intent installation process, which results |
| * in some changes to the environment, e.g. tunnel links being provisioned, |
| * flow rules being installed on the data-plane, optical lambdas being reserved. |
| * <p/> |
| * After an intent is submitted by an application, it will be sent immediately |
| * (but asynchronously) into a compiling phase, then to installing phase and if |
| * all goes according to plan into installed state. Once an application decides |
| * it no longer wishes the intent to hold, it can withdraw it. This describes |
| * the nominal flow. However, it may happen that some issue is encountered. |
| * For example, an application may ask for an objective that is not currently |
| * achievable, e.g. connectivity across to unconnected network segments. |
| * If this is the case, the compiling phase may fail to produce a set of |
| * installable intents and instead result in a failed compile. If this occurs, |
| * only a change in the environment can trigger a transition back to the |
| * compiling state. |
| * <p/> |
| * Similarly, an issue may be encountered during the installation phase in |
| * which case the framework will attempt to recompile the intent to see if an |
| * alternate approach is available. If so, the intent will be sent back to |
| * installing phase. Otherwise, it will be parked in the failed state. Another |
| * scenario that’s very likely to be encountered is where the intent is |
| * successfully compiled and installed, but due to some topology event, such |
| * as a downed or downgraded link, loss of throughput may occur or connectivity |
| * may be lost altogether, thus impacting the viability of a previously |
| * satisfied intent. If this occurs, the framework will attempt to recompile |
| * the intent, and if an alternate approach is available, its installation |
| * will be attempted. Otherwise, the original top-level intent will be parked |
| * in the failed state. |
| * <p/> |
| * Please note that all *ing states, depicted in orange, are transitional and |
| * are expected to last only a brief amount of time. The rest of the states |
| * are parking states where the intent may spent some time; except for the |
| * submitted state of course. There, the intent may pause, but only briefly, |
| * while the system determines where to perform the compilation or while it |
| * performs global recomputation/optimization across all prior intents. |
| */ |
| package org.onlab.onos.net.intent; |