Medium Access Control (MAC) and Physical Layer (PHY) - CISE

4-June-07 P1901_PRO_016_r0
4.3.10 Non-returnable Data Frame
The non-returnable data frame is a frame transmitted from a master to many (up to eight) of its slaves (usually
TDRs). The non-returnable data token transmitted at the end of the frame indicates which are the destination
nodes and for how long they will be allowed to transmit. This length of time is known as the token validity, and
is expressed as a number of symbols. The non-returnable data frame can only be sent by a master if Cluster
Discovery Protocol (See 0) messages have been received from the TDRs that are slaves to it.
Upon transmitting a non-returnable data token, the master will ignore any signals received until the validity
time is finished. At this point, the master will transmit a new frame. No frame will be expected by the
transmitter of the non-returnable data frame.
Upon reception of the non-returnable data frame, the slaves (usually TDRs) will start transmitting new frames.
However, they must not transmit any data in the upstream (data for the master that sent the non-returnable data
frame), or any channel estimation frames.
The non-returnable data frame allows the simultaneous transmission of data and tokens of several isolated
clusters, thus allowing for spatial reuse.
4.3.11 Clock Frame
The Clock frame is used to synchronize all nodes of a BPL cell.
Every node shall have an internal timer derived from a 312.5 kHz clock. The periodic timer shall count down from a
maximum value to zero. The maximum timer value (Tmax) shall be adapted to span 9 mains periods to allow enough
numerical accuracy. This value is transmitted in the Clock token together with the remaining cycles (TimerValue)
which shall be the value of the timer in the moment the Clock token is transmitted.
The information transmitted in the Clock frame shall be the remaining cycles for reaching the end of the timer
period. This information is used in the receiver node to calculate the delay between its timer and the transmitter
timer. The delay with the master shall be used to compensate the own timer. The Clock frame shall be transmitted
only from masters to its direct slaves. Therefore, when a node receives a Clock frame, it shall check that it comes
from its direct master before using the information. The master/slave tree topology allows the propagation of the
information.
The mains frequency is not a stable value and fluctuates depending on the energy demand. So, the maximum timer
value shall be continuously corrected to follow the mains variations. Tmax can be obtained in two different ways:
1. Using a zero-cross point detection circuit.
2. Using the MaximumCorrectionValue field of the Clock token. This field allows a slave to synchronize with
the network clock without using a zero-cross point detection circuit.
From Tmax the value of the actual mains periord (Tmains) can be calculated in the following way:
Submission page 104 UPA-OPERA