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8-22 PUBLIC AND PRIVATE DATA NETWORK CONNECTIONS
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ports, although Memotec also has higher capacity units. (See figure 8-13.)
X.25 HOST
X.25
APS
MODEM OR
PRIVATE LINE
X.25
SYSTEM
85
MEMOTEC
SP/630
PAD
7400A,
7400B,
ADU, OR
MPDM
•
•
ASYNC
ENDPOINTS
APS ACCUNET PACKET SERVICE - AT&T X.25 PDN
Figure 8-13. ACCUNET Packet Service
• REDI-ACCESS — For relatively low-volumes of data and intermittent APS access, a less expensive
alternative might be dial-up access to shared facilities. Control Data Corporation’s REDI-ACCESS
service offers you asynchronous, dial-up access to shared facilities that interface directly with APS.
Circuit-Switched Public Data Networks
AT&T offers two circuit-switched digital data network services for public access. These services are the
ACCUNET Switched Digital Services (SDS), and the Software Defined Digital Network (SDDN).
AT&T provides switched access to both SDS and SDDN. In addition, both SDS and SDDN offer two
transmission options: Switched 56 Service (SW56), and Switched 64 Service (SW64).
• SW56 is a dial-up 56-kbps data transmission service that allows DTEs to communicate with each other.
Access to the service is via analog line service, dedicated DATAPHONE Digital Service [DDS] private
lines, or T1.5 shared access lines. Access facilities are ordered from the LEC. The facilities connect a
System 75, System 85, Generic 1 or 2 communications system to SDS or SDDN at the AT&T point-
of-presence (POP).
• SW64 is a dial-up 64-kbps service that requires dedicated T1.5 ISDN-PRI access for connection of your
communications system to the AT&T POP.
SDS and SDDN Applications
SDS and SDDN applications include:
• Video conferencing — Low bit-rate, color video can be transmitted via SDS or SDDN. PICTURETEL,
Optel, and Compression Labs (CLI) build video equipment that interfaces with your communications
system for the transmission of video data over SDS or SDDN.
• High-speed facsimile — Facsimile equipment that interfaces with your communications system for the
transmission of facsimiles over SDS or SDDN can transmit a single page in 3 seconds.
• Bulk data transfer — SDS and SDDN support file transfers from PC to PC, mainframe to PC, and
mainframe to mainframe. DSP is a company that builds plug-in cards for personal computers that
facilitate the transfer of files from the PC, through your communications system, over SDS or SDDN.
• ALLIANCE 3000 service — This AT&T service provides interactive teleconferencing with as many as
59 locations.