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2.9.3.1 TDD frame format
On air transmission time is divided into frames by 802.16 PHY. Every frame is of a fixed length, and is first divided into the Downlink Sub-frame and after that the Uplink Sub-frame. Two types of transmission duplexing are there: Time Division Duplexing and Frequency Division Duplexing. In TDD, the entire DL sub-frame is sent by BS, that starts with downlink-MAP and uplink-MAP which explain the contents of the downlink and the uplink[24] (DL-MAP and UL-MAP are the directories of slot locations)

During the downlink, BS informs SS when it is planned to move transmission burst scheme. During UL, every SS is informed by the schedule that when it will be permitted exclusive use of the transmission spectrum[24]. In FDD, while DL-MAP and UL-MAP still schedule the transmissions, UL and DL transmissions occur simultaneously, on dissimilar frequencies.

Downlink Sub-frame
In downlink sub-frame, first there is a preamble. The function of this is to facilitate the SS to synchronize to the frame, because it may have lost synchronization towards the end of the preceding frame. Following this preamble there is DL-MAP and UL-MAP. The access to the downlink information is defined by the DL-MAP. It tells every SS about timings when changes in modulation and coding will take place. The subscriber station listens to all the data it is able to until it reaches data for itself. The access to the uplink channel is defined by the UL-MAP. In this, a burst profile and a time for every SS are specified to transmit their data. The BS transmits its TDM data following this DL-MAP and UL-MAP. The robustness of the transmitted data is decreased in terms of the burst profile. The reason for this is so that a SS does not drop synchronization.

Uplink Sub-frame
In Uplink sub-frame first there are ranging contention opportunities. This is to permit any SS, which have not previously registered to send a ranging request message. The function of this message for a SS, which is not registered, is to determine network delay and to discuss a burst profile or power change. Since this is the first communication this SS is having with the BS, there are no pre-defined uplink opportunities. All SS's, with no such uplink opportunities, transmit their range request in this initial ranging contention opportunity time. There is BW Request Contention following this ranging contention opportunity, which is used to send BW request message, and following this the SSs transmit their data through TDMA, in the time slot given to them by the UL-MAP.

2.10 ESTABLISHING a CONNECTION
Upon installation, in order to detect an operating channel, SS begins to scan its frequency. After detecting the channel SS may be programmed to register with a certain BS it wants to join; SS tries to synchronize to the downlink transmission. Then SS will wait for the periodically broadcast downlink channel descriptor (DCD) and uplink channel descriptor (UCD) messages to learn the modulation and the FEC schemes used on the carrier.

After learning what parameters it must use for initial ranging transmission, SS will scan the UL-MAP to get an opportunity to perform the ranging since it is very essential to tell SS about when to send the ranging, if various SS would try to join the network at the same time, that would have an extremely bad effect on the networ