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Friday, 28 September 2012

Mobile VoIP 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.



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