PHYSICAL – Physical service

Agents offering the Physical service are most commonly modem drivers or simulators. They support a set of messages and parameters that are explained below. Physical service providers may also provide optional capabilities to send frames triggered at a specified time, or send timestamped frames where the timestamp is embedded in the transmitted frame.


Agents implementing the PHYSICAL service typically directly access the channel, bypassing any medium access protocol that may be in use in the network. It is highly recommended that clients wishing to use the PHYSICAL service consult with the Medium Access Control (MAC) service for advise on when it is safe to access the channel, so as not to adversely affect the network performance.

Capability Description
TIMESTAMPED_TX Transmissions with timestamp encapsulated in frame
TIMED_TX Transmissions of frames at specified time

All agents supporting this service also support the Datagram service.


Requests and Responses

Request Possible Responses Description
DatagramReq AGREE, REFUSE, FAILURE Transmit a physical layer frame
TxFrameReq AGREE, REFUSE, FAILURE Transmit a physical layer frame
TxRawFrameReq AGREE, REFUSE, FAILURE Transmit a physical layer frame without headers
ClearReq AGREE, FAILURE Abort all transmissions/receptions
ParameterReq ParameterRsp Get/set/list parameters
CapabilityReq CONFIRM, DISCONFIRM, CapabilityListRsp Check/list capabilities


Notification Topic Description
RxFrameNtf default Frame addressed to node arrived
RxFrameNtf SNOOP Frame addressed to another node overheard
RxFrameStartNtf default Frame reception has started
BadFrameNtf default Received frame could not be successfully decoded
CollisionNtf default Frame detected during reception of another frame
ParamChangeNtf PARAMCHANGE Notification about the modified parameter


TxFrameReq extends the more generic DatagramReq and offers additional physical layer options. Similarly, RxFrameNtf extends DatagramNtf and provides additional information for physical layer frames.


Parameter r/w Description
rxEnable rw True if reception is enabled, false otherwise
propagationSpeed rw Signal propagation speed in m/s
timestampedTxDelay rw Delay in seconds to transmit timestamped frames
time ro Current physical layer clock time in µs
busy ro True if modem is busy transmitting/receiving, false if modem is idle
refPowerLevel ro Reference power level in dB
maxPowerLevel ro Maximum allowable transmission power in dB
minPowerLevel ro Minimum allowable transmission power in dB


All physical layer timestamps are in µs as per the clock provided by the time parameter. This clock is generally not synchronized with the agent’s own clock.

Indexed Parameters

Index range: { CONTROL, DATA }

Parameter r/w Description
MTU ro Maximum frame size in bytes
frameDuration ro Frame duration in seconds
powerLevel rw Transmission power level in dB
errorDetection rw Number of bytes used for error detection (CRC/Checksum)
frameLength rw Frame length in bytes (if modem supports variable frame size)
maxFrameLength ro Maximum allowable frame length in bytes
fec rw Foward error correction (FEC) code (0 = none/default, otherwise 1-base index in fecList)
fecList ro List of available FEC codes in increasing order of robustness (can be null if no FEC change supported)
dataRate ro Effective data rate in bits/second