Since the Voice-Over Internet protocol (VoIP) evolution was introduced to this generation technology, the mobile communication can be improving and shaping the effective costs.  The improvement of technology would enhance the capability of dual-mode cell phone handsets in Wi-Fi (802.11b) and GSM; the dual-mode handset is a mobile phone that can handle both techniques in sending and receiving data and voice.  And particular dual-mode Wi-Fi and GSM handset is mainly about cellular and broadband Wi-Fi networks.  Recently the combination of dual-mode Wi-Fi and GSM handsets have been every popular in the mobile communication industries.  The ultimate goals of this converged network are simply low costs and alter the absence of cellular networks.  Therefore, it has been popular in deploying the Wi-Fi (802.11b) network to the public and private locations around the world.  In recent studies show the sale of dual-mode handsets have exceed over hundred million devices in 2008.  These studies would prove the mobile communication can be altered the cellular technologies into the Wi-Fi VoIP environment.  Perhaps, cellular phone can roam around the globe freely likes a broadband cordless phone without additional costs.  Although, the effective costs have been dual-mode handset benefit, and what is about subscribers’ convenience?  In this research paper will present the dual-mode Wi-Fi and GSM handset and its application along with Unlicensed Mobile Access networks. In fact, this paper also discusses the issue of dual-mode and handset devices like Nokia 9500 Communicator, Motorola MPx, and D-Link’s V-CLICK.

        The Wi-Fi is an IEEE 802.11b; a simple wireless network likes radio technology.  Today, this type of network is very popular in telecommunication simply low cost.  And especially the absence of cellular network in certain airspace area such as hospitals, government, hotels, airports, and etc; therefore, the wireless IEEE 802.11b plays an important role in mobile communication.  The introduction to dual-mode cell phone with capability of voice-over-wireless network or better known as (VoIP) has certain ultimate goals in mobile communication.  In the recent years, the voice-over Wi-Fi software and hardware development have implemented the mobile communication.  This factor promotes a huge market benefit in deploying five hundred million cellular handsets to the market.  According to Phil Solis, a Senior Wi-Fi Analyst at ABI Research says, “Many enterprises now have established Wi-Fi networks and integrating voice-over-Wi-Fi functionality is a natural progression.  As Wi-Fi network proliferate, it only makes sense to give users the ability to switch from a cellular carrier’s network to the enterprise Wi-Fi network.”  The improvement of technology tailors the way of operating telecommunication with several factors.  The first factor is coming to the reduction costs secure the high performance services.  Secondly, network has improved yearly in upgrading the enhanced voice and data services to the cellular phone.  This factor includes the 3G data network, which was introduced to the mobile communication in the past five years.  Third factor is the augmentation of Wi-Fi technology to where is lacking cellular coverage.  For example, certain building in the urban area location cellular networks from towers are blocked by airspace.  Therefore, the Wi-Fi technology would provide more benefits through broadband networks.  Fourth factor is resources and bandwidth; a typical voice channel takes only 64 kilobit per second, and with the modern broadband network can provide plenty of voice channels.  The final factor is the telephony communication evolution from using the SIP-based signaling protocol, which known as Internet Protocol Multimedia Subsystems or IMS (for short).  The usage is simple and easy in handing-offs cellular and Wi-Fi infrastructure.

       The Unlicensed Mobile Access is a convergence network by using Wi-Fi standard network.  According to UMA Architecture define it as, “an extension of GSM/GPRS mobile service into the customer’s premises that is achieved by tunneling certain GSM/GPRS protocols between the customer’s premises and the Core Network over a broadband IP network, and replaying them through an unlicensed radio link inside the customer’s premises.”  The network delivers low cost with high performance in mobile communication at the office and public wireless network.  There are certain companies provide the low-cost UMA deployment likes T-Mobile IPAccess and HotSpot.  T-Mobile provides over millions HotSpot and IP Access at the Airliners lounges, private sectors, public sectors, Starbuck stores, and the mall kiosks within the United States.  The company also introduces T-Mobile at Home services, which the subscribers can use their broadband networks and SIM (Subscriber Identify Module) card to make the calls.  There are millions growth of mobile communication substitution in yearly, but the performance in maintaining the network is very challenges in delivering the services. The dual-mode Wi-Fi and GSM handset can be accessed through the Unlicensed Mobile Access router network.  Most of these devices are available usage at the home, company office, local libraries, and even convenient public places like shopping malls, airports, and hospitals.  With the Universal Mobile Access network, the operators and subscribers would save lot of money in operating and communicating.  Especially it is very convenient for the subscribers, which they could use their mobile services at anytime and anywhere within the operated locations.  The way of Universal Mobile Access work is starting from the mobile provider through their Mobile Core Network such as circuit packet, IMS services, and etc.  The UMA Network Controller (UNC) delivers these services over the broadband networks, and manages mobile services as well as the mobility access between works. The UMA Enabled Femtocells device can provide the UMT and GSM networks that work for most of the standard mobile cellular phone.  From there, cellular phone can access through the UMA device to the Mobile Core Network through VoIP.

          What are the issues that dual-mode Wi-Fi and GSM handset involve, and how these involvements become realities?  The most complicated one is the handoff situation between two networks; in particularly the problem with existed signaling while the device is in-used.  For example, a subscriber is GSM network for having a conversation with someone; however, the call must be interrupted before switching to the Wi-Fi network.  Perhaps, it is not allowing switchover while the call is in progress, unless the call is terminated due to no reception from the GSM network.  The second complication is the billing system; especially the Wi-Fi network is cheaper but not one hundred percents free.  Maybe, customers must subscribe for both networks in their service package plan, so it is more convenient for both subscriber and operator.  Other issues are the phone integration, device power management, and codec usage.  The phone can stay on the GSM network with the device on sleeping mode; however, in contrast Wi-Fi requires the phone to be on in order to scan for signaling.  Sometimes calls are affected by the latency and packet loss.

        When comes to dual-mode Wi-Fi and GSM handset devices, the mobile communication companies fears to lose their revenue due to low-cost in the Wi-Fi network.  Today there are many technology companies produce cellular phone with embed Wi-Fi capabilities.  According to Phil Solis, “but long term, as with most new developments, carriers will likely see dual mode cellular / voice-over-Wi-Fi handsets as a means to differentiate their offerings.”  The mobile communication companies have to accept the realities of changing the way of communication.  Therefore, T-Mobile was the first carrier to provide easy ways to communicate between cellular and Wi-Fi networks by using the same device.  So, what are the devices have capability to handle both Wi-Fi and GSM network out in the current market?  There are devices such as Nokia 9500 Communicator, Motorola MPx, HP 6300 Series, D-Link’s V-Click, and etc.  These handset devices are operated by Microsoft Windows Mobile, Symbian, Blackberry, and etc.

       The Nokia 9500 Communicator has capability to handle Wi-Fi, GSM/GPRS and EDGE networks.  It integrates with Wi-Fi 802.11b, which has the abilities to support 64 and 128 bit WEP data encryption.  It uses the latest Symbian operating system that is usually for the Smartphone.  It displays a high revolution graphic in color, and has large keyboard for text messaging.  The user can customize the setting such as profile, ringtones, speed dials, and much more in this application.  The calendar, personal contacts, message and personal folder are also including in the handset application.  Furthermore, the handset also supports SMTP, IMP4, and POP3 mail protocols; which user can have multiple email accounts in one devices.  

          The Motorola MPx is built similar to the Nokia 9500 Communicator, but the handset has unique QWERTY keyboard.  It has the tri-band services are built in the device such as capabilities to handle infrared, Bluetooth 1.1, IEE 802.11b, GSM 900, GSM 1800, GSM 1900, and GPRS networks.  The applications are including Pocket Outlook, MSN Messenger, Pocket Internet Explorer, Windows Media Player, Voice Recorder, Calculator, Calendar, Terminal Services, Excel, Word, and etc.  It able to handle 200 MHz, and has the Secured Digital and MMC memory expansion slot. 

       The D-Link’s V-CLICK phone has the dual-mode Wi-Fi and GSM capacity.  The company released the handset into the market in 2009 with full features like tri-band GSM.  Also, has the ability to handle Wi-Fi 802.11b with a speed of 2.4 GHz access.  The handset phone book is operated from the Subscriber Identification Module card.  The handset is built with a click of button can switch from cellular mode to Wi-Fi mode; however, the user must configure the wireless SIP profile.  This handset has strong security such as WEP, WPA, and WPA2 for data and voice encryptions.

         In brief, the dual-mode Wi-Fi and GSM networks availability would enhance the mobile communication network to the next generation.  The Unlicensed Mobile Access is getting more popular because of low-cost service with minimal maintenance.  The dual-mode issues are complicated; however, they will not stop in populating new services.  Due to improvement of technology yearly, the dual-mode handset device is getting more affordable to the customers.  With capabilities of new application features, the device can handle most of the user’s task and security to the high standard. 

References

• Chandra, Praphul & Lide, David. “Wi-Fi Telephony: Challenges and Solutions for Voice over WLANs.”  Elsevier Inc. Burlington, MA. 2007.
• Heine, Gunnar. “GSM Networks: Protocols, Terminology, and Implementation.”  Artech House Inc, Norwood, MA 1999.
• “White Paper on Dual-Mode Phone (GSM & Wi-Fi).” N Group.
• “Dual Mode Mobile”.  The Wikipedia. November 27, 2008.  <http://en.wikipedia.org/wiki/Dual_mode_mobile>
• McZeal, Al. “World’s First Dual-Mode Unlocked GSM/Wi-Fi Phone to Offer Free Calling Over World-Wide Network.” Free Press Release. November 30, 2008. <http://www.free-press-release.com/news/print-1186247150.html>
• Universal Mobile Access.  UMA Today. 2007. <http://www.umatoday.com>
• T-Mobile. The Wikipedia. November 29, 2008. < http://en.wikipedia.org/wiki/T-Mobile>
• “D-Link Introduces V-CLICK Dual-Mode GSM / Wi-Fi Phone.” Geekzone.com. October 4, 2006. <http://www.geekzone.co.nz/content.asp?contentid=6731>
• “Nokia 9500 Communicator” CNET Asia Reviews. <http://asia.cnet.com/reviews/handphones/0,39001713,39018327p,00.htm>
• “Motorola MPx.” Motorola . <http://www.motorola.com/mediacenter/news/detail.jsp?globalObjectId=3869_3244_23>
• ABI Search. December 1, 2008.  <http://www.abiresearch.com/home.jsp>

      In 1975, the Signal System Number 7 was recognized by the International Telecommunication Union as the standard in communication around the world.  The SS7 particularly replaced the SS6, which was the previous version of the protocol and was restricted to 28 bits in signaling messages.  This particular system provides the Public Switched Telephone Network and wireless communication network controllers.   The basic functions of SS7 are controlling the call from start to finish, such as setting up the call by transporting the signaling messages, managing the call, and terminating the call.  Other functions of SS7 include managing numbers, and charging the customers; call forwarding, conference calls, and secured voiced and data messaging.  SS7 provides unique roaming services and the customer with easy accessibility.  It operates in two modes:  Associated Mode and Quasi-Associated Mode.  These modes are the backbone of how SS7 transports its signal through network devices.  For example in the Associated Mode, SS7 signal must be transported through switches via the Public Switched Telephone Network.  On the other hand, Quasi-Associated Mode only requires a path from one switch to another without going through a third party.  The SS7 protocol has been widely used as the global standard network for telecommunication.  This paper will present a brief summary of the functions, and usage of the protocol.

       The SS7 protocol stack is similar to the Open System Interconnection or known as the OSI model.  However, there are only four levels are considered to be similar with the OSI layers.  The SS7 protocol stacks are identified at the Message Transfer Part (MTP) level 1, level 2, level 3, and the top level.  These are the same as the physical layer, data link layer, network layer, and the application layer.  The top level consists of TUP, TCAP, ISUP, and SSCP; each section of this level is important to the protocol stack.  The Message Transfer Part (MTP) level 1 is defined in the physical and electrical characteristics in providing the signaling; which include the E-1 network which has 2048 kb/s with providing 30 voice channels with a synchronizing channel and a common signal channel, and the DS-1 network has 1544 kb/s with providing 24 voice channels, or 23 voice channels and one common signaling channel.  The message Transfer Part (MTP) level 2 provides the accurate data transmission during the call including the call initiation and termination.  In this transmission, the layer implements sequence validation, error protection, and flow control.  If the error is detected during the signal transmission, the message will be retransmitted.  The MTP level 3 offers the routing function between the signal points, which avoids failure connection transmission when the signals are congested.  The ISDN User Part distinct the protocol is initiating the call, managing the call, and terminating the circuits to end the call.  Perhaps, if the call is made within the switch system network, it does not require using ISUP signaling.  The Telephone User Part is simpler than ISUP, example is no caller ID; however, TUP is used more in handling analog circuits.  Certain parts of the world still use TUP for setting up the call and terminating the call processes.  The majority networks in the globe replaced TUP by the ISUP, especially in the European Union Nations and North America.  The Signaling Connection Control Part (SSCP); is a connection-oriented and connectionless network.  Its functions are controlling the toll free number, calling card number, and customer identification number; therefore, it is easy to track the billing usage.  The SSCP would translate these numbers into the subsystem number to identify the destination signal to the Transaction Capabilities Application Part.  The TCAP provides information between non-circuits data across the SS7 by using SSCP services.  Its functions are authentication, personal identification number validation, equipment identification, and roaming services.

       The Signaling Links is known to transmit both directions between 56 to 64 kilobits per section.  These signals are transmitted on an out-of-band channel, separate from voice channel because they are Intelligent Network to separate these two types of signals.  It also prevents fraudulent network service usage, such as stealing network for commercial purposes and reselling the calling cards.  The Signaling Point are unique because the point codes.  Point codes are addresses in the SS7 network and identify the destination and source.  The Signaling points use routing table rule for the path of individual messages.  There are three types of Signaling Point in SS7:  Service Switching Point (SSP), Signal Transfer Point (STP), and Service Control Point (SCP).  The SSP’s are performing as switches that initiating and terminating the call.  The Signaling messages are being setup, manage and terminate in the voice circuits for every single call.  The STP provides signaling points by routing new message for every incoming message to the specific SSP.  It also acts as a firewall to ensure exchanged manages are secured.  The SCPs provide the configuration service in the event of signaling failure, or for special services like “800” numbers.  If the transmission failed, the SCP re-route the signaling messages to a different base links, or remove the call to a different destination for 800 services.

     There are six different Signaling Link types; these are from A to F, in respect to the SS7 protocol.  The A link is connecting between the signaling end points for message from or to the destination sources.  The B link is connecting between STP’s to provide signaling message transmission.  The C link is connecting between STP’s; however, it pairs up the signal point for reliability if a link fails.  The D link provides secondary connection in STP’s unless there is a problem with the primary, and then the D link temporarily replaces the B link connection.  The E link is connecting between SSP and STP, it is an alternating path in the event that the A link is not reachable.  The F link is connecting between the two end points likes the A link.  Normally, it is not used in STPs, unless there is a problem with STP’s, and not being used; therefore, the F link is replaced for straight connection.

      The typical call process in the SS7 involves two phone switches; one is as a sender “A” and the other one is a recipient “B.”   During the initial calling process, the sender signaling message goes through a switch “A” to determine the destination number and linking itself to the switch “B.”   The trunk voice routing would be setup in response to address message to define the destination source.  Therefore, from the switch “A” routing the message to the switch “B,” and determine whether the call is signaling or busy due to the recipient engaged in calls.  Once the setup is done, the switch “B” would start to formulate the answer message to identify the connection.  The answer message indicates if the destination reason has gone “off-hook.”  This leads to a voice channel connection.  If the sender hangs up the phone first, then the switch “A” would generate a release message (REL) to the recipient or switch “B.”  The opposite happens when a user hangs up.  In either this case, the other party receives a release complete message (RLC).

         In brief the SS7 is a global standard protocol defined by the ITU for telecommunication, and especially for wireless networks.  It consists of 4 different levels and similar to the Open System Interconnection Model.  It has three different signaling Point types and sign different link types.

References:

. Bates, Regis J. “Broadband Telecommunications Handbook.” McGraw-Hill Companies Inc, United States. 2002

. Heine, Gunnar.  “GSM Networks: Protocols, Terminology, and Implementation.” Artech House Inc., Norwood, MA. 1999.

. “SS7 Tutorial” International Engineering Consortium.  November 27, 2008.  <http://www.iec.org/online/tutorials/ss7>