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8-26 PUBLIC AND PRIVATE DATA NETWORK CONNECTIONS
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PRIVATE DATA NETWORKS
AT&T leases facilities to private companies for nonswitched connections to private network endpoints.
Applications for these connections include high-volume data transmission, bulk voice and data
transmission to multiple locations, interactive computer-aided design, and so forth. The leased facilities
over which the connections are made may be either terrestrial or satellite.
Terrestrial Private Data Network Links
The terrestrial services that AT&T offers for nailed-up connections are listed below.
• ACCUNET T1.5 service — With this service, a dedicated T1 trunk is connected between private
communications systems, between private communications systems and a central office, and between
central offices. Access is through a private communications system, a switched public data network,
the DATAPHONE Digital Data Service, or the SKYNET Digital Service.
• ACCUNET T45 service — This service provides fiber-optic digital transmission from a DS1 port to a
M28 multiplexer that multiplexes up to 28 DS1 trunks or 672 DS0 lines. From the M28, signals travel
at the DS3 level to the AT&T POP. At the POP, the transmission is demultiplexed and can access the
switched public data network, T1.5 service, the DATAPHONE Digital Data Service, and so on.
• ACCUNET Spectrum of Digital Services (ASDS) — Access to ASDS can be through analog or digital
facilities. Access need not be at the DS1 level — subrate channels as well as multiple DS0 channels
may be accommodated. Through ASDS, digital transmission is furnished at speeds ranging from 9.6,
56, or 64 kbps, up to the DS1 speed of 1.544 Mbps. This service is sometimes called fractional T1.
Private Connections Through ACCUNET T1.5 and T45
Connections through these facilities present their own special set of requirements. Figures 8-17 through
8-20 show some typical private data network connections. Table 8-7 lists the requirements for the
illustrated connections.
PRIVATE
DATA
NETWORK
S75/S85
G1/G2
S75/S85
G1/G2
MPDM/M1*
OR
7500B
MPDM/M1*
OR
7500B
T1.5 T1.5
DTEDTE
Figure 8-17. Private Data Network with Robbed Bit Trunks (Mode 1)