FMT-150 Introduction
The Fiber Multiplex Terminal (FMT) system was designed as a small to medium capacity optical transmission media. It incorporates the newest means of system maintenance and operational capabilities. (Refer to Figure 1)
FMT-150B/C/D System
The FMT-150B/C/D system is actually a combination of successful Northern Telecom products developed in response to the ever-changing requirements of the telecommunications industry. The product architecture supports such applications as subscriber loops, inter-office links, hub configurations, drop/insert configurations, and features an overhead transmission capacity for ease of operation and maintenance.
The FMT-150B/C/D is capable of combining mixtures of DS-1, DS-1C, and DS-2 data streams into an optical DS-3 output, while providing sophisticated surveillance and protection basis.
The FMT-150B/C/D fiber optic transmission system combines DM-13 multiplexers and 150 Mbps Fiber Transports (FT) in compact transmission capacity for ease of operation and maintenance on a network oriented basis.
The FMT-150 family consists of three products: (Refer to Figure 2)
Although the FMT-150B, FMT-150C, and FMT-150D are three different shelves, they are all composed of two basic building blocks:
Each FMT-150B/C/D system contains the following items:
FMT-150B Shelf:
FMT-150C Shelf:
FMT-150D Shelf:
Designed for Growth
All aspects of the FMT-150 system are designed to allow for easy growth as the user's circuit requirements change. For example, a customer could install a FMT-150 system carrying only a few DS-1 signals, with the rest of the interface board wired out to unused cross-connect panels. Later, the customer could add in more circuit packs (i.e., DS-1 circuits or, depending on need, add DS-1C or DS-2 circuits instead). Note that the configuration of the cable interface board is determined by the type of circuit being installed and must be wired accordingly.
Signal Flow
Transmission Capacity
The groups of a DM-13 multiplexer may consist of any combination of four DS-1, two DS-1C, or one DS-2 line tributary that result in an aggregate bit rate of 44.736 Mbps (the DS-3 bit rate). This is then handled by one 150 Mbps fiber interface module. Maximum capacities are as follows: (Refer to Figure 3)
A FMT-150C shelf can multiplex twice the maximum of an FMT-150B thus producing two DS-3 signals.
A FMT-150B used in conjunction with a FMT-150C can multiplex a total of three DS-3 signals.
Examples of other arrangements meeting the maximum capacity of the DM-13 are as follows:
Signaling
The FMT-150B & C architecture distinguishes between types of signaling:
In this terminology, optical signaling refers to the 149.76 Mbps optical signal rate and the STX refers to the Northern Telecom defined electrical signal containing the DS-3 payload information and overhead bit structure within a 49.92 Mbps signal rate. High-speed refers to the DS-3 rate (44.736 Mbps) and is limited to the DM-13 groups and tributaries at the DS-1, DS-1C or DS-2 rate (1.544 Mbps, 3.152 Mbps and 6.132 Mbps respectively).
Multiplexing
Multiplexing between low-speed signals (DS-1, DS-1C, and DS-2) and the high-speed signal is accomplished in two stages. In the first stage of multiplexing, the low-speed signals are synchronized into seven groups at the DS-2 signal rate. This is performed by DS-1, DS-1C, and DS-2 Tx/Rx modules. Also, this stage converts the signals from bipolar to unipolar format. The second stage of multiplexing organizes the seven groups into a single DS-3 digital signal, which is again bipolar. Each of the seven groups at the DS-2 rate may be composed of one DS-2, two DS-1C, or four DS-1 signals. Lastly, the electrical DS-3 signal is converted into an optical signal for transmission over optical fibers.
150 Mbps Fiber Transport
The 150 Mbps interface can receive up to 3 incoming DS-3 signals from the DM-13 multiplexers (or other DS-3 sources). In the transmit direction, each DS-3 signal is translated to a STX signal (49.92 Mbps). The overhead bits in the STX signal carry alarm, maintenance, and service channel information for the network. The signal processing, (and that for the opposite direction) is performed within the DS-3 translator module. There is one working translator and one standby translator per DS-3 signal. The three 49.92 Mbps signals are multiplexed together within the 150 Mbps optical Tx/Rx module to generate a single electrical signal with a line rate of 149.76 Mbps. The electrical signal is then converted into an optical equivalent for transmission over fiber optical cables. In the receive direction, an incoming 149.76 Mbps optical signal is converted to its electrical form and then demultiplexed to 3 STX signals. The signals are then routed to the appropriate translator module where each 49.92 Mbps signal is split into a DS-3 signal (44.736 Mbps) and corresponding overhead. The overhead containing the network information is fed to the Service Channel Unit (SCU) and Maintenance Control Unit (MCU) for processing. (Refer to Figure 4)
Configuration
Maintenance Control Unit
Each FMT-150 node is equipped with one Maintenance Control Unit (MCU). The MCU provides monitoring and performance control for the FMT-150 node. Monitoring and control is provided for the 150 Mbps fiber interface, up to three associated DM-13 multiplexers, one (optional) Service Channel Unit (for voice data) and all associated power supply units. The MCU gathers and process alarm information for transmission throughout the network. This gathered information is carried in the overhead of the 49.92 Mbps signal. Control commands sent to the node from the CRT interface are also carried in the 49.92 Mbps overhead and are processed by the MCU at the appropriate node.
Note: A "node" is defined as any place in the FMT-150 network where a MCU is located. The maximum number of nodes allowed in a FMT-150 network is 16.
Service Channel Unit
The FMT-150 B & D shelves can be fitted with a Service Channel Unit (SCU) which provides voice/data communication through the overhead. Two voice channels per DS-3 signal are provided: one Local Order wire channel, and one Express Order wire channel. Local Order wire accesses all sites common to a DS-3 signal. The Express Order wire accesses only Terminal sites common to a DS-3 signal. The Express and Local Order wires are accessible via a jack at the front panel of the shelf.
Each site in a FMT-150 network may be individually addressed using DIP switches on the SCU. Sites are accessed by dialing a 4-digit number from a handset/headset.
The SCU also provides customer input and output points. These are used to retrieve status and alarm information not only from the FMT-150, but also from any other external equipment desired. The NT7H75BA version of the SCU support 12 customer inputs and 4 customer outputs. The NT7H75BB version supports 8 inputs and 16 outputs.
Power Supply Unit
Each FMT-150 shelf is equipped with four power supply units which convert either -48V or -24V to +5/-5 Volts which is used for the entire shelf. Power supply units are monitored by the MCU for proper operation. A failure with a power supply unit is displayed on the CRT interface unit for quick and simple detection.
CRT Interface
The MCU supports control and monitoring of an FMT-150 network through a CRT interface. The CRT allows the user to display the network status, and any alarm that exist. Control over remote sites (e.g., force switch, loopback, etc.) can be implemented through commands entered at the CRT terminal. The software accepts commands entered by the user at the keyboard and responds by displaying information concerning alarms, status, control, and maintenance information on the CRT screen. The interface may operate at 300, 1200, 2400, or 9600 baud rates.
Protection
The FMT-150B/C/D provides low-level and high-level automatic switching. Low-level includes low-speed (DS-1, DS-1C, and/or DS-2 rate) automatic protection switching, while the high-level includes both high-speed (DS-3 rate), and translator (STX rate) automatic protection switching. The DS-1, DS-1C, DS-2, DS-3, and STX protection switches all operate independently.
DM-13 Multiplexer:
DS-1 Tx/Rx Module : 1:N (where N = 1-7) DS-1C Tx/Rx Module : 1:N (where N = 1-7) DS-2 Tx/Rx Module : 1:N (where N = 1-7) DS-3 Tx/Rx Module : 1 + 1
150 Mbps Fiber Transport:
DS-3 Translator : 1 + 1 Optical Tx/Rx Unit : 1 + 1
Common Equipment:
Power Supply Unit : 1 + 1
Modes of Operation
The DM-13 can be configured for either: (Refer to Figure 5)
The essential differences between the two modes of operation are in the low-speed stage of multiplexing. In Terminal mode, all DS-2 groups are demultiplexed to their composite low-speed signals. In Drop/Insert operation the low-speed signals do not have to be demultiplexed past the DS-2 line.
Terminal operation is generally required at sites where the DS-3 signals are terminated. In this case, the equipment is configured for bi-directional signal processing. Drop/Insert is required at intermediate sites where DS-3 signals must be accessed for information (either in whole or at lower bit rates). In Drop/Insert configurations, typically twice as much transmission equipment is required due to the uni-directional configuration.
In Terminal operation for the DM-13, all low-speed groups are demultiplexed from a DS-3 to their respective low-speed bit rates. The low-speed signals are the accessed for further processing. In Drop/Insert configurations, some of the low-speed tributaries within a DS-3 are not required at the location and must be "looped-through" the site. This is accomplished by using a special "loop-thru" module which is available for this process. This eliminates hard patch requirements. The tributaries are looped through at the 6.312 Mbps unipolar line rate. Looped through groups have their signals looped directly back into the multiplexer process. Typically, DM-13 Terminal configurations require one bi-directional DM-13, while Drop/Insert locations require one DM-13 per direction. (Refer to Figure 6)
Site Configurations
The FMT-150B/C/D shelves can be arranged together to form several types of site configurations:
Terminal Site
A Terminal site combines up to three DM-13 multiplexers with one 150 Mbps fiber interface. This could be formed with one FMT-150B shelf and one FMT-150C shelf, as shown in Figure 7.
Note: The FMT-150B has two independant signal processing units, the multiplexer and fiber interface units. Therefore, the FMT-150B shelf may be fed any mix of DS-3s from other external sources (i.e., radio products, existing DMT-300 sources, etc.).
Drop/Insert Site
A Drop/Insert site combines two 150 Mbps fiber interfaces with various combinations of DM-13 multiplexers. Each 150 Mbps interface (and any assorted multiplexer equipment) processes the signals for one direction. An example using two DM-13s can be derived from two FMT-150B shelves as shown in Figure 8. Note that this could also be done with one FMT-150C shelf and one FMT-150D shelf since the shelves in either configuration are functionally identical.
Repeater Site
A Repeater site combines two 150 Mbps fiber interfaces that serve to regenerate the optical signal for further transmission. Such a site could be formed from a single FMT-150D shelf, as shown in Figure 9.
Hub Site
A Hub site combines optical interfaces that enable us to route the DS-3 signals in different directions. This is done without the use of extra multiplexers. Therefore, the signal does not have to be broken down to the DS-1 level, as shown in Figure 10.