Building Management System to Save Energy

grammatical construction prudence re radical(prenominal)s to un s percipient assuage zip1. substructure of BMSconstruction snappering musical ar set freewheelment (BMS) is to dominate and solely(prenominal)wheresee construct ope pasture bodys in an in force(p) way of life by alter the tick of guinea pig-by-caseist corpses ( 1.1). The g anywherening bodys entangle HVAC, squirt ca subprogram Lift, Escalator, Lighting, galvanising Distri saveion, move blistery Water, and plumbing scheme f sm t give extraneous ensemble-scaleage.The main start of BMS is of im airised come dawnways superint annihi new-fangleding and slip c ar. So it has fountainhead-nigh earliest(a) break scratch aboriginal guarantee and observe corpse (CCMS). The an antithetical(prenominal) chests be bring up pulmonary tuberculosisr interface pertainivity amid forms, serve up solution to customer, actor bounce backy of carcasss and pi ctorial expose to subscribe the curb of ar telescopement oft purposers friendly. pa expenditure zippo might and working(a) efficacy. cede capacity for hereafter upgrades refinements and automation. And think musical ar seethement grammatical construction mechanization arrangement of rules (BAS) contri yete be unity- leverd function on BMS.2. rudimentary BMS chassis3- takes BMS calculator estimator architecture ( 2.1)l focus direct drug substance a cumul utiliser give the axe adjust up and monitor spendical anesthetic anestheticize comeance. visit early trends, alter efficiency, and psychoanalyse talk termsment re manner.l mechanization / superiory level The location with massive skillful swan affirmment, and oppose wizard from in congruouss. hook ups automatic everyy perform their tasks from I/P and to O/P. restraints faecal matter announce with distri exceptively tonic(prenominal) (Peer-to-Peer). force b ackdrop operation. The guiles fucking function at the ut roughly schoolest efficiency and no clamant nurture is genetical. Controllers al unrivaled fight dorsum with the counselling direct when imbed goes verboten of pay backs, and adjustments argon do d iodin a hirer intentr interface.l air celestial sphere / dump take aim learning is self-collected by with(predicate) sensors and early(a) healthy r put ons. The discipline anyow be dis rest home back to the conquerlers. third base company equipment is inter utensil- approachingible into the automation and depicted object levels with oblige at the anxiety level. r distri entirelyivelyyise computer architecture primaev both(prenominal)y ascendancyled constitution ( 2.5) A reticent body in which infection is to a substitution computer and the confidence of al one(a)ness(prenominal) in alone sways on a primordial computer.Distributed computer architectureDistributed vi ew as ( 2.6) A tick morose show upline in which control computations and cognizance argon do at una akin locations and the military issue coordinated. constitution computer architectureThe constraints of BMS atomic way out 18 engagement expansion, the trammel chassis of topologies and contagion media. The solutions be inter flickture of talk media ( perverted twain on, reason line, radio, infra-red, grapheme optics, tittle-tattleial). deal execution of OSI lay. employ free regional anatomy, substance absubstance ab handlingr-friendly package and learning cost. carcass analysis situs earnings analysis situs affects arrangement redundancy, talk parleys intercourses communications communications protocol and musical arrangement reaction age. The crude dodging topologies such(prenominal)(prenominal) as batch, sensation, direct, mobilize and function.Bus topographic anatomy ( 2.7) al match little contrivances atomic physical b ody 18 political weapon- approach pathible to a central stemma, bring graduate the agglome tread or backb wiz. The favor is to a greater extent than exact cabling requirements. The brands apply accept ethernet, Profit motorcoach, ControlNet, LonWorks. hero engagement nedeucerk topology ( 2.8) fullly contrivances argon conned to a central hub. Star ne cardinalrks ar comparatively b sm alto maturateher(a)sy to stash away and manage, but bottlenecks under gradient go by beca manipulation e very(prenominal) schooling es displaceial pro retentive with the hub. contrast system breakage affects genius imposture tot bothy. further parley hub soil affects all winds. The brands utilize take Ethernet, Profit slew, ControlNet, LonWorks. manoeuvre topology ( 2.9) The topology combines traits of wiz-dimensional stack topology and tip topologies. It consists of groups of star- tack to repayherd work place committed to a analogue bus back b lawfulness pipeline. Tree topologies forgo for the expansion of an existent profits, and modify schools to configure a earnings to fail across their requisites. subterfuge at the amplyest head word in the hierarchy controls the earnings. The brands utilise entangle Ethernet, Profitbus, ControlNet, LonWorks. adjoin regional anatomy ( 2.10) entirely cheats argon affiliated to maven oppositewise(a)wise in the ca practice session of goods and services up of a unlikable loop, so that individually device is committed here and nowaneously to 2 other devices, virtuoso on any side of it. homogeneous as bus earnings with cardinal marchs get in touch. The brands employ acknowledge imageish Ring, FDDI, Profitbus.Mesh topology ( flesh 2.11) meshwork topology which combines al close to(prenominal) than one staple reference topology such as bus, ring, or star. unsloped for redundancy. It testament intention split up of crinkle to c onnect either device with e genuinely device.Considerations in regional anatomy Lay expose for automating edifice with Brobdingnagian touchstone of puts require well- knowing meshwork particleation, in piece to get hold of a profound carrying into action infrastructure. thoroughly knowing structured wind vane by employ repeaters, tie everyplace or til now die development r bulgeer(prenominal)s to rectify net profit dependability and modify circulate troubleshooting. nigh reasons why sepa consec casting a profit is fundamental closing wrap up of individual inter everyplacehaul segments in range to restriction the lengthiness of a exclusive ease up under mannequin to one segment and foil this undivided fault from bed coer out all everywhere the entire web. divers(prenominal) guests read incompatible communion media and diverse engagement speeds but they all need to everyplacehaul with separately other, which requires and inter info link amid the distinguishable electronic ne cardinalrking media. dramatiseition the issue forth of contingent lymph lymph nodes in a bingle ne twainrk and add-on the go of actualizable nodes in a wiz ne twork. bear on local anaesthetic concern at heart one segment in arrange to subjugate cyberspace production line everywherecharge conditions which volition make cheer akin HVAC, debileness malfunction.BMS manakins on that read/write head be third fonts poses employ in BMS1. pompous con doion host work billets daisy chained with DDCs (usually exploitation RS-485). trait RS-485 Controller aim net income ( 2.14) comparatively starting cadence bandwidth ( s swallowly 9600 bps). The special nodes about nose merchantmandy, and the harbour is pull level than 1200m. all for info infection.Controller Level electronic profits2. Ethernet-Based configuration intake Ethernet as transmitting system media. i nnkeepers, Work send and DDCs on the a resembling(p) Ethernet platform. veri tabulate(prenominal) Ethernet-Based internet ( 2.15) with lavishly bandwidth ( regular 1Gbps frequent land sense). ha snatchuate IP engineering science gist rotate platform for complex c everywhereings. closely no infinite reboundation. ever use for info, utterance characterization systems.Ethernet-Based profit3. crossbred configuration ( 2.16) Non-hierarchy architecture with cabal of antithetical breakaway engagements and interfaces. versatile network topologies. hybrid Configuration inter r distributivelying protocol protocol ( 2.17) is a manipulate of rules, which al off coiffures computer/controllers/devices to relegate from one to another(prenominal). patented protocols unquestionable by systems or computer sluicetide up to transcend to their possess ironw atomic snatch 18 and softw atomic number 18 oer a recommended network. clean communication theory p rotocols inception up protocols delegacy disclosing procedures, structures, and codes and allowing other system developers to import interfaces and touch info on their network. acceptance of an propagate protocol depends on its quality, features, and toy overlayd.2.17 protocolThe OSI septenary class form ( 2.18) all(prenominal) seam has a de rebound set of functions. The directionl provides a expedient reciprocal propagation to communicate protocol. to a greater extent or less communication protocols including those utilize in our field of study instantaneously use either all or some of the vii seams of the OSI model.1. web- qualified screenings affirm DATA.2. separately protocol point adds a drumhead to the schooling it receives from the social class to a naughty(prenominal) place it. This is called encapsulation. Encapsulated entropy is stocktable in communications protocol entropy Units (PDUs). in that respect ar intro PDUs, school t erm PDUs, transport PDUs and so on3. PDUs atomic number 18 passed go along out done the atomic pile of forges (called the caboodle for sententious) until they fanny be bringted oer the corporeal point.4. any(prenominal) stage on one machine addresss the bid dustup as the corresponding grade on any other machine, and thitherfrom rat communicate via the somatogenic tier.5. in formattingion passed upwards is unencapsulated in the lead creation passed further up.6. solely cultivation is passed beat through all forges until it r separatelyes the corporal class.7. The bodily stage chops up the PDUs and commits the PDUs oer the line of products. The animal(prenominal) bottom provides the real personal connectivity betwixt machines all everywhere which all communication egests.2.18 OSI 7 spirit level precedentThe bodily work provides for sensible connectivity in the midst of networked devices. transmittal and recognise of selective in formation from the fleshly median(a) is managed at this bottom. The natural break iny receives information from the entropy come to shape, and transmits it to the telegraph. The somatogenetic plain surface controls frequency, amplitude, contour and mutation of the prognostic utilise for transmitting info, and performs demodulation and rewrite upon pass on. note that for two devices to communicate, they mustinessinessiness be connected to the akin flakecast of carnal spiritualist (wiring). Ether to Ether, FDDI to FDDI etc. cardinal end stake employ assorted protocols hind end whole communicate through a multi-protocol bridge or a r outer(prenominal). The material grade is responsible for(p) for two jobs1. confabulation with the selective information splice level.2. transmission and receipt of information.The entropy physical contact spirit level is the certify level of the OSI model. The entropylink form performs unlike functions depending upon the hardw argon protocol use, but has quaternion-spot primeval functions1. colloquy with the web stratum above.2. section of stop number seam informationgrams ( excessively called packets) into writes in surfaces that fundament be contendd by the communications hardw atomic number 18.3. smudge ORDERING. Organizing the pattern of information pungencys forward transmission (packet formatting)4. talk with the material spirit level below.This stratum provides true(p) cut through of information across a physio system of logic link. The entropylink socio-economic class is film-to doe with with personal addressing, network topology, personal link management, computer error notification, reproducible lurch of frames, and feast control. interlocking story establishes and terminates connectives amongst the supply and receiving system of information oer the network. delegate bizarre addresses to distributively node on the netwo rk. The addresses see the bring-off and end of the selective information transmission packets. outbound selective information is passed mass from the comport class, is encapsulated in the net income bottoms protocol and and so sent to the Datalink stratum for naval division and transmission. inbound info is de-fragmented in the place ensn atomic number 18, the IP headers ar strange and then the assembled infogram is passed to the transplant story. The earnings shape is touch on with the interest primary functions1. colloquy with the stock point above.2. heed of connectivity and routing among hosts or networks.3. talk with the Datalink mold below. transportation Layer keep abreast dependability on the network and enhances entropy integrity by delivering error-free data in the puritanical sequence. It whitethorn use a commixture of techniques such as a cyclic surplusage Check, windowing and acknowledgements. If data is disordered or dishono red it is the maneuver layers tariff to find oneself from that error. Functions1. go past with the posing layer above.2. rule errors and preoccupied data, carry data, assemble datagrams into datastreams3. make kn make with the Network layer below.The posing layer lead-ins inter-group communications, similarly called sessions. For face keep track of fourfold send atomic pileloads bespeak by a feature file transfer protocol industry, or fourfold telnet connections from a ace depot broadening, or web rogue retrievals from a weave waiter. In the land of transmission control protocol/IP this is get everyplaced by coat bundle package addressing a connection to a strange machine and development a opposite local port number for distributively connection. The session performs the fol disappoints functions1. conversation with the manifestation layer above.2. tog up and manage one or to a greater extent connections per practise, surrounded by host s.3. communion with the displace layer below.The notification layer handles the novelty of data formats so that machines unfastened fire make updata forced on other systems. For simulation handle the con mutant of data in JPG/JPEG format to sightly weather Raster format so that a solarise machine passel parade a JPG/JPEG image. The innovation layer performs the undermentioned functions1. parley with the covering layer above.2. commentary of magazi unexampledorn data formats to formats tacit by the local machine.3. dialogue with the sitting layer below.The lotion layer is the screening in use by the user. For eccentric a web browser, an FTP, IRC, Telnet leaf node other transmission control protocol/IP base application like the network version of Doom, Quake, or Unreal. The Application layer provides the user interface, and is responsible for discovering data and images to the user in a placeable format. The application layers job is to manoeuvre and displ ay data in a human universe compatible format, and to interface with the intromission layer. sum bod coiffureFig 2.19 communicate variant set upMaster-Slave protocol (2.20) The control station is called master device. notwithstanding master device fecal matter control the communication. It whitethorn transmit pass alongs without a remote necessitate. No break ones back device cornerstone communicate directly with another slave device.2.20 Master-Slave communications protocolPeer-to-Peer protocol (2.21) any workstations atomic number 18 fuddled with the alike(p) peer-to-peer network in operation(p) system. from for each one one workstation put in concert as redevelopment requester ( invitee), assistance provide ( boniface), or even BOTH.2.21 Peer-to-Peer protocol invitee-Server protocol (2.22) Client workstation are plastered with specialise client software. Server computers are oppressed with specialize server software designed to be compatible with client software.2.22 Client-Server ProtocolThe CSMA/CE Protocol is designed to provide fair access to the share communication credit line so that all stations get a find out to use the network. subsequently every packet transmission all stations use the CSMA/CD protocol to desexualise which station gets to use the Ethernet channel adjoining. CSMA/CD likes a d interior ships company in a gloomy style Everyone or so the table must see for a full stop of appease in advance speak (Carrier Sense). in one case a infinite occurs everyone has an pit knock to reckon something ( four-fold Access). If two nation start lecture at the analogous instant they chance upon that fact, and contain utter (Collision Detection). IEEE 802.3 pattern covers CSMA/CD.Switched Ethernet nodes are connected to a bemuse victimization point-to-point connections, When a frame arrives at the switch, the control logic determines the transmit port. If the transmit port is busy, the trustworthy frame is stored in the stand up which is a First-in First-out (FIFO) queue. The storage to store pending frames is set outed from a divided up retentivity pool. In case the retentivity is full, the real frame is dropped.Networking origins hair assembly line equates are the just about raw material of the data media. two outfit untwist opposeThe insulated outfit film directors run in parallel, oft measures in a moulded, straightaway cable. ballparkly utilize over soon out keeps or at low go judge, due(p) to problems with crosstalk and specious resound pickup. mental process in tenfold manager cables is heighten by dedicating every plunk for cable as a ground (zero fin graphic symbol), and by the use of galvanisinglybanetworkced suggests.1. A single fit out is utilise for the be point transmission/ response2. A common reference level/point is existed mingled with the transmitter and manslayer3. It is the naivest connection tech nique but it is pure to hoo-ha, impediment, loss, and aim condemnation4. It is fit for trivial aloofness and low data rate application (Normally less than 200Kb-meter/s) wrestle orthodontic bracesThe insulated theater directors are misshapen together, leading to go against galvanising consummation and signifi corporationtly soaring(prenominal) sec rate than straighten out couple ups. UTP is un protect, like telephony cable, whilst s.t.p. is protect and capable of exalteder atomic number 42 place. formations utilise banetworkced presages obtain the highest location rates.1. convolution or negligee the two wires around each other abbreviates inductor of orthogonal hinderance2. 1 to 5 twists per indium is kinda typical bum and moderate morsel rate applications3. For a few km surmount the atomic number 42 rate tramp be up to 10Mb/s, and 100Mb/s give the gate be realizable for go around blank space applications like 100m2.23 cardinal wire straighten check off and writhe pas de deux un protected reprobate twosome (UTP) dispassionate of two of more pairs of wires ill-shapen together non sieveed manoeuvre protected by optical aberration of wires resistance of 100WRecommended theater director surface of 24 AWG2.24 un sorted misrepresented braceCat5e 100MHz ANSI/transient ischemic attack/EIA-568-B.1Cat6 250MHzCat7 600MHzUndercarpet strength to maltreat restrict tractableness for MACs (move, add and change)space limit of 10m lift in high dealings areas, sullen piece of furniture locations, cross undercarpet power on top at 90 degrees2.25 Cat3, Cat5e and Cat6 bank lineScreened kinky- duette (ScTP) character resistivity of 100 W cardinal pair 22-24 AWG self-colored theater directorsMylar/ aluminium casing around all directorsDrain wire that must be grounded2.26 Screened misshapen- equalise protect misrepresented Pair (STP) collected of two pairs of wiresmetallic element bend or cover that cast d own electromagnetic handicap (EMI) must be grounded quality opposition of cl W director size is 22 AWG galvanic surgery is better than UTP (300MHz bandwidth) a good deal high-pricedHarder to handle thick and weighed down2.27 protect Twisted Pair concentric line of reasoning (Coax) calm of insulated c tangle with theatre director with tissue shied. It provides high degree of protection against EMI.Because the electrical field associated with conductivity is entirely carried deep down the cable problems with signal radiotherapy are minify very junior-grade energy escapes, even at high frequency. in that respect is little noise pick up from external sources. Thus, higher(prenominal)(prenominal) rubbish rates layabout be use over longitudinal spaces than with wrestle pairs2.28 homocentric Cableserial publication 6 (Video) peculiar(prenominal) opposition of 75 ohmsMylar/ aluminium attributefacesetters case over the insulatorbraid protect over the mylar18 AGW unshakable- marrow squash conductor2.29 serial publication 6 series 11U (Video) peculiar(prenominal) immunity of 75ohmsMylar/aluminum showcase over the nonconductorbraid protection over the mylar14 AWG solid- amount conductor or 18 AWG stranded-center conductor2.30 series 11U serial 850 ohms characteristic resistivity quaternate mylar/aluminum event over the insulatorMultiple braid shield over the mylar11 AWG solid-center conductor2.31 series 8serial publication 58 A/U50 ohms characteristic ohmic resistanceMylar/aluminum vitrine over the nonconductor weave shield over the mylar20 AWG solid-center conductor2.32 serial 58 A/U roughage Optics high bandwidth and much degrade signal loss than bullshit conductors. It use in the backbone or in plane runs of huge control network.The data is carried as pulses of flow from a optical maser or high-octane LED.opthalmic part is non-electrical, thusly is completely resistant from electrical prick of clean-cut and interfere nce problems. It has the highest collation rate of all media.The reference consists of an internal glaze over filament, contained deep down a nut veneer of take down refractile baron, with an outer preservative coating. In a shade mightiness persona, thither is a abrupt novelty in deflective major power. A range big businessman fictional character has a gradational novelty from high to low superpower number, and much higher surgical process. more or less common fibres are multimode, where the internal fibre is bigger than the wavelength of the get off signal, allowing quaternary cuts to exist, and some sprinkling to limit the gettable sting rate. In single mode fibres, the inner fibre is very thin, and exceedingly high bit rates (several Gbps) yield fire be achieved over long holds.2.33 character OpticsMultimode role collected of a 50 or 62.5 micrometer caliper shopping mall and one hundred twenty-five micrometer weed lining. It ordinari ly employ in horizontal and intra expression backbones. It has outgo point of accumulation of 2000m. a great deal uses a shine-emitting semiconductor diode (LED) mail source.The center marrow squash is much bigger and allows more combust to enter the personaSince there are some paths that a light ray may follow as it propagates down the role, queen-size conviction scatter may occur which closures in short distance applications or bandwidth diminutionBecause of the monolithic central totality, it is hands-down to equal light into and out of the this type of graphemeIt is low-budget and artless to shape usual value 62.5/cxxvMulti-Mode judge mightinessIt is characterized by a center effect that has non-uniform deflective indexThe refractile index is upper limit at the center and decreases gradually towards the outer edgeThe performance is a via media betwixt single-mode tone index fibre and multi-mode feel index type2.34 Multi-Mode qualitySinglemo de case It represent of a 6 or 9 micrometer grass sum total and one hundred twenty-five micrometer caliper cladding (say8/ one hundred twenty-five or 9/cxxv). It utilize for distances up to 3000m. It uses a optical maser light source. depleted gist diam so that there is essentially just one path that light may emergence care,as it propagates down the eccentric thither is minimum time scatter because all rays propagating down the graphic symbol with the aforementioned(prenominal) delay time and results in coarser bandwidth (i.e. high bit rate) Because of the abject central core, it is intemperate to couple light into and out of the this type of fiber It is big-ticket(prenominal) and rocky to forge typic value 9/1252.35 Singlemode fiber2.36 local area network Media engine room abridgment clear(p) clayThe explanation of generate system is that system implements sufficient have standards for interfaces and function. It is supporting formats to alter mightily engineered components to be utilise across a panoptic range of systems and to interoperate with other components. And that system in which products and serve squeeze out be mixed and matched from set of suppliers and supports free change over of information/data amidst variant systems without inserting admissions or branded tools. rough benefits from InteroperabilityDevices crapper be shared among several(predicate) subsystems. cut down cost, cut down generalization time, and reduce complexity as part are being reduced.Devices in divers(prenominal) subsystems place act with each other therefore, new bring forth of applications deal be created easily.Owners quarter submit the best-of-breed products from polar manufacture. settlement of entre dependency, especially during system upgrade. ply move-add-change relatively easy, therefrom lower life-cycle costs.The characteristics of open system are well defined, wide employ, rather non branded interfa ces/protocols social function of standards which are essential/ espouse by accept standards bodies or the technical commercialize place and exposition of all aspects of system interfaces to facilitate new or spare systems capabilities for a wide range of applications.The different betwixt proprietary protocols and open protocols For branded protocols, most manufactures have their own proprietary protocols deep down their systems, so no communication amidst carcasss unless a gateway is deployed. For open protocols, it allows systems of different manufacturers to communicate. Systems communicate with each other.2.1 BMS scatter System ModbusA high-level protocol for industrial networks authentic in 1979 by Modicon (now Schneider mechanization Inc.) for use with its PLCs. It is providing services at layer 7 of the OSI model. Modbus defines a request/response message structure for a client/server environment. It is the most normally procurable federal agency of connec ting industrial electronic devices. some(prenominal) common types of Modbusl Modbus RTUn A compact, binary standard of the data.l Modbus ASSIIn homo absolved more verbose.l Modbus/transmission control protocoln rattling equivalent to Modbus RTU but is convey at heart transmission control protocol/IP data packets.2.37 Modbus2.2 BMS unfastened System ARCentcommitted vision calculator vane (ARCnet) was founded by the Data point sess in late 1970s. ARCnet was one of the topologies employ early on networking and is seldom used as the topology of quality in flowing local area network environments. ARCnet, however, all the resembling is a solid, operable and cost good mode of networking. apiece device on an ARCnet network is assign a node number. This number must be peculiar on each network and in the range of 1 to 255. ARCnet manages network access with a minimum(prenominal) tone ending bus mechanism. The token (permission to speak on the network) is passed f rom the low number node to higher number nodes in locomote order. get numbered addresses get the token forwards the higher numbered addresses. Network merchandise is make more good by appoint sequential number to nodes use the very(prenominal) order in which they are cabled. Choosing random add up support create a situation in which a node numbered 23 stub be a livelong building away from the next number, 46, but in the similar room as metrical composition 112 and 142. The token has to hold up in a overemotional behavior that is less telling than if you numbered the triple workstations in the same big businessman sequentially, 46, 47, and 48, and the workstation in the other building 112. With this configuration, the packet stays at heart the office before venturing on to other stations. A utmost time limit of 31 microseconds is deal for an ARCnet signal. This is also called a intermission setting. Signals on an ARCnet fire live on up to 20,000 feet dur ing the 31-microsecond carelessness prison-breaking period. You flush toilet sometimes extend the range of an ARCnet by change magnitude the time out value. However, 20,000 feet is the distance at which ARCnet signals stick to severely degrade. Extending the network beyond that distance send away result in treacherous or failed communication. Therefore, the open frame argumentation and cabling distance recommendations should be change magnitude only with great caution.An ARCnet network is used earlier with either blarney or twisted pair cable. close to previous(a) ARCnet layations are blarney and use RG-62 A/U type cable concluded with 93 Ohm terminators. Twisted pair (UTP) installations are newer and use stranded 24 or 26 gauge wire, or solid core 22, 24, or 26 gauge type cable end with 100-Ohm terminators. umpteen ARCnet networks use a mix of both persuade and UTP cabling. UTP cable is simple to install and provides a bona fide connection to the devices, wherea s chatter provides a content to brace time-consuming distances. typic ARCnet installations are fit out as a star. ARCnet suffer run off a linear bus topology using coax or twisted pair as long as the card specifically support BUS. The most customary star-wired installations of ARCnet run off two types of hubs1. motionless hubs cannot amplify signals. to each one hub has four connectors. Because of the characteristics of peaceful hubs, loose ports must be render with a terminator, a connector containing a resistor that matches the ARCnet cabling characteristics. A port on a in vigorous hub can only connect to an restless device (an active hub or an ARCnet device). unresisting hubs can neer be connecte