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19/12/2005 - Segunda-feira
VoWLAN EM PROFUNDIDADE!!!
Dê 01 olhada:
In Depth: Wireless Voice-Over-IP
Page 1 of 7
Sales of VoWLAN phones averaged about 100,000 to 150,000 units in 2004, according to research organizations Infonetics and Synergy Research Group, and far fewer dual-mode phones were sold. Unit sales projections for 2009 come in at around 17 million for pure VoWLAN phones, with predictions for dual-mode handset sales ranging from 30 million to 100 million.
By comparison, more than 700 million cell phones were shipped in 2004, with unit volumes of 1 billion projected by 2009 or 2010. Even if you trust the most optimistic forecasts, four or five years down the road single and dual-mode VoWLAN phones will still account for only 3 percent to 10 percent of the total mobile phone market.
Most enterprises haven't embraced VoWLAN, but four vertical industries have: health care, retail, warehousing and hospitality. Health-care workers, with their constant need for mobility and accessibility, have taken advantage of standards-based wireless, such as Vocera's badge-style wireless communicator. In the retail sector, employees can avoid going to a fixed-line phone and assist customers on the spot. Stores can double the effectiveness of their existing wireless network used for inventory by extending voice into every aisle. For logistics and warehousing, where orders are tweaked and inventory verified on a continuing basis, cellular signals often don't penetrate the vast expanses of metal racks and shelving. But a VoWLAN solution, such as the one offered by SpectraLink, lets the salesperson in the office call the person loading the truck to make that last-minute change. The hospitality sector also has enjoyed modest success with VoWLAN. Rather than use a private radio system, hotel managers can employ the same Wi-Fi infrastructure that lets a guest surf the Web in his or her suite to connect to a bellhop or housekeeping.
Even if other specialized markets--such as universities, where students wander from class to class with cell phones to their ears, but where in-building cellular coverage is notoriously poor--were to adopt VoWLAN, however, the broadest acceptance will still depend on maturation of the wireless infrastructure for QoS and mobility, more pervasive Wi-Fi deployments and a reduction in handset prices.
Coverage and Savings
VoWLAN offers mobility, coverage where a cell phone can't reach and potential cost savings over cellular phones, while making use of existing wireless networks.
Although the wireless networking industry has matured, pervasive wireless deployments in the enterprise are far from common, and the complexities of transporting voice over wireless networks throw even the dominant infrastructure wireless vendors into a spin. For organizations whose employees stay in their cubicles with wired phones, wireless is unnecessary. But in other organizations, mobile employees must be available for contact by their peers, clients and customers. With a VoWLAN system, one extension is assigned to a mobile user, who can then be reached anywhere his work takes him.
VoWLAN also improves in-building coverage. Unless the walls are paper-thin or cellular repeaters have been installed (legally, of course), cell service may be poor or nonexistent. VoWLAN lets an organization provide pervasive and complete coverage, even in a building's sub-basement if the wireless LAN installation exists.
The costs related to a VoWLAN deployment aren't for the faint of heart. Unlike introductory model cellular handsets, which can be had for a penny and an obligatory two-year subscription, enterprises must bear, up front, the full costs for Wi-Fi handsets at $400 to $750 each. Plus, if you have a wireless infrastructure, you'll need to spruce it up to fill in the gaps. Otherwise, you must purchase and build that from scratch, too.
Dual-mode VoWLAN-cellular services, though, can translate into savings from mobile carrier charges, if enough employees move between customer sites and the office. Furthermore, a single-number solution for these on-the-go employees eliminates the time wasted tracking them down. End users can be reached regardless of their locations, have a single voicemail and take advantage of PBX features, such as four-digit dialing, while on the mobile carrier's network.
Page 2 of 7
A wireless network for VoWLAN raises the bar on wireless network design. In fact, representatives from Avaya told us that pilot deployments of its dual-mode solution have almost always required the organization to rip and replace. Why? Because VoWLAN needs complete, dense and seamless RF coverage. That includes elevators, stairwells, restrooms, storage closets and break rooms--anywhere someone might use a cell phone. Whereas applications such as e-mail or Web browsing can tolerate marginal coverage for short durations, and users are willing to reorient their laptops to obtain a better signal, voice requires a strong signal to ensure a clear call. VoWLAN handsets usually have a lower power output, in the range of 20 milliwatts to 50 milliwatts, compared with PC Cards that have an output of 50 mW to 100 mW. The only way to obtain a consistently strong signal is to raise the power output on the access point or locate APs near each other. Coverage should overlap to maintain voice calls when roaming between APs.
In fact, roaming is one of the greatest VoWLAN deployment problems. Even if adequate coverage has been engineered, long roaming times can interrupt voice conversations. Consumer networks usually have just one access point, so residential VoWLAN services haven't concerned themselves with this requirement. Cellular carriers resolved roaming problems a long time ago with their GSM and CDMA networks. Cellular base stations control the handset's roaming behavior, dictating when and to which neighboring cell it should roam. For that reason, handoffs between cellular towers are almost always successful, while 802.11-based wireless networks struggle to attain the same result because handsets initiate and manage the roam. Voice calls should not be interrupted for more than 50 milliseconds, a standard mirroring wireline carrier Sonet rings. But our own tests of wireless PC Cards earlier this year showed roaming times that ranged from 25 ms to 3 seconds when encrypted (see "Wireless LAN Battle Plan"). Roaming with open authentication fared poorly, too. Unless the handset has been optimized to work well with the wireless infrastructure equipment, roaming times can easily interrupt the conversation.
Several new standards will improve roaming. The soon-to-be-ratified 802.11k for radio-resource management will provide handsets with an AP table that includes SSID (service set ID), channel and signal strength, as well as usage load. The recently formed IEEE 802.11v task group is working on adding control to the radio-resource management of 11k. Fast, secure roaming, meanwhile, requires yet another standard: 802.11r. That task group began work in the spring of 2004 to address transitioning a station from one AP to another quickly but securely.
Capacity is another VoWLAN challenge. The maximum number of active calls per AP varies by 802.11 standard. 802.11b solutions, for instance, can handle only six to seven concurrent calls, because the standard has a maximum link rate of 11 Mbps and an actual throughput rate of about 6 Mbps. The 54-Mbps link rates of dedicated 802.11g voice, meanwhile, allow many more calls per AP--as many as 20 at a time. If you must serve data clients, however, consider using another radio (perhaps 802.11a) or plan for fewer users.
Cisco recommends no more than seven concurrent calls and only 15 to 20 handsets in standby mode. On the other end of the spectrum, Colubris Networks crammed in 16 handsets in a test audited by Craig Mathias, principal of the Farpoint Group, a wireless and mobile computing consultancy.
What can you do to reduce capacity problems? First, recognize that different bands serve different needs. Motorola will enable only the 5-GHz (802.11a) radio for voice in its first dual-mode phone, the CN620. You can continue to use the 2.4-GHz spectrum for wireless data. Second, consider reducing cell size. This requires more APs with more areas of overlap, often complex site design and possibly an increase in co-channel interference and roaming.
You also can limit the number of calls on an AP, using mechanisms such as call-admission control. SpectraLink provides this functionality in its gateway, and Meru Networks has designed an optional VSM (voice services module) in its wireless infrastructure product. Any call that exceeds the system's capacity receives a busy signal or doesn't go through. IEEE standards 802.11k and 802.11v will assist the handsets and infrastructure to spread the load such that neighboring APs can take over some of the handset connections.
Page 3 of 7
Even if APs are operating below capacity, adding data to a voice network can reduce call quality. Packet loss, latency and jitter are accentuated with the limited bandwidth of a shared-access medium.
Without QoS on the wireless side, data traffic can easily disrupt voice traffic. Even lightly loaded networks form a poor wireless infrastructure when the occasional burst of data packets (large Web pages or e-mail attachments), competes for time. SpectraLink has addressed this with SpectraLink Voice Priority (SVP), a proprietary standard many AP vendors have adopted. If SVP support is enabled on the AP, SVP gives voice packets priority over data packets.
The IEEE's 802.11e spec addresses QoS for wireless networks. It has been ratified and approved, but the last step of publication has not yet occurred. Meantime, the Wi-Fi Alliance has created the WMM, or Wi-Fi Multimedia, as an initial subset of 802.11e--in the same way they created WPA (Wi-Fi Protected Access), which served as a stopgap until the 802.11i spec was fully functional.
WMM's most important elements are multilevel priority support, admission control and automatic power-save delivery. The first offers a way to differentiate between high-priority traffic, such as voice, and lower-priority data. Admission control lets APs reject calls when they reach capacity. Automatic power-save delivery is a way to schedule the wireless device to sleep and then wake up. If voice packets are sampled with 30 ms of voice, for example, the handset wakes up every 30 ms to receive the traffic, rather than staying powered constantly or waking up for 30 ms and waiting another 10 ms to receive its packet.
WMM is just the first step. The Wi-Fi Alliance has drawn on some of the more advanced elements of 802.11e to create WMM-SA, or WMM Scheduled Access. This standard dictates to the associated clients when they may communicate. With WMM-SA, voice traffic quality levels can almost be guaranteed, if you have enough capacity and coverage. The question is whether vendors will accept this standard. WMM-SA won't be tested until the first half of next year.
(artigo com 7 páginas - leia o original)
09/09/2005 - Sexta-feira
wVoIP é uma das bolas da vez
Wi-FiVoIP ... Will Wi- Fi find its voice?
Wireless Asia June 2005
See more articles here ...
You might have spotted them already - people milling around a hotel lobby or pool area talking into a phone that looks very much like a cellular phone, or perhaps a smartphone PDA, only it's not. Today, that phone could actually be a Wi-Fi device using VoIP technology, or a PDA equipped with a Skype client. Or they may be using it in a business environment where there's a company-wide wireless LAN.
Voice over Wi-Fi, while still in its infancy, is a reality today, and in the future there will also be voice over WiMAX. The question is, what impact will this have on mobile operators, particularly on areas such as their lucrative international roaming revenues and business accounts? Or is it in fact an opportunity for the cellcos to better compete with fixed-line players by offering a wireless package that includes both WLAN and cellular options?
In the last year, interest in phones that combine mobile access with VoIP using WLAN technology has grown at a "fevered pitch," according to research house In-Stat. In a recent study, some 84.6% of respondents were at least somewhat interested in the prospect of using a "combo" device, and half of these were very interested or extremely interested in the prospects of such a phone.
Similarly, a study from ABI Research suggested that annual global sales of dual-mode mobile/Wi-Fi phones would exceed 100 million by 2010. It noted that while dual-mode handsets were virtually unknown to both consumers and enterprises until now, that was about to change. The dual-mode services planned by BT and Korea Telecom this year could start "a very large ball rolling," according to ABI Research senior analyst Philip Solis.
"The advantages of dual-mode handsets and services, when they arrive, can be summed up in two words: seamless and economical," Solis said. He believes that eventually there will be seamless handover between VoIP services on Wi-Fi networks and mobile networks, in the process saving consumers and businesses money by using cheaper VoIP networks whenever they're available.
So if users can switch to cheaper VoIP services such as a Wi-Fi hotspot in the lobby of a hotel or when they're in their business premises, surely it's going to eat into someone's revenue stream? Probably yes, the question is by how much and how soon.
Sigve Brekke, co-CEO of Thai mobile operator DTAC, has a view consistent with many mobile executives, which is that Wi-Fi and cellular services will be complementary. "Voice over Wi-Fi will not make a big impact, especially in the beginning," Brekke told Telecom Asia. "The bigger threat for us [from Wi-Fi] is with heavy data users domestically," he said, noting that the company was countering this by offering flat-rate GPRS service and easier set up. He also noted that the company was watching the situation and conceded that there was a possibility that a small amount of business traffic could move to VoIP WLAN services in the future.
A similar message comes from Jeremy Green, principal analyst of enterprise mobility at Ovum. "In an absolute sense, yes voice over Wi-Fi will have an impact on mobile operators because previously you could only do voice via international roaming. Having said that, I'd be surprised if there was an immediate impact any time soon," he said.
He cited the fact that there were still too few Wi-Fi phones on the market and advantages with mobile such as the breadth of coverage and ease of use. "With voice over Wi-Fi it's geek stuff at the moment. It's fair to say that the mobile operators are worried, but I wouldn't be holding my breath. In principle the only effect it can have on mobile is negative, but it won't be very much or very soon," Green said.
Of course, there was also a time when VoIP itself was "geek stuff," yet now it's fairly mainstream. How long it takes voice over WLAN to do the same remains to be seen. One person that's seen such transitions in the past is Tom Evslin, co-founder and former CEO of wholesale VoIP carrier ITXC, which last year was acquired by Teleglobe. He believes that voice over Wi-Fi is a threat to mobile phone companies, particularly their current roaming charges.
"Look for these [roaming charges] to deflate just as international rates did as the accounting rate structure collapsed," he told Telecom Asia. "If we define Wi-Fi loosely to include other radio technologies with slightly longer ranges, this is the same kind of threat to legacy mobile players that VoIP is to legacy landline players."
Evslin believes that dual-mode Wi-Fi/mobile handsets will be the transition devices of choice, and predicted that Wi-Fi coverage will keep growing and rates will have to be cut for traditional mobile coverage.
Another person that thinks that the threat to mobile players is not exaggerated is Ewan Sutherland, executive director of the International Telecommunications Users Group (INTUG). Sutherland, who travels with a laptop equipped for Skype and a Bluetooth headset, noted that through this solution people can see when they're online and can talk for "free."
"I think that if the mobile operators do not react, they will be hit by this," he said, noting corporate alternatives to Skype such as softphones from the likes of Avaya and Nortel Networks. "If a company can guarantee broadband in hotels, in airports (and even in planes) on trains and in meeting rooms, that meets a big part of the demand," Sutherland said.
"I think there are too many players and too many potential market entrants. The basis of the abomination of international roaming charges is the pressure among mobile network operators to keep up the prices to rip off their visitors, but this is absent in Wi-Fi," he claimed.
High international roaming charges have been an issue that INTUG has lobbied hard against for a number of years. Last year it issued a paper for best practices related to roaming and suggested that companies look to WLAN access as a cheaper alternative to mobile roaming. It said: "The inclusion of at least one driver for a WLAN card and the card itself in the standard build for laptops considerably eases deployment of this technology. However, it also requires additional security measures, including the use of a firewall on the laptop and IPSec. Some companies are experimenting with voice over WLAN and over broadband. These offer substantial potential savings on roaming charges and so should be watched and tested carefully."
Of course, one of the keys to the success of mobile roaming is its ubiquitous coverage thanks to roaming being part of the GSM standard. With Wi-Fi, that's not the case and improvements to roaming will need to happen to make it viable for voice services. That has already started.
The Wireless Broadband Alliance (WBA) recently announced roaming between Wi-Fi networks in China, Australia, Malaysia and Singapore. In China, for example, China Netcom will offer its Chinese customers free international roaming at over 500 points, such as airports, major hotels and office buildings.
There are also the Wi-Fi aggregators such as iPass, which recently notched up 20,000 active hotspots in over 50 countries that its members can access. Steve Terry, managing director of iPass in Asia Pacific, said that VoIP is being used with Wi-Fi by some of his customers today. "We don't care what application you're running once you're connected. A lot of people use VoIP today and we in fact use it too," Terry said.
He explained that iPass staff are all equipped with Avaya softphones, and the company network has Avaya gateways that allow for the use of wireless voice services. The company's sales staff target large enterprises, such as major banks, for Wi-Fi roaming. Terry noted that when one large customer uses this it can bring tens of thousands of customers in one hit - a large loss of revenue for the operator should they start using VoIP.
He said that while he wasn't sure if the revenues from Wi-Fi voice would be significant any time soon, he did believe that the mobile carriers were cautious. "They're worried because we still see them try to block it and muscle it out from a regulatory perspective," he said, adding that it will be "interesting to watch this play."
It's not all roses in the world of Wi-Fi though, particularly for voice. Other problems that need to be addressed include security, encryption, QoS, and charging and billing, according to Mohammad Akhtar, vice president, technology marketing for Motorola Asia Pacific. Another issue will be the availability of the devices.
"In the short term we expect the impact to be small as the dual-mode Wi-Fi/GSM phones will not be available in volume until 2006," he noted. "Additionally, the affordability of these devices might be a factor for mass-market adoption in the short term."
That said, he suggests that from a technology perspective, mobility between Wi-Fi access points has been addressed, with Motorola already offering seamless mobility manager solutions, both across areas such as campus environments as well as across Wi-Fi and cellular networks. Last month Motorola announced seven customer trials in Europe of Unlicensed Mobile Access (UMA), which provides access to GSM and GPRS over unlicensed spectrum technologies, including Wi-Fi and Bluetooth.
Akhtar believes that these will be beneficial to mobile operators rather than cannibalizing their existing revenues. "There will be little or no impact to cellular roaming revenues," he predicted, suggesting it was more important to emphasize the enhanced user experience gained from dual-mode devices. "As these newer devices are commercialized, the question is not about cellular roaming, but more about increasing the share of the consumer wallet and minimizing the churn," he said.
Rival equipment vendor Alcatel has a similar view, also predicting that the impact on roaming revenues was unlikely to be significant until issues such as QoS are ironed out. "The combination of Wi-Fi roaming and a dual-mode handset and appropriate QoS will have to be in place before any significant number of business consumers will be willing to risk productivity," said Alcatel communications manager Paul Ross, who noted that Wi-Fi was not carrier class and does not scale well to dynamic flows of subscribers in and out of the cell in real time.
That said, he believes that VoIP on WiMAX will have a bigger impact as it is a carrier class technology and will be able to scale. "The SOFDMA technology introduced with (WiMAX) Revision E will enable calls to adapt to dynamic ingress and egress of subscribers, making it possible to accommodate and support the mass market usage," Ross said.
Even then, however, handovers will still not be in real time, making WiMax more of a "nomadic" solution than a truly mobile one. According to Ross, there will always be an advantage for mobile operators that support conversations "on the move," although this advantage is offset by the higher throughput of WiMAX.
Alcatel is also a backer of UMA technology, and Ross suggests UMA also supports the idea of Wi-Fi and mobile services being partners rather than a threat for the mobile players. "Options such as UMA lend credence to the concept that WiMAX and Wi-Fi can complement rather than compete with service offered by mobile operators. It remains to be seen how this will ultimately play out though."
Indeed, if anything can be taken away from the debate on voice services over corporate WLANs, Wi-Fi hotspots and the coming WiMAX networks it is that it will be interesting to see how things play out. In the meantime, watch out for users milling around the pool using Wi-Fi phones as they nibble away at the mobile operator's roaming revenues.
Sexta-feira, 15 abril de 2005 - 11:37
No San Antonio Community Hospital, a VoIP é a segunda aplicação na lista das que estão sendo implementadas sobre a rede Wi-Fi já existente, logo depois do acesso via computador a registros e raio X de pacientes à beira de leitos e em centros cirúrgicos, explica Irv Hoff, gerente da rede do hospital.
Mobilidade real e custos menores foram os principais desafios que Hoff precisou superar em relação às redes Wi-Fi, mas agora ele está convencido de que a tecnologia satisfaz suas necessidades.
Alguns detalhes da implementação de VoIP ainda precisam ser solucionados para evitar problemas como queda de ligações entre pontos de acesso ou bloqueio de sinais devido aos obstáculos dos prédios. "Queremos que a qualidade da chamada seja igual à que você espera de um telefone com fio, tendo em vista que controlamos o ambiente", explica Hoff.
Os problemas desse tipo de solução são complexos porque VoIP sobre Wi-Fi reúne as peculiaridades das redes locais wireless (wireless LANs ou WLANs) e telefonia IP. Assim como as WLANs para dados são cada vez mais aceitas, o mesmo acontecerá com VoIP sobre Wi-Fi, prevê Will Stofega, analista da IDC.
Mas, para ele, os problemas potenciais de VoIP precisam ser enfrentados antes. "Se há retardo ou perda de pacotes, com VoIP você ouve", diz Stofega. E, à medida que telefones Wi-Fi VoIP proliferarem, as ligações telefônicas vão fomentar a demanda por redes wireless. "Se você dá mobilidade às pessoas na LAN, você tem que aumentar o número de pontos de acesso."
Apesar destes problemas, as redes Wi-Fi estão crescendo e as vendas mundiais de equipamentos de infra-estrutura para redes sem fio móveis deverão saltar de cerca de US$ 43 bilhões no ano passado para US$ 49 bilhões no final de 2008, de acordo com a IDC.
À medida que os executivos se familiarizarem com o transporte de dados através destas redes, cada vez mais eles irão acrescentar VoIP, diz Stofega. No momento, o uso de VoIP sobre Wi-Fi é muito limitado. Com avanços tecnológicos para facilitar o uso e garantir qualidade de voz, este uso vai aumentar, segundo Stofega.
A Airespace (que está sendo adquirida pela Cisco), a Siemens e a Trapeze Networks são algumas das empresas que estão vendendo pontos de acesso e switches capazes de suportar VoIP. De acordo com a Siemens, os principais usuários são hospitais, lojas de varejo, fabricantes e depósitos de mercadorias.
Chaves para a implementação
Para Hoff, do San Antonio Hospital, o primeiro passo é garantir que os pontos de acesso cubram cada local em que um usuário possa estar. Em seguida, ele precisa assegurar que haja pontos de acesso sobrepostos suficientes para suportar uma provável carga de usuários simultâneos, sem negar serviço a nenhum deles. Hoff usa equipamentos da Trapeze e uma ferramenta que a empresa fornece chamada RingMaster que mapeia prédios e a entrada eficaz de freqüências Wi-Fi através de paredes, chãos, portas e janelas.
Esse é um aspecto particularmente importante em hospitais, não só porque são comuns reformas que mudam a localização de paredes, mas também porque algumas destas paredes são blindadas contra raios X e, portanto, também hostis a transmissões Wi-Fi. "Fazemos muita remodelação - novas partições, novos escritórios", diz Hoff. É um processo em andamento, ou seja, à medida que o hospital realiza mudanças, registra-as no RingMaster, que identifica novos pontos cegos. Assim, os pontos de acesso são reconfigurados para contorná-los.
O balanço de carga entre pontos de acesso é fundamental para a distribuição eficiente de chamadas, dizem os fornecedores. Pontos de acesso Airespace, por exemplo, distribuem os usuários uniformemente em ambientes onde eles possam estar sob o alcance de diversos dispositivos ao mesmo tempo. Sem este recurso, equipamento do usuário disputaria entrada no ponto de acesso com o sinal mais forte. A Siemens diz que sua próxima leva de dispositivos também terá este recurso.
Presumindo que existam pontos de acesso suficientes para garantir cobertura, executivos de rede têm que garantir handoffs rápidos entre os dispositivos à medida que os chamadores entram e saem de alcance em locais diferentes. O switchover tem que levar menos de 50 milissegundos - isso significa que é essencial um projeto de rede cuidadoso. Com voz e dados trafegando na mesma rede, por exemplo, os handoffs podem levar de meio segundo a 10 segundos, com a presença ou ausência de dados na rede afetando o tempo de maneira imprevisível.
Além do desempenho da rede, qualquer uso de VoIP sobre Wi-Fi deveria incluir uma avaliação da qualidade da voz. "Você quer estar no meio de uma ligação com um cliente e mal conseguir ouvi-lo?" pergunta Stofega.
O futuro do roaming externo
Deslocar-se dentro de um prédio pode bastar para a equipe interna de um hospital, mas o pessoal de vendas que viaja pelo país também pode beneficiar-se de telefones wireless VoIP e economizar dinheiro para os clientes, diz Keith Waryas, analista da IDC.
O uso de telefones wireless VoIP ou mesmo de um software de softphone VoIP em um laptop transforma hotspots públicos em refúgios para os usuários que não querem gastar minutos em seus celulares onde tarifas mais caras poderiam ser aplicadas, explica Waryas.
"A maioria dos usuários corporativos está sendo reembolsada por seus empregadores pelo uso de seus celulares pessoais", diz. Para resolver esse dilema, a empresa designaria um telefone wireless VoIP para usuários que se deslocam e receberia menos relatórios de gastos para reembolso de celular. Uma das limitações expressivas para essa alternativa, no entanto, é o número de hotspots públicos disponíveis hoje, embora esse total esteja aumentando rapidamente.
Até mesmo quando existem hotspots públicos suficientes, as corporações não teriam controle sobre o design e o gerenciamento dessas redes públicas, e por isso, a qualidade poderia ser afetada. Além disso, cada usuário teria que transportar dois telefones, um Wi-Fi e outro celular, se quisesse permanecer ao alcance o tempo todo.
Visivelmente, porém, os fornecedores de serviços acham que existem clientes interessados em telefones Wi-Fi em número suficiente para justificar o suporte aos novos serviços. A Vonage, fornecedora de serviços VoIP, anunciou recentemente um serviço que suporta telefones WiFi. A Net2Phone está prestes a comercializar serviço similar nos Estados Unidos, após lançá-lo no Canadá.
Aliada a parceiros, a Motorola também está testando em campo os primeiros telefones wireless dual-mode, hotspots e PABXs que permitem aos usuários fazer ou receber chamadas em redes Wi-Fi corporativas e continuá-las em redes GSM quando saem do alcance Wi-Fi.
Assim, um médico que iniciasse uma conversa no hospital via Wi-Fi poderia sair do prédio, entrar em um carro e partir sem interromper a ligação porque ela seria transferida para uma rede celular.
Os sistemas compostos por telefones Motorola híbridos requerem o uso de PABXs Avaya e pontos de acesso da Proxim para coordenar o handoff de chamadas e são apresentados como um meio para as empresas reduzirem os custos de celular. As empresas comprariam os telefones e configurariam contas de celular corporativas, o que lhes permitiriam negociar tarifas mais baixas do que as que seus funcionários possuem individualmente.
Para que a solução funcione, no entanto, os telefones da Motorola só têm acesso a redes Wi-Fi específicas que contam com servidores de presença da empresa, capazes de rastrear a localização exata dos usuários.
Os fornecedores de serviços, por sua vez, poderiam oferecer um serviço gerenciado baseado nesta tecnologia. Waryas, da IDC, espera que pelo menos uma importante operadora norte-americana anuncie a oferta do serviço em meados desse ano. Isso daria aos usuários transição "sem costura" de celular para Wi-Fi em hotspots públicos.
O gerente de telecomunicações de um hospital, que preferiu não se identificar, está cogitando a adoção da tecnologia, mas manifestou preocupação com o sistema de billing. A grande dúvida, segundo ele, é saber como a rede decide qual tecnologia vai usar e se haverá uma tarifa diferenciada para as chamadas recebidas na rede Wi-Fi.
Os defensores deste tipo de serviço dizem que as empresas poderão negociar bons acordos para os celulares porque vão precisar de muitos minutos de chamadas. Segundo Waryas, estes serviços vão possibilitar a criação de roteamento menos dispendioso para manter o custo baixo. "Se o billing não é problema, estes serviços dual-mode poderiam acabar com algumas dificuldades de cobertura de Wi-Fi em prédios", acrescenta Waryas. "Quando um usuário entrasse em um ponto sem cobertura em um prédio, a ligação prosseguiria como uma chamada celular em vez de cair", conclui o analista.
Sim, nós temos VoIP com Wi-Fi
24/05/2004 - Segunda-feira
Sras e Srs. embora estejamos em Maio queremos
relatar que Março foi um mês de muitas surpresas em matéria de VoIP combinado
(ou não) com WLAN.
Veja abaixo uma coletânea variada do Weblog
Will Microsoft Dominate VoIP?
Tuesday, March 02 @ 00:19:00 PST
Clay Shirky explains it all; "Where Vonage and a number of the other VoIP startups present themselves to the customer as phone companies, emulating the incumbents they are challenging, you can think of Plan B as the Skype plan. Skype isn't taking on the trappings of a phone company; instead, it offers free two-way voice conversations over the internet."
"Wi-Fi and VoIP are powerful technologies on their own, but together, they are far more powerful. It's sort of like adding one plus one and getting three, " says Richard Webb at Infonetics Research.
But in order for VoIP over Wi-Fi to really take off, it will also have to combine cellular technology, said Joel Conover, an analyst at Current Analysis. Motorola and Nokia have shown handsets that support both cellular and Wi-Fi access. Avaya and Proxim have teamed to develop Proxim's new AP-4000 with Voice over IP features.
There has been an explosion of SIP Products. VoIP operators like Vonage, SIPphone and 8x8, often use ordinary phones. They plug into an adapter than connects to your broadband connection. Nothing is hotter than Mobilized VoIP. "Free" VoIP services include Skype, Pulver's Free World Dialup and Asterisk, an open-source SIP server.
it has been believed, helps to remove legal liability from "free" internet
providers. Currently, standalone WiFi VoIP phones may not be able to connect
or acknowledge the disclaimer. A method to provide that needs to be developed,
say some community lan activists.
Operadoras apostam em rede local sem fio
sobre wireless LAN (VoWLAN)
Celulares e provedores brigam pelo mercado de Wi-Fi, que deve atrair também
Os telefones Wi-Fi permitem ligar para o exterior sem pagar interurbano,
usando a conexão de internet rápida. Provedores de acesso, como o iG e o
Terra, e empresas celulares, como a Oi, já adotaram a solução. A Vivo e a BCP
também estão de olho.
Voz sobre wireless LAN (VoWLAN)
Já existe um novo acrônimo no mercado para descrever essa simbiose: VoWLAN
(Voice over Wireless LAN - WLAN). Há também quem aposte em VoWi-Fi (Voice
Esse telefone deverá chagar ao mercado em dois meses (de acordo com a InfoWorld já deveria ter chegado ao mercado em junho passado) e a um preço planejado de US$ 595 nos EUA. Os modelos da Spectralink são os: i640 (de US$ 599) e o e340 (modelo mais barato começando em US$ 399).
O que a Cisco e a Spectralink estão disputando? O mercado de aparelhos de
O software de VoIP (802.11b) para Pocket PCs está também disponível para os
Telesym. O padrão SIP
VoIP, adotado pela Microsoft, está começando a tornar-se um padrão
dominante. Os aparelhos de Wi-Fi anteriores com o da
Symbol e da
utilizavam o padrão H-232. Existe também o player
Vocera Communications System
cujo servidor é baseado em um Servidor Windows 2000, uma LAN ou WAN e pontos
de acesso wireless na tecnologia 802.11b.
Para melhorar ainda mais a competição nesse nicho, a Mitsubishi anunciou no início deste mês que já está testando seu telefone VoWLAN no Japão através de uma empresa do grupo a IP Talk.
Qual é o mercado dessa oferta? Antes de falar que ele é gigantesco, pois existe nos segmentos de varejo, manufatura, saúde, turismo (hotelaria), logística, oil & gas entre outros, vamos mostrar algumas oportunidades que já estão sendo trabalhadas.
Na saúde veja as referências:
Wi-Fi lower nurses' blood pressure? da CNET News.com e
Dutch Hospital in Spectralinks from Unstrung.
Existem ainda alguns segmentos onde esta oferta poderia fazer uma grande diferença, a saber: hotelaria e oil & gas (por exemplo refinarias ou em lugares com campus network).
Em alguns ambientes de oil & gas onde exista a presença de gases não poderemos utilizar equipamentos com teclado por causa do risco de explosões. A solução seria a utilização de Pocket PC sem teclado (touch panel).
Em suma, a tecnologia de VoWLAN é extremamente atrativa em empresas e instituições aonde os funcionários passem a maior parte do tempo fora das suas mesas como no caso de enfermeiras, de gerentes de varejo e de técnicos de campo de grandes corporações.
Um candidato natural para utilizar essa tecnologia é o caso de uma organização aonde exista a demanda de "mobilidade" mostrada acima e que já possua uma WLAN (já foi feito parte do investimento).
Segundo o instituto In-Stat/MDR, em recente relatório, espera que o mercado de handsets de VoWLAN evolua de 20 mil em 2001 para 80 mil em 2002 e ultrapasse a cifra de meio milhão em 2006. Bons números!
Existem problemas? Sim ainda existem.
O IEEE está trabalhando nesse padrão que adiciona o mecanismo de
Quality of Service (QoS) na tecnologia de WLAN - tal mecanismo
habilita serviços de voz em meios sem fio. Por quê?
27/DEZ/2003 - Sábado
VoWLAN RIDES AGAIN ...
Mais 1 da Série Didática de WLAN. Hoje com
Então ... VoWLAN é Voice over Wireless LAN.
VoWLAN vai ser muito interessante no mercado
Corporativo principalmente naquelas empresas aonde vc tem uma grande parte dos
empregados 80% do seu tempo de trabalho fora das suas mesas como os segmentos
de hotel, de hospital, do varejo e de logística para citar alguns.
1. Veja o que já estão pensando ...
Este WISP no Reino Unido jjá quer fornecer o
serviço de VoWLAN em 2004.
Smart Convergence on Saturday, November 22, 2003
By Vikki Lipset
November 21, 2003
Patrons of U.K. hotspots will soon be able to make voice calls over public wireless LANs, thanks to a new service from Internet access provider Broadreach Networks.
The service, called ReadytoTalk, won't officially launch until next summer, but Broadreach will do a test run with 40,000 customers in the interim. The voice over IP (VoIP) service will be an add-on to the company's ReadytoSurf hotspot service, which passed the 500,000 user mark this week.
All ReadytoSurf sites will also be ReadytoTalk-enabled, according to Broadreach CEO Magnus McEwen-King. There are currently 129 ReadytoSurf hotspots in coffee shops, retail stores, hotels and other locations across the United Kingdom.
Like ReadytoSurf, the VoIP service will be offered through ISPs and wireless carriers. Users will need to download software, developed by Broadreach, to their laptop or PDA (McEwen-King said the company plans to support all the major operating systems). Pricing for the service is not yet available.
Broadreach has been contemplating a VoIP service for a while, but has been waiting for the right time to enter the market, said McEwen-King. "VoIP has always been a much talked about proposition, but the quality levels have not been there. However, in the last six months, a number of companies have made significant strides in improving both the costs and quality. We feel there's another few months to go, but now is the time to start doing end-user testing with our ISP and mobile phone operator partners."
See the Press Release
2. Enquanto isto fique com esta boa matéria
By Nancy Gohring September 12, 2003
Some hurdles remain, but ubiquitous voice
communications may be the killer app for wireless LANs
WLANs (Wireless LANs) are still in the experimental phase at most companies. Why? Because wireless security standards remain in flux. But a more obvious obstacle to wholehearted adoption is the lack of a compelling need for wireless in the average office, which already has a perfectly functional, wired LAN in place.
Well, here’s a thought: How about replacing or supplementing your current phone system with a VoWLAN (Voice over WLAN) system? Just take an ordinary wireless network and add a VoWLAN server along with laptops, PDAs, or newfangled Wi-Fi phones to run the client. Instead of workers wasting time playing phone tag, they can field calls wherever they roam on campus — or even on the road, if there’s a Wi-Fi cloud nearby.
VoWLAN is a natural extension of VolP (Voice over Internet Protocol), a technology that has already taken root in enterprise telecommunications. (Today, more IP-based PBXs are sold than conventional models.) Yet VoWLAN presents its own unique QoS (quality of service) challenges relating to fluctuating wireless throughput and roaming among APs (access points), which is why most of today's local wireless voice systems are bundles of proprietary wireless network hardware and software.
Industries with highly mobile workers — such as retail, manufacturing and healthcare — can justify the premium for a proprietary network. (One of the most popular solutions, SpectraLink's Wireless Telephone System, costs between $400 and $700 per seat.) Yet the proliferation of Wi-Fi and its increasing reliability opens the possibility of deploying VoWLANs across commodity WLAN setups at much lower costs.
Technical hurdles remain. But on the hardware side, at least, everyone seems to be getting in the game. Cisco recently introduced its first VoWLAN handset and a slew of vendors including NEC, Qualcomm, Motorola and Dell promise hybrid phones next year that use both Wi-Fi and mobile phone networks.
A Very Local Exchange
“It’s just a matter of time before [VoWLAN] catches on in the mainstream enterprise,” says Ben Guderian, director of marketing for SpectraLink. SpectraLink recently introduced a new, lightweight, less rugged handset designed for mainstream enterprise users. Its lowest priced handset costs $399, which compares to around $350 for many desk phones with standard wiring.
Proprietary wireless voice vendors such as SpectraLink and Symbol have been among the first to release VoWLAN solutions for commodity wireless infrastructure. But there’s a new breed of VoWLAN provider as well: the softphone developers. These companies, such as TeleSym, IP blue, and VLI have built software that can be loaded onto PDAs or laptops, enabling users to initiate and receive voice calls over WLANs.
Basically, VoWLAN systems work in two different ways. Offerings from SpectraLink, Symbol, and Cisco route calls from the phone to the WLAN AP to a VoIP gateway — one that may already be in use to deliver VoIP over the wired network — which translates calls between the IP network and the PBX. That setup allows all regular PBX functions that are available on workers’ wired desk phones to be available on the VoWLAN phones. Calls that are made to phones outside the enterprise go through the PBX to the PSTN (Public Switched Telephone Network).
By contrast, softphone developers such as TeleSym provide systems that route calls outside the enterprise over the Internet. In this scenario, road warriors could use the softphone on their PDA or laptop to place calls from a hotel that offers a WLAN. The call could route entirely over the Internet. “Then the call is completely free,” said Raju Gulabani, TeleSym’s CEO.
The downside is QoS. Like any voice call that
uses the Internet, users can’t control the quality of the connection.
Unfortunately, even over the local network, VoWLAN has its shortcomings. The problem is that the 802.11 standards — including those that cover QoS, security, and roaming — simply weren’t designed to support voice.
For example, 802.11 entirely lacks a QoS mechanism. This lack means that no special priority is given to voice, so when traffic spikes on the network, dropouts may occur. The IEEE is working on 802.11e, a QoS standard that should be finalized next year. In the meantime, Symbol and SpectraLink have implemented their own proprietary QoS mechanisms through their hardware.
But it’s security, or a lack thereof, that’s the biggest deal breaker for VoWLAN today. Enterprises view today's wireless security measures (such as the Wireless Encryption Protocol) as weak, forcing them to opt for wireless VPNs. But VoWLAN offerings that use phones, as opposed to those that use PDAs or laptops, often can’t employ VPNs because the client software usually can’t be loaded onto the phone. (Several vendors, including NEC and Cisco, plan to produce phones next year with VPN support built in.)
But using VPNs for voice has other problems. “A VPN tends to encapsulate voice packets, so it obscures them from the network and it can’t discern high priority voice from low priority data,” says Ron Seide, product line manager for Cisco’s wireless networking business unit. In addition, VPN’s cause latency that degrades the quality of voice, says Richard Watson, an engineer at Symbol and director of telephony product marketing.
Instead of using VPNs, users can protect against unwanted intruders by putting voice and data on different subnets or VLANs, allowing clients in the voice subnet to communicate only with the telephone gateway, Watson says. With this separation, the widely used encryption and authentication standards offer good enough security, say some vendors. That’s because the threat of eavesdroppers is remote as the listener would have to be within range of the same AP as the phone user. “The joke here is watch out if you have someone walking behind you with an antenna,” says Watson. “It’s an overblown thing.”
An added challenge, though, is that encryption and authentication must happen fast enough so that a call isn’t dropped or degraded when a user moves from the coverage area of one AP to the next. The existing 802.11 standard can’t support that handoff fast enough and neither can the security solutions developed by gateway vendors. Even 802.1x, the upgraded security standard in development, won’t work quickly enough. “When standards bodies developed all this, they were more concerned with security on laptops,” says Watson.
The handoff between APs should happen in under 50 milliseconds to cleanly support a voice call, says Doug Klein, CTO of Vernier Networks, a security gateway vendor. Vernier’s gateway does the transfer in a matter of a few hundred milliseconds. “It’s not optimum,” admits Klein.
As a result, vendors have developed their own fast authentication processes. These generally work by dispensing a certificate to the client proving that it is authenticated, so that when a user moves into range of another AP, the client offers that certificate as proof of authentication.
Cisco employs a similar scheme, where one AP is designated as a master AP within a subnet. Rather than require each AP to acquire an encryption key from a backend server as the user roams, the master AP gets a master key and from that, each AP in the subnet spawns a session key. But even Cisco’s solution takes 150 milliseconds.
Maybe Next Year
The available VoWLAN security solutions aren’t robust enough for many enterprises. “I don’t think it’s likely that we’ll be deploying VoIP on Wi-Fi networks anytime soon,” says Joshua Wright, senior network and security architect for Johnson and Wales University, which already has an extensive WLAN for data users. Current offerings don’t enable the kind of reliability he wants in a voice network.
The efficiency of the security and QoS also affects the load that APs can handle. Most AP vendors say each AP can support 10 simultaneous calls, but when pressed, will usually admit to half that number in live deployments. Chris Kozup, META Group's program director of technology research service, says his clients who have tested VoWLAN report on average four or possibly five calls without any data use per AP. “It becomes a problem because there are finite resources here in terms of channel and frequency,” Kozup indicates. “It’s not as easy as lighting up another AP.”
New standards, including the faster 802.11g and the QoS specification, 802.11e, should increase the number of users an AP can support. Combined, those upgrades could allow 15 to 25 simultaneous calls, says Cisco's Seide.
Ultimately, although the hurdles of deploying a
robust VoWLAN are many, they are also surmountable. The key to robust and
reliable VoWLAN networks lies in the ability to support security and all
capabilities fast enough to hand off between APs seamlessly. As more customers
demand support for voice, vendors say they’ll deliver it. “We’ll get around to
doing the work that needs to be done,” said Vernier’s Klein.
3. Veja Notícias do IEEE sobre QoS (IEEE
MAC Enhancements for Quality of Service
The purpose of Task Group E is to: Enhance the
current 802.11 MAC to expand support for applications with Quality of Service
requirements, and in the capabilities and efficiency of the protocol.
4. Um Trabalho Nosso sobre o Assunto
5. Uma Grande Matéria sobre o Assunto
17/NOV/2003 - Segunda-feira
VoIP & VoWLAN: Um Folhetim
sobre estes 02 "moços" ....
Intros Wireless VoIP
Complemente sua pesquisa: Google (com opção de páginas em português)
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