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

4-June-07 P1901_PRO_016_r0
Tokens are addressed to a single port and when they are generated by the master, they shall have enough
validity for the polled TDR to transmit Active and Alive Polling Frames, TDR Polling Frames and Access
Frames within the maximum intervals.
This kind of frame is also used by the TDR to indicate whether it wants to be Active or stay Idle; in this case
this frame can only contain service class 7 traffic, except if it is an Active TDR Polling Reply Frame, case in
which any data can be transmitted, according to the remaining validity.
4.3.7 CSMA Frame
The aim of this type of frame is to provide the nodes which do not have access to the channel, an opportunity to
gain access. This type of frame is addressed to:
• Idle nodes that have data packets to send in order to change them into active ones.
• Idle nodes that generates bursty traffic
When a node receives a CSMA token and wants to transmit, it must contend for the channel. This contention is
performed through a Backoff. If the node wins the contention it starts transmitting; otherwise, the node waits for
another CSMA token.
Each node will contend for channel access with a different value depending on its contention priority;
contention is prioritized in the following way:-
• High Service class Data traffic and idle state: in order to minimize the probability of collision between
nodes that are in the same case each of them will select a random value in the range [P1min, P1max]. In
this case, the MAC must configure the node to transmit only packets with service class 7. The idea is to
only send the Resource Request Packet and not send the High Service class Data traffic to avoid
glitches in the audio or the video application.
• Idle node with control packets: this contention range [P2min, P2max] is reserved in order the idle
nodes send the control packets.
• Idle node with Bursty Traffic: this contention range [P3min, P3max] is reserved for nodes with very
low throughput of low service class data traffic.
Submission page 101 UPA-OPERA