## 5 D-MSR Management Phases
### Establishing an End-to-End Connection for Periodic Sensor Data Communication (Phase-5)  
Having allocated the initial resources, as well as the management resources, the focus of this phase is to establish an end-to-end connection between a sensor and an actuator or a sensor and the gateway for transporting the application data. _Control in the field_ (_i.e._, closed-loop control through a peer-to-peer communication between a sensor as a publisher and an actuator as a subscriber. This is part of traditional Fieldbus technologies) is important for process control applications (see Class 1 in Table 1). WirelessHART networks support peer-to-peer communication between sensors and actuators only if the traffic is routed via the gateway. This is required from WirelessHART's security mechanism to prevent potential safety threats resulting from undetected and unmonitored communications [4]. ISA100.11a addresses control in the field by providing a secured peer-to-peer communication. D-MSR addresses real-time communication between sensors and actuators (providing control in the field) as well as between sensors and the gateway.  
As we focus on applications that require constant data traffic rates, D-MSR allocates a virtual circuit for each traffic flow. This implies that the resources reserved for each end-to-end connection depend on the traffic characteristics requested by the source node. The source node initiates this phase by sending a _Setup_ message as was shown in Figure 10. The format of this message is similar to the Request Service in WirelessHART and the Contract Request in ISA100.11a.  
In WirelessHART, if the sensor node needs to have a connection with another device, which can be an actuator or gateway, it will send the Request Service to the network manager with specified bandwidth and latency characteristics. The network manager needs time to schedule new communications along an uplink graph from the sensor to the gateway, and from the gateway to the actuator along a downlink graph. It will then reply to the requesting node. The process of asking for more communication resources is discussed in more detail in [25]. However, unlike in ISA100.11a and WirelessHART, which both send the request to a centralized network manager, in D-SAR the source node sends the _Setup_ message toward the destination node along the route defined by the routing layer in a distributed way.  
The traffic ID parameter, which is included in the _Setup_ message, is used to specify the allocated resources for that traffic ID. For example, in case of releasing the specific connection resources, the traffic ID is used to identify the related communication resources that are allocated for that connection. However, to allow for the efficient utilization of each link during the normal network operation, they are shared, upon their allocation, between multiple traffic flows rather than assigned specifically to one particular traffic flow. This means that the communication resources, which are reserved for initial communications, management communications, or different end-to-end connections between sensors and actuators, are shared between different traffic flows. For example, let us consider nodes A and B in Figure 13. Five links are established between the two nodes in different phases (e.g., link (II) that belongs to the superframe with 2 s length is established in Phase-4 for exchanging management messages, and link (III) that belongs to the superframe with 250 ms length is established in Phase-5 for forwarding traffic ID i). Using the ATM networking concepts, management traffic, traffic ID i, traffic ID j, and traffic ID k are allowed to use all the defined links between node A and B during the normal operation of the network.