MT8930C
Line Code
The line code used on the S-interface is a Pseudo
ternary code with 100% pulse width as seen in
Figure 6 below. Binary zeros are represented as
marks on the line and successive marks will
alternate in polarity.
BINARY
VALUE
0
1
0
0
0
1
0
0
1
1
criterion (13 bit criterion in the direction TE to NT)
specified in Recommendations I.430 and T1.605 is
satisfied. If the B1-channel is not all binary ones, the
first zero following the L-bit will violate the line code
sequence, thus allowing subsequent marks to
alternate without bipolar violations.
The Fa and N bits can also be used to identify a
multiframe structure (when this is done, the 14 bit
criterion may not be met). This multiframe structure
will make provisions for a low speed signalling
channel to be used in the TE to NT direction
(Q-channel). It will consist of a five frame multiframe
which can be identified by the binary inversion of the
Fa and N-bit on the first frame and consequently on
every fifth frame of the multiframe. Upon detection of
the multiframe signal, the TE will replace the next Fa-
bit to be transmitted with the Q-bit.
The DC balancing bits (L) are used to remove any
DC content from the line. The balancing bit will be a
mark if the number of preceding marks up to the
previous balancing bit is odd.
If the number of
marks is even, the L-bit will be a space.
The A-bit is used by the NT during line activation
procedures (refer to state activation diagrams). The
state of the A-bit will advise the TE if the NT has
achieved synchronization.
The E-bit is the D-echo channel. The NT will reflect
the binary value of the received D-channel into the
E-bits.
This is used to establish the access
contention resolution in a point-to-multipoint
configuration. This is described in more detail in the
section of the D-channel priority mechanism.
The M-bit is a second level of multiframing which is
used for structuring the Q-bits. The frame with M-
bit=1 identifies frame #1 in the twenty frame
multiframe. The Q-channel is then received as
shown in Table 1. All synchronization with the
multiframes must be performed externally.
FRAME #
1
LINE
SIGNAL
Violation
Figure 6 - Alternate Zero Inversion Line Code
A mark which does not adhere to the alternating
polarity is known as a bipolar violation.
Framing
The valid frame structure transmitted by the NT and
TE contains the following (refer Fig. 5):
NT to TE:
- Framing bit (F)
- B1 and B2 channels (B1,B2)
- DC balancing bits (L)
- D-channel bits (D0, D1)
- Auxiliary framing and N bit (Fa, N), N=Fa
- Activation bit (A)
- D-echo channel bits (E)
- Multiframing bit (M)
- S-channel bit
TE to NT:
- Framing bit (F)
- B1 and B2 channels (B1, B2)
- DC balancing bits (L)
- D-channel bits (D0, D1)
- Auxiliary framing bit (Fa) or Q-channel bit
The framing mechanism on the S-interface makes
use of line code violations to identify frame
boundaries. The F-bit violates the alternating
line code sequence to allow for quick identification of
the frame boundaries. To secure the frame
alignment, the next mark following the frame
balancing bit (L) will also produce a line code
violation. If the data following the balancing bit is all
binary ones, the zero in the auxiliary framing bit (Fa)
or N-bit (for the direction NT to TE) will provide
successive violations to ensure that the 14 bit
Q-Bit
Q1
M-Bit
1
6
11
16
Q2
Q3
Q4
0
0
0
Table 1. Q-channel Allocation
Bit Order
When using the B-channels for PCM voice, the first
bit to be transmitted on the S-Bus should be the sign
bit.
This complies with the existing telecom
standards which transmit PCM voice as most
significant bit first. However, if the B-channels are to
9-40
MITEL [ MITEL NETWORKS CORPORATION ]
