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59Chapter 8 - The E1 and T1 Interfaces, With Signaling
Cyclades-PR4000
The CCS Signaling Mode (ISDN-PRI)
ISDN, the Integrated Services Digital Network, was intended to be a digital upgrade to the current analog telephone
system. The ISDN discussed in this chapter is N-ISDN, where the N is for Narrow Band. A Broad Band ISDN also
exists. There are two ISDN interfaces:
• BRI — Basic Rate Interface — used for residential or small-business access.
• PRI — Primary Rate Interface — used to provide access or used by large businesses for access.
Two PRI interfaces are provided on the PR4000 via E1 or T1 ports with CCS Signaling. These connections can
be digital or analog (via a modem). The data layer protocols CHAR, PPPCHAR and Slip are used with a modem
connection.
A typical application in an Internet Service Provider is shown in Figure 8.2.
PC
PC
Integrated
RAS
Remote Users
ISDN Line
Application
Server
Router
Telephone/
ISDN Network
Analog Line
BRI Line
FIGURE 8.2 ISDN-PRI APPLICATION EXAMPLE