User's Manual Chapter 13

Base FCC Regulatory Test Report
7-90
AT&T Wireless Services
FCC Type Acceptance Application
10991 Rev. 1.0 7/6/99
HSD network elements are managed in the same fashion and utilize the
same systems as the telephony NEs.
7.1.8 HSD Medium Access
A number of physical channels have been set aside for HSD services
within each sector of all PWAN Bases. The number of channels
allocated for HSD services may be provisioned per Base to
accommodate the data traffic requirements within each sector or cell.
This pool of physical channels is divided into groups, resulting in
subsets of logical channels (or data streams) over which data transfer
between the Base and RU may take place. The logical channels
corresponding to the Base-RU airlink constitute the “downlink” and the
logical channels corresponding to the RU-Base airlink constitute the
“uplink”. Depending upon the data requirements in either of these two
directions, the channel capacities of the two airlinks may differ.
The downlink can be considered a connectionless broadcast channel
handling traffic from the Base to RU only (refer to Figure 7.6—). Data
destined for a specific RU is broadcast to the entire RU population
within the Base sector, where it is simultaneously received and decoded
by all RUs within that sector. Although all RUs receive the same data
from the downlink, only the destination RU (determined by its IP
address) will pass the received data up the protocol stack to the
customer’s computer equipment. All other RUs will discard any
received data not intended for them.
The uplink is shared among all RUs associated with a given sector on a
Base. Access to the uplink from any RU is managed through an
arbitration process administered by the Base. In so doing, the Base can
assist RUs in gaining access to the uplink, as well as notifying them
when contention has occurred by means of channel status indicators on
the downlink.
The HSD airlink is considered a reliable transport medium for
messages exchanged between an RU and its associated Base. This is
achieved through the use of error-detection and retransmission
mechanisms supported by the physical layer.