Wimax standards and Security The Wimax

TABLE 8.2
802.16 Mesh Control Packets
Packet Type Channel Type Scheduling Purpose

MSH-NENT	Basic	Best effort	Network entry
MSH-NCFG	Broadcast	Distributed election	Network configuration
MSH-CSCF	Broadcast	Tree scheduling	Centralized scheduling configuration
MSH-CSCH	Broadcast	Tree scheduling	Centralized schedule distribution
MSH-DSCH	Broadcast	Distributed election,	Decentralized scheduling negotiation
		Best effort

data slots of the data subframe in an additional unreliable broadcast channel. We elaborate on the purpose of each of the control packets further in the rest of this section.

3. 
   Transmission Scheduling in the Logical Channels
   

Each channel type has its own method to assign transmission opportunities to the nodes sharing the channel. The assignment method is usually specified in terms of a scheduling protocol and a scheduling algorithm. The rest of the section elaborates on the scheduling protocols and algorithms used for each channel type.

1. 
   The Basic Channel
   

The basic channel is used by nodes entering the network to transmit the net- work entry MSH-NENT packets. The basic channel transmission opportunities are allocated in the first control transmission opportunity of every network configuration frame (Figure 8.3). The basic channel is a best effort channel, so it does not guarantee collision-free transmissions. Nodes transmitting in the basic channel use a 1 s timer to retransmit unacknowledged packets. The
802.16 mesh standard does not specify a back-off mechanism for the basic channel, even though such a mechanism may be useful in case the channel is busy. The standard assumes that the mesh nodes are static and that they are always on. However, if 802.16 mesh nodes are used in scenarios where the mesh nodes are mobile, or frequently off, a back-off mechanism can be added to the channel without any changes to the 802.16 standard.

2. 
   Distributed Election Scheduling Broadcast Channels
   

Network configuration messages (MSH-NCFG) and coordinated distributed scheduling messages (MSH-DSCH) use broadcast channels with distributed


MSH-NENT MSH-NCFG

Control subframe
Data subframe
Control subframe
Data subframe

Network configuration frame

Scheduling frame