## 3 D-MSR Protocol Stack Architecture
### Lower Data Link Sub-Layer  
In the centralized approach the network manager constructs the communication schedule in line with the network devices requirements based on the global knowledge it has obtained from the network. For instance, the network manager in WirelessHART maintains a global schedule-matrix to keep track of the timeslot-channel cell usage by the network devices. Allocation of an interference-free cell to one pair of neighbor devices is feasible since the network manager manages the usage of that cell by any other pairs (the term \"interference\" refers to the \"internal interference\" caused by the concurrent transmissions in the same channel in the network). In addition, the network manager avoids spatial reuse of that cell in the network. However, in the distributed approach we need a distributed management scheme to avoid allocating the same cell to another interfering pair of devices, either in the network or neighborhood. The interference models can generally be classified into: (1) _physical_ and (2) _protocol_ interference model [16, 17]. In the _physical_ model, the feasibility of an interference-free communication is determined by the signal-to-interference ratio (SIR) of a receiver. In the _protocol_ model, the feasibility of an interference-free communication is determined based on graph neighborhood relationship. In this paper, conform the _protocol_ model, a node uses information about the allocated cells in its two-hop neighborhood to reserve interference-free cells, after which it will monitor the status of its scheduled cells to guarantee interference-free communications. To this end, a two-hop neighborhood schedule-matrix (the terms \"schedule-matrix\" and \"two-hop neighborhood schedule-matrix\" are used interchangeably) is defined in the lower data link sub-layer, in which each node maintains the current usage of its two-hop neighborhood cells. Each entry in the schedule-matrix represents the cell usage at that timeslot on that channel and is specified by the node addresses of the scheduled link. In order to establish initial links and to enable further communication between neighbors in different network operation phases, the neighboring nodes need to find the same unused cell in their schedule-matrices. The procedure for constructing and updating the schedule-matrix are discussed later on in Section 4.1. In D-MSR, we use an idle listening to update the schedule-matrix in each node. The nodes listen to their one-hop neighbors advertisements to update their schedule-matrices. To this end, the advertisement (in TSCH nodes broadcast advertisements to enable network formation and to exchange timing information) also includes additional information about the subset of the advertiser link table (_i.e._, node address, timeslot, channel offset, and superframe ID) that are used by the receiver to construct and update its schedule-matrix. Furthermore, in TSCH it is assumed that the network manager schedules the advertisement links between the advertiser and its neighbors. In order to assure that in D-MSR the node can hear their neighbors advertisements, we modified the TSCH matrix in the lower data link sub-layer by defining two periods in the superframe; the _advertisement period_ and the _data communication period_. In the _advertisement period_, nodes either send their advertisements or listen to their neighbor advertisement. No further communication links are scheduled allowing for more data sharing between the nodes in the advertisement period. The additional information that is included in the advertisement is listed in Table 2. In the _data communication period_, communication schedules are reserved to enable the communication between neighboring nodes. Figure 6 shows this setup. The figure illustrates a superframe with a length of 250 ms consisting of 25 slots. In the _advertisement period_, the nodes can choose a free advertisement cell in channels 15, 20, and 25 (these three channels do not overlap with any of the three common IEEE 802.11 channels.