Understanding the network.pdf - Back to Home

Ordering Your T1
Today, the common provisioning for T-carrier circuits is ESF/B8ZS. However, it is
always best to specify ESF/B8ZS with your carrier when you are ordering your
circuit. You also need to specify what your timing source is. Depending on the
carrier, they might or might not provide a line timing source, but if they do, have
them provide timing. As far as D4/AMI provisioned circuits are concerned, there are
some channel banks that prefer D4/AMI to ESF/B8ZS. So, for channel bank
applications, it's best to check with your equipment manufacturer before ordering.
CPE T-Carrier Network Equipment
When your T1 is installed on your premises, it will be terminated on an network
interface unit (NIU) or what is commonly referred to as the "smart jack." NIU is the
demarcation between the CPE and the carrier network. Everything beyond the NIU
is considered CPE. The NIU provides the DC power termination, loopback
capabilities, and a bypass access for Bit Error Rate (BER) testing. The NIU provides
an RJ-45 interface for interfacing with the CSU.
In many cases, the LEC's D-mark will not be close to where your equipment is
located. Consequently, you might be required to install an extension between the
NIC and your equipment location. Some LECs will install the in-house extension
wiring to a specified D-mark point, such as an office or computer room. Having the
LEC install the extension has an advantage over doing it yourself. When the LEC
installs the extension, it becomes responsible for the extension cabling along with
the NIU. This can save you aggravation later if a problem arises. If you have
installed the extension, the LEC will claim it is only responsible for problems up to
the NIU. If the LEC installs the extension, they are responsible. Whenever possible,
it is always better to have the smart jack installed in the same place as your
equipment. The NIC can provide valuable information about the status of the circuit
in the form of display indicators, which you will need to see in some cases when
troubleshooting circuit problems over the telephone with the LEC.
Channel Service Unit
The channel service unit (CSU) is the CPE termination point for the T1 carrier circuit.
Before the AT&T divestiture, the CSU was the telephone company demarcation. The
CSU provides the following functions:
• Circuit termination—The CSU terminates the local T1 circuit and provides
isolation between the CPE network and the PSTN.