Specifications

Chapter 1 Installation
1-10
is required at their demarcation network interface (NI). A T1 level from the Access BankTM which is too
high for the engineered facility can result in bipolar violations seen by the carrier. Too low a level can
result in loss of signal seen by the carrier. Note that the LBO option does not effect the Access BankTM
T1 Line receive input automatic gain sensitivity, which is 0 to -30 dBsx.
Switch #3 - Clocking
T1 Clocking options supported are Looped (Normal) timing from the incoming T1 line or Master timing.
The Access BankTM T1 line transmit output can thus be synchronized to the common carrier's or private
network's precision clock source (Looped) or provide a crystal timing source to an isosynchronous T1 line
(Master).
The Access BankTM derives T1 and data port timing from a Phase Lock Loop (PLL) circuit internally.
This system-wide timing source may be phase-locked to the T1 Line signal received or the Access
BanksTM own Internal crystal clock. The T1 Line and Internal clocks are all 1.544 Mbps sources. The
default (Looped) clock source is the clock recovered from the incoming T1 line. The default external
clock frequency is 1.544 Mbps.
T1 Line clocking (looped) is the most common configuration for accessing switched voice, fractional T1,
or Digital Cross-Connect System (DACS) based carrier services. The telecommunications carrier
providing a T1 access line to these services synchronizes the line to a highly precise (atomic) clock source.
This is the same source that is used to synchronize the carrier's entire switched network. The user of these
services on a T1 access line is required to synchronize to the carrier to avoid slips, or lost frames.
The second most common clocking configuration is in applications of point-to-point full T1 lines, called
isosynchronous lines(master). In this case, the user is leasing a full T1 "digital pipe" from the carrier.
There are no carrier switches or DC devices attached to the line, only fiber optic multiplexers and copper
to fiber loop converters. In this case, the customer is responsible for providing their own master clock
source at one side of the line, and recovering clock (loop timing) from that source at the other end of the
T1 line. Either end can be chosen as the master clock source. The Access BankTM at the loop timing
end is configured to derive clocking from the T1 Line. The Access BankTM at the master timing end of
the line is typically configured to provide clocking from the Internal crystal clock of the Access BankTM
It may be chosen as the master clock source on an isosynchronous or point-to-point copper T1 line. Note
that isosynchronous lines may run between buildings, or from coast-to-coast on a long distance carrier
network - there is no distance limitation.
Switch #4 - T1 Framing
T1 Framing options are Extended Superframe (ESF) or Superframe (SF, also known as D4 framing). The
Access Bank can provide D4 or ESF frame format on the T1 network interface. SF (D4) is the mode that
now is most commonly configured for voice traffic. Note that most U.S. telecommunications common
carriers (including AT&T) are adopting ANSI standard T1.403 for ESF framing.
Switch #5 - Line Coding
T1 Line Coding options are Zero Code Substitution (AMI, "straight" Alternate Mark Inversion), or Binary
8 Zero Substitution (B8ZS, sometimes called "clear channel" T1).