G.703/G.704 NTU W/V35
12
are sent as spaces, i.e., no pulse. Every other pulse is inverted from the
previous pulse in polarity, so that the signal can be effectively transmit-
ted. This means, however, that a long sequence of zeros in the data
stream will cause problems, since the NTU receiving the signal relies on
the signal to recover the 2.048 Mb/s clock.
If you must use AMI, you should ensure that the data terminal equipment
connected to the unit provides a minimally acceptable pulse density. For
this reason, there are advantages to using HDB3 instead. AMI coding
does not inherently account for ones density. To meet this requirement,
the user should ensure that the data inherently meets pulse density
requirements.
2.3.22 S
WITCH
SW2-2: CRC-4 M
ULTIFRAME
In framed mode, SW2-2 is used for CRC-4 MF. When CRC-4 is enabled, the unit
monitors the incoming data stream for CRC-4 errors. It transmits CRC-4 error
counts to the transmitting unit. When using timeslot zero (TS0), excessive errors
may cause loss of frame or loss of sync. If CRC-4 MF is used, both units must be
set for set for CRC-4 MF. Otherwise, the one using CRC-4 MF will detect loss of
sync.
Note
When the data rate is set to 2.048Mb/s, then the unit is forced into G.703
mode, and it transmits user data on all 32 time-lots. There is no framing
information; therefore, the CRC4 MF (SW2-2) switch is ignored. In all
other rate settings, the unit employs G.704 framing; TS0 is reserved for
signaling.
2.3.23 S
WITCH
SW2-3 D
ATA
I
NVERSION
Set Switch S2-3 to determine whether or not the data stream from the local DTE
is inverted within the MT335A before being passed to the G.703/G.704 network.
An inverted data stream may be required when you use the MT335A to commu-
nicate with a G.703 device (that inverts the data) on the remote end. In typical
installations, data inversion is not necessary.
SW2-2
Option
Off
CRC-4 Disabled
On
CRC-4 Enabled
SW2-3
Option
Off
Data not inverted
On
Data inverted
