Microsoft Azure Service Bus is an enterprise integration broker that's fully managed in Microsoft Azure. While it's considered a solid platform for asynchronous data transfer between apps and services, as well as state transfer, via messages, Azure Service Bus is most often used for decoupling applications and services from one another. An example of how Azure Service Bus would typically use messaging to transfer business data, would be a scenario where a retail store needs to transfer information such as sales orders and inventory adjustments. Using Azure Service Bus to decouple applications allows an organization to improve the reliability of an application or service by allowing transactions to occur even if the client side of the application and the server side of the application are not online at the same time. This also helps drive scalability of the application as well. Azure Service Bus can also be used to deploy workflows that involve message ordering and even message deferral. Key terms to be aware of when working with Azure Service Bus include namespaces, queues, and topics. Namespaces are essentially application containers or scopes that contain sets of messaging components. A single namespace can include multiple queues and multiple topics. Speaking of queues, queues are often used for point-to-point communication are used to send and receive messages. 

They also hold messages until a receiving application can process them. Messages held in a queue are protected via redundant storage and they're delivered in pull mode, which means that such messages are delivered on request. Like queues, topics can also be used to send and receive messages. However, unlike queues, which typically facilitate point-to-point communications, topics are generally used for publish/subscribe scenarios. A given topic supports multiple, independent subscriptions, which can then receive a copy of each message being sent to that topic. You can leverage Azure Service Bus to solve complex messaging problems, using its advanced features. Such advanced features include things like Message Sessions, Auto-Forwarding, Dead-Lettering, Scheduled Delivery, Message Deferral and more. Leveraging message sessions provides a first-in, first-out guarantee in Service Bus because what it does is it offers joint and ordered processing of unbound, yet related, message sequences. Auto-forwarding allows you to chain queues or subscriptions to other queues or even topics that fall within the same namespace. 

Enabling auto-forwarding causes Azure Service Bus to automatically remove messages in the first queue or subscription and put them in the second queue or topic. Dead-lettering hold messages that cannot be delivered or that cannot be processed for some reason and these messages are held in a dead-letter queue. Messages can then be manually removed from the dead-letter queue and inspected later on. Scheduled delivery allows you to submit messages to a queue or topic and then hold them there for delayed processing. An example of this might be a retail outlet that sends sales transactions to a queue or topic throughout the day and then schedules an end of day job to come through and process those transactions. Other features such as message deferral offer the ability to set certain messages aside in a queue or subscription instead of retrieving them right away. Batching allows a queue or topic client to delay sending a message for a specific period of time and then if additional requests come from the same client, it can then transmit those messages in a single batch. For more information on the entire collection of advanced features offered by Azure Service Bus, visit the URL that you see on your screen. As with many other Azure service offerings, Azure Service Bus offers full integration with many other Azure services and features including Event Grid, Logic Apps, Functions, Dynamics 365, and Stream Analytics. In the next lesson, we're going to use Azure Portal and Service Bus to update inventory for some fictional retail outlets.