Risunok 1. Funkcional'naya shema apparatury Watchdog
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PC-router--eto IBM PC, nizhe srednego klassa (po segodnyashnim merkam), bez monitora, klaviatury i gibkogo diska, s operacionnoi sistemoi OS Linux i svobodnym programmnym obespecheniem dlya OS Linux. Vo vremya podgotovki k ustanovke v gorodskuyu telekommunikacionnuyu sistemu PC-router snabzhaetsya setevoi periferiei (komplektnost' zavisit ot primeneniya), a ego programmnoe obespechenie konfiguriruetsya tak, chtoby:
Takim obrazom, PC-router-specializirovannaya PEVM, kotoraya v razlichnyh konfiguraciyah realizuet raznoobraznye funkcional'nye ustroistva v gorodskoi telekommunikacionnoi seti. Pri etom stoimost' lyubogo takogo ustroistva ves'ma skromnaya: $400-$1,000.
Podcherknem vysokuyu modul'nost' dannogo podhoda k realizacii sistemy: bol'shaya chast' gorodskoi sistemy telekommunikacii postroena iz:
Bazovym komplektom apparatury RS-routera:
Pri zakupke tol'ko novyh komplektuyushih, dostupnyh na komp'yuternom rynke, poluchaem sleduyushuyu ocenku stoimosti bazovogo komplekta apparatury PC-routera:
| korpus minitower s blokom pitaniya | $30 |
| materinskaya plata SIS 496 PCI | $60 |
| processor AMD 486DX4-100 | $35 |
| SIMM 72 pin 8 MB | $35 |
| HDD 850 MB | $160 |
| ITOGO | $320 |
Interfeisnoe oborudovanie PC-routera prednaznacheno dlya podklyucheniya obsluzhivaemyh im kanalov i ustroistv. Ih sostav i kolichestvo opredelyaetsya konkretnym primeneniem PC-routera.
V kachestve interfeisnoi apparatury rekomenduem ispol'zovat' sleduyushie izdeliya(4):
| Naznachenie | Izdelie | Cena |
| Interfeis lokal'noi seti | setevaya karta Ethernet 10Mbps NE2000 ISA | $20 |
| setevaya karta Ethernet 10Mbps NE2000 PCI | $20 | |
| setevaya karta Ethernet 10Mbps NE2100 PCI | $20 | |
| setevaya karta Ethernet 10Mbps 3C509 ISA | $70 | |
| setevaya karta Ethernet 100Mbps DEC21140 PCI | $76 | |
| setevaya karta Ethernet 100Mbps 3C595 PCI | $100 | |
| Podklyuchenie modemov (asinhronnye porty) | interfeisnaya plata Titan 9006, 4 x RS-232C, FIFO, ISA | $85 |
| interfeisnaya plata SCS-16, 16 x RS-232C, FIFO, ISA (sobstvennaya razrabotka laboratorii Botik) | $250 | |
| Podklyuchenie sinhronnyh modemov | interfeisnaya plata SDL Riscom N2, 2xV.35, do 4 Mbps, ISA | $1,000 |
| Kanaly Radio-Ethernet | setevaya karta RadioEthernet WaveLAN 2.4GHz, 2Mbps, ISA | $900 |
Parallel'nye i asinhronnye posledovatel'nye porty, kak pravilo, prisutstvuyushie v bazovom komplekte apparatury PC-routera, takzhe mogut ispol'zovat'sya dlya podklyucheniya kanalov i ustroistv.
Vyshe perechislena vsego lish' ta chast' iz vozmozhnogo interfeisnogo osnasheniya PC-routera, kotoraya predstavlyaetsya nam naibolee osmyslennoi na segodnyashnem etape razvitiya gorodskih telekommunikacionnyh podsistem.
Zametim, chto PC-router obladaet neobychainymi gibkost'yu i vozmozhnostyami narashivaniya proizvoditel'nosti svoei interfeisnoi chasti i podderzhki vsevozmozhnyh interfeisov i protokolov. Tak, uzhe segodnya interfeisnaya chast' PC-routera mozhet podderzhivat' 100Base-T, FDDI, ATM i pr.(5) Odnako shirokoe ispol'zovanie etih telekommunikacionnyh tehnologii v gorodskih telekommunikacionnyh sistemah predstavlyaetsya seichas v bol'shinstve sluchaev prezhdevremennym.
PC-router (pri lyubom apparatnom i programmnom napolnenii) vypolnen tak, chto operaciya re-inicializacii (sbros ili otklyuchenie-vklyuchenie pitaniya):
Takim obrazom:
Bolee togo, dlya bolee bystrogo vosstanovleniya rabotosposobnosti "podvisshego" PC-routera bez vmeshatel'stva mestnogo personala, nastoyatel'no rekomenduetsya vo vseh PC-routerah ustanavlivat' special'nuyu apparaturu (tak nazyvaemyi watchdog) slezheniya za rabotosposobnost'yu PC-routera i avtomaticheskogo vosstanovleniya (re-inicializacii) "podvisshego" PC-routera.
Snabzhennyi watchdog-apparaturoi PC-router yavlyaetsya predel'no nadezhnym neobsluzhivaemym setevym ustroistvom i ne predpolagaet nalichiya personala v tochke ego raspolozheniya.
Programmno-apparatnyi kompleks watchdog prednaznachen dlya:
Slezhenie za rabotosposobnost'yu sistemy i vyrabotka signala o normal'noi rabote sistemy (dalee--O'K) realizovano programmno: v PC-routere zapuskaetsya watchdog-draiver--Unix-process, postoyanno sledyashii za ispravnost'yu sistemy. Konkretnyi nabor vypolnyaemyh proverok zavisit ot konfiguracii i periferii PC-routera.
Poka uslovie "vse rabotaet normal'no" vypolnyaetsya, dannyi process (watchdog-draiver) s nekotorym periodom t vydaet apparatnyi signal O'K na interfeis watchdog-apparatury.
Apparatnaya chast' watchdog vyrabatyvaet signal Reset v sluchae, esli v techenie perioda T > t ne postupil signal O'K podtverzhdeniya normal'noi raboty sistemy. Takim obrazom, vne zavisimosti ot prichin sboya (apparatnoe "zavisanie", programmnye oshibki), poteryannaya rabotosposobnost' PC-routera budet garantirovanno vosstanovlena bez vmeshatel'stva personala.
Dlya peredachi ot watchdog-draivera k watchdog-apparature signala O'K ispol'zovan standartnyi raz'em dlya podklyucheniya vnutrennego dinamika IBM PC--raz'em speaker, prisutstvuyushii na materinskih platah vseh tipov. Takoe reshenie obuslovleno zhelaniem isklyuchit' dorabotku materinskih plat i ne zanimat' standartnye raz'emy shiny, kotorye yavlyayutsya kritichnym resursom PC-routera, tak kak ih mozhno ispol'zovat' dlya podklyucheniya setevoi periferii. Ispol'zovanie raz'ema speaker kak interfeisa mezhdu draiverom i apparaturoi watchdog:
Risunok 1. Funkcional'naya shema apparatury Watchdog
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Funkcional'no Watchdog predstavlyaet soboi odnovibrator i sostoit iz dvuh uzlov (sm. Risunok 1):
Chastota generatora--5.5 +/- 0.5 KGc, chto pozvolyaet poluchit' na vyhode delitelya signal s periodom T okolo 3 min. Takaya velichena zaderzhki neobhodima dlya togo, chtoby watchdog dozhdalsya (ne sdelal sbrosa) vypolneniya zagruzki operacionnoi sistemy, zapuska watchdog-draivera i polucheniya pervogo signala O'K ot nego.
Posle zapuska programmnogo obespecheniya, watchdog-draiver vyrabatyvaet signal O'K s periodichnost'yu t < T. Etot signal sbrasyvaet v nol' schetchik watchdog-apparatury. Pri otsutstvii signala sbrosa v techenie perioda T schetchik perepolnyaetsya i apparatura watchdog vyrabatyvaet signal Reset--proizvodit perezagruzku sistemy.
Sbros schetchika watchdog-apparatury (ustanovka ego v nulevoe sostoyanie) proishodit takzhe:
Dlya indikacii raboty watchdog-apparatury ispol'zuetsya svetodiod TurboLED (signal LED ).
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v shemu apparatnoi chati Watcdog vneseny sleduyushie izmeneniya:
Eto povysilo udobstvo kontrolya rabotosposobnosti Watcdoga i pozvolilo ispol'zovat' apparaturu s materinskimi platami, na kotoryh signal na vyhode raz'ema speaker imet nebol'shuyu amplitudu.
Risunok 2. Principial'naya shema apparatury Watchdog
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Shema watchdog (sm. Risunok 2) realizovana na rasprostranennoi specializirovannoi chasovoi mikrosheme K176IE12, imeyushei v svoem sostave dva invertora i dva delitelya na 32768 i 60. Eto pozvolilo oboitis' pri proektirovanii odnim korpusom.
Generator realizovan na dvuh invertorah mikroshemy DD1 (vyvody 12, 13, 14) i vneshnih elementah R8, C3 i C4, zadayushih chastotu generacii. Chastota generatora podobrana dostatochno vysokoi dlya obespecheniya stabil'nosti generacii i oblegcheniya zapuska generatora.
Schetchik sobran na delitelyah mikroshemy DD1, vklyuchennyh posledovatel'no.
Dlya indikacii raboty watchdog ispol'zovan svetodiod Turbo LED korpusa sistemnogo bloka, migayushii s chastotoi vzyatoi s vyhoda delitelya na 32768.
Signal Reset vyrabatyvaetsya pri poyavlenii "1" na vyhode delitelya na 60 (vyvod 4). Formirovanie signala proizvoditsya tranzistorami VT3 i VT4. Ispol'zovanie dvuh tranzistorov pozvolyaet podklyuchat' raz'em reset s proizvol'noi polyarnost'yu. Signal Reset derzhitsya vklyuchennym v techenie 1/120 T, a zatem proishodit sbros schetchika i snyatie signala Reset. Eto realizovano na tranzistore VT2, vypolnyayushem funkcii logicheskogo "I" s odnim invertirovannym vhodom.
Na diodah VD1, VD2 i tranzistore VT1 sobran trehvhodovyi logicheskii element "ILI". Otklyuchenie watchdog proizvoditsya knopkoi Turbo korpusa sistemnogo bloka, pri etom proishodit ustanovka na vhode sbrosa schetchika logicheskoi edinicy.
Pri ustanovke watchdog-apparatury i podklyuchenii ee k materinskoi plate PC-routera sleduet uchityvat' polyarnost' raz'emov Speaker i TurboLED.
V sluchae otsutstviya zemli na raz'eme Speaker materinskoi platy mozhno ispol'zovat' kontakt zemli s raz'ema reset. Dlya etogo sleduet vmesto tranzistora VT4 ustanovit' peremychku mezhdu ego kollektorom i emitterom. Posle takoi peredelki sleduet osobenno vnimatel'no sledit' za polyarnost'yu podklyucheniya watchdog-apparatury k raz'emam Speaker i Reset.
Specifikaciya detalei platy Watchdog privedena v tablice 3.
29.06.98| Poziciya | Oboznachenie | Naimenovanie | Kol. | Primechanie |
| Kondensatory | ||||
| 1 | C1,C2,C5 | KM-6-25V-100nF | 3 | |
| 2 | C3 | KM-6-25V-220pF | 1 | |
| 3 | C4 | KM-6-25V-3nF | 1 | |
| Mikroshema | ||||
| 4 | DD1 | K176IE12 | 1 | |
| Rezistory | ||||
| 5 | R1,R12 | MLT 0,125Vt-180 Om 5% | 2 | |
| 6 | R2 | MLT 0,125Vt-1 kOm 5% | 1 | |
| 7 | R3,R4,R5 | MLT 0,125Vt-100 kOm 5% | 3 | |
| 8 | R6,R7,R9-R11 | MLT 0,125Vt-20 kOm 5% | 5 | |
| 9 | R8 | MLT 0,125Vt-200 kOm 5% | 1 | |
| 10 | R13 | MLT 0,125Vt-51 Om 5% | 1 | |
| Tranzistory | ||||
| 11 | VT1,VT2 | KT3107B | 2 | KT3107 |
| 12 | VT3-VT5 | KT3102E | 3 | KT3102G,D |
| Diody | ||||
| 13 | VD1,VD2 | KD522 | 2 | |
| Raz'emy | ||||
| 14 | XP2 | 4-h shtyr'kovyi | 1 | |
| 15 | XP3,XP4 | 2-h shtyr'kovye | 2 | |
Pri akkuratnoi sborke watchdog po sheme (sm. Risunok 2) s sootvetstvuyushimi nominalami (sm. Tablica 3) shema ne trebuet naladki.
Zametim, chto sredi prochego ustanovka watchdog v PC-router povyshaet distancionnuyu upravlyaemost' sistemy: administrator poluchaet sredstvo udalennogo vypolneniya zhestkogo sbrosa lyubogo PC-routera-dlya etogo dostatochno ostanovit' watchdog-draiver i cherez vremya T PC-router budet zhestko re-inicializirovan.
29.06.98Nizhe privedeno izobrazhenie pechatnoi platy watchdog v uvelichennom massshtabe. Pechatnaya plata vypolnena odnostoronnei, s kontaktnymi ploshadkami uvelichennogo diametra i shirokimi (0.65 mm) provodnikami. Eto pozvolyaet pri neobhodimosti vosproizvesti ee v kustarnyh usloviyah. K kontaktam XS1 i XS2 sleduet pripayat' provodniki, zakanchivayushiesya sootvetstvuyushimi raz'emami, plya podklyucheniya k materinskoi plate. Bolee polnuyu konstruktorskuyu dokumentaciyu sleduet smotret' v Prilozhenii 5.
V kachestve operacionnoi sistemy (OS) PC-routera ispol'zovana OS Linux--svobodnyi klon OS UNIX. Yadro Linux obespechivaet marshrutizaciyu IP-paketov, fil'traciyu paketov (IP firewalling), podschet paketov (IP accounting), i rabotu s razlichnymi tipami setevyh interfeisov i protokolov. Nami ispol'zovalis':
V obshem sluchae vnezapnye vyklyucheniya Unix-komp'yutera mogut privesti k narusheniyam korrektnosti failovoi sistemy. Povrezhdeniya voznikayut iz-za togo, chto operacii s failovoi sistemoi ne yavlyayutsya nedelimymi; naprimer, modifikaciya faila vklyuchaet v sebya izmenenie kak blokov faila, tak i opisatelya faila (i-node), spiska svobodnyh blokov i t.d., kotorye zapisyvayutsya na disk neskol'kimi razdel'nymi operaciyami zapisi. Posle vypolneniya pervoi iz operacii i vplot' do zaversheniya poslednei failovaya sistema na diske nahoditsya v promezhutochnom, perehodnom sostoyanii; esli v etot moment proizoidet vyklyuchenie, failovaya sistema tak i ostanetsya v nekorrektnom sostoyanii i budet trebovat' pochinki (fsck).
Vo mnogih sluchayah povrezhdeniya okazyvayutsya neser'eznymi, tak chto pri zagruzke sistemy vozmozhna avtomaticheskaya pochinka bez poteri failov (fsck -a). Tem ne menee, sushestvuet veroyatnost' ser'eznogo povrezhdeniya, kotoroe potrebuet pochinki v ruchnom rezhime i, vozmozhno, vosstanovleniya poteryannyh failov. Poetomu dopuskat' povrezhdeniya failovoi sistemy PC-routera nel'zya, ibo eto protivorechit principu neobsluzhivaemosti izdeliya.
Nami predlozheno sleduyushee reshenie dannoi problemy. Poskol'ku povrezhdeniya voznikayut isklyuchitel'no kak rezul'tat nezavershennyh operacii zapisi na disk, my mozhem izbezhat' povrezhdenii, rabotaya s diskom v rezhime "tol'ko na chtenie" (read-only, r/o). Odnako prosto smontirovat' ves' disk read-only nel'zya, poskol'ku dlya polnocennoi raboty sistemy trebuetsya, chtoby nekotorye katalogi (/tmp, /var/run, /var/log, ...) rabotali v rezhime "chtenie i zapis'" (read/write, r/w). Pri etom zapisyvaemaya v eti katalogi informaciya nosit prehodyashii harakter (vremennye faily, .pid faily, faily s otladochnymi protokolami i t.d.) Poetomu polnocennoe reshenie problemy vyglyadit tak:
Detal'no realizaciya ustoichivosti PC-routera k otklyucheniyu pitaniya v proizvol'nye momenty vremeni obsuzhdaetsya v prilozhenii "Obespechenie celostnosti failovoi sistemy pri vnezapnyh vyklyucheniyah routera".
Dlya mnogih primenenii PC-routerov dostatochno staticheskoi marshrutizacii, no vozmozhen i zapusk na PC-routere demona dinamicheskoi marshrutizacii (gated, protokoly BGP-4, OSPF-2).
Mozhet byt' podderzhana (ipfwadm) i fil'traciya IP-paketov
Yadro Linux podderzhivaet rabotu PC-routera v rezhime mosta (bridge), pozvolyaya ob'edinyat' segmenty Ethernet v edinuyu logicheskuyu set'. Pri etom podderzhivaetsya protokol IEEE Spanning Tree 802.1d, pozvolyayushii vnosit' izbytochnost' v graf seti s cel'yu povysheniya ustoichivosti k otkazam otdel'nyh segmentov seti.
Linux podderzhivaet rabotu PC-routera v rezhime IPX-marshrutizatora (IPX router specification v1.20). Takzhe podderzhivaetsya peredacha IPX paketov po PPP-kanalam, i tunnelirovanie IPX-in-IP. Podderzhana fil'traciya IPX-paketov.
Vozmozhna organizaciya na baze PC-routera servera bezopasnosti (firewall), obespechivayushego stroguyu reglamentaciyu dostupa k mashinam obsluzhivaemoi seti iz vneshnego mira.
PC-router mozhet vypolnyat' statisticheskii uchet (ipfwadm-2.3) po IP/IPX-trafiku i po ispol'zovaniyu modemnogo pula.
Pri nevysokoi skorosti linii svyazi mezhdu lokal'noi set'yu i vneshnim mirom, vremya razresheniya domennyh imen (preobrazovaniya imen v IP-nomera) dlya mashin lokal'noi seti mozhet byt' sushestvenno uluchsheno za schet zapuska na PC-routere demona named v keshiruyushem rezhime.
Podklyuchenie k PC-routeru printera pozvolyaet ispol'zovat' ego kak setevoi printer. Prichem vozmozhna organizaciya preobrazovaniya dannyh pered pechat'yu, naprimer, iz formata Postscript v format komand printera.
V ST "Botik" modemnyi pul podklyuchen ne k central'nomu serveru, a k PC-routeru trub-router, dostatochno udalennomu ot central'nogo servera (6 km, dva IP-perehoda: 10Base-FL i RadioEthernet).
Takim obrazom, sredi prochego dannyi PC-router rabotaet i kak terminal'nyi server. On obsluzhivaet 16 asinhronnyh portov s modemami, obrabatyvaet vhodnye zvonki dial-up pol'zovatelei i organizuet peredachu "po IP-tunelyam" potokov dannyh ot modemov k central'nomu serveru. Real'no zhe ("soderzhatel'no") rabotaet s dial-up pol'zovatelyami central'nyi server.
Po etoi zhe sheme organizovan priem FAX-soobshenii na etot zhe modemnyi pul.
Organizaciya terminal'nogo servera na PC-routere ves'ma effektivnoe reshenie. Ono pozvolyaet osvobodit' central'nyi server ot obrabotki mnogochislennyh preryvanii ot asinhronnyh portov i razmestit' modemnyi pul tam, gde eto udobno.
Zainteresovannomu chitatelyu rekomenduem sravnit' funkcii i ceny PC-routera trub-router s ego "zheleznym" firmennym analogom--pretendentom v nominacii "produkty dlya komp'yuternoi svyazi" na vystavke "Comdex/Spring'97" (sm. http://www.equinox.com/termserv/termserv.html).
Udalennaya konfiguraciya routera proizvoditsya v rezhime terminal'nogo dostupa po protokolam telnet ili rlogin/rsh. Vozmozhno takzhe ispol'zovanie protokola SNMP.
