User's Manual Chapter 13

Chapter 7: Operational Description
AT&T Wireless Services
7-89
FCC Type Acceptance Application
10991 Rev. 1.0 7/6/99
7.1.6 PWAN FAX/Modem VF Traffic Functions
The bandwidth efficiencies of LD-CELP compression place limitations
on the type of VF traffic that can transverse the airlink. For example,
FAX and voice-band modem signals will not pass through LD-CELP
without distortion. To eliminate this problem, both the RU and Base are
capable of detecting the presence of these signals in the VF data. When
FAX or voice-band modem data is detected, both the Base and RU will
route the VF signals to special FAX/modem demodulation-
remodulation circuitry. In so doing, the Base will accept FAX/modem
VF data from the incoming 64 kbps PCM stream and remodulate it for
inclusion in the 16 kbps traffic-channel bitstream, bypassing LD-CELP
compression. Consequently, the RU will demodulate this data stream
and encode it as 64 kbps PCM for conversion to analog in the RU line
interface, where the signals appear as voice-band FAX/modem tones.
FAX/modem data sent from the RU to the Base follows this same
process in reverse.
7.1.7 PWAN High-Speed Data Functions
In addition to telephony services, the PWAN also provides customers
with a connectionless packet data service to an Enhanced Service
Provider (ESP). In this application, the RU serves as an IP gateway.
The High Speed Data (HSD) airlink provides a reliable connectionless
packet-switched connection between an RU and its serving Base. This
virtual connection supports data transfer between the customer and an
ESP, as well as the transfer of traffic management information between
the Base and RU. The airlink forms one segment of the connection over
which packet data travels between the customer’s PC and the ESP, as
depicted in Figure 7.5—.
Figure 7.5— PWAN HSD Architecture
PC
PC NIC
RUBaseDSNESP
DSN Data Service Node
ESP Enhanced Service Provider
NIC Network Interface Card
WEMS Wireless Element Management System
WEMS