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Chapter 2 - Setting Up Your System Hardware
© Polycom, Inc. 2-13
PRI Network Interface Module
The PRI network interface module allows you to make ISDN calls using a PRI line.
You may need one of these items in addition to the PRI network interface module
and the items provided with it:
❑ External Channel Service Unit (CSU) — If you connect a PRI T1 network
interface module outside a PBX, you may wish to connect it through a CSU.
The CSU isolates the PRI from the network, and continues to transmit a signal
to the network even if the PRI network interface module loses power or is
disconnected. This prevents the line from being deactivated. CSUs are used
only in North America.
❑ PBX crossover cable — An RJ-45 crossover cable may be required when
connecting the PRI network interface module to a PBX or other third-party
network access device.
❑ 75 Ω coaxial adapter — The PRI E1 line termination is 120 Ω. In some areas,
however, the E1 network connection is via a 75 Ω coaxial cable. The PRI
network interface module does not directly support this, but you can obtain
passive adapter devices from various vendors.