AT&T 2500 series 用户手册
1-16
TRANSMISSION STATES
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DCP-line port. The only caveat is that the destination data module must be set for mode-2 DMI
communication. (See appendix D for a discussion of DMI modes.)
communication. (See appendix D for a discussion of DMI modes.)
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Voice-grade data can be carried over a DS1 facility as long as the destination DCE is a modem
compatible with the originating modem.
compatible with the originating modem.
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When a mismatch exists between the types of signals used by the endpoints in a connection (for
example, the DCE at one end of the connection is an analog modem, and the DCE at the other end is a
digital data module), a modem-pool member must be inserted in the circuit. When the endpoints are on
different switches, the best place to insert the modem-pool member depends upon the transmission
medium, but it is recommended that the modem-pool member be put on the origination or destination
switch. (Note that a modem-pool member will always be inserted automatically for calls to off-
premises sites. For internal calls, however, only the Generic 1 and 2 communications systems are
capable of automatically inserting a modem-pool member.)
example, the DCE at one end of the connection is an analog modem, and the DCE at the other end is a
digital data module), a modem-pool member must be inserted in the circuit. When the endpoints are on
different switches, the best place to insert the modem-pool member depends upon the transmission
medium, but it is recommended that the modem-pool member be put on the origination or destination
switch. (Note that a modem-pool member will always be inserted automatically for calls to off-
premises sites. For internal calls, however, only the Generic 1 and 2 communications systems are
capable of automatically inserting a modem-pool member.)
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Data cannot be carried over analog facilities unless, inside the switch, it is represented as a PCM-
encoded analog signal. To accomplish this for data originating at a digital terminal, the signal enters the
switch at a digital port and exits the switch at a digital port. The signal then reenters the switch through
a modem-pool connection (data-module to modem to analog-port) and exits the switch again at an
analog port.
encoded analog signal. To accomplish this for data originating at a digital terminal, the signal enters the
switch at a digital port and exits the switch at a digital port. The signal then reenters the switch through
a modem-pool connection (data-module to modem to analog-port) and exits the switch again at an
analog port.
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Although DS1 is commonly referred to as a trunk speed, here it names the protocol used at layer 1 for
digital trunks. There are trunks that use different signaling methods, but use DS1 protocol at layer 1
(for example, PRI and 24th-channel signaling trunks). (See the Trunking section of this chapter for an
explanation of these trunk types.)
digital trunks. There are trunks that use different signaling methods, but use DS1 protocol at layer 1
(for example, PRI and 24th-channel signaling trunks). (See the Trunking section of this chapter for an
explanation of these trunk types.)