TableOfContents

Case studies

Non importa quanta progettazione occorre nella pianificazione delle locazioni dei nodi o dei collegamenti, dovrete inevitabilmente lanciarvi e realmente installare qualcosa. Questo è il momento della verità che dimostra proprio quanto le vostre valutazioni e previsioni risultano essere esatte.

È raro il caso in cui tutto va precisamente come previsto. Anche dopo aver installato il vostro primo, decimo, o centesimo nodo, state tranquilli che le cose non sempre si risolveranno come avevate previsto. Questo capitolo descrive alcuni dei nostri più memorabili progetti della rete. Se state per intraprendere il vostro primo progetto wireless o siete un esperto in questo, è bene ricordarsi che c'è sempre qualcosa in più da imparare.

Consigli generali

Le economie dei paesi in via di sviluppo sono molto differenti dal mondo evoluto e così un processo o una soluzione progettata per un paese evoluto non può essere adatta in Africa Occidentale, o in Asia Meridionale. Specificamente, il costo dei materiali prodotti localmente ed il costo del lavoro sono trascurabili, mentre le merci importate possono essere molto più costose se confrontate al loro costo nel mondo evoluto. Per esempio, si può produrre ed installare una torre per un decimo del costo di una torre negli Stati Uniti, ma il prezzo di un'antenna potrebbe essere il doppio. Le soluzioni che sfruttano i vantaggi competitivi locali, vale a dire lavoro a buon mercato e materiali trovati localmente, saranno più facili da replicare.

L'individuazione della giusta apparecchiatura è una delle mansioni più difficili nei mercati in via di sviluppo. Poiché il trasporto, la comunicazione ed i sistemi economici non sono evoluti, i giusti materiali o attrezzature possono essere difficili e spesso impossibili da trovare. Un fusibile, per esempio, è difficile da trovare, così trovare un filo che ha un burn-up ad un determinato amperaggio che possa sostituirlo è un grande vantaggio. Trovare sostituti locali per i materiali inoltre incoraggia l'attività imprenditoriale locale, la proprietà, e può far risparmiare soldi.

Involucro delle apparecchiature

La plastica economica si trova dappertutto nel mondo evoluto, ma è fatta di materiali poveri e sottili, così principalmente è inadatta per l'involucro delle apparecchiature. I tubi in PVC sono molto più resistenti e sono costruiti per essere impermeabili. In Africa Occidentale, il PVC più comune è usato per gli impianti idraulici, di grandezza da 90mm a 220mm. Gli access points come i Routerboard 500 e 200 possono essere inseriti in tale tubazione con le estremità finali saldate, che possono costituire involucri impermeabili molto robusti. Inoltre essi hanno l'ulteriore beneficio di essere aerodinamici e passare inosservati. Lo spazio lasciato intorno all'apparecchiatura assicura sufficiente circolazione di aria. Inoltre, è spesso meglio lasciare un foro di scarico nella parte inferiore dell'involucro del PVC. L'autore ha trovato che lasciare i fori aperti può trasformarsi in in un problema. Una volta le formiche decisero di fare il nido 25 metri sopra la terra all'interno del PVC che conteneva l'access point. Si raccomanda l'uso di una copertura a rete metallica fatta con materiale schermato localmente disponibile per impedire infestazioni al foro di scarico.

Supporti di antenna

Recuperare i materiali usati si è trasformato in un'industria importante per i paesi più poveri. Dalle vecchie automobili alle televisioni, tutto il materiale che ha valore sarà smontato, venduto, o riutilizzato. Per esempio, vedrete veicoli smontati pezzo per pezzo quotidianamente. Il metallo risultante è ordinato e poi è caricato su un camion per la vendita. I lavoratori del metallo locali già sono a conoscenza di come fare i supporti per la televisione con la ferraglia. Alcuni adattamenti rapidi e questi stessi supporti possono essere riutilizzati per le reti wireless.

Il supporto tipico è il palo di 5 metri, formato da un singolo tubo di diametro di 30mm che è poi piantato nel cemento. È meglio costruire il supporto in due parti, con una parte removibile che si inserisce in una base che è un po' più grande di diametro. In alternativa, il supporto può essere fatto con aste che possono essere cementate saldamente ad una parete. Questo progetto è facile, ma richiede l'uso di una scala per completarlo e quindi è suggerita una certa attenzione.

Questo tipo di supporto può essere allungato di parecchi metri con l'uso di cavi di ritegno. Per irrobustire il palo, piantare tre cavi a 120 gradi, con una diminuzione di almeno di 33 gradi dalla punta della torre.

Importante: far partecipare la comunità locale

La partecipazione della comunità è di importanza fondamentale nell'assicurare il successo e la sostenibilità di un progetto. Far partecipare la comunità in un progetto può essere la sfida più grande, ma se essa non viene coinvolta la tecnologia non servirà alle sue esigenze, né sarà accettata. Inoltre, una comunità potrebbe impaurirsi e mandare a monte l'iniziativa. Indipendentemente dalla complessità dell'impresa, un progetto per avere successo ha bisogno di supporto e credito da parte di coloro a cui servirà.

Una strategia efficace nel guadagnare il supporto è di trovare un campione di persone rispettato che abbia motivi sufficientemente allettanti alla collaborazione. Trovate la persona, o le persone che più probabilmente si interesseranno al progetto. Spesso, avrete la necessità di far partecipare campioni come consiglieri, o membri di un comitato di coordinamento. Questa gente avrà già la fiducia della comunità, saprà chi avvicinare e può parlare la lingua della comunità. Prendetevi il vostro tempo ad essere selettivo nell'individuazione della giusta gente per il vostro progetto. Nessun'altra decisione interesserà il vostro progetto più dell'avere gente locale efficace e di fiducia nella vostra squadra.

In più, prendete nota delle persone chiave in un'istituzione, o nella comunità. Identificate la gente che probabilmente rappresenta avversari e fautori del vostro progetto. Prima possibile, cercate di guadagnare il supporto dei potenziali fautori e di allontanare gli avversari. Ciò è una difficile operazione che richiede la conoscenza approfondita dell'istituzione o della comunità. Se il progetto non ha un alleato locale, è necessario tempo per acquistare queste conoscenze e la fiducia dalla comunità.

Fare attenzione nella scelta dei vostri alleati. Un incontro in municipio è spesso utile per vedere i politici , le alleanze ed le ostilità locali in gioco. Da allora in poi, è più facile decidere chi sia l'alleato, il campione e chi è da allontanare. Cercate di non sollevare entusiasmo ingiustificato. È importante essere onesto, franco e non fare promesse che non possiate mantenere.

Nelle comunità in gran parte analfabeta, focalizzatevi sui servizi digitali e analogici come Internet per le stazioni radiofoniche, stampando articoli e foto on line ed altre applicazioni non testuali. Non cercate di introdurre una tecnologia ad una comunità senza capire quali applicazioni veramente serviranno alla comunità. Spesso la comunità ha poche idee di come le nuove tecnologie la aiuteranno nei suoi problemi. Semplicemente fornire le nuove caratteristiche è inutile senza una comprensione di come la comunità se ne avvantaggerà.

Nel riunire le informazioni, verificare i fatti di cui avete i dati. Se desiderate conoscere la situazione finanziaria di un'azienda/organizzazione, chiedete di vedere una fattura dell'elettricità, o la fattura del telefono. Stanno pagando le loro fatture? A volte, beneficiari potenziali compromettono i loro propri valori nella speranza di vincere fondi monetari o attrezzature. Molto più spesso, partners locali che si fidano di voi saranno molto franchi, onesti ed utili.

Un altro trabocchetto comune è quello che io chiamo sindrome dei genitori divorziati, dove NGOs, donatori e partners non parlano di altri coinvolgimenti con il beneficiario. I beneficiari di Savvy possono guadagnare ricompense attraenti lasciando gli NGOs ed i donatori elargire loro apparecchiature, addestramento e fondi monetari. È importante sapere quali altre organizzazioni sono coinvolte in modo da poter capire come le loro attività potrebbero impattare sulle vostre. Per esempio, io una volta disegnai un progetto per una scuola rurale nel Mali. La mia squadra installò un sistema open source con i calcolatori utilizzati e spese parecchi giorni ad addestrare la gente su come usarlo. Il progetto fu ritenuto un successo, ma subito dopo l'installazione, un altro donatore è arrivato con i nuovissimi calcolatori Pentium 4 con in funzione Windows XP. Gli allievi abbandonarono rapidamente i calcolatori più vecchi e si predisposero ad utilizzare i nuovi calcolatori. Sarebbe stato meglio negoziare in anticipo con la scuola, conoscere il loro impegno nel progetto. Se fossero stati franchi, i calcolatori che ora sono accantonati inutilizzati potevano essere stati assegnati ad un'altra scuola dove sarebbero stati usati.

In molte comunità rurali nelle economie sottosviluppate, la legge e le politiche sono deboli ed i contratti possono essere effettivamente insignificanti. Spesso, altre assicurazioni devono essere trovate. Qui i servizi prepagati sono ideali, poiché non richiedono un contratto legale. L'impegno è assicurato dall'investimento dei fondi monetari prima che il servizio sia erogato.

Ottenere credito inoltre richiede che quelli che sono coinvolti investano nel progetto essi stessi. Un progetto dovrebbe chiedere la partecipazione reciproca dalla comunità.

Soprattutto, l'opzione "no-go" dovrebbe essere valutata sempre. Se non si possono avere un alleato e una comunità locali acquirenti, il progetto dovrebbe considerare la possibilità di scegliere una comunità o un beneficiario differente. Ci deve essere una trattativa; l'apparecchiatura, i soldi e l'addestramento non può essere regalato. La comunità deve essere coinvolta e deve anche contribuire.

--Ian Howard

Case study: Realizzare il divide con un semplice ponte in Timbuktu

In definitiva le reti collegano insieme la gente e quindi hanno sempre una componente politica. Il costo di Internet nelle economie meno sviluppate è alto e la possibilità di pagare è bassa, che si aggiunge alle sfide politiche. Tentare di sovrapporre una rete dove le comunicazioni umane non sono completamente funzionanti è quasi impossibile a lungo termine. Comportarsi in questo modo può portare un progetto su un terreno sociale instabile, minacciando la sua esistenza. È qui dove il basso costo e la mobilità di una rete wireless possono risultare convenienti.

La squadra dell'autore fu richiesta dai finanziatori per determinare come collegare una stazione radiofonica rurale con un telecentro molto piccolo (2 computer) ad Internet in Timbuktu, la capitale del deserto di Mali. Timbuktu è ampiamente conosciuto come un avamposto nell'area più remota del mondo. In questo posto, la squadra decise di implementare un modello che è stato chiamato il modello wireless parassita. Questo modello prende alimentazione wireless generata da una rete esistente ed estende quella rete fino al posto del client usando un semplice ponte di rete. Questo modello fu scelto perché non richiede un significativo investimento dall'organizzazione di supporto. Esso non aggiunse significativi costi di funzionamento, mentre aggiunse una fonte di reddito per il telecentro. Questa soluzione significò che nel posto del client si poteva ottenere Internet economico, anche se non così veloce o affidabile come una soluzione dedicata. A causa dell'uso di modelli opposti fra un ufficio e un telecentro non vi era un grande ritardo della rete da ambedue le parti. Comunque in una situazione ideale sarebbe stato meglio consigliare un maggior sviluppo del piccolo telecentro in un ISP, ma allora nè il telecentro nè il mercato erano pronti. Come spesso è il caso, vi erano serie preoccupazioni circa la possibilità di questo telecentro di auto-sostenersi una volta che i suoi finanziatori fossero andati via. Quindi, questa soluzione ha minimizzato l'investimento iniziale realizzando due obiettivi: in primo luogo, ha reso disponibile Internet,una stazione radiofonica, al beneficiario di riferimento ad un costo accessibile. In secondo luogo, ha aggiunto una piccola fonte supplementare di reddito per il telecentro senza aumentare le sue spese di funzionamento, o senza aggiungere complessità al sistema.

La gente

Sebbene abbia un nome famoso nel mondo, Timbuktu è lontana. Rappresentando il simbolo di lontananza, molti progetti hanno voluto piantare una bandiera nelle sabbie di questa città del deserto. Quindi, c'è un certo numero di informazioni e di attività di tecnologie di comunicazioni (ICT) nella zona. Alla fine si contano 8 collegamenti satellitari in Timbuktu, la maggior parte dei quali servono interessi speciali tranne che per due compagnie, SOTELMA e Ikatel. Attualmente esse usano VSAT per collegare le loro reti telefoniche al resto del paese. Questo telecentro ha usato un collegamento X.25 ad uno di questi telcos, che poi ha trasmesso il collegamento indietro a Bamako. Rispetto ad altre città remote nel paese, Timbuktu ha il numero giusto di personale IT addestrato, tre telecentri esistenti , più il telecentro recentemente installato alla stazione radiofonica. La città è ad un certo grado di saturazione con Internet, precludendo rinnovabilità ad ogni interesse privato e commerciale.

Scelta di progettazione

In questa installazione il luogo del client è lontano soltanto 1 chilometro direttamente a vista. Furono installati due access points Linksys modificati, con piattaforma OpenWRT in ponte fra di loro. Uno fu installato sulla parete del telecentro e l'altro fu stato installato a 5 metri sul palo della stazione radiofonica. Gli unici parametri di configurazione richiesti su entrambi i dispositivi erano l'ssid e il canale. Furono usate 14 semplici antenne a pannello dBi (da http://hyperlinktech.com/). Sul lato Internet, l'access point e l'antenna furono fissati usando tasselli di cemento e viti sul lato dell'edificio, di fronte al luogo del client. Dal lato del client, fu usato un palo di antenna esistente. L'access point e l'antenna urono montati usando anelli sul tubo.

Per disconnettere il client, il telecentro scollega semplicemente il ponte dal suo lato. Un posto supplementare eventualmente potrebbe essere installato ed ugualmente avrà il suo proprio ponte al telecentro in modo che il personale possa staccare fisicamente il client se non è stato effettuato il pagamento. Benchè rozza, questa soluzione è efficace e riduce il rischio che il personale faccia un errore mentre effettua il cambiamento della configurazione del sistema. Avere un ponte dedicato ad un collegamento inoltre semplificò l'installazione al posto centrale, poichè la squadra di installazione potette scegliere il miglior posto per il collegamento ai posti dei client. Benchè non sia ottimale creare un ponte su una rete (piuttosto che instradare il traffico di rete), quando la conoscenza della tecnologia è bassa e si desidera installare un sistema molto semplice, questa può essere una soluzione ragionevole per piccole reti. I sistemi forniti di ponte installati sul posto remoto (la stazione radiofonica) appaiono come se fossero semplicemente collegati alla rete locale.

Modello finanziario

Il modello finanziario qui è semplice. Il telecentro fa pagare una tassa mensile, circa $30 per il calcolatore collegato alla stazione radiofonica. Questo era molte volte più economico di ogni altra alternativa. Il telecentro è situato nel cortile dell'ufficio del Sindaco, in modo che il client principale del telecentro sia il personale del Sindaco. Ciò era importante perché la stazione radiofonica non desiderava contendere la clientela con il telecentro ed i sistemi della stazione radiofonica erano previsti soprattutto per il personale della stazione radiofonica. Questo rapido ponte ridusse i costi, dando indicazione del fatto che questa base di client avrebbe potuto sostenere il costo di Internet senza competere con il telecentro, il suo fornitore. Il telecentre inoltre ha la capacità di staccare facilmente la stazione radiofonica se non viene effettuato il pagamento. Questo modello inoltre ha permesso la compartecipazione delle risorse della rete. Per esempio, la stazione radiofonica ha una nuova stampante laser, mentre il telecentro ha una stampante a colori. Poiché i sistemi del client sono sulla stessa rete, i clients possono stampare in uno o nell'altro posto.

Addestramento

Per supportare questa rete, fu richiesto pochissimo addestramento. Fu mostrato al personale del telecentro come installare l'apparecchiatura e il troubleshooting di base, come eseguire il rebooting (power cycling) degli access points e come sostituire l'unità se si rompe. In questo modo la squadra dell'autore adesso può semplicemente spedire gli aggiornamenti ed evitare il viaggio di due giorni a Timbuktu.

Sommario

L'installazione è stata considerata una misura ad interim. Questo significa che è servita da misura transitoria mentre si andava avanti con una soluzione più completa. Mentre essa può essere considerata un successo, ancora non si sono sviluppare altre infrastrutture fisiche. Essa è quella che ha portato l'ICTs più vicino ad una soluzione radiofonica e ha rinforzato i rapporti locali fornitore/cliente.

Così com'è, l'accesso ad Internet è ancora un'impresa costosa in Timbuktu. Sono in corso politiche locali ed iniziative in concorrenza sovvenzionate, ma questa semplice soluzione è risultata ideale. Alla squadra sono stati necessari parecchi mesi di analisi e di riflessioni critiche per arrivare al traguardo attuale, ma sembra che la soluzione più semplice abbia fornito il maggior beneficio.

--Ian Howard

Case study: Individuazione di un solido terreno in Gao

One day's drive east from Timbuktu, in Eastern Mali, is Gao. This rural city, which seems more more like a big village, sits up the the river Niger just before it dips South crossing into Niger and onto Nigeria. The city slopes into the river gently, and has few buildings taller than two stories. In 2004, a telecentre was installed in Gao. The project's goal was to provide information to the community in the hope that a better informed community would yield a healthier and more educated citizenry.

The centre provides information via CD-ROMs, films and radio, but the cornucopic source of information for the centre is the Internet. It is a standard telecentre, with 8 computers, an all-in-one printer, scanner, fax, a telephone and a digital camera. A small two room building was built to house the telecentre. It is located a bit outside of downtown, which is not an ideal location for attracting customers, but the site was chosen because of its sympathetic host. The site received funding for all construction needed, and equipment and initial training was supplied as well. The telecentre was expected to be self-sustaining after one year.

Several months after its opening, the telecentre was attracting few customers. It used a modem to dial-up to connect to an Internet provider in the capital. This connection was too slow and unreliable, and so the funder sponsored the installation of a VSAT system. There are a number of VSAT systems now available to the region; most of these services have just recently become available. Previously only C-band (which cover a larger area than Ku-band) systems were available. Recently, fiber has been laid in almost every subway tunnel and canal throughout Europe, and thus it has supplanted the more expensive satellite services. As a result, providers are now redirecting their VSAT systems to new markets, including middle and Western Africa, and South Asia. This has led to a number of projects which use satellite systems for an Internet connection.

After the VSAT was installed, the connection provided 128 Kbps down and 64 Kbps up, and cost about $400 per month. The site was having trouble earning enough revenue to pay for this high monthly cost, so the telecentre asked for help. A private contractor was hired, who had been trained by the author to install a wireless system. This system would split the connection between three clients: a second beneficiary, a radio station, and the telecentre, each paying $140. This collectively covered the costs of the VSAT, and the extra revenue from the telecentre and the radio station would cover support and administration of the system.

The people

Though capable and willing, the author's team did not do the actual installation. Instead, we encouraged the telecentre to hire the local contractor to do it. We were able to reassure the client by agreeing to train and support the contractor in the fulfillment of this installation. The premise of this decision was to discourage a reliance on a short-term NGO, and rather to build trust and relationships between domestic service providers and their clients. This design proved to be fruitful. This approach took much more time from the author's team, perhaps twice as much, but this investment has already begun to pay-off. Networks are still being installed and the author and his team are now home in Europe and North America.

Design choices

Initially, it was conceived that a backbone connection would be made to the radio station, which already had a 25 meter tower. That tower would be used to relay to the other clients, avoiding the need to install towers at the client sites, as this tower was well above any obstacles in the city. To do this, three approaches were discussed: installing an access point in repeater mode, using the WDS protocol, or using a mesh routing protocol. A repeater was not desirable as it would introduce latency (due to the one-armed repeater problem) to an already slow connection. VSAT connections need to send packets up to the satellite and back down, often introducing up to 3000 ms in delay for a round trip. To avoid this problem, it was decided to use one radio to connect to clients, and a second radio for to the dedicated backbone connection. For simplicity it was decided to make that link a simple bridge, so that the access point at the radio station would appear to be on the same physical LAN as the telecentre.

In testing this approach functioned, though in the real world, its performance was dismal. After many different changes, including replacing the access points, the technician decided that there must be a software or hardware bug affecting this design. The installer then decided to place the access point at the telecentre directly using a small 3 meter mast, and to not use a relay site at the radio station. The client sites also required small masts in this design. All sites were able to connect, though the connections were at times too feeble, and introduced massive packet loss.

Later, during the dust season, these connections became more erratic and even less stable. The client sites were 2 to 5 km away, using 802.11b. The team theorized that the towers on either side were too short, cutting off too much of the Fresnel zone. After discussing many theories, the team also realized the problem with the performance at the radio station: the radio frequency 90.0 MHz was about the same as the frequency of the high-speed (100BT) Ethernet connection. While transmitting, the FM signal (at 500 watts) was completely consuming the signal on the Ethernet cable. Thus, shielded cable would be required, or the frequency of the Ethernet link would need to be changed. The masts were then raised, and at the radio station the speed of the Ethernet was changed to 10 Mbps. This changed the frequency on the wire to 20 MHz, and so avoided interference from the FM transmission. These changes resolved both problems, increasing the strength and reliability of the network. The advantage of using mesh or WDS here would be that client sites could connect to either access point, either directly to the telecentre to the radio station. Eventually, removing the reliance on the radio station as a repeater likely made the installation more stable in the longer-term.

Financial model

The satellite system used at this site cost approximately $400 per month. For many IT for Development projects this expensive monthly cost is difficult to manage. Typically these projects can purchase equipment and pay for the establishment of a wireless network, but most are not able to pay for the cost of the network after a short period of time (including the recurring Internet costs and operational costs). It is necessary to find a model where the monthly costs for a network can be met by those who use. For most community telecenters or radio stations, this is simply too expensive. Often, the only feasible plan is to share the costs with other users. To make the Internet more affordable, this site used wireless to share the Internet to the community, allowing a greater number of organizations to access the Internet while reducing the cost per client.

Typically in Mali, a rural community has only a few organizations or companies that could afford an Internet connection. Where there are few clients, and the Internet connection cost is high, the model developed by his team included anchor clients: clients whom are solid and are low-risk. For this region, foreign NGOs (Non Governmental Organizations), the United Nations Agencies and large commercial enterprises are among the very few whom qualify.

Among the clients selected for this project were three anchor clients, who collectively paid the entire monthly cost of the satellite connection. A second beneficiary, a community radio station, was also connected. Any revenue earned from the beneficiaries contributed to a windfall, or deposit for future costs, but was not counted upon due to the small margins that both of these community services operated on. Those clients could be disconnected and could resume their service once they can afford it again.

Training needed: who, what, for how long

The contractor taught the telecentre technician the basics of supporting the network, which was fairly rudimentary. Any non-routine work, such as adding a new client, was contracted out. Therefore it was not imperative to teach the telecentre staff how to support the system in its entirety.

Lessons learned

By sharing the connection, the telecentre is now self-sustaining, and in addition, three other sites have Internet access. Though it takes more time and perhaps more money, it is valuable to find the right local talent and to encourage them to build relationships with clients. A local implementor will be able to provide the follow-up support needed to maintain and expand a network. This activity is building local expertise, and demand, which will allow subsequent ICT projects to build on this base.

--Ian Howard

Case Study: Spectropolis, New York

In September 2003 and October 2004, NYCwireless produced Spectropolis. This event celebrated the availability of open wireless (Wi-Fi) networks in Lower Manhattan and explored their implications for art, community, and shared space. Spectropolis is the world's first wireless arts festival, and was envisioned as a way to bring the techno-centric nature of Wi-Fi into a more accessible form. The idea was to create a way for average residents and visitors to New York to "see" and "feel" the wireless signals that permeate the city (especially the free Wi-Fi that NYCwireless provides in many city parks) that are otherwise invisible.

The idea for Spectropolis came from a series of discussions in the winter of 2003 between Dana Spiegel, then a member-at-large for NYCwireless, and Brooke Singer, an independent New Media artist and associate professor at SUNY Purchase.

Spectropolis took place at City Hall Park, a well-known free wireless hotspot in New York City, New York. The festival featured works of art from 12 international artists. Each art piece integrated and made use of one or more forms of wireless technology, including Wi-Fi, Bluetooth, Radio, GPS, and others. Each piece was intended to explore how wireless technologies affect our everyday urban experiences. The pieces were exhibited outdoors in the park for three days, and the artists were out exhibiting artwork and explaining their work to park visitors.

In addition to the works of art, Spectropolis offered five workshops and three panel discussions. The workshops offered an up-close look at wireless communication technologies and an opportunity for hands-on play and participation. The workshops aimed to educate both the technical and non-technical public and demystify a range of technologies through engaging presentations.

The panels explored the larger scale implications of wireless technologies for society, public policy, activism, and art. Each panel focussed on a particular area of influence for wireless technology, with commentary by a number of recognized leaders.

An outdoor park/public space was chosen for the event primarily because this location provided a way to both attract a large number of attendees as well as situate the event in a space that many people pass through both during the workday and on the weekend. One of the goals of the event was to reach out to local residents and people who wouldn't otherwise attend a technology-centric event. During the time that Spectropolis was in City Hall Park, thousands of people came through the park each day, and many stopped to look at one or more artworks.

From a visibility point of view, holding Spectropolis in an outdoor public space was important, and the foot traffic around the area definitely resulted in attracting a number of people into the park who would otherwise not have come to the event. In addition, New York City has a long history of outdoor public art, however this art is almost entirely sculptural in form, and meant to participate in the landscape but not really be interactive. Bringing highly interactive new media art from a museum or gallery into an outdoor public space created discordance with people's expectations.

Why Spectropolis is important

Spectropolis is an attempt to give wireless technology and Wi-Fi in particular a life beyond email and websurfing. The interactive works of art showcased at Spectropolis are engaging beyond the "work-use" that is associated with Wi-Fi by the general public. By introducing wireless technologies via "play" and "exploration", Spectropolis removes much of the fear that people have about new technologies, and enables people to consider the larger implications of wireless technologies and their lives without getting caught up in the "how" of the technology itself.

Spectropolis is a unique event because it focuses on the social impact of wireless technologies, as opposed to the technologies themselves. The vast majority of people are either scared by raw technology (this is common in adults more than children) or are merely disinterested. While Wi-Fi and cellular technologies have made significant inroads into general society, they have done so by riding on the coat-tails of two well established social activities: talking on the phone and accessing the Internet (email, web, IM, etc.)

In addition, Spectropolis puts a face on the ethereal nature of wireless signals. That Wi-Fi is available in a park may be indicated by signs and stickers on windows, but creating a tangible artifact in the form of works of art drives this concept home in the same way that benches, trees, and grass showcase the public amenities that a park provides. Wi-Fi in public spaces isn't a gated community, but rather a public resource that can be shared and appreciated by all just like the shade of a large tree.

Participating organizations

NYCwireless, through Dana Spiegel, took on the role of producing Spectropolis. NYCwireless is a non-profit organization that advocates and enables the growth of free, public wireless Internet access in New York City and surrounding areas. NYCwireless, founded in 2001, is an all-volunteer organization with seven board members, five special interest working groups and approximately sixty active members.

NYCwireless partnered with other local organizations and prominent individuals from the New York Arts community who volunteered their time to help curate and produce the event. Spectropolis was sponsored by the Alliance for Downtown New York (DTA), a Business Improvement District (BID) company. The DTA also sponsors a number of free, public, wireless hotspots in downtown New York, including the hotspot at City Hall Park, where Spectropolis was held. The Lower Manhattan Cultural Council (LMCC), an arts funding and promotion organization, sponsored the curation of Spectropolis. LMCC hosted a number of meetings and oversaw the process of inviting and evaluating artists and their works in preparation of the event. In addition, a number of individuals contributed a significant amount of time to Spectropolis: Wayne Ashley (Curator, LMCC), Yury Gitman (Curator), Jordan Silbert (Producer), and Jordan Schuster (Producer)

Community Reception

The local community received Spectropolis quite well. The primary groups of people who attended the event were: wireless researchers, wireless proponents, artists, and the general public.

Leading up to the event, we reached out to the local artist and local university communities to generate interest. We received a large number of email inquiries from people both locally and around the continent (primarily US and Canada) about attending the event. Some wireless enthusiasts even traveled from Europe in order to attend. The local university community was particularly interested, with students from NYU, SUNY, New School, Parsons, and other nearby schools attending. During the event we even had a few people bring their own projects to the park and set them up.

We also sent out a press release to local media outlets and websites to inform the general NYC community about the event. While we weren't contacted prior to the event by anyone from the general public, there were some people from this group who signed up for our workshops and our panels who had not ever handled wireless equipment. Primarily, local residents and visitors just showed up to the event to experience the artwork. We had thousands of people each day come through the park and experience at least a few of the works.

In addition to the art, we had a number of people ask questions about wireless technology in general, and public Wi-Fi in specific. Many of these people were directed to the NYCwireless information booth that was set up in the middle of the park. A number did speak directly to the artists (we had expected this, and this was one of the reasons why we wanted artists to show their own work) about the works they created, and ask about how they worked and why the artist created the work.

For a number of attendees, Spectropolis was the first time they experienced Wi-Fi as something more than just an Internet technology. Many were surprised that wireless technologies could be more than just a cell phone call or a web page in a cafe, and they were pleased to get a better grasp on the alternative uses for Wi-Fi that the art works explored. In some instances, the relationship between wireless signals and the works of art were hidden and obscure--such as Akitsugu Maebayashi's Sonic Interface. In other works, like Upper Air by the DSP Music Syndicate, the art was designed to support the existence of the wireless technology, and the piece explored the the technology's relationship to both the viewer and the art.

Some pieces, such as Jabberwocky by Eric John Paulos and Elizabeth Goodman, made use of the technology to explore social relationships in urban environments. These works were important and meaningful because they related wireless technology to something that is clearly a human experience, such as seeing familiar strangers in a crowd. In Jabberwocky in particular, the viewer is forced to see also the limits of the wireless technology, and make use of human abilities to fill in the gaps.

GPS drawings, a workshop held by Jeremy Wood, extended the notion of humans + technology equaling something greater than the sum of its parts. Wood actually led groups of people around parts of downtown New York City to create large scale drawings out of their movements. This artwork personalized the experience of wireless technologies more than any other project.

All of the projects forced people to re-evaluate their relationships with their technologies. More than just seeing public spectrum and wireless networks in a new light, Spectropolis caused people to think about how these technologies enrich and permeate their lives. In speaking with artists after the event, all of them were surprised by how engaged people were. People who interacted with the artworks had a better understanding of the otherwise ephemeral nature of wireless signals. For visitors to the event, Spectropolis made abstract concepts of spectrum and public wireless much more concrete, and gave them a way to understand these concepts in a way that merely using a cell phone or Wi-Fi laptop could not, and in this way, Spectropolis was a complete success.

Projects

Spectropolis featured the following projects and artists:

• WiFi Ephemera Cache by Julian Bleecker

• UMBRELLA.net by Jonah Brucker-Cohen and Katherine Moriwaki

• Microrardio Sound Walk by free103point9 Transmission Artists

• Urballoon by Carlos J. Gomez de Llarena

• Bikes Against Bush by Joshua Kinberg

• InterUrban by Jeff Knowlton and Naomi Spellman

• Hotspot Bloom by Karen Lee

• Sonic Interface by Akitsugu Maebayashi

• Jabberwocky by Eric John Paulos and Elizabeth Goodman

• Upper Air by The DSP Music Syndicate

• Twenty-Four Dollar Island by Trebor Scholz

• Text Messaging Service and Following 'The Man of the Crowd' by Dodgeball + Glowlab

Planning

The planning for Spectropolis began about one year prior to the event. At the outset, representatives from NYCwireless, LMCC, and DTA, as well as the producers and curators, met on a monthly basis to establish the plan and execute the event. The cost of producing Spectropolis was about $11,000 USD.

More information can be found on the Spectropolis 2004 website at http://www.spectropolis.info/ and at my Wireless Community blog at http://www.wirelesscommunity.info/spectropolis.

--Dana Spiegel

Case study: The quest for affordable Internet in rural Mali

For several years the international development community has promoted the idea of closing the digital divide. This invisible chasm that has formed separating access to the wealth of information and communications technologies (ICT) between the developed and the developing world. Access to information and communications tools has been shown to have a dramatic impact on quality of life. For many donors fatigued by decades of supporting traditional development activities, the installation of a telecentre in the developing world seems like a realizable and worthwhile effort. Because the infrastructure does not exist, this is much more expensive and difficult to do in the developing world than it is in the West. Moreover, few models have been shown to sustain these activities. To help mitigate some of the cost of bringing the Internet to rural areas of the developed world, the author's team has promoted the use of wireless systems to share the cost of an Internet connection. In November of 2004, an affiliated project asked the author's team to pilot such a wireless system at a recently installed telecentre in rural Mali, 8 hours South-West by four-by-four from Bamako, the capital.

This rural city, located on the margin of a man-made reservoir, holds water for the Manitali dam that powers a third of the country. This location is fortunate as hydroelectric power is much more stable and available than diesel generated power. While diesel generated power is far less stable, some rural communities are lucky to have any electricity at all.

The city is also endowed to be in one of the most fertile regions of the country, in its cotton belt, Mali's main cash crop. It was believed that this site would be the least difficult of the rural areas in Mali to make a self-sustaining telecentre. Like many experiments, this pilot was fraught with challenges.

Technologically it was a simple task. In 24 hours the team installed an 802.11b wireless network that shares the telecenter's VSAT Internet connection with 5 other local services: the Mayor, the Governor, the health service, the district's Mayor's council (CC) and the community advisory service (CCC).

These clients had been selected during a reconnaissance two months prior. During that visit the team had interviewed potential clients and determined which clients could be connected without complicated or expensive installations. The telecentre itself is housed at the community radio station. Radio stations tend to be great sites to host wireless networks in rural Mali as they are often well placed, have electricity, security and people who understand at least the basics of radio transmissions. They are also natural hubs for a village. Providing Internet to a radio station provides better information to its listeners. And for a culture which is principally oral, radio happens to be the most effect means to provide information.

From the list of clients above, you will note that the clients were all government or para-governmental. This proved to be a difficult mix, as there is considerable animosity and resentment between the various levels of government, and there were continuing disputes regarding taxes and other fiscal matters. Fortunately the director of the radio station, the network's champion, was very dynamic and was able to wade through most of these politics, though not all.

Design choices

The technical team determined that the access point would be installed at 20 meters up the radio station tower, just below the FM radio dipoles, and not so high as to interfere with coverage to client sites below in the bowl-like depression where most were found. The team then focused on how to connect each client site to this site. An 8 dBi omni (from Hyperlinktech, http://hyperlinktech.com/) would suffice, providing coverage to all client sites. The 8 dBi antenna that was chosen has a 15 degree down-tilt, assuring that the two clients less than a kilometer away could still receive a strong signal. Some antennae have very narrow beam width and thus "overshoot" sites that are close. Panel antennae were considered, though at least two would be required and either a second radio or a channel splitter. It was deemed unnecessary for this installation. The following calculation shows how to calculate the angle between the client site's antenna and the base station's antenna, using standard trigonometry.

tan(x) = difference in elevation
       + height of base station antenna
       - height of CPE antenna 
       / distance between the sites

tan(x) = 5m + 20m - 3m / 400m
     x = tan-1 (22m / 400m)
     x =~ 3 degrees

In addition to the equipment in the telecentre (4 computers, a laser printer, 16 port switch), the radio station itself has one Linux workstation installed by the author's project for audio editing. A small switch was installed in the radio station, an Ethernet cable was run through plastic tubing buried at 5 cm across to the telecentre, across the yard.

From the main switch, two cables run up to a Mikrotik RB220, access point. The RB220 has two Ethernet ports, one that connects to the VSAT through a cross-over cable, and the second that connects to the radio station's central switch. The RB 220 is housed in a D-I-Y PVC enclosure and an 8 dBi omni (Hyperlink Technologies) is mounted directly to the top of the PVC cap.

The RB220, runs a derivative of Linux, Mikrotik version 2.8.27. It controls the network and provides DHCP, firewall, DNS-caching and routes traffic to the VSAT, using NAT. The Mikrotik comes with a powerful command line and a relatively friendly and comprehensive graphical interface. It is a small x86 based computer, that is designed for use as an access point or embedded computer. These access points are POE capable, have two Ethernet ports, a mini-pci port, two PCMCIA slots, a CF reader (which is used for its NVRAM), are temperature tolerant and support a variety of x86 operating systems. Despite that the Mikrotik software requires licensing, there was already a substantial install base in Mali and the system has a powerful and friendly graphical interface that was superior to other products. Due to the above factors the team agreed to use these systems, including the Mikrotik software to control these networks. The total cost of the RB220, with License Level 5, Altheros mini-pci a/b/g and POE was $461. You can find these parts at Mikrotik online at http://www.mikrotik.com/routers.php#linx1part0.

The network was designed to accommodate expansion by segregating the various sub-networks of each client; 24 bit private subnets were alloted. The AP has a virtual interface on each subnet and does all routing between, also allowing fire-walling at the IP layer. Note: this does not provide a firewall at the network layer, thus, using a network sniffer like tcpdump one can see all traffic on the wireless link.

To limit access to subscribers, the network uses MAC level access control. There was little perceived security risk to the network. For this first phase, a more thorough security system was left to be implemented in the future,, when time could be found to find an easier interface for controlling access. Users were encouraged to use secure protocols, such as https, pops, imaps etc.

The affiliate project had installed a C-band VSAT (DVB-S) system. These satellite systems are normally very reliable and are often used by ISPs. It is a large unit, in this case the dish was 2.2 meters in diameter and expensive, costing approximately $12,000 including installation. It is also expensive to operate. A 128 kbps down and 64 kbps up Internet connection costs approximately $700 per month. This system has several advantages compared to a Ku system though, including: greater resilience to bad weather, lower contention rates (number of competing users on the same service) and it is more efficient at transferring data.

The installation of this VSAT was not ideal. Since the system ran Windows, users were able to quickly change a few settings, including adding a password to the default account. The system had no UPS or battery back up, so once a power outage occurred the system would reboot and sit waiting for a password, which had since been forgotten. To make this situation worse, because the VSAT software was not configured as an automatic background service it did not automatically launch and establish the link. Though the C-band systems are typically reliable, this installation caused needless outages which could have been resolved with the use of a UPS, proper configuration of the VSAT software as a service, and by limiting physical access to the modem. Like all owners of new equipment, the radio station wanted to display it, hence it was not hidden from view. Preferably a space with glass doors would have kept the unit secure while keeping it visible.

The wireless system was fairly simple. All of the client sites selected were within 2 km of the radio station. Each site had a part of the building that could physically see the radio station. At the client site, the team chose to use commercial, client grade CPEs: Based on price, the Powernoc 802.11b CPE bridge, small SuperPass 7 dBi patch antennas and home-made Power Over Ethernet (POE) adaptors. To facilitate installation, the CPE and the patch antenna were mounted on a small piece of wood that could be installed on the outside wall of the building facing the radio station.

In some cases the piece of wood was an angled block to optimize the position of the antenna. Inside, a POE made from a repurposed television signal amplifier (12V) was used to power the units. At the client sites there were not local networks, so the team also had to install cable and hubs to provide Internet for each computer. In some cases it was necessary to install Ethernet adapters and their drivers (this was not determined during the assessment). It was decided that because the client's networks were simple, that it would be easiest to bridge their networks. Should it be required, the IP architecture could allow future partitioning and the CPE equipment supported STA mode. We used a PowerNOC CPE bridge that cost $249 (available at http://powernoc.us/outdoor_bridge.html).

Local staff were involved during the installation of the wireless network. They learned everything from wiring to antenna placement. An intensive training program followed the installation. It lasted several weeks, and was meant to teach the staff the day to day tasks, as well as basic network troubleshooting.

A young university graduate who had returned to the community was chosen to support the system, except for the cable installation, which the radio station technician quickly learned. Wiring Ethernet networks is very similar to coaxial cable repairs and installations which the radio technician already performed regularly. The young graduate also required little training. The team spent most of its time helping him learn how to support the basics of the system and the telecentre. Soon after the telecentre opened, students were lined up for the computer training, which offered 20 hours of training and Internet use per month for only $40, a bargain compared to the $2 an hour for Internet access. Providing this training was a significant revenue and was a task that the young computer savvy graduate was well suited for.

Unfortunately, and somewhat unsurprisingly, the young graduate left for the capital, Bamako, after receiving an offer for a government job. This left the telecentre effectively marooned. Their most technically savvy member, and the only one who was trained in how to support the system, had left. Most of the knowledge needed to operate the telecentre and network left with him. After much deliberation, the team determined that it was best not to train another tech savvy youth, but rather to focus on the permanent local staff, despite their limited technical experience. This took much more time. Our trainers have had to return for a total of 150 hours of training. Several people were taught each function, and the telecentre support tasks were divided among the staff.

Training did not stop there. Once the community services were connected, they too needed access. It seemed that although they were participating, the principals, including the mayor, were not using the systems themselves. The team realized the importance of assuring that the decision makers used the system, and provided training for them and their staff. This did remove some of the mystique of the network and got the city's decision makers involved.

Following training, the program monitored the site and began to provide input, evaluating ways that this model could be improved. Lessons learned here were applied to other sites.

Financial Model

The community telecentre was already established as a non-profit, and was mandated to be self-sustaining through the sale of its services. The wireless system was included as a supplementary source of revenue because early financial projections for the telecentre indicated that they would fall short of paying for the VSAT connection.

Based on the survey, and in consultation with the radio station whom manages the telecentre, several clients were selected. The radio station negotiated contracts with some support from its funding partner. For this first phase, clients were selected based on ease of installation and expressed ability to pay. Clients were asked to pay a subscription fee, as described later.

Deciding how much to charge was a major activity which required consultation and expertise that the community did not have in financial projections. The equipment was paid for by the grant, to help offset the costs to the community, but clients were still required to pay a subscription fee, which served to assure their commitment. This was equivalent to one month of the service fee.

To determine the monthly cost for an equal slice of bandwidth we started with the following formula:

VSAT + salaries + expenses (electricity, supplies) = telecentre revenue + wireless client revenue

We had estimated that the telecentre should earn about $200 to $300 per month in revenue. Total expenses were estimated to be $1050 per month, and were broken down as: $700 for the VSAT, $100 for salaries, $150 for electricity, and about $100 for supplies. About $750 in revenue from the wireless clients was required to balance this equation. This amounted to roughly $150 from each client. This was just tolerable by the clients, and looked feasible, but required fair weather, and had no room for complications.

Because this was becoming complicated, we brought in business geeks, who modified the formula as such:

Monthly expenses + amortization + safety funds = total revenue

The business experts were quick to point out the need of amortization of the equipment, or one could say "re-investment funds" as well as safety funds, to assure that the network can continue if a client defaults, or if some equipment breaks. This added about $150 per month for amortization (equipment valued at about $3,000, amortized over 24 months) and the value of one client for default payments, at $100. Add another 10% to account for currency devaluation ($80), and that equals an expense of $1380 per month. In trying to implement this model, it was finally determined that amortization is a concept that was too difficult to convey to the community, and that they would not consider that clients might default on payment. Thus, both formulae were used, the first by the telecentre and the second for our internal analysis.

As was soon discovered, regular payments are not part of the culture in rural Mali. In an agrarian society everything is seasonal, and so too is income. This means that the community's income fluctuates wildly. Moreover, as many public institutions were involved, they had long budget cycles with little flexibility. Although they theoretically had the budget to pay for their service, it would take many months for the payments to be made. Other fiscal complications arose as well. For example, the mayor signed on and used the back-taxes owed by the radio to pay for its subscription. This of course did not contribute to cash flow. Unfortunately, the VSAT providers have little flexibility or patience, as they have limited bandwidth and only have room for those that can pay.

Cash flow management became a primary concern. First, the revenue foreseen in financial projections showed that even with an optimistic outlook, they would not only have trouble earning enough revenue on time to pay the fee, but getting the money to the Bamako-based bank also presented a problem. Roads near the village can be dangerous, due to the number of smugglers from Guinea and wayward rebels from the Ivory Coast. As projected, the telecentre was not able to pay for its service and its service was suspended, thereby suspending payment from their clients as well.

Before the project was able to find solutions to these problems, the cost of the VSAT already began to dig the telecentre into debt. After several months, due to technical problems, as well as concerns raised in this analysis, the large C-band VSAT was replaced with a cheaper Ku band system. Although cheaper, it still sufficed for the size of the network. This system was only $450, which by ignoring amortization and safety margins is affordable by the network. Unfortunately, due to default payments, the network was not able to pay for the VSAT connection after the initial subsidized period.

Conclusions

Building a wireless network is relatively easy, but making it work is much more of a business problem than a technical problem. A payment model that considers re-investment and risk is a necessity, or eventually the network will fail. In this case, the payment model was not appropriate as it did not conform to fiscal cycles of the clients, nor did it conform to social expectations. A proper risk analysis would have concluded that a $700 (or even a $450) monthly payment left too narrow a margin between revenue and expenses to compensate for fiscal shortcomings. High demand and education needs limited the expansion of the network.

Following training the network operated for 8 months without significant technical problems. Then, a major power surge caused by a lightning strike destroyed much of the equipment at the station, including the access point and VSAT. As a result, the telecentre was still off-line at the time that this book was written. By that time this formula was finally deemed an unsuitable solution.

--Ian Howard

Case study: installazioni commerciali in Africa orientale

Descrivendo installazioni wireless commerciali in Tanzania e Kenya, questo capitolo evidenzia le soluzioni tecniche fornendo una solida affidabilità del 99.5% della connettività dati e Internet in paesi in via di sviluppo. Al contrario di progetti finalizzati all'accessibilità da ogni luogo, ci siamo concerntrati sul fornire servizi ad organizzazioni, in particolare quelle con bisogni di critici di comunicazioni internazionali. Verranno descritti due approcci commerciali radicalmente differenti alla connettività dati wireless, riassumendo le lezioni chiave imparate nel corso degli anni in Africa orientale.

Tanzania

Nel 1995, insieme a Bill Sangiwa, fondai il CyberTwiga, uno dei primi ISP in Africa. I servizi commerciali, limitati al traffico email in dialup trasportati su un colllegamento SITA a 9.6 kbps (che costava più di $4000 al mese!), cominciarono a metà 1996. Frustrati da servizi PSTN sbagliati e spinti dalla riuscita implementazione di una rete punto-multipunto (PMP) da 3 nodi per l'autorità Tanzania Harbours, negoziammo con una compagnia di cellulari locale il posizionamento di una stazione base PMP sul loro palo. Connettendo una serie di corporation a questo sistema WiLan a 2.4 Ghz proprietario nel 1998, mettemmo alla prova il mercato e la nostra capacità tecnica di fornire servizi wireless.

Appena la concorrenza si azzardò a installare reti a 2.4 Ghz, due fatti vennero a galla: per i servizi wireless esisteva un mercato in buona salute, ma un crescente livello di rumore RF a 2.4 Ghz avrebbe diminuito la qualità della rete. La nostra fusione con il carrier cellulare, nella metà del 2000, incluse piani per una rete wireless di portata nazionale costruita sull'infrastruttura cellulare esistente (torri e collegamenti di trasmissione) e ripartizione proprietaria dello spettro RF.

L'infrastruttura era in piedi (torri cellulari, collegamenti di trasmissione, ecc.), quindi la progettazione e l'installazione della rete wireless di dati fu diretta. Dar es Salaam è molto pianeggiante, e siccome il partner cellulare forniva una rete analogica, le torri erano molto alte. Una compagnia sorella negli UK, Tele2, cominciò ad aoperare con dispositivi Breezecom (ora Alvarion) a 3.8/3.9 Ghz, quindi seguimmo il loro suggerimento.

Alla fine del 2000, avevamo fornito copertura a diverse città, usando circuiti di trasmissione E1 frazionati per la connessione delle celle. Nella maggior parte dei casi le piccole dimensioni delle città connesse giustificavano l'uso di una stazione PMP omnidirezionale singola; solo nella capitale commerciale, Dar es Salaam, erano installate stazioni base a 3 settori. I limiti di larghezza di banda erano configurati direttamente sulla radio del cliente; ai clienti veniva fornito normalmente un solo IP pubblico. I router finali ad ogni stazione base inviavano il traffico agli indirizzi IP statici delle postazioni dei clienti e impedivano al traffico di broadcast di soffocare la rete. La pressione del mercato abbassò i prezzi fino a circa $100 al mese per 64 kbps, ma a quei tempi (metà/fine 2000) gli ISP potevano lavorare con margini impressionanti, molto proficui. Le applicazioni affamate come il file sharing peer-to-peer, traffico voce e gli ERP semplicemente non esistevano in Africa orientale. Con le alte tariffe PSTN internazionali, le aziende si spostarono velocemente dal traffico fax a quello email, anche se i prezzi di acquisto delle loro apparecchiature wireless oscillavano da $2000-3000.

Le capacità tecniche furono sviluppate internemente, richiedendo il training dello staff oltreoceano in materie come l'SNMP e Unix. Oltre che migliorare il set di skill dell'azienda, queste opportunità di training crearono fedeltà nello staff. Dovevamo competere in un mercato del lavoro IT contro compagnie di estrazione dell'oro, l'ONU ed altre agenzie internazionali.

Per assicurare la qualità ai siti dei clienti, le installazioni furono eseguite da un'azienda di radio e telecomunicazioni tra le migliori, tracciando accuratamente i progressi su moduli. Le alte temperature, il brutale sole equatoriale, le abbondanti piogge, e i fulmini erano tra le aggressioni ambientali subite dalle componenti all'aperto; l'integrità del cablaggio RF era vitale.

I clienti spesso mancavano di staff IT competente, incaricavano i loro impiegati con il compito di configurare molti tipi di topologie di rete e hardware.

Gli ostacoli infrastrutturali e normativi spesso impedivano le operazioni. La compagnia cellulare controllava strettamente le torri, e ogni volta che c'era un problema tecnico ad una stazione base potevano passare ore o giorni prima di avervi accesso. Nonostante i generatori di backup e i sistemi UPS in ogni sito, la corrente elettrica era sempre problematica. Per la compagnia cellulare la fornitura di corrente alle stazioni base era meno critca. I telefoni si associavano semplicemente ad una stazione base diversa; le nostre comunicazioni wireless fisse andavano offline.

Dal lato normativo, un'importante interruzione avvenne quando le autorità delle telecomunicazioni decisero che le nostre attività erano responsabili dell'interruzione delle funzionalità dei satelliti in banda C nell'intero paese e ci ordinarono di spegnere la nostra rete.

Nonostante dimostrammo duramente con i dati che non ne avevamo colpa, le autorità compirono una confisca molto pubblicizzata delle nostre apparecchiature. Ovviamente l'interferenza persistette e in seguito fu individuata la fonte in una nave radar russa, coinvolta nel tracciamento delle attività spaziali. Negoziammo silenziosamente con le autorità e alla fine fummo ricompensati con uno spettro proprietario di 2 x 42 MHz nella banda dei 3.4/3.5 GHz. I clienti furono spostati su dialup nel mese circa di riconfigurazione delle stazioni base e di installazioni dei nuovi CPE.

Alla fine la rete crebbe fino a circa 100 nodi fornendo buona connettività, se non ottima, a 7 città attraverso più di 3000 Km di linee di trasmissione. Solo la fusione con l'operatore di telefonica cellulare rese fattibile questa rete, la dimensione del business dati/Internet da solo non avrebbe giustificato la costruzione di una rete dati di queste dimensioni ed avrebbe reso necessari investimenti per frequenze proprietarie. Sfortunatamente l'operatore cellulare prese la decisione di chiudere il business Internet nella metà del 2002.

Nairobi

Agli inizi del 2003 fui contattato da una compagnia Kenyota, AccessKenya, che aveva un forte giro d'affari in UK ed un background tecnico , per progettare e implementare una rete wireless a Nairobi e dintorni. Beneficiando di superbi professionisti del business e networking, hardware wireless superiore, progressi nell'internetworking e un mercato più vasto, progettammo una rete ad alta disponibilità in linea con i limiti normativi.

Due fattori normativi guidarono la nostra progettazione. A quel tempo, in Kenya, i servizi Internet erano licenziati separatamente dagli operatori pubblici di reti di dati, e una sola compagnia non poteva avere entrambe le licenze. Trasportando il traffico di più ISP in concorrenza o utenti aziendali, la rete doveva operare in totale neutralità. Anche le frequenze "proprietarie", cioè 3.4/3.5 GHz, non venivano rilasciate ad un provider solo, ed eravamo preoccupati sulle interferenze e sull'arbitrio tecnico/politivo che dovevamo accettare dalle autorità. Inoltre, lo spettro 3.4/3.5 GHz era costoso, circa USD 1000 per MHz all'anno per stazione base. In altre parole, una stazione base che usava 2 x 12 MHz richiedeva un costo di licenza di oltre $10,000 all'anno. Dato che Nairobi è in una zona collinare con molti alberi alti e vallate, le reti wireless a banda larga richiesero molte stazioni base. I costi operativi delle licenze semplicemente non erano sensate. Al contrario, le frequenze 5.7/5.8 GHz erano soggette solo ad un canone annua, circa USD 120, per radio installata.

Per aderire al primo requisito normativo scegliemmo di fornire servizi usando tunnel VPN punto-punto, non tramite una rete di rotte IP statiche. Un IPS avrebbe fornito un indirizzo pubblico al alla nostra rete dal loro NOC. La nostra rete realizzava una conversione IP pubblico-privato e il traffico attraversava la nostra rete in uno spazio IP privato. Nel sito del cliente, una conversione IP privato-pubblico forniva l'indirizzo (o il range) routabile globalmente alla rete del cliente.

La sicurezza e la criptazione aggiunse alla rete neutralità e flessibilità, caratteristiche commericali uniche della nostra rete. La larghezza di banda era limitata al livello di tunnel VPN. Basandoci sulle esperienze operative della nostra azienda sorella in UK, VirtualIT, scegliemmo Netscreen (ora assorbita dalla Juniper Networks) come marca dei router/firewall VPN.

La nostra scelta per gli apparati wireless a banda larga eliminò la necessità di apparati di grossa portata, alte performance e ricchezza di funzionalità. Dimensioni, affidabilità e facilità di installazione e manutenzione erano più importanti del throughput. Tutte le connessioni Internet internazionali in Kenya nel 2003, e mentre sto scrivendo, sono trasportate via satellite. Con cosi 100 volte superiori di una fibra globale, la connettività satellitare mise un tetto finanziario alla quantità di bandwidth acquistata dagli utenti finali. Stimammo che il traffico degli utenti nella popolazione richiedeva capacità nell'ordine dei 128/256 Kbps. Scegliemmo la piattaforma Motorola Canopy da poco annunciata che era in linea con il nostro modello di rete e di business.

Broadband Access Ltd. andò in oda nel luglio 2003, lanciando la "Blue" network. Iniziammo con poco, con una sola stazione base. Volevamo che la domanda guidasse l'espansione della nostra rete piuttosto che credere nella strategia di costruire grosse condotte e sperare di poterle riempire.

Canopy e gli apporti delle terze parti come le stazioni base ominidirezionali ci permisero di far crescere la nostra rete al crescere del traffico, ammorbidendo le spese ed i capitali iniziali. Sapevamo qual'era Canopy, and third-party enhancements such as omnidirectional base stations, permitted us to grow our network as traffic grew, softening initial capital expenditures. We knew the tradeoff was that as the network expanded, we would have to sectorize traffic and realign client radios. The gentle learning curve of a small network paid big dividends later. Technical staff became comfortable with customer support issues in a simple network environment, rather than have to deal with them on top of a complex RF and logical framework. Technical staff attended two-day Motorola training sessions.

A typical PMP design, with base stations linked to a central facility via a Canopy high-speed microwave backbone, the network was deployed on building rooftops, not antenna towers. All leases stipulated 24x7 access for staff, mains power and, critically, protected the exclusivity of our radio frequencies. We did not want to restrict landlords from offering roof space to competitors, rather to simply guarantee that our own services would not be interrupted.

Rooftop deployments provided many advantages. Unlimited physical access, unconstrained by night or rain, helped meet the goal of 99.5% network availability. Big buildings also housed many big clients, and it was possible to connect them directly into our core microwave network. Rooftop sites did have the downside of more human traffic—workers maintaining equipment (a/c) or patching leaks would occasionally damage cabling. As a result all base stations were set up with two sets of cabling for all network elements, a primary and a spare.

Site surveys confirmed radio path availability and client requirements. Survey staff logged GPS positions for each client, and carried a laser rangefinder to determine height of obstacles. Following receipt of payment for hardware, contractors under the supervision of a technical staffer performed installations. Canopy has the advantage that the CPE and base station elements are light, so that most installations do not need extensive civil works or guying. Cabling Canopy units was also simple, with outdoor UTP connecting radios directly to customer networks. Proper planning enabled completion of many installations in less than an hour, and contractor crews did not need any advanced training or tools.

As we compiled hundreds of customer GPS positions we began to work closely with a local survey company to overlay these sites on topographical maps. These became a key planning tool for base station placement.

Note that the point-point VPN tunnel architecture, with its separate physical and logical layers, required clients to purchase both wireless broadband and VPN hardware. In order to tightly control quality, we categorically refused to permit clients to supply their own hardware—they had to buy from us in order to have service and hardware guarantees. Every client had the same hardware package. Typical installations cost on the order of USD 2500, but that compares to the $500-600 monthly charges for 64 to 128 kbps of bandwidth. A benefit of the VPN tunnel approach was that we could prevent a client's traffic from passing over the logical network (i.e. if their network was hit by a worm or if they didn't pay a bill) while the radio layer remained intact and manageable.

As it grew from one base station to ten, and service was expanded to Mombasa, the network RF design evolved and wherever possible network elements (routers) were configured with fallover or hot swap redundancy. Major investments in inverters and dual conversion UPS equipment at each base station were required to keep the network stable in the face of an erratic power grid. After a number of customer issues (dropped VPN connections) were ascribed to power blackouts, we simply included a small UPS as part of the equipment package.

Adding a portable spectrum analyzer to our initial capital investment was costly, but hugely justified as we operated the network. Tracing rogue operators, confirming the operating characteristics of equipment, and verifying RF coverage enhanced our performance.

Fanatical attention to monitoring permitted us to uptweak network performance, and gather valuable historical data. Graphed via MRTG or Cacti (as described in chapter six), parameters such as jitter, RSSI, and traffic warned of rogue operators, potential deterioration of cable/connectors, and presence of worms in client networks. It was not uncommon for clients to claim that service to their site had been interrupted for hours/days and demand a credit. Historical monitoring verified or invalidated these claims.

The Blue network combined a number of lessons from Tanzania with improved RF and networking technologies.

Lessons learned

For the next few years satellite circuits will provide all international Internet connectivity in East Africa. Several groups have floated proposals for submarine fiber connectivity, which will energize telecommunications when it happens. Compared to regions with fiber connectivity, bandwidth costs in East Africa will remain very high.

Wireless broadband networks for delivery of Internet services therefore do not need to focus on throughput. Instead, emphasis should be placed on reliability, redundancy, and flexibility.

Reliability for our wireless networks was our key selling point. On the network side this translated into sizable investments in infrastructure substitution, such as backup power, and attention to details such as crimping and cabling. The most ordinary reasons for a single customer to lose connectivity were cabling or crimping issues. Radio failures were essentially unheard of. A key competitive advantage of our customer installation process is that we pushed contractors to adhere to tight specifications. It was common for well-managed customer sites to remain connected for hundreds of days with zero unscheduled downtime. We controlled as much of our infrastructure as possible (i.e building rooftops).

As attractive as potential alliances with cellular providers seem, in our experience they raise more problems than they solve. In East Africa, Internet businesses generate a fraction of the revenue of mobile telephony, and so are marginal to the cellular companies. Trying to run a network on top of infrastructure that doesn't belong to you and is, from the point of view of the cellular provider, a goodwill gesture, will make it impossible to meet service commitments.

Implementing fully redundant networks, with fail-over or hotswap capability is an expensive proposition in Africa. Nonetheless the core routers and VPN hardware at our central point of presence were fully redundant, configured for seamless fail-over, and routinely tested. For base stations we took the decision not to install dual routers, but kept spare routers in stock. We judged that the 2-3 hours of downtime in the worst case (failure at 1AM Sunday morning in the rain) would be acceptable to clients. Similarly weekend staff members had access to an emergency cupboard containing spare customer premises equipment, such as radios and power supplies.

Flexibility was engineered into both the logical and RF designs of the network. The point-to-point VPN tunnel architecture rolled out in Nairobi was extraordinarily flexible in service of client or network needs. Client connections could be set to burst during off-peak hours to enable offsite backup, as a single example. We could also sell multiple links to separate destinations, increasing the return on our network investments while opening up new services (such remote monitoring of CCTV cameras) to clients.

On the RF side we had enough spectrum to plan for expansion, as well as cook up an alternative radio network design in case of interference. With the growing number of base stations, probably 80% of our customer sites had two possible base station radios in sight so that if a base station were destroyed we could restore service rapidly.

Separating the logical and RF layers of the Blue network introduced an additional level of complexity and cost. Consider the long-term reality that radio technologies will advance more rapidly than internetworking techniques. Separating the networks, in theory, gives us the flexibility to replace the existing RF network without upsetting the logical network. Or we may install a different radio network in line with evolving technologies (Wimax) or client needs, while maintaining the logical network.

Finally, one must surrender to the obvious point that the exquisite networks we deployed would be utterly useless without unrelenting commitment to customer service. That is, after all, what we got paid for.

Maggiori informazioni

• Broadband Access, Ltd. http://www.blue.co.ke/

• AccessKenya, Ltd. http://www.accesskenya.com/

• VirtualIT http://www.virtualit.biz/

--Adam Messer, Ph.D.