Abstract—Smartphone docking stations and strongly converged VoIP /Telephony clients are proposed and demonstrated as a new and practical model for fixed-mobile voice and video convergence.
I. INTRODUCTION Convergence between fixed (or enterprise) networks, and
mobile (macro-cellular) networks, has been the subject of considerable discussion over the last decade. Carriers, network and customer equipment manufacturers, client developers, and the academic community have all proposed, and in many cases implemented, different solutions [1-3]. To date, none of the implemented solutions has been completely satisfactory, thus leading to the plethora of alternatives.
In this paper, a endpoint based model for Fixed-Mobile Convergence (FMC) is discussed in which different telephony “accounts 1 ” are strongly (bi-directionally) converged by a telephony client, in much the same way as different email accounts can converge to an email client. This solution differs from previously discussed endpoint solutions in that the convergence is symmetrical in direction and service features; in addition to fixed networks being converged to mobile networks, mobile networks are now also converged to the fixed (or enterprise) network. As this client traverses networks, it is agnostic to the underlying technology (circuit switched, or IP); it is made practical by the emergence of smartphones that natively connect to circuit switched and IP networks, and can execute sophisticated service logic. This – endpoint or application layer - model of convergence provides a functionally rich solution to FMC. It also provides a simple and graceful migration to wireless mobile networks with packet switched cores, such as those developed for the IP Multimedia Subsystem (IMS).
In addition to the client itself, the notion of a smartphone docking station is also introduced. The use of a docking station provides the voice quality (e.g. high quality speakerphones, wideband audio and video codecs, QoS, etc.) and ease of use
1 Ignoring such complexities as alias’, ghost numbers, etc., a telephony “account” can be defined by its Telephone Number or Mobile Directory Number in the same way that an email account is defined by its URI.
(handset, large keyboard with function specific keys, etc.) traditionally associated with a wired deskphone. Use of docking station thus overcomes barriers sometimes associated with using a mobile phone in a fixed/enterprise environment. It is also highly cost effective, as the combination of smart phone and docking station is approximately 2/3 the cost of a smart phone and a mid to high level enterprise VoIP deskphone.
The confluence of commercially available smartphones, a strongly converged VoIP client, and a media enabled docking station, offers a very practical solution for convergence between existing fixed/enterprise networks and circuit or packet based mobile networks.
II. ONE WAY (WEAK) CLIENT BASED, FIXED MOBILE CONVERGENCE
While a full review of FMC methodologies is well beyond the scope of this paper (c.f. [4]), a short discussion of the typical FMC solution provided by hosted call servers or IP-PBXs is provided for context.
A. One Way (or Weak) Client Based FMC The traditional mechanism for FMC (figure 1) uses two call
legs (i.e., call forking, simultaneous ring, etc. for ingress, and 2 stage dial or the equivalent for egress) to converge calls from/to the fixed/enterprise call server to/from the mobile network. Because this mechanism does not converge calls to or from the mobile directory number through the Enterprise call server, it can be thought of as one-way (or weak) convergence.
Figure 1:Example of traditional FMC. Calls to the mobile directory number (C) never appear on the enterprise handset. Calls displaying the mobile callerID (D) cannot be made from the enterprise handset. Native features of the mobile handset (contacts, call logs, etc.) are not used with the enterprise call server.
2012 IEEE Wireless Communications and Networking Conference: Services, Applications, and Business
This convergence model, along with many different variations and solutions (including various “one number solutions), are often provided by IP-PBXs[5], multi-tenant carrier based hosted call servers[6], and other applications provided by internet based Application Service Providers.
Weak client based FMC solves the issue of receiving fixed/enterprise calls on a mobile device (presumably, when the end-user is away from the desk), but it does not solve for convergence from the wireless mobile network back to the fixed/enterprise network. This functionality is useful not just from a coverage perspective2, but also to provide the voice quality (e.g., speakerphone, high definition codecs, QoS, etc.) of a wired endpoint. Symmetrical convergence is also useful to the subscriber by providing merged call logs, having a single contacts directory (or database on the handset), or being able to present a calling identity that is appropriate to the called party. These issues can be solved using a two way, strongly converged, FMC client.
III. TWO WAY (STRONG) CLIENT BASED, FIXED MOBILE CONVERGENCE
In contrast to the one-way, or weak, client based FMC presented in section II, a two way (strong) form of client based FMC converges the fixed/enterprise and mobile telephone networks in both directions. Calls to the fixed/enterprise telephone number (TN) are available to the smartphone while in the mobile (macro-cellular) network, and – symmetrically - calls to the mobile directory number (MDN) are available to the smartphone while in the fixed/enterprise network. In addition to the symmetrical handling of calls, other telephony features of the smartphone are contextually shared across networks: the contacts database on the smartphone can be used to place calls from either network, call logs are intelligently merged for display and are available for callback from either network, the subscriber can set the calling party identify (caller ID) on outbound calls to either enterprise TN or wireless MDN regardless of network connectivity.
A. Convergence in the Fixed (Enteprise) Network Figure 2 shows the architecture for a strongly converged
client in the fixed/enterprise network. Calls to the wireless MDN are forwarded through the PSTN to an account on the call server. Calls to the fixed/enterprise TN are forwarded to a different account on the call server. The trunk side interface on the call server is connected to the PSTN through a conventional TDM interface or a SIP trunk. The VoIP client on the smartphone registers to both accounts on the call server. Call forwarding of the wireless MDN can be triggered by docked state of the smartphone, or can be statically set and invoked using an out-of-band mechanism to change the call routing in the mobile network. The use of two separate accounts on the call server provides three functions:
2 Convergence of the wireless mobile network => fixed/enterprise network can be useful in providing coverage where the radio access network is weak, such as in-building or fringe locations.
1. it supports re-direction of unanswered calls to the appropriate voicemail server,
2. it enables presentation of both the Called Party Identify (was the call to the subscriber’s MDN, or to the fixed/enterprise TN?) and Caller ID for inbound calls, and
3. it allows a choice of Calling Party ID (Caller ID) for outbound calls based on the subscriber’s preferred identity for a given call.
Point (3) above is relevant given that the MDN and TN are
often thought of as representing different “modes” of the same identity. The TN is often considered to be a “work” mode, while the mobile MDN is considered a “personal” mode. This is consistent with the notion of “Bring Your Own Device (BYOD) in which an end-user subscribes for personal services on a mobile handset or tablet, while the enterprise subscribes (and pays) for services that are needed as part of the end-users’ job. The concept of BYOD seems to be rapidly gaining acceptance.
In addition to the loose binding of mobile and
fixed/enterprise networks through a Call Forwarding mechanism, a more tightly bound integration is possible from both networks using Intelligent Network (IN) service logic and triggers that are enabled when the smartphone is docked.
Figure 2 – Smartphone docking station and client in the fixed/enterprise network, converged to a circuit switched wireless mobile network. Calls to the subscriber’s MDN are forwarded through the PSTN to an account on the call server. Calls to the subscriber’s TN are terminated to a second account on the call server. Registration, signaling and media on the line side of the Call Server are SIP and RTP/RTCP. If the mobile network implements an IMS core, the client on the smartphone can register directly to the S-CFCS for mobile calls, and to the fixed/enterprise call server for PSTN calls.
If the wireless mobile network utilizes an IP Multimedia System (IMS) core for switching and service delivery, the smartphone client can register directly with the Serving Call
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Session Call Server (S-CSCF) without requiring an account on the fixed/enterprise call server. In this case, no call forwarding is required, the cloud based IMS account is directly registered to the client through an external (non-wireless) IP network, and only one account required on the fixed/enterprise call server.
There are other variations of the architecture shown in Figure 2, including those in which there is only a single account (single number solution), and those in which the Call Server is hosted in a carrier’s cloud.
B. Convergence in the Mobile (macro-cellular) Network Convergence in the circuit switched (macro-cellular)
mobile network is similar to the one way client based FMC described in Section I. In this case (Figure 3), calls from the PSTN are either forked or forwarded by the Call Server to the mobile network using the Calling Party Identity (CallerID) of the originator. Since most mobile network providers do not support delivery of Original Called Number (OCN) in the radio access network, delivery of Called Party Identity can be provided out of band by the fixed/enterprise call server over the mobile data network prior to connection of the circuit call. As call control is directly passed to the mobile switch in this scenario, some form of answer confirmation is often used by the Call Server to prevent calls from rolling over to the mobile voicemail system.
Figure 3 – Smartphone client in the circuit switched wireless mobile network, converged to a fixed/enterprise call server via call forking or call forwarding based on client registration in the fixed/enterprise network. The packet data network is shown as a mechanism for delivery of Called Party Identity. An alternative architecture uses the packet data component of the radio access network to deliver SIP/RTP/RTCP from the fixed/enterprise network, and does not require call forking/forwarding.
Another architecture that we have used for convergence in the mobile wireless network is to retain IP connectivity over WiFi/4G to the smartphone client from the fixed/enterprise call server. In this case, no call forwarding to the mobile switch is required. Moreover, wideband voice codecs can be used, rather than the narrowband codecs used in circuit switched GSM or CDMA networks. These wideband codecs
provide a noticeable improvement in voice quality. As 4G networks become more prevalent, this form of “over the top” convergence becomes more attractive.
Finally, it is extremely important to note that the solution to convergence for a smartphone in the fixed/enterprise network becomes identical to the solution for a smartphone in the wireless mobile space, when the mobile network utilizes an IMS (or any VoIP based) architecture. In this case, because the client has two IP based registrations - one to the mobile IMS/VoIP core, and one to the fixed/enterprise VoIP core - the functionality of the client becomes independent of the network providing IP transport (wireless mobile, or fixed/enterprise).
C. Voice Call Continuity (VCC) In addition to the standard suite of voice related services,
subscribers expect the ability to move an active call between networks. This feature is often called Voice Call Continuity (VCC). For example, a subscriber could answer a call in the fixed/enterprise network (e.g., the speakerphone of a smartphone docking station, as described in section IV) and then remove the smartphone from the docking station and walk out into the macro-cellular network (e.g., his or her car) without interrupting or dropping the call.
VCC across heterogeneous networks has been well described [7-8]. VCC is provided for all call scenarios in our integrated solution, except for calls to a MDN that terminate in the mobile network. In this case, the practical difficulty of implementing mid-call control to a mobile switch (MSC) combined with smartphone hardware restrictions that limit the audio path for a circuit call to the smartphone’s internal audio interfaces (microphone and speaker), do not permit these calls to be moved to a docking stations’ audio devices. Table 1 provides a summary of the VCC capabilities based on what network the call is moving From and To. If the wireless mobile network utilizes an IMS (or other VoIP protocol) core for switching and service delivery, Voice Call Continuity becomes fully symmetrical and independent of the From and To networks.
Table1: VCC capabilities for two way FMC in a circuit switch wireless mobile network, with a smartphone docking station.
IV. SMARTPHONE DOCKING STATIONS
The adoption of strongly converged, two way, smartphone clients is significantly enhanced by the introduction of a smartphone docking station. While some benefits of such a client – such as a uniform contacts database, call log integration, and choice of calling party identity – do not
require a docking station, the concept is made truly compelling by the ability to replace a traditional, wired VoIP phone with a smartphone and docking station. In addition to providing enhanced functionality, this solution provides the voice quality and ease of use as a medium to high end VoIP deskphone, and is approximately 2/3 the cost the deployment model that it replaces (the common practice of providing both a traditional VoIP phone and a mobile phone to a knowledge worker3. )
Figure 4 shows one version of a docking station we designed for use with Android based smartphones. The docking station provides Ethernet connectivity to a wired LAN, as well as encapsulation of Ethernet frames in USB packets for delivery to the VoIP client through the USB port on the smartphone. In addition to network connectivity through a wired Ethernet, the docking station can be configured to use network connectivity via smartphone’s WiFi, 3G, or 4G radios by correctly setting the routing table on the smartphone4.
Figure 4 – Smartphone docking station with a smartphone almost completely inserted into the micro-USB connector of the adaptor sleeve.
From a USB perspective, the docking station acts as a USB host, and the smartphone as a USB client. While there are advantages to allowing the smartphone to act as a USB host (and there are standards compliant charging modes that allow
3 Given that the cost of phones in an enterprise deployment is roughly 1/2 to 2/3 the cost of the deployment, the total cost of ownership reduction incurred by adopting the smartphone/strongly converged client/docking station solution in a greenfield deployment is roughly (1/3) x (2/3), or about 20%. 4 Split routing can also enabled, so that some applications can traverse one network (e.g., the wired Ethernet), while others traverse a different network (e.g., WiFi or 3G/4G). For example, SMS can be delivered over a 4G circuit switched network, while other applications can use WiFi or wired Ethernet. Similarly, the docking station itself can support VLAN tags, so that different applications can take different network paths over the wired Ethernet.
devices to act as USB hosts without having to source charging current [9]), a USB client mode is currently more compatible with the underlying Android operating system. Smartphones mate with the docking station through a micro-USB connector. The docking station in figure 4 also provides an additional USB A connector that is hubbed to allow conventional USB devices to connect to the docking station, thus providing additional functionality from enhanced hook switch features for headsets, to conventional uses such as keyboards, memory sticks, etc.
The docking station in Figure 4 can act as either a router/NAT with a private subnet between the docking station and the smartphone, or an Ethernet bridge in which the smartphone has a routable IP address on the LAN. Each network model has a variety of advantages and disadvantages; the (configurable) choice often depends upon the customer’s implementation model (large enterprise to small-medium business). In both cases, SIP/RTP etc. passes through the docking station to the smartphone, while a variety of protocols can be used to support signaling and media transfer between the docking station and the phone. The docking station also provides facilities for firewalling and enterprise security, remote service assurance, a variety of provisioning and operational functions, and battery charging.
We believe that the user experience of docking and undocking to be key to successful subscriber adoption. As such, this docking station has been built so that the smartphone can be smoothly slid into place and mated with the micro-USB connector found on smartphones. Sleeves that mate with a universal connector on the docking station are used to adapt different smartphone models/geometries to a single docking station. Sleeves for smartphones with front facing cameras are designed to tilt the phone so that the camera and user will be in alignment during a video enabled call.
In addition to the experience of docking and undocking, the
user interface is similarly important to user adoption. The docking station provides the usual functional hard keys found on most high quality VoIP deskphones, such as transfer, hold, mute, etc. The typical Android hard buttons (Home, Search, Back, and Options) are also replicated as keys on the dock, and a Directional Navigation Pad (“D-pad”) is included. Additional context sensitive functionality is provided through the smartphone touchscreen. Other conventional Android applications can utilize the high quality speaker or selected buttons on the docking station through extensions to the Android operating system, keeping in mind that the telephony application will override other applications and bring the VoIP client into focus during call arrival.
From a signaling perspective, the VoIP client supports both
SIP and IMS, and is designed to work with a variety of IP-PBXs and Hosted Call Servers. The current implementation provides for multiple call appearances per registration, shared-call (e.g., bridged line) appearances, multiple “High
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Definition” codecs such as G722 and Speex, three-way conferencing, and other typical features found on mid to high level VoIP deskphones.
V. VIDEO AND THE RICH COMMUNICATIONS SUITE Support for Video IP Telephony (also known as V-VoIP)
can be easily obtained by using a smartphone with a front facing camera, and adding a video codec to the VoIP client. In this case, no infrastructure changes are required, and a video session can be negotiated directly between appropriate endpoints. More sophisticated video and other rich communication services (including transcoding) can be supported through a variety of architectural frameworks, including those adopted by the Global System for Mobile Communications [10].
From a practical perspective, use of a wired Ethernet can
provide QoS as well as bandwidth off-load from the 3G/4G network. While our initial experiments to utilize a video codec have been promising (Figure 5), improvements in performance (particularly for high definition H.264 streams from the smartphone to the network) are expected as smartphone device manufactures and the underlying operating system(s) provide better access to the compressed video via the smartphone’s video encode hardware (chip set), rather than relying on software based compression.
Figure 5 – Video IP Telephony Client. For smartphones with front facing cameras, the adaptor sleeve is shaped so that the camera and end-user are naturally in-line.
SUMMARY
In summary, a new, highly functional solution for Fixed Mobile Convergence has been implemented. The confluence of commercially available smartphones, a strongly converged client with connectivity to both fixed/enterprise VoIP networks and circuit switched mobile networks, and a media enabled docking station, offers a practical and cost-effective solution for FMC. This solution has been demonstrated to provide a seamless migration path to FMC over 4G and IMS enabled carrier networks, and provides an effective video as well as audio user experience.
ACKNOWLEDGMENTS The authors gratefully acknowledge LG-Ericsson Inc.,
IMG-HelloSoft Inc., and Streamwide Inc. for their support during the development of the smartphone docking stations and the related systems.
The authors also gratefully acknowledge the support and guidance of M. Weintraub (Verizon) and P. Atreya, G. Puranik, and P. Singh (VerizonWireless).
REFERENCES [1] Mayank Raj, Avinash Narayan, Sajib Datta, Sajal k. Das, and Jorgen K.
Pathak, “Fixed Mobile Convergence: Challenges and Solutions,” IEEE Communications, 2010, pp 26-34.
[2] A. Cadenas, A. Hermida, and A. Arias., “Distributed PBX Gateways to Enable the Hosted Enterprise Services Architecture in a NGN Scenario,” 2008, First ITU-T Kaleidoscope Academc Conference.
[3] John Murphy, Jesper Kjeldskov, Steve Howard, Grame Shanks, Elizabeth Hartnell-Young, “The Converged Appliance: I Love It .. But I Hate It”, 2005, Proceedings of OZCHI 2005, ACM Digital Library.
[4] Djamal-Eddine Meddour, Usman Javad, Nccolas Bihannic, Tinu Rasheed, Raouf Boutaba, “Completing the Convergence Puzzle: a survey and a roadmap,” IEEE Wireless Communications, 2009, pp 86-96
[5] Cisco 2008, “Cisco Mobile Office: A Flexible, Feature-Rich Fixed-Mobile Communications Solution,” ‘www.cisco.com/en/US/solutions/collateral/ns341/ns523/ns519/solution overview_cisco_mobile_office_flexible_feature_rich_fixed_mobile_communications_solution.pdf’
[7] Ashutosh Dutta, Subir Das, David Famolari, Yoshihiro Ohba, Kenichi Taniuchi, Victor Fajardo, Rafa Marin Lopez, Toshikazu Kodama, and Henning Schulzrinne, “Seamless Proactive Handover Across Heterogeneous Networks,” 2007, Wireless Personal Communications, 837-855.
[8] H.Y. Hsieh, C.W. Li, S.W. Liao, Y.W. Chen, T.L. Tsai, and H.P. Lin, “Moving toward end-to-end support for handoffs across heterogeneous telephony systems on dual-mode mobile devices”, 2008, Computer Communications, pp 2726-2738.
[9] “USB On-The-Go and Embedded Host Supplement to the USB Revision 2.0 Specification”, 2011, www.usb.org.
