Zhone Technologies 800, 900, 600 manual IAD Isdn PBX

ISDN-PRI Card Introduction

Figure 5-3shows an application that requires 3 D channels. The user has ordered a 23B+D facility to each of two different carriers. The third facility is a local NFAS (47B+D) connection to the user’s PBX. In this application, the system will route calls from the PBX to the appropriate carrier based on called phone number (see Call Routing section later in this chapter).

Carrier A	Carrier B
ISDN Switch	ISDN Switch

23B+D 23B+D

	NFAS 47B+D
IAD	ISDN PBX

Figure 5-3. ISDN-PRI Links to Two Carriers from an ISDN PBX

5.1.2.1Network and User Side Protocols

In the example application shown in Figure 5-3,there is an important difference between the two D channels terminating in the carrier switches and the D channel terminating in the user’s PBX. The ISDN signaling protocol that runs on the D channel is not symmetrical. Signaling messages are treated differently depending on whether the D channel is setup to run the network side protocol or the user side protocol. All carrier switches run the network side protocol, and all user devices connected directly to a network switch must run the user side protocol. In general, network side applications cannot be connected to other network side applications. Local routing, the exception to this rule, is explained in the next section.

Server Cards 5-5