Medium Access Control

Service

MAC – Medium access control service

Agents offering the MAC service provide some implementation of a medium access control protocol. They support a set of messages and parameters that are explained below. MAC service providers may also provide optional capabilities in the form of reliability through acknowledgement messages.

Capability Description
RELIABILITY Reliability supported (usually via acknowledgement messages)
PRIORITY Honors priority settings in reservation request
TTL Honors time-to-live settings in reservation request
TIMED_RESERVATION Scheduling of reservations in the future supported

Implementations

  • AlohaACS – Aloha with adaptive carrier sensing
  • MACA – MACA with early-ACK and multi-ACK extensions

Requests and Responses

Request Possible Responses Description
ReservationReq ReservationRsp, REFUSE Reserve the channel for a specified duration
ReservationCancelReq AGREE, REFUSE Cancel a pending reservation request
ReservationAcceptReq AGREE, REFUSE Piggyback payload in a reservation PDU
TxAckReq AGREE, REFUSE Transmit acknowledgement payload
ParameterReq ParameterRsp Get/set/list parameters
CapabilityReq CONFIRM, DISCONFIRM, CapabilityListRsp Check/list capabilities

MAC protocols that use PDUs for channel reservation may support piggybacking of client data in the PDU. If such support is available, it is advertised using a non-zero reservationPayloadSize parameter. A ReservationReq should provide the payload data to be sent to a peer node (as part of RTS or equivalent PDU) to whom the reservation is made. If that node wishes to send payload data back (as part of CTS or equivalent PDU), it may send a ReservationAcceptReq in response to a ReservationStatusNtf to provide its payload data.

For MAC implementations that support RELIABILITY, the agent must support the TxAckReq request to provide acknowledgement payload to be transmitted to the peer node at the end of the reservation. On reception, this would generate a RxAckNtf on the peer node.

Notifications

Notification Topic Description
ReservationStatusNtf default Current status of reservation request
RxAckNtf default Acknowledgement payload notification
ParamChangeNtf PARAMCHANGE Notification about the modified parameter

Parameters

Parameter r/w Description
channelBusy ro True if channel is busy, false otherwise
reservationPayloadSize ro Maximum size of payload (bytes), which can be piggybacked in a reservation PDU
ackPayloadSize ro Maximum size of acknowledgement (bytes), which can be included in an ACK PDU
maxReservationDuration ro Maximum duration of reservation in seconds
recommendedReservationDuration ro Recommended duration of reservation in seconds (null, if unspecified)