Initiator timing

This section introduces the different situations that happen with the Initiator when establishing a connection.

When establishing a connection with no other connections active, the Initiator will establish the connection in the minimum time and allocate the first central link connection event transmitWindowDelay after the connect request was sent, as shown in the following figure.

Figure 1. Initiator - first connection

When establishing a new connection with other connections already made as a Central, the Initiator will start synchronously to the connected link timing-events and schedule the new central connection’s first timing-event in any free time between existing central timing-events or after the existing central timing-events. Central link timing-events will be scheduled close to each other (without any free time between them). The minimum time between the start of two central role timing-events is the event length of the central role to which the first timing-event belongs. This minimum time is referred to as t_event. The following figure illustrates the case of establishing a new central connection with one central connection already running.

Figure 2. Initiator - one central connection running

When a central link disconnects, the timings of other central link timing-events remain unchanged. The following figure illustrates the case when central link C1 is disconnected, which results in free time between C0 and C2.

Figure 3. Initiator - free time due to disconnection

When establishing a new connection in cases where free time is available between already running central link timing-events, best-fit algorithm is used to find which free time space should be used. Initiator - one or more connections as a Central illustrates the case when all existing central connections have the same connection interval and the initiator timing-event starts around the same time as the 1st central connection (C0) timing-event in the schedule. There is available time between C1–C2 and between C2–C3. A timing-event for new a connection, Cn, is scheduled in the available time between C2–C3 because that is the best fit for Cn.

Figure 4. Initiator - one or more connections as a Central

Initiator - free time not enough illustrates the case when any free time between existing central link timing-events is not long enough to fit the new connection. The new central link timing-event is placed after all running central link timing-events in this case.

Figure 5. Initiator - free time not enough

The Initiator is scheduled relative to existing central connections or the Quality of Service (QoS) channel survey. This is illustrated in Initiator - scheduling and connection setup. The application requests the Initiator to start at (1). A reference point, t_r, is determined from the existing links. From t_r, the earliest possible scan window is found by subtracting the scan interval (T_SI) until the nearest point in the future is found. In the example, the Initiator blocks the second connection (C1) during its second scan window. In that window, it receives a connectable advertisement (2) and responds with a connection indication (3). The Initiator has now become a Central (C3) and its link is placed between C1 and C2 by the best-fit algorithm.

Figure 6. Initiator - scheduling and connection setup