ComNet New ProduCt release:
ComNet t-1/e-1 optical transceiver/
extender units
By Bruce M. Berman
ComNet is introducing our new product series FDXT1/E1 Point-to-Point Fiber Optic T-1/E-1 Transceiver Unit. These units are intended for the optical transmission of T-1 or E-1 data that is commonly used in numerous digital telephony applications.
What is T-1 or E-1?
A T-1 line refers to a specific type of copper or fiber optic telephone line that can carry significantly more data than traditional dial-up POTS (Plain Old Telephone Service) telephone lines. The T-carrier line, as it is sometimes called, was developed by AT&T Bell Labs in 1957, and implemented in the early 1960s to support long-haul pulse-code modulation (PCM) voice transmission in North America, South Korea, and Japan. Twisted copper telephone lines have been the standard for decades, transmitting voice and data via analog signals. The primary innovation of T-1 was to introduce “digitized” voice transmission over metallic or copper wire circuits, and to create a telephone network fully capable of digitally representing what was up until then, a fully analog telephone system.
Today, the T-1 or E-1 standard has in many cases been upgraded to fiber optic tranmission, but most T-1 and E-1 circuits still utilize twisted copper pairs.
While standard POTS telephone lines can transfer data at a rate of about 30,000 bits per second (30 kbps) using a dial-up modem, a T-1 line operates at a data rate of 1.544 mbps, and it can be used to transmit 24 simultaneous individual digitized voice channels. T-1 or E-1 are typically used to provide standard telephone service in a commercial building, or for data transfer on a telephone network, providing service up to 60 times faster than a traditional POTS dial-up telephone line.
E-1 is very similar in concept to T-1, except the data rate is 2.048 mbps. The E-1 system is incompatible with T-1 (although cross-compliant conversion equipment exists), and E-1 is widely used in most locations outside of North America, Japan, and Korea.
The basic unit of the T-carrier system is the DS0, which has a transmission rate of 64 kbs, and is commonly used for one digitized voice or data circuit. T-1 combines 24 separate DS0 voice-grade telephone circuits onto one single T-1 channel, using a technique known as channel bonding or channel aggregation. As such, T-1 is ideal for multiple-channel telephony or data transmission applications. T-1 is also referred to as DS-1.
Conventional analog CCTV video may be transmitted on a T-1 or E-1 circuit when a T-1 or E-1 codec is employed, and this has been a popular application in older, legacy-based systems.
As a practical example, business users with more than 8 telephone lines may save money by getting a dedicated T-1 line to loop to their place of business from the local phone company central office, to reduce telecom charges and provide high-speed Internet access at the same time. The business is charged for one T-1 line, rather than multiple separate POTS telephone lines. Pricing for the T-1 line will depend on the distance of the loop, or the wire line mileage between the telephone central office and the location of the user.
A T-1 or E-1 line is usually not cost-effective for individual or residential use. In this case, DSL or cable service and VOIP (Voice Over Internet Protocol) are better choices, and are widely deployed in current applications. Small businesses and government agencies, particularly those using a private branch exchange (PBX), benefit most from a dedicated T-1 line.
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Although T-1 and E-1 have largely been replaced by VOIP (Voice Over Internet Protocol) telephony, many legacy and new installation opportunities remain for these two protocols.
For those more technically inclined: When T-1 (or E-1) is transported over metallic outside plant cable, the signal travels over conditioned cable pairs known as a T-1 (or E-1) span. A copper T-1 span may have up to -130 volts of DC power superimposed on the associated four-wire cable pairs to provide operating power to T-1 repeaters. T-1 span copper-circuit repeaters are typically engineered for repeater-to-repeater distances of up to 6000 feet (1800 m) apart, depending on cable gauge, and at no more than 36 dB of loss before requiring another repeated span. As can be seen, the transmission distance of T-1 or E-1 signals through copper media is limited to a maximum distance of 6000 feet before a repeater regenerates and retransmits the signal, and this is where the long-distance advantages of fiber optic transmission (up to 43 miles or 69 km with the ComNet FDXT1/E1 equipment) of T-1/E-1 become highly desirable and cost-effective.
Indeed, many T-1 and E-1 copper transmission circuits are or have been replaced by equivalent optical transport systems, and this is where the ComNet FDXT1/E1 product line will find most of its potential applications.
The code which is used in T-1 is referred to as AMI, or Alternate Mark Inversion. This means that if a “1” or mark is coded as a positive voltage, the very next “1” must be a minus voltage, or the result will be a Bipolar Violation (BPV). Binary Eight Zero Substitution (or B8ZS) is utilized in the T-1 format as a means of digital encoding. B8ZS is essentially a patch to AMI, and is a method of overcoming a string of zeros by inserting a defined pattern (which will cause BPV’s) but retaining synchronization, and is especially useful when digital encoding is used.
Product Description & Overview:
ComNet FDXT1/E1 data transceivers are industrially-rated/environmentally hardened T-1 or E-1 fiber optic transceiver modems/extenders that also support AMI and B8ZS data signals over one multimode or single mode optical fiber. Unlike conventional T-1 or E-1 metallic transmission circuits which are limited to a maximum distance of 6000 feet (1800 m), optical transmission distances of up to 69 km (43 miles) are readily achievable without the need for T-1 repeater units.
A variant of the FDXT1/E1 family permits replacement of the popular IFS D1200-R3 series of rack-mountable T-1/E-1 transceiver units. Details on this will be found below in the “Product Features and Advantages” section of this NPR. The following products are offered within the FDXT1/E1 series:
Model Description
FDXT1/E1M1A Single-Fiber Multimode, A-End, ComFit Package
FDXT1/E1M1B Single-Fiber Multimode, B-End, ComFit Package
FDXT1/E1S1A Single-Fiber Single Mode, A-End, ComFit Package
FDXT1/E1M1B Single-Fiber Multimode, B-End, ComFit Package
FDXT1/E1M1A/R3 Single-Fiber Multimode, A-End, IFS D1210-R3 Replacement
FDXT1/E1M1B/R3 Single-Fiber Multimode, B-End, IFS D1210-R3 Replacement
FDXT1/E1S1A/R3 Single-Fiber Single Mode, A-End, IFS D1230-R3 Replacement
The FDXT1/E1 series includes a full complement of LED indicators for locally monitoring the operating status of the transceiver unit and the optical circuit it is connected to. These transceiver units are packaged within the ComFit surface-mount/rack-mount housing.
The digital modulation format employed in the FDXT1/E1 series eliminates the possibility of random or externally induced bit errors in the T-1 or E-1 data stream, ensuring the highest possible communications reliability of the link, a requirement which is mandatory in the common carrier/telephony industry..
Because of these features, the FDXT1/E1 is ideally suited to those applications where the user demands the highest level of reliability for their T-1/E-1 telephony requirements.
These units are available in numerous variants and with different options. Please review the FDXT1/E1-series data sheet for this information. The data sheet for this product is available on the ComNet website.
Product Features and Advantages:
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Low Cost & Simplicity of Installation: The FDXT1/E1 series is priced very competitively when compared to other similar single-channel, environmentally-hardened T-1 or E-1 modems of similar performance and feature set, as currently offered by IFS, Meridian, and TC Communications. It provides the most economical and reliable solution available for creating a single T-1 channel point-to-point network.•
No User Configuration or Programming Required: The FDXT1/E1 series are truly plug-and-play transceiver units, making them ideal for those users who may not be familiar with the intricacies of setting up and maintaining a T-1 or E-1 network. No user adjustments or settings are required in the course of installation or to establish the network.•
Supports Point-to-Point Optical Network Topologies•
Digital Modulation Yields Superior Performance: The ComNet FDXT1/E1 utilizes digital modulation for the mostbit error-free T-1/E-1 transmission possible, and unlike T-1/E-1 optical transceivers using the now-inferior and obsolete FM system, such as the IFS D1200-series, the quality of the T-1 or E-1 signal remains consistent and unaffected by the optical transmission distance.
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Optional Single-Mode and Multimode Variants Available: As with all ComNet single-mode optical transmissionproducts, the single-mode FDXT1/E1 utilizes high-stability laser diode optical emitters that are unconditionally stable over the full operating temperature range of the equipment. As the optical ports are fixed in this product, it will not accept SFPs. The optical ports are available for use with multimode or single mode fiber, and like all ComNet products with fixed optics, the model number ordered determines the optical port configuration.
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Only One Optical Fiber Required: IFS, Fiber Options, TC Communications, and several other current and nowout-of-business suppliers of this equipment have traditionally offered only 2-fiber T-1/E-1 transceivers. None of these 2-fiber products are currently available for single-fiber operation, and their use obviously requires that the integrator or installer provide the more costly two optical fibers at the time of installation. The ComNet FDXT1/E1 requires only one multimode or single-mode optical fiber for operation. When the single-fiber FDXT1/E1 is used as a replacement in an existing legacy two-fiber installation, the second fiber may be used as a spare, or for the installation of additional equipment. The single-fiber variants of the FDXT1/E1 series are also priced to be less costly than their competitive two-fiber counterparts.
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power from the power supply within the card cage. As the ComNet version of the IFS product employs digital transmission technology, it is not optically compatible with the D1200 stand-alone or D1200-R3 series units; as such, when the ComNet T-1/E-1 units are used as replacements for the IFS equipment, the transceiver units must be replaced as pairs to successfully establish the link.
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Industrial-Rated: The FDXT1/E1 series is designed and tested for operation in the most severe unconditionedindustrial or out-of-plant environments. The ambient operating temperature rating is -40 to +75 degrees C, and the equipment is fully compliant with and certified to the requirements of NEMA TS-1/TS-2 and the Caltrans Specification for Traffic Signal Control Equipment, for use in ITS-specific or other difficult roadside or out-of-plant environments. It is important to note that this industrial rating may also be used to our significant advantage when selling the FDXT1/E1 series to the common carrier/telephony market, or other in-plant markets where the environmental conditions may be less demanding. It can connote to the potential customer the high level of robustness and the attendant very high level of reliability these products provide when fielded in the traditionally more benign and less stressful telco central office or equipment room operating environments.
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T-1 or E-1 Loopback Test Capability is Included: Two DIP switches are provided for user-selection of the desired loopback test mode, so the modem and the optical fiber path may be checked for proper operation. These test modes are as follows:1.
Normal Operation.2.
Optical Loopback (Analog) Test: The receive fiber input is routed to the transmit fiber output, through the analog circuitry of the FDXT1/E1, for an almost-complete end-to-end test of the link.3.
Optical Loopback (Digital) Test: The receive fiber input is routed to the transmit fiber output, only through the digital circuitry of the FDXT1/E. This would be the next level down if the analog loopback fails.4.
Copper Circuit Loopback – This test mode routes whatever T-1 or E-1 data comes in on the copper receive connection, to the copper transmit connection, with no fiber involved.•
Voltage Transient/Surge Protected: Voltage transient protection on all power and signal input/output linesprovides unconditional protection from power surges and other voltage transient events.
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Small Size: Ideal for use in those installations where space is at a premium, the FDXT1/E1 series is packaged in the popular ComNet ComFit stand-alone/wall-mount or rack-mount configuration. Occupying only one rack-slot position, the FDXT1/E1 series may be installed in the C1, C2, or C3 Card Cages.•
Rugged Aluminum Housing: The aluminum housing used in the FDXT1/E1 series materially aids in the dissipationof heat from the transceiver, significantly increasing the long-term reliability of the equipment, and aids in the robustness of the product.
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DIN-Rail Mountable: The FDXT1/E1 may also be DIN-rail mounted when used with the ComNet model DINBKT1adaptor plate.
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LED Status Indicators: Rapidly determines the operating status of the T-1/E-1 modem and the optical link.Operating power, receive and transmit data activity, and modem loopback test status are displayed.
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ComNet Environmentally Friendly Product: The FDXT1/E1 series offers the least power consumption, for thelowest possible operating costs over the lifetime of the product, and meets or exceeds the standards and criteria associated with all of our environmentally friendly products.
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Certifications: CE, UL, and RoHS Compliant. Compliance with numerous other electrical, environmental, safetyand IEEE standards is provided.
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Designed and Manufactured in the U.S.AProduct Disadvantages:
The variant of the FDXT1/E1 which is the replacement for the IFS D1200-R3 series of rack-mountable T-1/E-1 transceiver units is not optically compatible with the IFS D1200 stand-alone or D1200-R3 units; as such, when the ComNet T-1 units are used as replacements for the IFS equipment, the transceiver units must be replaced as pairs.
Competition:
IFS: D1200 series
Meridian: 1100 series.
RLH Industries: Product Series 8806 and 8805. Note that RLH is a supplier primarily to the electrical utility and telecommunications/common-carrier markets.
Typical Applications:
Figure 1: Typical optical extension of a remotely-located PBX (Private Branch Exchange) unit to the PSTM (Public Switched Telephone Network).
Figure 2: Typical optical extension of a remotely-located CSU/DSU (Channel Service Unit/Data Service Unit) to a PBX.
Figure 3: Typical optical extension of a telephone service provider to a remotely located customer premise where T-1/E-1 telephony equipment, etc., exists.
Figure 4: Typical optical extension of a remotely-located CCTV camera and T-1 or E-1 video encoder, to a remotely-located CCTV video monitoring station.
FDXT1/E1 FDXT1/E1
Telephone Set
Public Switched Telephone Network MM or SM Fiber
(Up to 69km/43mi SM)
T1/E1 T1/E1
PBX PBX
FDXT1/E1 FDXT1/E1 Data Terminal Equipment
Public Switched Telephone Network
MM or SM Fiber (Up to 69km/43mi SM)
T1/E1 T1/E1
PBX CSU/DSU
FDXT1/E1 FDXT1/E1
MM or SM Fiber (Up to 69km/43mi SM)
T1/E1 T1/E1
Customer Premises Service
Provider
CCTV T1/E1 Video Encoder FDXT1/E1 FDXT1/E1 T1/E1 Video Decoder
MM or SM Fiber (Up to 69km/43mi SM)
T1/E1 T1/E1
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Applications:
In the Common Carrier/Telephony Market:
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Replacement of copper/metallic 4-wire T-1/DS-1 or E-1 transmission circuits in electrically noisy or hazardous environments, where optical transmission offers significant advantages•
Optical extension of copper/metallic T-1/DS-1 or E-1 transmission circuits beyond the normal 6000 foot (1800 m) distance limitation•
Telco central office T-1/E-1 switch connections•
Optical connection of telco central office-to-client T-1/DS-1 or E-1 circuits•
Optical extension of T-1/E-1 PBX telephony networksIn the ITS/transportation Market:
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Closed-loop traffic signal control networks•
T-1/DS-1 or E-1 multiplexer cross connects•
Optical extension of CCTV cameras for incident detection, video detection systems (VDS), IP-compatible variable message signs, wireless access points, and other legacy T-1/DS-1 or E-1 networks for ITS-specific roadside control, communications, and telemetry equipment•
Roadside CCTV for surveillance and incident detection, when the FDXT1/E1 is used in conjunction with a T-1/E-1 video codecIn the Electrical Utilities/Transmission and Distribution Market:
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Replacement of copper/metallic 4-wire T-1/DS-1 or E-1 transmission circuits in electrically noisy or hazardous environments, where optical transmission offers significant advantages, including electrical isolation in high-voltage substations and switchyard.•
Optical extension of copper/metallic T-1/DS-1 or E-1 transmission circuits beyond the normal 6000 foot (1800 m) distance limitation•
Protective relaying, metering, and control applications In the Industrial Security Market:ComNet offers an extensive line of environmentally hardened fiber optic and copper-based video and data transmission equipment as well as a line of Ethernet networking equipment that is uniquely designed to meet the needs of the Industrial Security, Intelligent Transportation, and industrial control markets.
Bruce Berman is responsible for directing and promoting the application of ComNet products in markets that can benefit from their use. In many cases he educates System Designers and customers on all levels about the benefits that ComNet products and technology bring to their projects.
