Thinking Inside the Box

Abstract

The BizTalk Messagebox is the core of the messaging subsystem. It has the responsibility of storing all message items within the product. The Message Bus subsystem queries the Messagebox and looks for messages that match a subscription. The BizTalk Message Bus is a publisher/subscriber model, or pub/sub. Simply stated, every message going into the Messagebox is “published” so that endpoints with matching message subscriptions can receive the message and send it to the appropriate orchestration or send port and finally to the corresponding adapter. Each BizTalk process that runs on a machine has something called the Message Agent, which is responsible for searching for messages that match subscriptions and routing them to the End Point Manager (EPM), which actually handles the message and sends it where it needs to go. The EPM is the broker between the Messagebox and the pipeline/ port/adapter combination or orchestration that has a subscription for the message. Both the EPM and Message Agent are executed within the BTSNTSvc.exe process that runs on the host. Figure 3-1 shows the Message Bus architecture.