The Segmentator module is responsible for sending segmented requests or responses. Incoming segments need to be handled manually or through the BACnet.Stack.SegmentsStore module.

The Segmentator segments the given APDU (ComplexACK or ConfirmedServiceRequest) into segments of maximum APDU size and checks if the remote device supports the amount of segments. Both parameters need to be discovered by the user and given to this module, when creating a segmented sequence.

The Segmentator will automatically send segments in the window size given by the remote device and wait for their acknowledgement. Timeouts and retransmissions are handled automatically. Responses and retransmissions to the destination of a segmented request or response are automatically sent.

When the remote device is outside of the local network (packets are routed through a router), this module will automatically overwrite the "Proposed Window Size" with 1, to ensure segments ordering. Due to the nature of the UDP protocol (which BACnet/IP is based on), UDP re-ordering can occur and thus segments may arrive out-of-order. Re-ordering through the network may not occurr on other transport mediums. Whether a destination is outside of the local network is determined through the BACnet.Stack.TransportBehaviour module.

The Segmentator module is transport layer agnostic due to the nature of using the TransportBehaviour.

Users of this module need to route incoming Abort, Error, Reject and SegmentACK APDUs to this module, so the Segmentator can function properly. See the handle_apdu/3 documentation.

This module is written to not require one instance per destination or transport layer protocol, as such when creating a new sequence, the transport module, transport, portal, and destination parameters need to be given.

When wanting to send a new segmented request or response, first a new sequence must be created. As soon as the sequence is created, transmitting the segments, retransmissions and timeouts are handled automatically.