Inter-Tel AXXESS Manual page 118

Specifications
® ®
INTER-TEL AXXESS
NOTE:
and the external CSU must be located in the same building, and the cabling between them must
be no longer than 133 feet.
4.158 When a T1 span is used to connect the phone system to the public network or to another
telephone system, it is important that the two endpoints communicate at the same frequency.
Because it is practically impossible for both endpoints to have clocks running at identical fre-
quencies, one endpoint is given "master" clock status and the other endpoint is given "slave"
clock status. The slave clock can then extract and lock onto the master clock frequency from
the incoming T1 information. This master/slave synchronization is programmed in the data-
base. When connected to the public network, the T1 Cards should be designated as public net-
work slaves.
4.159 When information (currently, voice only) is transmitted over a T1 span, a "framing" bit
is added so that the receiving end can recognize where the information begins and ends (as
long as the clock circuitry of the two endpoints is synchronized). Currently, the phone system
supports the two major types of framing schemes in use today: D4 Superframe, which is the
most common, and Extended Superframe (ESF), which is required to support future ISDN and
DMI features. For voice transmissions, D4 Superframe is quite adequate. However, for data
transmissions (not currently supported), ESF is much more reliable and efficient.
4.160 Digital information is transmitted over the T1 span as a series of 1s and 0s (e.g., 1000
0000 0000 0001...). If there are too many consecutive zeroes, the T1 clock extraction circuitry
does not operate correctly. To prevent this, T1 carrier equipment limits the number of consecu-
tive zeroes. The Inter-Tel system supports the two major types of zero code suppression
schemes in use today: Alternate Mark Inversion (AMI), also called bit-7 stuffing, and Bipolar
Eight Zero Substitution (B8ZS). Again, for voice transmissions, AMI is quite adequate. How-
ever, for 64 kbps clear channel data transmissions (not currently supported), B8ZS is required.
4.161 Like the line build-out attenuation, the framing scheme type and zero code suppression
scheme type are also available from the T1 provider. In fact, when ordering a T1 span, always
request the following information from the T1 provider:
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•
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4.162 Each card has circuitry for up to 24 trunk channels. The 24 channels (or circuits) can be
any combination of loop start trunks, ground start trunks, DID trunks, E&M trunks, or OPX
trunks.
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MANUAL VERSION 11.0 – May 2008
To use an external CSU instead, the card can be set to DSX mode. However, the card
Framing Scheme: D4 Superframe or ESF
Zero Code Suppression Scheme: AMI or B8ZS
Recommended Line Build-Out Attenuation: 0dB, 7.5dB, 15dB, or 22.5dB
T1 Cards (T1Cs)