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Mobile VoIP or simply mVoIP is an extension of mobility to a Voice over IP network. Two types of communication are generally supported: cordless/DECT/PCS protocols for short range or campus communications where all base stations are linked into the same LAN, and wider area communications using 3G/4G protocols. There are several methodologies that allow a mobile handset to be integrated into a VoIP network. One implementation turns the mobile device into a standard SIP client, which then uses a data network to send and receive SIP messaging, and to send and receive RTP for the voice path. This methodology of turning a mobile handset into a standard SIP client requires that the mobile handset support, at minimum, high speed IP communications. In this application, standard VoIP protocols (typically SIP) are used over any broadband IP-capable wireless network connection such as EVDO rev A (which is symmetrical high speed — both high speed up and down), HSPA, Wi-Fi or WiMAX. Another implementation of mobile integration uses a soft-switch like gateway to bridge SIP and RTP into the mobile network's SS7 infrastructure. In this implementation, the mobile handset continues to operate as it always has (as a GSM or CDMA based device), but now it can be controlled by a SIP application server which can now provide advanced SIP-based services to it. Several vendors offer this kind of capability today. Mobile VoIP will require a compromise between economy and mobility. For example, voice over Wi-Fi offers potentially free service but is only available within the coverage area of a single Wi-Fi access point. Cordless protocols offer excellent voice support and even support base station handoff, but require all base stations to communicate on one LAN as the handoff protocol is generally not supported by carriers or most devices. High speed services from mobile operators using EVDO rev A or HSPA may have better audio quality and capabilities for metropolitan-wide coverage including fast handoffs among mobile base stations, yet may cost more than Wi-Fi-based VoIP services. As device manufacturers exploited more powerful processors and less costly memory, smartphones became capable of sending and receiving email, browsing the web (albeit at low rates) and allowing a user to watch TV. Mobile VoIP users were predicted to exceed 100 million by 2012 and InStat projects 288 million subscribers by 2013.〔(【引用サイトリンク】title=VoIP user figures )〕 The mobile operator industry business model conflicts with the expectations of Internet users that access is free and fast without extra charges for visiting specific sites, however far away they may be hosted. Because of this, most innovations in mobile VoIP will likely come from campus and corporate networks, open source projects like Asterisk, and applications where the benefits are high enough to justify expensive experiments (medical, military, etc.). == Technologies == Mobile VoIP, like all VoIP, relies on SIP — the standard used by most VoIP services, and now being implemented on mobile handsets and smartphones and an increasing number of cordless phones. UMA — the Unlicensed Mobile Access Generic Access Network allows VoIP to run over the GSM cellular backbone. When moving between IP-based networks, as is typically the case for outdoor applications, two other protocols are required: * IEEE 802.21 handoff, permitting one network to do call setup and initial traffic, handing off to another when the first is about to fall out of range - the underlying network need not be IP-based, but typically the IP stream is guaranteed a certain Quality of Service (QoS) during the handoff process * IEEE 802.11u call initiation when the initial contact with a network is not one that the user has subscribed to or been in contact with before. For indoor or campus (cordless phone equivalent) use, the IEEE P1905 protocol establishes QoS guarantees for home area networks: Wi-Fi, Bluetooth, 3G, 4G and wired backbones using AC powerline networking/HomePlug/IEEE P1901, Ethernet and Power over Ethernet/IEEE 802.3af/IEEE 802.3at, MoCA and G.hn. In combination with IEEE 802.21, P1905 permits a call to be initiated on a wired phone and transferred to a wireless one and then resumed on a wired one, perhaps with additional capabilities such as videoconferencing in another room. In this case the use of mobile VoIP enables a continuous conversation that originates, and ends with, a wired terminal device. An older technology, PCS base station handoff, specifies equivalent capabilities for cordless phones based on 800, 900, 2.4, 5.8 and DECT. While these capabilities were not widely implemented, they did provide the functional specification for handoff for modern IP-based telephony. A phone can in theory offer both PCS cordless and mobile VoIP and permit calls to be handed off from traditional cordless to cell and back to cordless if both the PCS and UMA/SIP/IEEE standards suites are implemented. Some specialized long distance cordless vendors like Senao attempted this but it has not generally caught on. A more popular approach has been full-spectrum handsets that can communicate with any wireless network including mobile VoIP, DECT and satellite phone networks, but which have limited handoff capabilities between networks. The intent of IEEE 802.21 and IEEE 802.11u is that they be added to such phones running iPhone, QNX, Android or other smartphone operating systems, yielding a phone that is capable of communicating with literally any digital network and maintaining a continuous call at high reliability at a low access cost. Most VoIP vendors implement proprietary technologies that permit such handoff between equipment of their own manufacture, e.g. the Viera system from Panasonic. Typically providing mobility costs more, e.g., the Panasonic VoIP cordless phone system (KX-TGP) costs approximately three times more than its popular DECT PSTN equivalent (KX-TGA). Some companies, including Cisco, offer adapters for analog/DECT phones as alternatives to their expensive cordless. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mobile VoIP」の詳細全文を読む スポンサード リンク
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