This retry process continues until the maximum number (i.e., Request Retries for bandwidth requests and Contention Ranging Retries for initial ranging) of retries has been reached. At this time, for bandwidth requests, the PDU shall be discarded. For initial ranging, proper actions are specified in 6.2.9.5. Note that the maximum number of retries is independent of the initial and maximum backoff windows that are defined by the BS.

For bandwidth requests, if the SS receives a unicast Request IE or Data Grant Burst Type IE at any time while deferring for this CID, it shall stop the contention resolution process and use the explicit transmission opportunity.

The BS has much flexibility in controlling the contention resolution. At one extreme, the BS may choose to set up the Request (or Ranging) Backoff Start and Request (or Ranging) Backoff End to emulate an Ethernet-style backoff with its associated simplicity and distributed nature as well as its fairness and efficiency issues. This would be done by setting Request (or Ranging) Backoff Start = 0 and Request (or Ranging) Backoff End = 10 in the UCD message. At the other end, the BS may make the Request (or Ranging) Backoff Start and Request (or Ranging) Backoff End identical and frequently update these values in the UCD message so that all SS are using the same, and hopefully optimal, backoff window.

6.2.8.1 Transmission opportunities

A transmission opportunity is defined as any minislot in which an SS is allowed to start a transmission. The number of transmission opportunities associated with a particular IE in a map is dependent on the total size of the interval as well as the size of an individual transmission.

As an example, consider contention-based bandwidth requests for a system where the PHY protocol has a frame duration of 1 ms, 4 symbols for each PS, 2 PSs for each minislot, an uplink preamble of 16 symbols (i.e., 2 minislots), and an SS Transition Gap of 24 symbols (i.e., 3 minislots). Thus, assuming QPSK modulation, each transmission opportunity requires 8 minislots: 3 for the SS Transition Gap, 2 for the preamble, and 3 for the bandwidth request message.

If the BS schedules a Request IE of, for example, 24 minislots, there will be three transmission opportunities within this IE. Details of the three transmission opportunities are shown in Figure 44.

One Request IE

Figure 44—Example of Request IE containing multiple transmission opportunities

6.2.9 Network entry and initialization

The procedure for initialization of an SS shall be as shown in Figure 45. This figure shows the overall flow between the stages of initialization in an SS. This shows no error paths and is shown simply to provide an overview of the process. The more detailed finite state machine representations of the individual sections (including error paths) are shown in the subsequent figures. Timeout values are defined in 10.1.

Scan for

Downlink

Channel

Figure 45—SS Initialization overview

The procedure can be divided into the following phases:Scan for downlink channel and establish synchronization with the BS

c)Obtain transmit parameters (from UCD message)

d)Perform ranging

e)Negotiate basic capabilities

f)Authorize SS and perform key exchange

g)Perform registration

h)Establish IP connectivity

i)Establish time of day

j)Transfer operational parameters

k)Set up connections

Each SS contains the following information when shipped from the manufacturer:

a)A 48-bit universal MAC address (per IEEE Std 802-2001) assigned during the manufacturing process. This is used to identify the SS to the various provisioning servers during initialization.

b)Security information as defined in Clause 7 (e.g., X.509 certificate) used to authenticate the SS to the security server and authenticate the responses from the security and provisioning servers.

6.2.9.1 Scanning and synchronization to the downlink

On initialization or after signal loss, the SS shall acquire a downlink channel. The SS shall have nonvolatile storage in which the last operational parameters are stored and shall first try to reacquire this downlink channel. If this fails, it shall begin to continuously scan the possible channels of the downlink frequency band of operation until it finds a valid downlink signal.

Once the PHY has achieved synchronization, as given by a PHY Indication, the MAC Sublayer shall attempt to acquire the channel control parameters for the downlink and then the uplink.

6.2.9.2 Obtain downlink parameters

The MAC sublayer shall search for the DL-MAP MAC management messages. The SS achieves MAC synchronization once it has received at least one DL-MAP message. An SS MAC remains in synchronization as long as it continues to successfully receive the DL-MAP and DCD messages for its Channel. If the Lost DL-MAP Interval (Table 118) has elapsed without a valid DL-MAP message or the T1 interval (Table 118) has elapsed without a valid DCD message, an SS shall try to reestablish synchronization. The process of acquiring synchronization is illustrated in Figure 46. The process of maintaining synchronization is illustrated in Figure 47.

Scan for

Downlink

Channel

DL-MAP

Start

Lost DL-MAP

Start

T1

Start

T12

Downlink

Synch.

Established

Synchronized

Figure 46—Obtaining downlink synchronization

Synchronized

Synchronized

Figure 47—Maintaining downlink synchronization