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

4-June-07 P1901_PRO_016_r0
The following diagram ¡Error! No se encuentra el origen de la referencia.depicts a transmission sequence
using this kind of token. As it is outlined in the above diagram, a transmission sequence starts with a Distributor
Token. This type of token assigns the channel to a list of nodes. The Data Token is used by slaves to release the
token to the next detination node. Further sections describe this diagram in more detail.
List Info
Dst1 = Slave 1 Validity1 SessionId1
Dst2 = Slave 4 Validity2 SessionId2
IPPDUS1
Dst3 = Slave 3 Validity3 SessionId3
Dst4 = Slave 2 Validity4 SessionId4
IPPDUS2 IPPDUS2 IPPDUS2
IPPDUS2
MASTER
DISTRIBUTOR
TOKEN
Slave 1
Slave 4 DATA
TOKEN to Slave 2
Slave 3
Slave 2
DATA TOKEN
To Slave 4
DATA
From SessionId1
≤ Valitdity1
DATA
≤ Valitdity2
From SessionId2
DATA TOKEN to Slave 3
DATA
From SessionId3
≤ Validity3
Figure 24: Transmission Sequence
DATA
From SessionId4
≤ Validity4
DATA TOKEN
to MASTER
Submission page 85 UPA-OPERA
DISTRIBUTOR
TOKEN
Using the previously described channel access, a programmed timming interval can be set, synchronized or not
with the mains meriod using the clock token, where several nodes in a preestablished order can transmit.
4.1.2 Contention medium access example
In the previous examples, the destination of the token, and so, the next token holder is explicity defined in the
information that the token contains. In the case of CSMA or Access Replay frame, the next token holder is not
predefined by the node that transmit the token, but a priorized contention period is open to decide the node that
will be the next token holder.
Asume again the topology described in Figure 23.