AT&T 7300 series, 7500 series, 7100 series, 2500 series manual Connectivity Rules, ⎜DMI Mode Code

TRANSMISSION STATES 1-15

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Note that both the physical-layer protocol and the DMI mode used in the connection are dependent upon the type of 8-bit code used at layer 2 between the DTE and DCE. (See tables 1-4and 1-5.)

Table 1-4.Physical-Layer Protocol vs. Character Code

_
⎜	⎜		⎜
⎜Protocol	⎜	Code	⎜
⎜	⎜		⎜
⎜	⎜		⎜
⎜ RS-232	⎜	Asynchronous 8-bit ASCII	⎜
⎜	⎜ Synchronous		⎜
_	⎜		⎜
⎜
⎜	⎜		⎜
⎜ RS-449	⎜	Asynchronous 8-bit ASCII	⎜
⎜	⎜	Synchronous	⎜
_	⎜		⎜
⎜
⎜ V.35	⎜	Synchronous	⎜
⎜	⎜		⎜

Table 1-5.DMI Mode vs. Character Code

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⎜		⎜		⎜
⎜DMI Mode		⎜	Code	⎜
⎜		⎜		⎜
⎜	0	⎜	Synchronous (64 kbps)	⎜
⎜		⎜		⎜
__________________________________________________				⎜
⎜		⎜
⎜	1	⎜	Synchronous (56 kbps)	⎜
⎜		⎜		⎜
⎜		⎜		⎜
⎜	2	⎜ Asynchronous 8-bit ASCII (up to 19.2 kbps)		⎜
⎜		⎜	Synchronous	⎜
⎜		⎜		⎜
⎜		⎜		⎜
⎜	3	⎜ Asynchronous 8-bit ASCII		⎜
⎜		⎜ Private Proprietary		⎜
⎜		⎜		⎜

Connectivity Rules

Figure 1-3implies certain connectivity rules:

∙In the figure, only the DS1 port and the analog trunk port are trunking facilities (all other ports shown are line ports). For communication over these facilities, the destination DCE may be a hemisphere away from the switch, and the signal may traverse any number of intervening switching systems before reaching the destination DCE.

∙Data originating at any type of digital device, whether DCP or BRI, can exit the switch at any type of digital port — BRI, digital-line, GPP, PRI, DS1, and so on — as long as the call destination is equipped with a data module using the same DMI mode as that used at the call origin. This is because, once the data enters the switch through a digital port, its representation is uniform (raw bits — that is, digital data — at layer 1, and DMI at level 2), regardless of where it originated.

∙Although data entering the switch through an EIA port has not been processed through a data module, the EIA port itself has a built-in data module. This means that inside the switch EIA-port data is identical to digital-line or GPP data. Therefore, data entering the switch at a DCP-line port (digital-line or GPP) can exit at an EIA port. Conversely, data entering the switch at an EIA port can exit at any