Preliminary Information
Functional Description
The MT9173 and MT9174 are multifunction devices
capable of providing high speed, full duplex digital
transmission at up to 160 kbit/s over a twisted wire
pair. They use adaptive echo-cancelling techniques
and transfer data in a format compatible to the ISDN
basic rate. Several modes of operation allow an easy
interface to digital telecommunication networks
including PCS wireless base stations, smart
telephone sets, workstations, data terminals and
computers. The device supports the 2B+D channel
format (two 64 kbit/s B-channels and one 16 kbit/s D-
channel) over two wires as recommended by the
CCITT. The line data is converted to and from the
ST-BUS format on the system side of the network to
allow for easy interfacing with other components
such as the S-interface device in an NT1
arrangement, or to digital PABX components.
Smart telephone sets with data and voice capability
can be easily implemented using the MT9173/74 as
a line interface. The device’s high bandwidth and
long loop length capability allows its use in a wide
variety of sets. This can be extended to provide full
data and voice capability to the private subscriber by
the installation of equipment in both the home and
central office or remote concentration equipment.
Within the subscriber equipment the MT9173/74
would terminate the line and encode/ decode the
data and voice for transmission while additional
electronics could provide interfaces for a standard
telephone set and any number of data ports
supporting standard data rates for such things as
computer communications and telemetry for remote
meter reading. Digital workstations with a high
degree of networking capability can be designed
using the DNIC for the line interface, offering up to
160 kbit/s data transmission over existing telephone
lines. The MT9173/74 could also be valuable within
existing computer networks for connecting a large
number of terminals to a computer or for
intercomputer links. With the DNIC, this can be
accomplished at up to 160 kbit/s at a very low cost
per line for terminal to computer links and in many
cases this bandwidth would be sufficient for
computer to computer links.
Figure 1 shows the block diagram of the MT9173/74.
The DNIC provides a bidirectional interface between
the DV (data/voice) port and a full duplex line
operating at 80 or 160 kbit/s over a single pair of
twisted wires. The DNIC has three serial ports. The
DV port (DSTi/Di, DSTo/Do), the CD (control/data)
port (CDSTi/CDi, CDSTo/CDo) and a line port (L
IN
,
L
OUT
). The data on the line is made up of information
from the DV and CD ports. The DNIC must combine
information received from both the DV and CD ports
MT9173/74
and put it onto the line. At the same time, the data
received from the line must be split into the various
channels and directed to the proper ports. The
usable data rates are 72 and 144 kbit/s as required
for the basic rate interface in ISDN. Full duplex
transmission is made possible through on board
adaptive echo cancellation.
The DNIC has various modes of operation which are
selected through the mode select pins MS0-2. The
two major modes of operation are the MODEM
(MOD) and DIGITAL NETWORK (DN) modes. MOD
mode is a transparent 80 or 160 kbit/s modem. In
DN mode the line carries the B and D channels
formatted for the ISDN at either 80 or 160 kbit/s. In
the DN mode the DV and CD ports are standard ST-
BUS and in MOD mode they are transparent serial
data streams at 80 or 160 kbit/s. Other modes
include: MASTER (MAS) or SLAVE (SLV) mode,
where the timebase and frame synchronization are
provided externally or are extracted from the line and
DUAL or SINGLE (SINGL) port modes, where both
the DV and CD ports are active or where the CD port
is inactive and all information is passed through the
DV port. For a detailed description of the modes see
“Operating Modes” section.
In DIGITAL NETWORK (DN) mode there are three
channels transferred by the DV and CD ports. They
are the B, C and D channels. The B1 and B2
channels each have a bandwidth of 64 kbit/s and are
used for carrying PCM encoded voice or data. These
channels are always transmitted and received
through the DV port (Figures 3, 4, 5, 6). The C-
channel, having a bandwidth of 64 kbit/s, provides a
means for the system to control the DNIC and for the
DNIC to pass status information back to the system.
The C-channel has a Housekeeping (HK) bit which is
the only bit of the C-channel transmitted and
received on the line. The 2B+D channel bits and the
HK bit are double-buffered. The D-channel can be
transmitted or received on the line with either an 8,
16 or 64 kbit/s bandwidth depending on the DNIC’s
mode of operation. Both the HK bit and the D-
channel can be used for end-to-end signalling or low
speed data transfer. In DUAL port mode the C and D
channels are accessed via the CD port (Figure 7)
while in SINGL port mode they are transferred
through the DV port (Figures 5, 6) along with the B1
and B2 channels.
9-141
MITEL [ MITEL NETWORKS CORPORATION ]
