Wiley.Developing.Software.for.Symbian.OS.2nd.Edition.Dec.2007 (Symbian Books), страница 4

While GSM alone is circuitswitched, GPRS is based on packet-switching technology. This meansthat the radio bandwidth is used only when data is actually transferred,even though you are constantly connected (circuit switching keeps thefull bandwidth reserved throughout a connection).GPRS, in theory, supports bandwidths up to 170 Kbps. In practice,however, you’ll get between 20 and 60 Kbps, depending on networkconditions – but this is still significantly faster than the GSM dialup datarate! The best way to think of the speed of GPRS is that it matchesapproximately with a PC connected to the network via a wired telephonemodem. However, GPRS can feel better than dialup since it connectsalmost instantly to the network without the lengthy delay in dialing anumber and establishing a call.GPRS is categorized as a 2.5G technology due to its speed.

Althoughmany networks now support higher-speed protocols, GPRS was an excellent stepping stone and preview for the now-available 3G technologies.HSCSDHSCSD is the high-speed version of CSD. HSCSD is another 2.5Gstandard that supplies a comparable speed to that of GPRS (althoughon the lower side in many cases), but with a significant difference – thebandwidth is reserved to the smartphone throughout the connection. Thisis because HSCSD, like CSD and GSM, is a circuit-switched technology.This makes HSCSD better suited for applications that require a constantbit rate, although the practical bandwidth is rather low for good real-timemultimedia transfers, and these are the transfers that would benefit themost from constant bit rates.HSCSD is not widely used due to the higher costs to implement.

TheNokia 6600 and the Motorola A920 are examples of smartphones thatsupport HSCSD.EDGEEDGE, short for Enhanced Data Rates for GSM Evolution, is a GSM-basedprotocol that provides theoretical speeds up to 384 Kbps. It is a 2.5Gtechnology that is sometimes referred to as 3G because of its higher speed.It is not yet as widely used as GPRS, but is gaining support.

For example,AT&T has deployed EDGE on its GSM networks in the USA, reachingspeeds of around 90 Kbps in practice. Most modern GSM smartphonesnow support EDGE.UMTSUMTS, short for Universal Mobile Telecommunication Services, is ahigh-speed data transfer which supports bandwidths up 2 Mbps. ThisSMARTPHONE FEATURES7protocol is the basis of third generation mobile communications thatmake many media-rich services a possibility. UMTS is not based on GSMtechnology – it uses a technology called W-CDMA. However, the UMTSplatform is designed to work with GSM systems to ease its deployment.It’s exciting that many service providers now have this high-speed service.HSDPAHSDPA, short for High-Speed Data Packet Access, is based on UMTS andsupports even higher speeds than UMTS (up to 3.6 Mbps).

It is knownas a 3.5G technology. Many service providers have launched HSDPAsupport recently.Wi-FiWi-Fi is a popular communication protocol used to connect devices suchas PCs, game consoles, PDAs, and mobile phones to a network wirelessly.Wi-Fi service is found not just at corporations for their employees to accesstheir network, but also for Internet users at coffee shops, hotels, bookstores, airports, and even parks.Wi-Fi is a high-speed protocol when compared with cell tower-basedprotocols – it supports speeds up to 54 Mbps.

Wi-Fi is a much shorterrange protocol when compared with cell-based radio protocols, with itsrange being about 600 ft.In the last couple of years, numerous smartphones have been releasedwith Wi-Fi capability. This allows for high-speed data transfer when inrange of a Wi-Fi ‘hotspot’.A standard called WiMAX, which is in its beginning stages now,promises to extend the range of Wi-Fi to 2–3 miles for more global areacoverage.1.3.2 Smartphone MessagingText messaging, such as email and instant messaging, is widely usedon PCs connected to the Internet. It makes sense that similar modes ofcommunication be used in mobile devices.

Below are the messagingfeatures supported by smartphones.SMSSMS stands for Short Messaging Service. SMS allows mobile phone usersto send and receive short text messages up to 160 characters. Thesemessages are sent between phones with only a small delay and can occureven while a voice call is in progress. SMS is well suited for many typesof communication exchange, and is less intrusive than making a voice8SMARTPHONES AND SYMBIAN OScall. SMS is a part of the GSM communication platform and used bycell phones all over the world. SMS is not yet widely used in the UnitedStates, but is slowly growing in popularity. SMS is a standard feature ontoday’s smartphones.MMSMMS, short for Multimedia Messaging Service, is an extension of SMSthat provides the ability to send media data such as pictures, audio, andeven video along with your text message.

MMS is a natural complementto smartphones due to its need for, and use of, audio and video capabilityand, in many cases, an attached video camera. For example, a smartphoneuser could snap a picture of a landmark, record a quick voice commenton it, and send it instantly to another mobile phone user.MMS messages can even be sent to people who have only SMScapability by sending a text link to a browser URL containing the MMSmessage. You can also send and receive MMS messages between asmartphone and an email account used from a PC.EmailHaving the ability to keep up with your email while on the road is astandard feature found in smartphones. With the high-resolution scrollable displays and alphanumeric entry methods, it does not feel muchdifferent from email on a PC. Smartphones allow the user to set upmultiple POP3 and IMAP email accounts.FaxMany smartphones include the ability to send and receive faxes, or canbe customized to do so with fax software.1.3.3 Web BrowsingInternet browsing is a standard feature for smartphones.

There are manydifferent browsers available, and they fall into two main types: WAP andHTML.WAPWAP, which stands for Wireless Application Protocol, was specifically designed for Internet browsing on resource-constrained devices.It includes lightweight markup languages designed to minimize the processing power and memory needed by the mobile device to render theweb page. WAP also ensures that the page is useable on a small screen.Markup languages include WML and xHTML (mobile profile).SMARTPHONE FEATURES9In many cases, proxy servers are used, which will automaticallytranslate traditional HTML websites to the WAP markup language beforetransferring to the mobile device.

This is known as transcoding.HTMLAlthough WAP was considered important for earlier mobile devices, thesmartphones today have better memory, processing power, and displays.Because of this, it is feasible to include traditional HTML browsers thatload websites directly in their native format, similar to a browser on a PC.Many smartphones have HTML browsers and those usually include WAPcapability as well – sometimes combined in one browser.1.3.4 Local Device Communication FeaturesSmartphones have a variety of communication features in addition to basicaccess to the cellular network. These features allow a smartphone to linkdirectly with other devices, including PCs, PDAs, wireless headsets, andother smartphones to undertake a wide variety of data transfer functions.Below are the popular device-to-device communication mediums, alongwith some of their uses.USB/Serial cable connectionSmartphones can be connected to a PC via either a USB or serialcable (varies from phone to phone).

This high-speed link is normallyused for downloading new applications to the smartphone as well assynchronizing user data, such as calendar and contact entries. Manyproducts provide a cradle into which the smartphone can be plugged, forboth PC connectivity and for charging the phone’s battery.Infrared (IR)The smartphone provides the capability to communicate through aninfrared port to a PC or other device such as a PDA or phone.

You cando all the things that can be done with the USB/serial cable, but withoutplugging in any wires. IR requires a line-of-sight connection between thedevices in the same way that a TV remote control does.Bluetooth technologyBluetooth technology is a short-range radio technology that enablesdevices to find and connect to each other and communicate. Whiletechnologies like GSM replace long lengths of wire, Bluetooth technology replaces the rat’s nest of short wires connecting various pieces of10SMARTPHONES AND SYMBIAN OSequipment.

Unlike infrared, Bluetooth technology does not require a lineof sight and will even communicate through walls.With Bluetooth technology, you can connect more conveniently to PCsand PDAs than you can with cable and IR to download applications andsynchronize user data. In addition to providing basic PC-to-smartphonelinkage, Bluetooth technology makes more device-to-device communication scenarios possible. For instance, you can snap a picture on yoursmartphone and send it to a nearby printer for printing or connect to awireless headset for hands-free operation.Some smartphones allow themselves to be used as a modem, withaccess to the cellular network. In this case, a device such as a PCconnects to the smartphone via Bluetooth technology, cable, or IR toprovide the PC with Internet connectivity.As more devices become available with Bluetooth technology, expectmany new possibilities for Bluetooth-enabled smartphones.1.3.5 Location Based ServicesMore smartphones are being equipped with features that allow a deviceto know its physical location.

In some cases – for example, the NokiaN95 – Global Positioning Satellite (GPS) hardware is built into the phone.Alternatively, the phone may use the cell service’s location information(e.g., the GSM cell id can tell which particular cell tower you are communicating with), which is being increasingly supported for emergencypurposes.Location Based Services (LBS) uses the device’s location to provide apersonalized experience to the user. The most obvious (and useful!) is thetraditional map-based turn-by-turn navigation service.

Other interestingapplications are:•Software that shows the hotels, stores, theaters, and other businessesin your immediate vicinity along with any special discounts or otherdeals offered. Weather and traffic can also be reported for yourvicinity.•Software that allows you to track your children who are carryingLBS-enabled smartphones.•Software to help with health and fitness by tracking how far and fastyou are walking or jogging.•Games that use your location as input.