Monday, April 4, 2011


The 802.16 standards can support 255 different management type of messages. According to IEEE 802.16e, 66 messages are defined from which 50–66 are used explicitly for handover and sleep mode operation. 

In the following, we describe the most important messages for sleep mode operation. Each message has three parts. The first part is casually MOB (implying Mobility) while the second part carries the scope of the message (SLP, TRF, HO, BSHO, MSHO, PAG, etc.). For the case of sleep mode operation, we are mainly concerned with SLP (implying Sleep) and TRF (implying Traffic). The final part of each message is usually REQ (implying Request), RSP (implying Response), or IND (implying Indication).

MOB_SLP-REQ: Sleep Request Message, type: 50, Connection: Basic.
A MS sends this message to request definition/activation of several PSCs. The actual definition occurs when a MS suggests a PSC for an incoming connection. The message contains a Power Saving Class ID, which is a unique identifier for a group of PSCs associated with a MS. This ID is also used for the exchange of many similar message types and response messages. Other parameters are also defined like the Initial Sleep WindowFinal Sleep Window Base, and Exponent quantities measured in IEEE 802.16e frames. Moreover if the MS handles more than one class, the Number_of_CIDs field carries this number. 

MOB_SLP-RSP: Sleep Response Message, type: 51, Connection: Basic.
This message is sent in response to a request for the definition/activation of a PSC from the BS to a MS using a broadcast CID (Connection ID) or the MS’s basic CID. If a new definition was requested, then a new PSC is defined and the assigned ID is returned. When the MS receives this message, it activates the defined PSC. The MOB_SLP-RSP message contains fields such as the Length of Data, for the number of bytes per PSC, the start frame number for the first sleep window, and the relative intervals. Additionally, CIDs and windows (base and exponent) are described in MOB_SLP-REQ.

MOB_TRF-IND: Traffic Indication Message, type 52, Connection: Broadcast.
By the time the MS wakes up, it starts listening for a possible MOB_TRF-IND message, sent from the BS on broadcast CID or sleep mode multicast CID. This message is sent from a BS to a MS in the listening interval to indicate if there has been traffic addressed to the MS while it remained in sleep mode and functions only when there are one or more PSC IDs defined for PSC type I (as described below). Any other MS ignores this message. An explicit occasion in which the BS may arbitrarily include a positive indication for a MS is if the MS’s periodic ranging operation is scheduled to start in the next sleep window.
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