Digital loop carrier
A digital loop carrier is a system which uses digital transmission to extend the range of the local loop farther than would be possible using only twisted pair copper wires. A DLC digitizes and multiplexes the individual signals carried by the local loops onto a single datastream on the DLC segment. Subscriber Loop Carrier systems address a number of problems: Electrical constraints on long loops. Insufficient available cable pairs. Cable route congestion Construction challenges when limited cable pairs are available Expense due to cable cost and the associated labour-intensive installation work Long loops, such as those terminating at more than 18,000 feet from the central office, pose electrical challenges; when the subscriber goes off-hook, a cable pair behaves like a single loop inductance coil with a -48 V dc potential and an Electric current of between 20–50 mA dc. Electric current values vary with cable gauge. A minimum current of around 20 mA dc is required to convey terminal signalling information to the network.
There is a minimum power level required to provide adequate volume for the voice signal. A variety of schemes were implemented before DLC technology to offset the impedance long loops offered to signalling and volume levels, they included the following: Use heavy-gauge conductors – Up to 19 gauge, costly and bulky. The heavy-gauge cables yielded far fewer pairs per cable and led to early congestion in cable routes in bridge crossings and other areas of limited space. Increase battery voltage – This violation of operating standards could pose a safety hazard. Add amplifiers to power the voice signal on long loops; this however, requires volumes of auxiliary equipment, a myriad number of cross wiring points, extensive record-keeping. Add signal regeneration and signal extension equipment – The comments regarding amplifiers apply here as well. Add loading coils to reduce the attenuation of voice signals over long loops; these have detrimental effect to new transmission technologies using the local loop, like DSL, must be removed.
DLC eliminates the need for these remedies by extending out closer to the customer the line card which digitises the voice signal for use by the PSTN. Once the voice signal is digitised, it is manipulated and is no longer subject to the vagaries of the analog loop caused by distance, impedance and noise; the DLC solution was dubbed "pair gain". In a typical configuration, DLC remote terminals are installed in new neighbourhoods or buildings as a means of reducing the labour and complexity of installing individual local loops from the customer to the central office. A fibre optic cable or several copper pairs for the whole system from the CO to the DLC remote terminal replace the individual pair needed for each loop. DLC remote terminals are stored in Serving Area Interfaces–metal cabinets alongside or near roadways that overlie communications rights-of-ways. With the growth in popularity of digital subscriber line and the benefits provided by shorter metallic loops used with DLC systems, digital loop carriers are sometimes integrated with digital subscriber line access multiplexers, both systems taking advantage of the digital transmission link from the DLC to the CO. Fibre in the loop systems are functionally equivalent to DLC.
FITL accomplishes the same two primary functions DLC was intended for: pair gain and the elimination of electrical constraints due to long metallic loops. FITL architectures vary from deploying fibre feeder plants to "fibre to the curb" and "fibre to the home" where an optical network unit is located at each home. See Remote concentrator
Digital subscriber line
Digital subscriber line is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is understood to mean asymmetric digital subscriber line, the most installed DSL technology, for Internet access. DSL service can be delivered with wired telephone service on the same telephone line since DSL uses higher frequency bands for data. On the customer premises, a DSL filter on each non-DSL outlet blocks any high-frequency interference to enable simultaneous use of the voice and DSL services; the bit rate of consumer DSL services ranges from 256 kbit/s to over 100 Mbit/s in the direction to the customer, depending on DSL technology, line conditions, service-level implementation. Bit rates of 1 Gbit/s have been reached. In ADSL, the data throughput in the upstream direction is lower, hence the designation of asymmetric service. In symmetric digital subscriber line services, the downstream and upstream data rates are equal. Researchers at Bell Labs have reached speeds over 1 Gbit/s for symmetrical broadband access services using traditional copper telephone lines, though such speeds have not yet been deployed elsewhere.
It was thought that it was not possible to operate a conventional phone line beyond low-speed limits. In the 1950s, ordinary twisted-pair telephone cable carried four megahertz television signals between studios, suggesting that such lines would allow transmitting many megabits per second. One such circuit in the United Kingdom ran some 10 miles between the BBC studios in Newcastle-upon-Tyne and the Pontop Pike transmitting station, it was able to give the studios a low quality cue feed but not one suitable for transmission. However, these cables had other impairments besides Gaussian noise, preventing such rates from becoming practical in the field; the 1980s saw the development of techniques for broadband communications that allowed the limit to be extended. A patent was filed in 1979 for the use of existing telephone wires for both telephones and data terminals that were connected to a remote computer via a digital data carrier system; the motivation for digital subscriber line technology was the Integrated Services Digital Network specification proposed in 1984 by the CCITT as part of Recommendation I.120 reused as ISDN digital subscriber line.
Employees at Bellcore developed asymmetric digital subscriber line by placing wide-band digital signals at frequencies above the existing baseband analog voice signal carried on conventional twisted pair cabling between telephone exchanges and customers. A patent was filed in 1988. Joseph W. Lechleider's contribution to DSL was his insight that an asymmetric arrangement offered more than double the bandwidth capacity of symmetric DSL; this allowed Internet service providers to offer efficient service to consumers, who benefited from the ability to download large amounts of data but needed to upload comparable amounts. ADSL supports two modes of transport -- interleaved channel. Fast channel is preferred for streaming multimedia, where an occasional dropped bit is acceptable, but lags are less so. Interleaved channel works better for file transfers, where the delivered data must be error-free but latency incurred by the retransmission of error-containing packets is acceptable. Consumer-oriented ADSL was designed to operate on existing lines conditioned for Basic Rate Interface ISDN services, which itself is a digital circuit switching service, though most incumbent local exchange carriers provision rate-adaptive digital subscriber line to work on any available copper pair facility, whether conditioned for BRI or not.
Engineers developed high speed DSL facilities such as high bit rate digital subscriber line and symmetric digital subscriber line to provision traditional Digital Signal 1 services over standard copper pair facilities. Older ADSL standards delivered 8 Mbit/s to the customer over about 2 km of unshielded twisted-pair copper wire. Newer variants improved these rates. Distances greater than 2 km reduce the bandwidth usable on the wires, thus reducing the data rate, but ADSL loop extenders increase these distances by repeating the signal, allowing the LEC to deliver DSL speeds to any distance. Until the late 1990s, the cost of digital signal processors for DSL was prohibitive. All types of DSL employ complex digital signal processing algorithms to overcome the inherent limitations of the existing twisted pair wires. Due to the advancements of very-large-scale integration technology, the cost of the equipment associated with a DSL deployment lowered significantly; the two main pieces of equipment are a digital subscriber line access multiplexer at one end and a DSL modem at the other end.
A DSL connection can be deployed over existing cable. Such deployment including equipment, is much cheaper than installing a new, high-bandwidth fiber-optic cable over the same route and distance; this is true both for SDSL variations. The commercial success of DSL and similar technologies reflects the advances made in electronics over the decades that have increased performance and reduced costs while digging trenches in the ground for new cables remains expensive. In the case of ADSL, competition in Internet access caused subscription fees to drop over the years, thus making ADSL more economical than dial up access. Telephone companies were pressured into moving to A
An access network is a type of telecommunications network which connects subscribers to their immediate service provider. It is contrasted with the core network; the access network may be further divided between feeder plant or distribution network, drop plant or edge network. An access network referred to as an outside plant, refers to the series of wires and equipment lying between a consumer/business telephone termination point and the local telephone exchange; the local exchange contains banks of automated switching equipment which direct a call or connection to the consumer. The access network is one of the oldest assets a telecoms operator would own. In 2007–2008 many telecommunication operators experienced increasing problems maintaining the quality of the records which describe the network. In 2006, according to an independent Yankee Group report, globally operators experience profit leakage in excess of $17 billion each year; the access network is perhaps the most valuable asset an operator owns, since this is what physically allows them to offer a service.
Access networks consist of pairs of copper wires, each traveling in a direct path between the exchange and the customer. In some instances, these wires may consist of aluminum, used in the 1960s and 1970s following a massive increase in the cost of copper; as it happened, the price increase was temporary, but the effects of this decision are still felt today as electromigration within the aluminum wires can cause an increase in on-state resistance. This resistance causes degradation which can lead to the complete failure of the wire to transport data. Access is essential to the future profitability of operators who are experiencing massive reductions in revenue from plain old telephone services, due in part to the opening of nationalized companies to competition, in part to increased use of mobile phones and voice over IP services. Operators offered additional services such as xDSL based IPTV to guarantee profit; the access network is again the main barrier to achieving these profits since operators worldwide have accurate records of only 40% to 60% of the network.
Without understanding or knowing the characteristics of these enormous copper spider webs, it is difficult, expensive to'provision' new customers and assure the data rates required to receive next generation services. Access networks around the world evolved to include more optical fiber technology. Optical fibre makes up the majority of core networks and will start to creep closer and closer to the customer, until a full transition is achieved, delivering value added services over fiber to the home; the process of communicating with a network begins with an access attempt, in which one or more users interact with a communications system to enable initiation of user information transfer. An access attempt. An access attempt ends either in successful access or in access failure - an unsuccessful access that results in termination of the attempt in any manner other than initiation of user information transfer between the intended source and destination within the specified maximum access time.
Access failure can be the result of access outage, user blocking, incorrect access, or access denial. Access denial can include: Access failure caused by the issuing of a system blocking signal by a communications system that does not have a camp-on busy signal feature. Access failure caused by exceeding the maximum access time and nominal system access time fraction during an access attempt. An access charge is a charge made by a local exchange carrier for use of its local exchange facilities for a purpose such as the origination or termination of network traffic, carried to or from a distant exchange by an interexchange carrier. Although some access charges are billed directly to interexchange carriers, a significant percentage of all access charges are paid by the local end users. GERAN UTRAN E-UTRAN CDMA2000 GSM UMTS 1xEVDO voLTE Wi-Fi in* WiMAX A passive optical distribution network uses single mode optical fibre in the outside plant, optical splitters and optical distribution frames, duplexed so that both upstream and downstream signals share the same fibre on separate wavelengths.
Faster PON standards support a higher split ratio of users per PON, but may use reach extenders/amplifiers where extra coverage is needed. Optical splitters creating a point to multipoint topology are the same technology regardless of the type of PON system, making any PON network upgradable by changing the optical network terminals and optical line terminal terminals at each end, with minimal change to the physical network. Access networks also must support point-to-point technologies such as Ethernet, which bypasses any outside plant splitter to achieve a dedicated link to the telephone exchange; some PON networks use a "home run" topology where roadside cabinets only contain patch panels so that all splitters are located centrally. While a 20% higher capital cost could be expected, home run networks may encourage a more competitive wholesale market since providers' equipment can achieve higher use. Internet access IP Connectivity Access Network Local loop Passive Optical Network "The Network Story".
British Telecom. 2005. Archived from the original on 5 May 2010. Interactive presentation introducing the technology and design of access networks
WiMAX is a family of wireless broadband communication standards based on the IEEE 802.16 set of standards, which provide multiple physical layer and Media Access Control options. The name "WiMAX" was created by the WiMAX Forum, formed in June 2001 to promote conformity and interoperability of the standard, including the definition of predefined system profiles for commercial vendors; the forum describes WiMAX as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL". IEEE 802.16m or WirelessMAN-Advanced was a candidate for the 4G, in competition with the LTE Advanced standard. WiMAX was designed to provide 30 to 40 megabit-per-second data rates, with the 2011 update providing up to 1 Gbit/s for fixed stations; the latest version of WiMAX, WiMAX release 2.1, popularly branded as/known as WiMAX 2+, is a smooth, backwards-compatible transition from previous WiMAX generations. It is compatible and inter-operable with TD-LTE.
WiMAX refers to interoperable implementations of the IEEE 802.16 family of wireless-networks standards ratified by the WiMAX Forum. WiMAX Forum certification allows vendors to sell fixed or mobile products as WiMAX certified, thus ensuring a level of interoperability with other certified products, as long as they fit the same profile; the original IEEE 802.16 standard was published in 2001. WiMAX adopted some of its technology from WiBro, a service marketed in Korea. Mobile WiMAX is the revision, deployed in many countries and is the basis for future revisions such as 802.16m-2011. WiMAX is sometimes referred to as "Wi-Fi on steroids" and can be used for a number of applications including broadband connections, cellular backhaul, etc, it is similar to Long-range Wi-Fi. The scalable physical layer architecture that allows for data rate to scale with available channel bandwidth and range of WiMAX make it suitable for the following potential applications: Providing portable mobile broadband connectivity across cities and countries through various devices Providing a wireless alternative to cable and digital subscriber line for "last mile" broadband access Providing data, telecommunications and IPTV services Providing Internet connectivity as part of a business continuity plan Smart grids and metering WiMAX can provide at-home or mobile Internet access across whole cities or countries.
In many cases, this has resulted in competition in markets which only had access through an existing incumbent DSL operator. Additionally, given the low costs associated with the deployment of a WiMAX network, it is now economically viable to provide last-mile broadband Internet access in remote locations. Mobile WiMAX was a replacement candidate for cellular phone technologies such as GSM and CDMA, or can be used as an overlay to increase capacity. Fixed WiMAX is considered as a wireless backhaul technology for 2G, 3G, 4G networks in both developed and developing nations. In North America, backhaul for urban operations is provided via one or more copper wire line connections, whereas remote cellular operations are sometimes backhauled via satellite. In other regions and rural backhaul is provided by microwave links. WiMAX has more substantial backhaul bandwidth requirements than legacy cellular applications; the use of wireless microwave backhaul is on the rise in North America and existing microwave backhaul links in all regions are being upgraded.
Capacities of between 34 Mbit/s and 1 Gbit/s are being deployed with latencies in the order of 1 ms. In many cases, operators are aggregating sites using wireless technology and presenting traffic on to fiber networks where convenient. WiMAX in this application competes with microwave radio, E-line and simple extension of the fiber network itself. WiMAX directly supports the technologies; these are inherent to the WiMAX standard rather than being added on as carrier Ethernet is to Ethernet. On May 7, 2008 in the United States, Sprint Nextel, Intel, Bright House, Time Warner announced a pooling of an average of 120 MHz of spectrum and merged with Clearwire to market the service; the new company hopes to benefit from combined services offerings and network resources as a springboard past its competitors. The cable companies will provide media services to other partners while gaining access to the wireless network as a Mobile virtual network operator to provide triple-play services; some analysts questioned how the deal will work out: Although fixed-mobile convergence has been a recognized factor in the industry, prior attempts to form partnerships among wireless and cable companies have failed to lead to significant benefits to the participants.
Other analysts point out that as wireless progresses to higher bandwidth, it competes more directly with cable and DSL, inspiring competitors into collaboration. As wireless broadband networks grow denser and usage habits shift, the need for increased backhaul and media service will accelerate, therefore the opportunity to leverage cable assets is expected to increase. IEEE 802.16REVd and IEEE 802.16e standards support both Time Division Duplexing and Frequency
In telephony, the demarcation point is the point at which the public switched telephone network ends and connects with the customer's on-premises wiring. It is the dividing line which determines, responsible for installation and maintenance of wiring and equipment—customer/subscriber, or telephone company/provider; the demarcation point has changed over time. Demarcation point is sometimes DMARC, or similar; the term MPOE is synonymous, with the added implication that it occurs as soon as possible upon entering the customer premises. A network interface device serves as the demarcation point. Prior to the Bell System divestiture on January 1, 1984, American Telephone & Telegraph Company through its Bell System companies held a natural monopoly for telephone service within the United States and Canada. AT&T owned the local loop, including the telephone wiring within the customer premises and the customer telephone equipment. A similar arrangement existed with smaller, regional telephone companies such as GTE.
As a result of deregulation of the telephone system, unbundling of the local loop, lawsuits by companies wishing to sell third-party equipment to connect to the telephone network, there was a need to delineate the portion of the network, owned by the customer and the portion owned by the telephone company or the common carrier. Where the portions meet is called the demarcation point; the demarcation point varies from building service level. In its simplest form, the demarcation point is a junction block where telephone extensions join to connect to the network; this junction block includes a lightning arrester. In multi-line installations such as businesses or apartment buildings, the demarcation point may be a punch down block. In most places this hardware existed before deregulation. In the United States, the modern demarcation point is a device defined by FCC rules to allow safe connection of third-party telephone customer-premises equipment and wiring to the Public Switched Telephone Network.
The modern demarcation point is the network interface device or intelligent network interface device known as a "smartjack". The NID is the telco's property; the NID may be indoors. The NID is placed for easy access by a technician, it contains a lightning arrestor and test circuitry which allows the carrier to remotely test whether a wiring fault lies in the customer premises or in the carrier wiring, without requiring a technician at the premises. The demarcation point has a user accessible RJ-11 jack, connected directly to the telephone network, a small loop of telephone cord connecting to the jack by a modular connector; when the loop is disconnected, the on-premises wiring is isolated from the telephone network and the customer may directly connect a telephone to the network via the jack to assist in determining the location of a wiring fault. In most cases, everything from the central office to and including the demarcation point is owned by the carrier and everything past it is owned by the property owner.
As the local loop becomes upgraded, with fiber optic and coaxial cable technologies sometimes replacing the original unshielded twisted pair to the premises, the demarcation point has grown to incorporate the equipment necessary to interface the original premises POTS wiring and equipment to the new communication channel. Demarcation points on houses built prior to the Bell System divestiture do not contain a test jack, they only contained a spark-gap surge protector, a grounding post and mount point to connect a single telephone line. The second wire pair was left unconnected and were kept as a spare pair in case the first pair was damaged. DEMARCs that handle both telephony and IT fiber optic internet lines do not look like the ones pictured above. In many places several customers share one central DEMARC for a strip mall setting. A DEMARC will be located indoors if it is serving more than a single customer; this may impede access. Outdoor ones provide easier access, without disturbing other tenants, but call for weatherproofing and punching through a wall for each new addition of wires and service.
Indoor DEMARC's will be identified by a patch panel of telephone wires on the wall next to a series of boxes with RJ48 jacks for T-1 lines. Each business or individual customer can expect their own separate box for internet access T-1 lines. A demarcation point extension, or demarc extension is the transmission path originating from the interface of the access provider's side of a demarcation point within a premises and ending at the termination point prior to the interface of the edge Customer Premises Equipment; this may include in-segment equipment, media converters and patch cords as required to complete the circuit's transmission path to the edge CPE. A demarc extension is more termed "Service Interface Extension", may be referred to as inside wiring, extended demarc, circuit extension, CPE cabling, riser cabling or DMARC extension. A demarc extension became an important factor to consider in a building's telecommunications infrastructure after the 1984 deregulation of AT&T as well as the supplemental FCC rulings of 1991, 1996 and 1997.
Preceding these rulings, the Bell System Companies held a monopoly and did not allow an interconnection with third party equipment. The incumbent local exchange carriers and other local access providers are now mandated by federal law to provide a point where the operational control or ownersh
Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted balanced pair, a twisted pair reduces electromagnetic radiation from the pair and crosstalk between neighboring pairs and improves rejection of external electromagnetic interference, it was invented by Alexander Graham Bell. In a balanced line, the two wires carry equal and opposite signals, the destination detects the difference between the two; this is known as differential signaling. Noise sources introduce signals into the wires by coupling of electric or magnetic fields and tend to couple to both wires equally; the noise thus produces a common-mode signal which can be canceled at the receiver when the difference signal is taken. Differential signaling starts to fail; this problem is apparent in telecommunication cables where pairs in the same cable lie next to each other for many miles.
Twisting the pairs counters this effect as on each half twist the wire nearest to the noise-source is exchanged. Provided the interfering source remains uniform, or nearly so, over the distance of a single twist, the induced noise will remain common-mode; the twist rate makes up part of the specification for a given type of cable. When nearby pairs have equal twist rates, the same conductors of the different pairs may lie next to each other undoing the benefits of differential mode. For this reason it is specified that, at least for cables containing small numbers of pairs, the twist rates must differ. In contrast to shielded or foiled twisted pair, UTP cable is not surrounded by any shielding. UTP is the primary wire type for telephone usage and is common for computer networking; the earliest telephones used open-wire single-wire earth return circuits. In the 1880s electric trams were installed in many cities. Lawsuits being unavailing, the telephone companies converted to balanced circuits, which had the incidental benefit of reducing attenuation, hence increasing range.
As electrical power distribution became more commonplace, this measure proved inadequate. Two wires, strung on either side of cross bars on utility poles, shared the route with electrical power lines. Within a few years, the growing use of electricity again brought an increase of interference, so engineers devised a method called wire transposition, to cancel out the interference. In wire transposition, the wires exchange position once every several poles. In this way, the two wires would receive similar EMI from power lines; this represented an early implementation of twisting, with a twist rate of about four twists per kilometre, or six per mile. Such open-wire balanced lines with periodic transpositions still survive today in some rural areas. Twisted-pair cabling was invented by Alexander Graham Bell in 1881. By 1900, the entire American telephone line network was either twisted pair or open wire with transposition to guard against interference. Today, most of the millions of kilometres of twisted pairs in the world are outdoor landlines, owned by telephone companies, used for voice service, only handled or seen by telephone workers.
Unshielded twisted pair cables are found in many Ethernet networks and telephone systems. For indoor telephone applications, UTP is grouped into sets of 25 pairs according to a standard 25-pair color code developed by AT&T Corporation. A typical subset of these colors shows up in most UTP cables; the cables are made with copper wires measured at 22 or 24 American Wire Gauge, with the colored insulation made from an insulator such as polyethylene or FEP and the total package covered in a polyethylene jacket. For urban outdoor telephone cables containing hundreds or thousands of pairs, the cable is divided into small but identical bundles; each bundle consists of twisted pairs. The bundles are in turn twisted together to make up the cable. Pairs having the same twist rate within the cable can still experience some degree of crosstalk. Wire pairs are selected to minimize crosstalk within a large cable. UTP cable is the most common cable used in computer networking. Modern Ethernet, the most common data networking standard, can use UTP cables.
Twisted pair cabling is used in data networks for short and medium length connections because of its lower costs compared to optical fiber and coaxial cable. UTP is finding increasing use in video applications in security cameras. Many cameras include a UTP output with screw terminals; as UTP is a balanced transmission line, a balun is needed to connect to unbalanced equipment, for example any using BNC connectors and designed for coaxial cable. Twisted pair cables incorporate shielding in an attempt to prevent electromagnetic interference. Shielding provides an electrically conductive barrier to attenuate electromagnetic waves external to the shield; such shielding can be applied to individual quads. Individual pairs are foil shielded, while an overall cable may use any of braided screen or foi
In telecommunication, the term outside plant has the following meanings: In civilian telecommunications, outside plant refers to all of the physical cabling and supporting infrastructure, any associated hardware located between a demarcation point in a switching facility and a demarcation point in another switching center or customer premises. In the United States, the DOD defines outside plant as the communications equipment located between a main distribution frame and a user end instrument; the CATV industry divides its fixed assets between head end or inside plant, outside plant. The electrical power industry uses the term outside plant to refer to electric power distribution systems. Network connections between devices such as computers and phones require a physical infrastructure to carry and process signals; this infrastructure will consist of: Cables from wall outlets and jacks run to a communications closets, sometimes referred to as station cable. Cables connecting one communications closet to another, sometimes referred to as riser cable.
Racks containing telecommunications hardware, such as switches and repeaters. Cables connecting one building to another. Exterior communications cabinets containing hardware outside of buildings. Radio transceivers used inside or outside buildings, such as wireless access points, hardware associated with them, such as antennas and towers; the portion of this infrastructure contained within a building is the inside plant, the portion of this infrastructure connecting buildings or facilities is the outside plant. Where these two plants meet in a given structure is the demarcation point. Outside plant cabling, whether copper or fiber, is installed as aerial cable between poles, in an underground conduit system, or by direct burial. Hardware associated with the outside plant must be either protected from the elements or constructed with materials suitable for exposure to the elements. Installation of the outside plant elements require construction of significant physical infrastructure, such as underground vaults.
In older large installations, cabling is sometimes protected by air pressure systems designed to prevent water infiltration. While this is not a modern approach, the cost of replacement of the older cabling with sealed cabling is prohibitively expensive; the cabling used in the outside plant must be protected from electrical disturbances caused by lightning or voltage surges due to electrical shorts or induction. In civilian telecommunications, the copper access network providing basic telephone or DSL services consists of the following elements: In-house wiring that connects customer premises equipment to the demarcation point in residential installations contained in a weather protected box. One or more twisted pairs, called a drop wire; the drop wires connect to a splice case, located in line for aerial cables, or in a small weather protected case for underground wiring, where the local cabling is connected to a secondary feeder line. These cables contain fifty or more twisted pairs. Secondary feeder lines run to a streetside cabinet containing a distribution frame called a Serving Area Interface.
The SAI is connected to the main distribution frame, located at a Telephone exchange or other switching facility, by one or more primary feeder lines which contain hundreds of copper twisted pairs. An SAI may contain a Digital subscriber line access multiplexer supporting DSL service. Active equipment can be connected to the line in order to provide service, but this is not considered part of outside plant; the environment can play a large role in the quality and lifespan of equipment used in the outside plant. It is critical that environmental testing criteria as well as design and performance requirements be defined for this type of equipment. There are four operating environments or classes covering all outside plant applications, including wireless facilities. Class 1: Equipment in a Controlled Environment Class 2: Protected Equipment in Outside Environments Class 3: Protected Equipment in Severe Outside Environments Class 4: Products in an Unprotected EnvironmentElectronic equipment located in one or more of these environmental class locations is designed to withstand various environmental operating conditions resulting from climatic conditions that may include rain, sleet, high winds, salt spray, sand storms.
Since outside temperatures can range from −40 °C to 46 °C, with varying degrees of solar loading, along with humidity levels ranging from below 10% up to 100%, significant environmental stresses within the enclosure or facility can be produced. Telcordia GR-3108, Generic Requirements for Network Equipment in the Outside Plant, contains the most recent industry data regarding each Class described above, it discusses what is happening in ATIS and Underwriters Laboratories. The document includes Environmental criteria such as operating temperatures, particulate contamination, pollution exposure, heat dissipation Mechanical criteria such as structural requirements, susceptibility to vibration and handling Electrical protection and safety including protection from lightning surges, AC power induction and faults, Electromagnetic Interference, DC power influences Handholes and other below-ground splice vaults house telecommunications components used in an Outside Plant environment. Handholes are plastic or polymer concrete structures set below