User's Manual Chapter 13

Chapter 7: Operational Description
AT&T Wireless Services
7-87
FCC Type Acceptance Application
10991 Rev. 1.0 7/6/99
Figure 7.3— PWAN Airlink Protocol Profile
The support of VF telephony signals in the PWAN differs from a
traditional RDT (refer to Figure 7.4—). In a traditional RDT, analog
VF signals are converted to 64 kbps Pulse Coded Modulation (PCM)
for transmission across the network. However, to conserve airlink
resources the WRDT supports Low Delay-Codebook Excited Linear
Prediction (LD-CELP) voice compression. This implementation
provides PCM voice quality at one fourth the bandwidth (16 kbps).
As is the case in a traditional RDT, the RU line interface converts
incoming analog VF signals to 64 kbps PCM. However, unlike a
traditional RDT, the resulting PCM signals are compressed by LD-
CELP for transmission over the airlink at 16 kbps. The received LD-
CELP voice data is decompressed at the Base and restored to 64 kbps
PCM for compatibility with the LDS. Conversely, the Base utilizes LD-
CELP to compress the incoming 64 kbps PCM to 16 kbps for
transmission over the airlink to the RU, where it is decompressed and
restored to 64 kbps PCM. The PCM signal is then converted to an
analog VF signal in the RU line interface.
CAC
CL BR BR CL
CAC
Datalink Control
Media Access
NetworkNetwork
Media Access
Datalink Control
RME
RME
LD-CELP
to 64 kbps
PCM
LD-CELP
to 64 kbps
PCM
Base PWAN Protocol
Profile
RU PWAN Protocol
Profile
Network
Layer
Datalink
Layer
Physical
Layer
Air Medium
DL SAP DL SAP
CL SAPBC SAPBC SAPCL SAPCA SAP CA SAP L SAPL SAP
16kbps LD-CELP 16kbps LD-CELP
LC
Tr a f f i c
LC
Tra f fi c
To TR-303
Interface
To Analog
Telephony
Interface