User guide

Understanding Bandwidth Management Link Characteristics

pmp-0229 (Mar 2013)

Bandwidth requests are sent as control slots, which are half the size of a data slot. The operator

configures a number of reserved control slots. In addition to the reserved control slots, space in

any data slots in a given uplink frame not assigned by the uplink map is also available for

bandwidth requests.

An SM makes a bandwidth request when it has data to transmit. Bandwidth requests are

contention requests and are the only part of the Media Access Layer that uses contention. If two or

more SMs make bandwidth requests using the same control slot (or half-unused-data slot), it is

likely the AP will not be able to understand the requests. The SMs retransmit any bandwidth

requests that do not result in assignments in the uplink map.

Slot Calculation

The frame consists of slots which hold 64-byte fragments of packet data. The number of uplink

and downlink data slots is determined by

• the Downlink Data % configured by the operator, which determines the ratio of downlink to

uplink data slots.

• the Max Range setting configured by the operator, which determines how much time in the

frame must be reserved for air delay and not used for data.

• the number of reserved Control Slots configured by the operator. Control slots are half the

size of data slots and every other reserved control slot (starting with either the first or second,

depending on how the Max Range setting has influenced frame structure) reduces the number

of data slots by one.

Startup Sequence

When an SM boots, the following sequence occurs:

1. The SM detects the beacon slot from an AP.

2. The SM synchronizes with the AP.

3. If an authentication server is configured on the AP, and the AP is licensed for authentication,

then

a) the AP sends a Registration Request message to the authentication server for

authentication.

b) following a successful challenge, the authentication server returns an Authentication

Grant message to the AP.

c) the AP sends a Registration Grant to the SM.

If an authentication server is not configured on the AP, or if the AP is not licensed for

authentication, then the AP simply returns the Registration Grant to the SM.