Wimax standards and Security The Wimax

Paging and Location Update

The IEEE 802.16e system defines an MS idle mode to provide paging and location update mechanisms. The MS can be in idle mode when there is no traffic to/from the MS for a given period. Idle mode allows an MS to become periodically available for DL broadcast traffic messaging without registering with a specific BS while it traverses an air link environment consisting of multiple BSs. An MS in idle mode does not have to perform HO and can suspend all normal operation requirements. Hence, it can conserve power

and operational resources, and the network can eliminate air interface and HO traffic. However, for MSs in idle mode, a network and BS broadcasts or multicasts a paging message periodically in the paging area to inform the MS of its pending DL traffic, and the MS should scan for the paging message in every discrete interval and inform the network of its current location.

Several BSs compose a logical group called a paging group, the purpose of which is to offer a contiguous coverage region in which the MS checks only the DL paging message to see whether there is traffic targeted to it. The paging groups are defined and managed by the management system (e.g., paging controller) in the network. For idle mode, the following messages are defined:

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  DREG-REQ is sent by the MS to request deregistration from its serving BS or initiation of idle mode.
  
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  DREG-CMD is transmitted by the BS to force the MS to change its state. The BS can transmit the DREG-CMD in an unsolicited man- ner or as a response to the DREG-REQ message. Upon receiving a DREG-CMD, the MS performs the action indicated by this command message.
  
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  MOB_PAG-ADV is broadcasted or multicasted by the BS during the paging interval. This message requests the MS to update its location or reenter the network.
  

1. Basic Paging Operation

Paging begins after the MS deregisters. Figure 6.11 illustrates the basic paging operation. First, an MS in active mode sends a DREG-REQ to request dereg- istration and enters idle mode. If the BS receives the DREG-REQ, it sends a DREG-CMD message to the MS. A serving BS may also induce an MS to enter idle mode by sending an unsolicited DREG-CMD message. Upon receipt of the unsolicited DREG-CMD message from the serving BS, the MS sends a DREG-REQ message and then enters idle mode.
In idle mode, the MS and BS release all connections, all air resources, and IP address, but the serving BS or the paging controller that administers idle mode activity for the MS can retain certain MS services and operational infor- mation, which it can use to expedite a future network reentry from idle mode on the part of the MS. For idle mode operation, the MS maintains an idle mode timer and the paging controller maintains an idle mode system timer. These two timers are set to the same value and start when the serving BS transmits the DREG-CMD message that directs the MS to enter idle mode, and recycle whenever the MS updates its location successfully while in idle mode. These two timers provide a time interval during which the MS should update its location so that it can be found in the network managed by the current paging controller. If the idle mode system timer has expired or if the MS enters/reenters the network and resumes normal operation, the paging controller discards all MS services and operational information retained for




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Alternation of paging unavailable interval and paging listening interval