Learn about the Motorist Information Sign (MIS) program and how to get your business included on a blue service information sign.
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Motorist Information Signs (MIS) are installed along state highways to alert travelers to services available at or near a freeway interchange or a highway intersection. These signs use a blue or brown background with business logo signs attached, helping to direct travelers to your fuel, food, lodging, camping, recreation activity, tourist activity, or 24-hour pharmacy business.
The MIS program is a great way to connect travelers to your motorist service business. Our state highways carry hundreds of thousands of people every day, and they drive past many of these signs. We install the main signs - you provide the business logo signs.
There are limits on how many business logos may be installed for a particular service and highway type. Businesses are selected on a first come, first served basis. Additional businesses are placed on a waiting list and contacted in order as space becomes available. Businesses with installed logos that change ownership can remain if the business name does not change and it still meets eligibility requirements - otherwise, it is considered a new business and must go through the application process again. Participating business owners who are selling their business are requested to contact their MIS program representative.
Logo signs are limited to one sign per direction per any activity (fuel, food, lodging, camping, recreation, tourist activity, or 24-hour pharmacy) for any business, and located at the interchange or intersection closest to the advertised business.
Motorist Information Signs are installed in advance of freeway off-ramps and highway intersections. The main sign (back panel) is installed by us. Participating businesses provide the logo signs. Typically, a maximum of six logo signs can be installed on one back panel sign, and a total of four back panels can be installed at an interchange or intersection, depending on available space. Typically, each back panel includes one or more different service types - it is not common to have more than one back panel with the same service type.
If there are no back panels at an interchange or intersection, a new one may be installed if it will not be in visual conflict with other signing in the area. MIS back panels must be 800 feet from any green guide or directional highway signs. Back panels on freeways and expressways may only be installed where a motorist can conveniently exit and then re-enter the highway and continue in the same direction, and may not be installed at interchanges leading from one freeway or expressway to another.
To be eligible to participate in the MIS program, your business must be open to the public, including minors, and must conform to all applicable federal and state laws regarding non-discrimination on grounds of race, religion, color, age, sex, or national origin when providing service to the public.
Businesses shall be located within the following distances from the highway, in any direction, depending on the type of highway:
If no services are available, or choose to participate in the MIS program, within these distance limits, we are able to extend these distances in three mile increments, up to a maximum of 15 miles in most cases, or 20 miles in a distressed area.
If your business is located on the highway, and the business or on-premise sign is visible at least 300 feet prior to an intersection or business entrance, your business does not qualify for the MIS program.
Your business must receive its principle source of revenue from the sale of goods, products, or services that fall within the applicable service category below. Each category has its own additional criteria which must be met.
Food facilities located within a fueling facility can qualify for food signing if all of the food activity criteria below are met.
Camping is only applicable for activities available from interstate highways.
Recreational activities are only applicable for activities available from non-interstate highways. Recreational activities consist of sports and activities of interest to family groups and the public, in which people generally participate for the purposes of physical exercise, collective amusement, or the enjoyment of nature.
Tourist oriented businesses shall be one of the following:
Tourist activities must be open to the motoring public without appointment, at least six hours per day, five days a week, including Saturday and/or Sunday.
RV Symbols are an add-on to your business logo, and are not a standalone category. To be eligible to include an RV symbol on your logo sign, your business must provide the following amenities and accommodations for recreational and other large vehicles:
Seasonal businesses may participate in the MIS program. Seasonal businesses still pay the full annual fee for having their logo on the sign. It is preferred that seasonal businesses include the months of operation as part of the logo sign. Otherwise, the sign must be covered or removed during the time the business is not in operation, which incurs additional fees.
Participation in the MIS program is paid for through an annual fee. There are three fee zone types, which are broken down by type of highway and number of average daily vehicles.
Signs are installed in both directions approaching an interchange or intersection, and two logo signs must be provided. If signing can only be installed in one direction, only one logo sign needs to be provided and a reduced annual fee is charged. Fees for each zone are as follows:
If a logo sign is damaged or in need of replacement, or the business requests to have the logo sign replaced, there is a $115 fee for us to remove and replace the logo sign. The business is required to provide the replacement logo sign.
The MIS program representative that you work with will let you know if there are any other applicable special fees, such as seasonal business sign management.
Business logo signs are provided by the business. It is your responsibility to design the sign, and then have it manufactured and delivered to us for installation.
Choosing a sign manufacturer is up to you, but our MIS program representatives may be able to provide a list of sign manufacturers upon request. There are regulations regarding the size of the sign panel and the materials used. These requirements will be included in the information you will receive after your application is approved and all required fees are paid. It is highly recommended that customers ask for a seven year warranty against deterioration of the sign. Sign manufacturers may also help you to design your logo sign to be most effective as part of the service sign.
We do not keep current costs for business logo signs, as they vary over time and with different manufacturers. Historically, average costs have been in the range of:
Only your manufacturer can provide current pricing.
Thousands of motorists will see your sign, but they may be driving by it at 60 MPH or faster. Keeping your logo simple makes it easier to register with drivers. Here are some tips for effective logo signs.
The following items are not permitted on logo signs:
Your logo sign must be approved by one of our MIS program representatives before it is installed. It is highly recommended that this approval be received before being manufactured.
Applications are quick and easy. Create and submit your application online.
If you have any questions or are not certain if your business qualifies, please contact the MIS program representative for your location.
Fatma Madkour
[email protected]
2714 N Mayfair St
Spokane, WA 99207-2050
(509) 342-9762
Ryan Ashley
[email protected]
2830 Euclid Ave
Wenatchee, WA 98801-5916
(509) 667-2826
*Note: In King County, for Interstate 90 east of Exit #32 (436th Ave SE Interchange), contact South Central Region.
Rebecca Kaska
[email protected]
Mailing Address
PO Box 330310
Seattle, WA 98133-9710
Physical Address
15700 Dayton Ave N
Shoreline, WA 98133
(206) 440-4409
(206) 440-4804 (Fax)
Heather Britton
[email protected]
Mailing Address
PO Box 47440
Olympia, WA 98504-7440
Physical Address
5720 Capitol Blvd SE
Tumwater, WA 98501
(360) 357-2753
(360) 357-2793 (Fax)
Brad Cuillier
[email protected]
2809 Rudkin Rd
Union Gap, WA 98903-1648
(509) 577-1985
(509) 577-1740 (Fax)
Gary Weiss
[email protected]
11018 NE 51st Circle
Vancouver, WA 98682-6686
(360) 905-2257
(360) 905-2066 (Fax)
Trevor McCain
[email protected]
(360) 705-7282
PO Box 47300
Olympia, WA 98504-7300
Should you disagree with a permit decision that has been made, you have the right to have the Washington State Traffic Engineer hear the issue and recommend a final order. To make such a request, submit the request in writing to:
WSDOT
Attn: State Traffic Engineer
PO Box 47344
Olympia, WA 98504-7344
Transmitter, receiver, transmission medium – these are the basic elements that make up a communication system. Every human being is equipped with a basic communication system. The mouth (and vocal cords) is the transmitter, ears are the receivers, and air is the transmission medium over which sound travels between mouth and ear. The transmitter and receiver elements of a data modem (such as the type used in a traffic signal system controller box) may not be readily visible. However, look at a schematic of its components, and you will see elements labeled as "XMTR" and "RCVR". The modem's transmission medium is typically copper wire, fiber, or radio.
Almost all communications networks have as their basis the same set of Telephony (Telepho–Ny) standards and practices. "Ma Bell" (the Bell Telephone System and American Telephone & Telegraph, and others) spent years and billions of dollars creating, perfecting and maintaining a telecommunications network dedicated to providing the most reliable voice communication service in the world. All other communication technology and process evolved based on that communications network. Engineers and scientists involved in the development of new communication technologies and processes had to make certain that their "product" could be used within the existing telephone networks. And, the telephone company required backward compatibility. Telephones manufactured in 1950 still work in today's network. Modems manufactured in 1980 still work in the current system.
As you read through this chapter, and the rest of the handbook, please keep in mind that telecommunication standards, practices, and protocols were developed for the communication industry. All of these systems must be adapted for use in a traffic signal or freeway management system.
Today, in North America, Mexico, most of Europe and the Pacific Rim, voice services are in fact sent as digital signals and converted to analog just before leaving (and arriving at) the serving central office, at the end-user points. The reader might ask: "If voice is converted to digital isn't that the same as data?" The answer is no – "digital transmission" does not automatically infer data communications compatibility. Analog transmission systems can, and do, carry data. In telecommunications, digital and analog are distinct forms of communication transmission. This chapter provides information about the basics of telecommunications – the transmission media and transmission systems, as well as an explanation of the differences between analog and digital transmission. Transmission media are those elements that provide communication systems with a path on which to travel. Transmission systems are those elements (hardware and software) that provide management of the communication process and the use of the transmission path.
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The telecommunications world would be very simple if the distinction between transmission media and systems (protocols) were easily defined. Often, a specific transmission system will only work within a specific medium. Spread Spectrum Radio is one example. Radio (RF) is the transmission medium, and spread spectrum is the transmission system (protocol). Although it is possible to create a spread spectrum communications signal over wireline, the process is not typically used because there are other more efficient methods of transmission signaling. Therefore, spread spectrum transmission signaling is almost always associated with RF. There is always a point at which the Spread Spectrum Radio system must interface with another transmission medium, and/or system. This is accomplished by converting from RF to a wireline signaling protocol. The telecommunications process can be viewed as an excellent example of multi-modalism.
The chapter is divided into sections that cover
Sub-topics in the sections look at:
Transmission media are the highways and arteries that provide a path for telecommunications devices. There is a general tendency to say that one transmission medium is better than another. In fact, each transmission medium has its place in the design of any communication system. Each has characteristics which will make it the ideal medium to use based on a particular set of circumstances. It is important to recognize the advantages of each and develop a system accordingly.
Transmission efficiency is generally viewed as the amount of signal degradation created by the use of a particular transmission medium. The transmission medium presents a "barrier" to the communication signal. The "barrier" can be measured by many different factors. However, one common question is asked about all communication media. How far will the communication signal energy travel before it becomes too weak (or distorted) to be considered usable? There is equipment available to extend the distance for transmitting a signal, but that adds to the overall cost and complexity of deployment.
Ease of installation of the communication medium is relatively simple to define. Generally, all communication media require care when being installed. The installation should be accomplished by trained and knowledgeable technicians and managers. For purposes of this discussion, consider the relative degree of difficulty for the placement of the transmission medium. Cables (fiber or copper) require a supporting infrastructure, as does radio or infrared. Consider the following:
If you are planning to use fiber optic (or copper cable) and the system plan calls for crossing the Delaware River, there will be significant installation (construction) challenges. The construction may require a bore under the river, or finding a suitable bridge. Either of these methods may add significantly to your budget. Wireless might seem like a good option. It eliminates the need to find a suitable crossing location for your cable. However, you will need to place the antenna at sufficient height to clear trees buildings and other objects, and account for terrain differences on both sides of the river. Local residents of the nearby Yacht Club condominiums may complain about the radio tower spoiling their view of the sunset. Don't forget to add in the cost of hiring a graphic artist to create a drawing that shows how lovely the rays of the setting sun are when reflected off the radio tower.
Some products may be more readily available than others. For example, the most common type of fiber cable available is outside plant with armor shielding, 96 strands of single mode fiber arrayed in loose buffer tubes, on 15,000 foot reels. Make certain that you allow enough time for product to be manufactured, especially if a special cable or hardware configuration is required. Availability of product due to manufacturing delays will impact on overall project schedule and may impact on overall project costs.
Cables that contain combinations of different types of fiber strands such as single mode and multimode fibers, or mixtures of copper and fiber, or odd (different from standard put-ups) numbers of fiber strands will require more time to produce and could add several months to the delivery cycle.
Fiber, copper, radio, infrared all have different transmission characteristics. Fiber is considered to have the best overall characteristics for transmission efficiency. That is, the effective loss of signal strength over distance. Cable is rated by the manufacturer for signal loss. Signal loss factors are stated in terms of dB per 1000 meters. Typical single mode fiber may have a signal attenuation factor of between 0.25 dB/km and 0.5 dB/km. The cable manufacturer will provide a specification description for each product they offer. In theory, you can send a signal further on fiber than via most other transmission media.
However, consider that radio signals at very low frequencies (below 500 kilohertz) can travel for thousands of miles. This type of radio signal can be used to carry data, but very impractical for use in traffic signal and freeway management systems. VLF radio signals are only capable of efficiently carrying data at very low bit rates. This type of system was used by the Associated Press organization to transmit news articles between Europe and North America, and is also used by the Military for very long distance data communications.
Maintenance and operational costs are two other factors that should be considered when comparing transmission media for any given application. Fiber optic cable can be installed in conduit six feet below grade, and never touched for decades. Maintenance of the fiber cable is minimal. Microwave systems may be constructed in less time and at a lower cost than fiber cable placed in conduit, but the tower sites require significantly more maintenance, including re-painting the tower, and annual inspections for rust.
In summary, take all of the attributes of the potential media that could be used for a specific application and determine which will provide the most "bang for the buck". This does not always mean most bandwidth, highest transmission speed, easiest to install, or lowest cost – all factors that may influence your choice of transmission media. The best media are the ones that will support as many of the system requirements as possible and help to assure satisfaction with overall performance.
We begin with basic information about the most common types of transmission media used today:
Many engineers will argue that one transmission medium is the best, or better than some of the others. The reader should keep in mind that each medium has advantages and disadvantages. Which medium is best depends upon the purpose of the communications system and the desired end results. In fact, most systems are a hybrid. That is, two or more media are combined to effect the most efficient communication network infrastructure. There are many traffic signal systems that combine a twisted copper pair infrastructure with wireless links to serve part of the system. The decision to create this type of system may have been based on economics, but that is certainly one of the reasons to choose one medium over another, or to combine the use of several.
The electrical properties of copper wire create resistance and interference. The further communication signals travel the more they are weakened by the electrical properties associated with the copper cable. Electrical, resistance within the copper medium slows down the signal or flow of current. The electrical properties of copper wire are the key factors that limit communication transmission speed, and distance. However, it was those same properties together with cost, ease of manufacture, ability to be drawn into very thin strands, and others that made copper a logical choice for its selection as a communication transmission medium, and a conductor of electricity. Aluminum and gold are also used for communication purposes, but gold (the most efficient) is too expensive to use for this purpose and aluminum is not an efficient conductor for communication purposes.
There are two primary types of cables containing copper wire used for communication:
Communication signals sent over copper wire are primarily direct electrical current (DC) which is modulated to represent a frequency. Any other electrical current near the communication wire (including other communication signals) can introduce interference and noise. Multiple communication wires within a cable bundle can induce interfering electro-magnetic currents, or "cross-talk". This happens when one signal within the cable is so strong that it introduces a magnetic field into an adjacent wire, or communication pair. Energy sources such as power transmission lines, or fluorescent lighting fixtures can cause electromagnetic interference. This interference can be minimized by twisting a pair of wires around a common axis, or by the use of metallic shielding, or both. The twisting effectively creates a magnetic shield that helps to minimize "crosstalk".
Twisted pair is the ordinary copper wire that provides basic telephone services to the home and many businesses. In fact, it is referred to as "Plain Old Telephone Service" (POTS). The twisted pair is composed of two insulated copper wires twisted around one another. The twisting is done to prevent opposing electrical currents traveling along the individual wires from interfering with each other.
Twisted copper pair, is what Alexander Bell used to make the first telephone system work and is generally the most common transmission medium used today. A broad generalization is that twisted copper pair is in fact the basis for all telecommunication technology and services today. Ethernet – originally developed to work over coaxial cable – is now a standard based on twisted pair. By comparison, a basic voice telephone conversation uses one (1) twisted pair, where as an Ethernet session uses at least two (2) twisted pair (more about Ethernet later in this chapter).
Each connection on twisted pair requires both wires. Since some telephone sets or desktop locations require multiple connections, twisted pair is sometimes installed in two or more pairs, all within a single cable. For some business locations, twisted pair is enclosed in a shield that functions as a ground. This is known as shielded twisted pair (STP). Ordinary wire to the home is unshielded twisted pair (UTP). Twisted pair is now frequently installed with two pairs to the home, with the extra pair making it possible to add another line – perhaps for modem use.
Twisted pair comes with each pair uniquely color coded when it is packaged in multiple pairs. Different uses such as analog, digital, and Ethernet require different pair multiples. There is an EIA/TIA standard for color coding of wires, wire pairs, and wire bundles. The color coding allows technicians to install system wiring in a standard manner. A basic single telephone line in a home will use the red and green wire. If a second phone line is provided, it will use the yellow and black wire.
The most common cause of telecommunication system problems is incorrect wiring. This wiring protocol is for standard telephone set jack connections. Data systems use different arrangements and color codes. The most common is the EIA/TIA standard. Please note that NEMA and ICEA have color codes for electrical wire. Do not confuse these with telecommunication wire color coding standards.
Twisted pair is categorized by the number of twists per meter. A greater number of twists provides more protection against crosstalk, and other forms of interference and results in a better quality of transmission. For data transmission, better quality equates to fewer transmission errors. Later in this chapter, we'll look at the effects of transmission errors as they impact on throughput and delay times.
There are two types of twisted pair cables used for most in-building situations today – Category 3 UTP (CAT 3) and Category 5 UTP (CAT 5). However, as of the writing of this handbook, all new and replacement installations use CAT 5. These cables have been developed based on a set of standards issued by the EIA/TIA (Electronic Industry Association/Telecommunications Industry Association). CAT 3 is used primarily for telephone cabling and 10Base-T installations, while CAT 5 is used to support 10/100Base-T installations. CAT 5 wiring can also be used for telephone systems. Therefore, most new installations use CAT 5 instead of CAT 3. The CAT 5 cable is pulled to a cubicle or office and connected to a universal wall plate that allows for installation of data and voice communication systems. Category 5E (CAT 5E) has been developed to accommodate GigE installations. CAT 5E is manufactured and tested under stricter guidelines than CAT 3 or CAT 5. Two new standards – CAT 6 and CAT 7 – have been adopted to meet criteria for 10GigE (and higher) transmission speeds.
Category Maximum Data Rate Usual Application CAT 1 Less than 1 Mbps Analog Voice (POTS), Basic Rate ISDN, Doorbell wiring CAT 2 4 Mbps Primarily used for Token Ring Networks CAT 3 16 Mbps Voice and Data, and 10Base-T Ethernet. Basic telephone service CAT 4 20 Mbps Used for 16 Mbps Token Ring CAT 5 100 Mbps up to 1 Gbps 10Base-T, 100Base-T (fast Ethernet), GigE, FDDI, 155 Mbps ATM CAT 5E 100 Mbps FDDI, ATM CAT 6 Greater than 100 Mbps Broadband Applications CAT 7 Emerging Standard GigE plusCoaxial cable is a primary type of copper cable used by cable TV companies for signal distribution between the community antenna and user homes and businesses. It was once the primary medium for Ethernet and other types of local area networks. With the development of standards for Ethernet over twisted-pair, new installations of coaxial cable for this purpose have all but disappeared.
Coaxial cable is called "coaxial" because it includes one physical channel (the copper core) that carries the signal surrounded (after a layer of insulation) by another concentric physical channel (a metallic foil or braid), and an outer cover or sheath, all running along the same axis. The outer channel serves as a shield (or ground). Many of these cables or pairs of coaxial tubes can be placed in a single conduit and, with repeaters, can carry information for a great distance. In fact, this type of cable was used for high bandwidth and video service by the telephone companies prior to the introduction of fiber in the 1980's.
There are several variations. Triaxial (Triax) is a form of cable that uses a single center conductor with two shields. This composition affords a greater transmission distance with less loss due to interference from outside electrical signals. Twinaxial (Twinax) is two coaxial systems packaged within a single cable.
Coaxial cable was invented in 1929 and first used commercially in 1941. AT&T established its first cross-continental coaxial transmission system in 1940. Depending on the carrier technology used and other factors, twisted pair copper wire and optical fiber are alternatives to coaxial cable.
Coaxial cable was originally used by some traffic departments to provide communications between field controllers and the central controller in an automated traffic signal system. It was also the medium of choice for early implementation of video incident management systems used in ITS. However, with the introduction of fiber optics, the use of coaxial cable has all but been abandoned for this purpose.
Coaxial cable is still used for connecting CCTV cameras to monitors and video switchers. As the cost of using fiber optics has begun to drop, camera manufacturers are installing fiber optic transceivers in the camera. This is especially useful for preventing interference from electrical systems, or creating a secure video transmission network.
Fiber optic (or "optical fiber") refers to the medium and the technology associated with the transmission of information as light impulses along a strand of glass. A fiber optic strand carries much more information than conventional copper wire and is far less subject to electromagnetic interference (EMI). Almost all telephone long-distance (cross country) lines are now fiber optic.
Transmission over fiber optic strands requires repeating (or regeneration) at varying intervals. The spacing between these intervals is greater (potentially more than 100 km, or 50 miles) than copper based systems. By comparison, a high speed electrical signal such as a T-1 signal carried over twisted-pair must be repeated every 1.8 kilometers or 6000 feet.
Fiber optic cable loss is calculated in dB per kilometer (dB/KM), and copper cables are rated in dB per meter (dB/M). Note: The Appendix of this handbook includes an explanation of how to calculate a fiber optic loss budget.
The fiber optic strand is constructed (see graphic) in several layers. The core is the actual glass, or fiber, conductor. This is covered with a refractive coating – called cladding – that causes the light to travel in a controlled path along the entire length of the glass core. The next layer is a protective covering that keeps the core and coating from sustaining damage. It also prevents light from escaping the assembly, and has a color coding for identification purposes. The core, coating and covering are collectively referred to as a "strand". Fiber strand sizes are always referred to in terms of the diameter of the core.
Fiber strands are typically bundled within a cable. The strands can be placed in a "tight" or "loose" buffer tube array. The loose buffer tube array is the most commonly deployed for outside plant applications. Tight buffered cable is generally used within a building for riser and horizontal cable. Tight buffer cable is also used for an "indoor/outdoor" application. This cable is constructed with a weather/moisture resistant cable sheath, and is generally used to get from a splice box located within several hundred feet of a building utility entrance, and must be run several hundred feet within a building to the main fiber distribution point. If the main fiber distribution point is less than 100 feet from the building entrance, there may be no advantage to using the indoor/outdoor cable.
Fiber strands are placed in a large (relatively) diameter tube and allowed to "float" with considerable movement. As the fiber cable is pulled into place (in conduit, directly buried, or placed on a pole) the strands are not subjected to the forces of the pulling tension. The strands therefore sustain minimal damage or distortion from stretching.
Fiber cables are (as are all communications cables) manufactured based on their intended use. Each cable will have a standard set of markings indicating its primary use, the name of the manufacturer a National Electrical Code rating and a UL approval code, the number of fibers contained within the cable, the outside diameter of the cable, and the manufacturer's product nomenclature. All of these items should be checked when the cable is delivered to a storage area and then at the job-site before the cable is installed. Generally, fiber cables fall into one of the following classifications:
Fiber Cable Classification General Purpose Inside Plant Device to device wiring Horizontal, or Intra-office Run on a single floor and between rooms Riser or intra-building Run between floors in a building, usually in an elevator shaft or conduit Plenum Specially coated cable to meet fire codes for cable run within an air space. Aerial Cable Usually strung on Utility poles and designed to be either self-supporting or lashed to a supporting cable. Cables are usually constructed with materials that are resistant to aging from exposure to sunlight. Direct-burial Cables that are designed to be directly buried in a trench. Duct Cable Cables that are designed to be installed in a conduit Submarine Cable Cables that are designed to be submerged. Inside-Outside Cables that are used to transition between outside plant and inside plant.Some cables are manufactured with a metallic armored sheath to provide added strength and protection against rodents. Fiber cable that is placed in underground conduit, is normally filled with a waterproof gel compound. Outside plant cables are generally manufactured with a gel filling in the buffer tubes and a water blocking tape between the inner and outer jackets. Both outer and inner jackets are made of materials designed to withstand immersion and resist corrosion.
Fiber strands and cables are manufactured with a standard color coding. This permits effective management of cables because of the normally high strand counts contained within a cable. There are 24 color combinations used. A loose buffer tube cable with 576 strands would have 24 tubes colored as indicated in the chart below. Within each buffer tube would be 24 fiber strands using the same color scheme. Therefore, strand number 47 would be in an orange buffer tube and have a rose with a black tracer colored protective coating.
Buffer Tube / Fiber Strand Number Color 1 Blue 2 Orange 3 Green 4 Brown 5 Slate 6 White 7 Red 8 Black 9 Yellow 10 Violet 11 Rose 12 Aqua 13 Blue/Black Tracer 14 Orange/Black Tracer 15 Green/Black Tracer 16 Brown/Black Tracer 17 Slate/Black Tracer 18 White/Black Tracer 19 Red/Black Tracer 20 Black/Yellow Tracer 21 Yellow/Black Tracer 22 Violet/Black Tracer 23 Rose/Black Tracer 24 Aqua/Black TracerAnother aspect of fiber construction is the actual size of the fiber strand. Most fiber is produced in a diameter of 125µm – a combination of the fiber core and its cladding. Most multimode cable used today has a core diameter of 62.5µm and most single mode fiber has a core diameter of 9µm. Therefore, the fiber strand size will normally be listed as 62.5µm/125µm for multimode and 9µm/125µm for single mode fiber.
The strand diameter is kept consistent to help with the manufacturing and installation processes. The core diameter varies because of differences in some of the transmission characteristics of the fibers. When purchasing fiber cable to be added to an existing system, make certain that strand diameter and the core diameters match. Fusion splicing (see chapter 8 for an explanation of splicing) fibers with different core diameters is possible. However, there will probably be a misalignment that is the cause of poor system performance. If you must use fibers with different core diameters it is best to use a mechanical splice to assure proper alignment. Never splice multimode fiber to single mode fiber. If you must place single mode and multimode in the same system use a "mode converter" to facilitate the transition.
Fiber cables are produced in two basic forms:
Loose tube cables are primarily used in outside plant applications. They are designed to protect the fibers from damage (stretching and kinking) that might result from an overly aggressive cable puller. The tube arrangement also allows for easier transition to fiber drops at buildings or communication cabinets. The fiber strands float within the buffer tubes and are not part of the cable structure. Loose tube cables are ideal for metropolitan and long distance cable installations.
Tight buffer cables are specified for inside plant use. These types of cables are designed for use within a controlled environment such as a building or inside plant equipment cabinets. Because the cable is used within a building the cable it requires less physical protection and has greater flexibility. The fibers within the cable are susceptible to damage from aggressive cable pulls because the fiber strands are part of the cable structure. The strands are tightly bound in a central bundle within the outer cable sheath.
Fibers are assembled into either stranded or ribbon cables. Stranded cables are individual fibers that are bundled together. Ribbon cable is constructed by grouping up to 12 fibers and coating them with plastic to form a multi fiber ribbon. Stranded and ribbon fiber bundles can be packaged together into either loose or tight buffering cable.
Loose Buffered Cable Tight Buffered Cable Individual fibers move freely within a buffer tube Fibers are tightly bound into a bundle Large cable diameter to accommodate buffer tubes Smaller cable diameter Fibers protected from cable pulling forces Fibers sensitive to pulling forces Used primarily for outside plant Used for inside plant and distributionFiber strands are produced in two basic varieties: Multimode and Single mode. Each variety is used to facilitate specific requirements of the communication system.
Multimode is optical fiber that is designed to carry multiple light rays or modes concurrently, each at a slightly different reflection angle within the optical fiber core. Multimode fiber transmission is used for relatively short distances because the modes tend to disperse over longer lengths (this is called modal dispersion). Multimode fibers have a core diameter of between 50 & 200 microns. Multimode fiber is used for requirements of less than 15,000 feet. Multimode fiber became available during the early 1980's and is still being used in many older systems. With the advances in fiber technology and the number of product choices available, multimode fiber is almost never deployed for new systems. There are mechanical devices available that accommodate a transition from multimode fiber to single mode fiber. Multimode fiber is generally "lit" with LED (Light Emitting Diodes) which are less expensive than LASER transmitters. Multimode fiber is generally manufactured in two sizes 50µm and 62.5µm.
Single mode is optical fiber that is designed for the transmission of a single ray or mode of light as a carrier. Single mode fiber has a much smaller core than multimode fiber. Single mode fiber is produced in several variations. The variations are designed to facilitate very long distances, and the transmission of multiple light frequencies within a single light ray. Following chapters will discuss transmission system capabilities – See: Ethernet, SONET and DWDM. Single mode fiber is generally manufactured with core diameters between 7 and 9 microns.
During the past 10 years, a number of variants of single mode fiber have been developed. Some of the fibers are used for long distance systems, and others are used for metropolitan systems. Each of these has been developed with special characteristics designed to enhance performance for a specific purpose. The most widely used all purpose single mode fiber is SMF-28 which can be used for all purposes, except long reach DWDM systems.
Freeway Management and Traffic Signal Control would be considered – from a communications perspective – as general purpose systems. Designers of Transportation Management Systems using fiber should strongly consider specifying SMF-28 type single mode fiber. This fiber is very available and normally is lowest in price.
Fiber optic cable is priced on the basis of strand feet. A 5,000 foot cable with two fiber strands is 10,000 fiber strand feet. A 5,000 foot cable with 24 fibers is 120,000 strand feet. The cost of the first cable might be $5,000, or 50 cents per strand foot. The cost of the second cable might be $24,000, but the cost per strand foot is only 20 cents. Therefore, when purchasing fiber optic cable, it is always best to consider potential system additions in order to incur a lower overall materials cost. Remember, price per fiber strand foot is not the only factor to consider in overall system costs. Digging a four (4) foot deep trench, placing conduit in the trench, and repairing the street carries the same cost regardless of the strand count, and that's about 90% of the total cost of deploying fiber optic cable. If construction costs $100 per linear foot, then the overall cost per strand foot is $50.50 per foot for two (2) strands and $4.37 for twenty-four (24) strands. Items not included in this calculation are the costs associated with splicing, optimization and engineering. Those are 10% of the total cost.
Following is a general comparison of Single Mode and Multimode fibers:
Characteristic Single Mode Multimode Bandwidth Virtually Unlimited Less than virtually unlimited Signal Quality Excellent over long distances Excellent over short distances Primary Attenuation Chromatic Dispersion Modal Dispersion Fiber Types Step Index & Dispersion Shifted Step & Graded Index Typical Application Almost anything (including Ethernet) Analog Video; Ethernet; Short Range CommunicationsSingle mode fiber has a very small core causing light to travel in a straight line and typically has a core size of 8 to 10 microns. It has (theoretically) unlimited bandwidth capacity, that can be transmitted for very long distances (40 to 60 miles). Multimode fiber supports multiple paths of light and has a much larger core – 50 or 62.5 microns. Because multimode fibers are five to six times the diameter of single mode, transmitted light will travel along multiple paths, or modes within the fiber. Multimode fiber can be manufactured in two ways: step-index or graded index. Step-index fiber has an abrupt change or step between the index of refraction of the core and the index of refraction of the cladding. Multimode step-index fibers have lower bandwidth capacity than graded index fibers.
Graded index fiber was designed to reduce modal dispersion inherent in step index fiber. Modal dispersion occurs as light pulses travel through the core along higher and lower order modes. Graded index fiber is made up of multiple layers with the highest index of refraction at the core. Each succeeding layer has a gradually decreasing index of refraction as the layers move away from the center. High order modes enter the outer layers of the cladding and are reflected back towards the core. Multimode graded index fibers have less attenuation (loss) of the output pulse and have higher bandwidth than multimode step-index fibers.
Single mode fibers are not affected by modal dispersion because light travels a single path. Single mode step-index fibers experience light pulse stretching and shrinking via chromatic dispersion. Chromatic dispersion happens when a pulse of light contains more than one wavelength. Wavelengths travel at different speeds, causing the pulse to spread. Dispersion can also occur when the optical signal gets out of the core and into the cladding, causing shrinking of the total pulse.
Single mode shifted fiber uses multiple layers of core and cladding to reduce dispersion. Dispersion shifted fibers have low attenuation (loss), longer transmission distances, and higher bandwidth.
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