User guide

Understanding Canopy Networks March 2005
Through Software Release 6.1
Issue 1 Page 59 of 425
Canopy System User Guide
7 CANOPY LINK CHARACTERISTICS
7.1 UNDERSTANDING BANDWIDTH MANAGEMENT
7.1.1 Downlink Frame Contents
The AP broadcasts downlink frames that contain control information, allocating slots in
succeeding or future uplink frames to SMs that have requested service. The downlink
frame also contains a beacon frame, control information, and data that specific SMs have
requested. Each SM
◦ examines the downlink frame to distinguish whether data is addressed to
that SM.
◦ retrieves data addressed to that SM.
◦ directs such data to the appropriate user.
7.1.2 Uplink Frame Contents
Uplink frames contain control information from each SM that request service on
succeeding uplink frames. SMs insert data into the uplink frames in an amount that the
AP has established.
In a scenario in which 200 SMs (the maximum number of SMs that an AP can support)
simultaneously request to pass data to the AP in the uplink frame, the AP acknowledges
all of these requests within 80 msec. This interval is based on the frame size 2.5 msec,
400 frames per second, and 3 SMs per frame.
7.1.3 Frame Structure
With a 64-byte slot capacity, the Canopy frame consists of
◦ 33 data slots, subject to the following variables:
− Maximum range decreases the number of available slots to 32.
− Background bit error rate (BER) mode decreases the number of available
data slots by one (and bandwidth by 200 kbps).
− Every two control slots that are allocated decrease the number of available
data slots by one.
◦ 6 control slots
− 3 uplink control slots
− 3 downlink control slots
◦ 6 acknowledgement slots
− 3 uplink ACK slots
− 3 downlink ACK slots