Rainbow Electronics DS2180A - Manual (Page 23)

DS2180A
041995 23/36
T1 OVERVIEW
Framing Standards
The DS2180A is compatible with the existing Bell Sys-
tem D4 framing standard described in ATT PUB 43801
and the new extended superframe format (ESF) as de-
scribed in ATT C.B. #142. In this document, D4 framing
is referred to as 193S and ESF (also known as Fe) is re-
ferred to as 193E. Programmable features of the
DS2180A allow support of other framing standards
which are derivatives of 193E and 193S. The salient dif-
ferences between the 193S and 193E formats are the
number of frames per superframe and use of the F-bit
position. In 193S, 12 frames make up a superframe, in
193E, 24. A frame consists of 24 channels (timeslots) of
8-bit data preceded by an F-bit. Channel data is trans-
mitted and received MSB first.
F-Bits
The use of the F-bit position in 193S is split between the
terminal framing pattern (know as F
T
-bits) which pro-
vides frame alignment information and the signaling
framing pattern (known as F
S
-bits) which provides mul-
tiframe alignment information. In 193E framing, the F-bit
position is shared by the framing pattern sequence
(FPS) which provides frame and multiframe alignment
information, a 4 KHz data link known as FDL (Facility
Data Link), and CRC (Cyclic Redundancy Check) bits.
The FDL bits are used for control and maintenance (in-
serted by the user at TLINK) and the CRC bits are an in-
dicator of link quality and may be monitored by the user
to establish error performance.
Signaling
During frames 6 and 12 in 193S, A and B signaling in-
formation is inserted into the LSB of all channels trans-
mitted. In 193E, A and B data is inserted into frames 6
and 12 and C and D data is inserted into frames 18 and
24. This allows a maximum of four signaling states to be
transmitted per superframe in 193S and 16 states in
193E.
Alarms
The DS2180A supports all alarm pattern generation and
detection required in typical Bell System applications.
These alarm modes are explained in ATT PUB 43801,
ATT C.B. #142 and elsewhere in this document.