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P
4
AGE
S
1
ECTION
The transmitter at one end (TxA) of a link will transmit in the
lower half of the spectrum. Consequently the receiver at the other
end will receive in the lower half of the band and transmit in the
upper half. Thus, a system will operate in one of two frequency
plans -- transmit in the upper and receive in the lower or vice
versa. These two plans are called Plan A and Plan B. One end of
a path will be on Plan A and the other will be on Plan B. Shipment
of a link will consist of an A and a B unless specified otherwise.
F
E
ORWARD
RROR
With the addition of overhead data, error detection and correction
capability can be added to a data stream. Error correction can be
accomplished by allowing the receiver to request the re-
transmission of an errored block once detected. The Tracer, on
the other hand, implements forward error correction (FEC) which
adds enough overhead data for the receiver to detect and correct
errors in the data stream. This capability comes at the cost of
bandwidth. The addition of FEC decreases the required signal-
to-noise (S/N) ratio by approximately 5.5 dB to achieve a given
bit error rate (BER).
T1 O
PERATION
F
RAMING
The data in a T1 stream is delimited by framing bits. The pattern
of the framing bits follows one of two formats -- extended
superframe (ESF) or superframe (SF). The T1 interface must be
prepared for the format that will be used.
L
C
INE
ODE
A mark in the data stream is coded as a pulse on the T1 line. A
space is coded as "no activity" on the T1 line. As a form of error
detection, subsequent marks in the data stream are coded as pulses
of alternating polarity, either positive going or negative going. This
type of line coding is called alternate mark inversion (AMI).
C
ORRECTION
61280.003L1-1B
4/12/99
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