Anypoint ALRMs are plug-in software modules that manage Anypoint traffic through the switch. Each ALRM implements frame redirection and transformation logic for a given service. ALRMs are installed through a privileged management interface.
An ALRM is an event-driven, asynchronous, deterministic, non-blocking module supporting the interface in Table 1. ALRMs affect only traffic for specific designated ports. At most one ALRM is bound to each connection. ALRMs may access only the frame data and private structures of bounded size. We intend that the processing required per frame is statically bounded, and that the ALRM's memory references are statically verifiable.
Inside the switch, common low-level functions examine transport headers to classify packets into flows (connections), pass each frame to the redirect() function of the ALRM bound to its flow, and merge the transformed frames into the destination transport stream for the selected target node. These functions manipulate transport headers to extract frames from incoming transport segments and pack them into outgoing segments. The ALRM itself may perform deep processing beyond the transport headers.
ALRMs must be deterministic so they do not apply inconsistent transforms or violate exactly-once delivery for retransmitted frames. The RTX handle passed to redirect() indexes a unique state field for each distinct frame, enabling the ALRM to cache arbitrary state for each transformed frame. When the receiver is known to have processed an ack for the frame, the switch calls retire(*rtx) so the ALRM may recycle this state.