PUSH-TO-TALK OVER CELLULAR: STILL SEARCHING THE FLOW OF SUCCESS

Raili KoivistoHelsinki University of Technology

E-mail: raili.koivisto@hut.fi

Abstract

Push-To-Talk over Cellular is a VoIP solution which continuously is under standardization, market research and operator business development. In best case it will provide a future-proof solution to make the future IP based Multimedia services to interwork globally over different air interface standards. There are several key technologies still competing of the industry leader position. The proprietary solutions already taken into production may slow down the interoperability diffusion and ruin the weak customer interest. The operators have challenges to package the PoC product in profitable way and create especially in Europe a new kind of user behaviour in order to increase their average revenue per user (ARPU). The report describes the main challenges related to technology, vendor and operator strategies during the next few years.

Key WordsPush-To-Talk, PTT, PoC, GSM/GPRS, IMS, OMA

1. Introduction

Push-to-talk (PTT) feature is a half-duplex voice service, basically instant messaging with speech instead of text. . In cellular networks PTT is a wireless VoIP service called Push-To-Talk over Cellular (PoC).Implementing it into cellular networks is still one of the most interesting topics in the business. The operators and vendors are fighting for positions in the business while the standardization is still under finalizing.

The purpose of this document is to illuminate the status of Push To Talk over Cellular service related business. The main objective is to analyze strategic actions related to standardization, vendor product strategy, substitutes, regulation and service provision in order to achieve successful service diffusion for PoC.

2. Background

PTT has been used decades in walkie-talkie terminals over different radio bands by for example military, truck drivers, event organizers and hunters. Push-to-talk has been widely used in USA and Great Britain in circuit-switched networks. Today, when cellular networks are transitioning to packet-switched technology, there is a clear need to launch new services

for that domain also when the cost of data transfer has decreased to reasonable level along with GPRSSo in near future the key technology and business selections has to be made in order to get on right track. Current cellular packet switched networks are still narrow band, so the latencies and error rates are too high for full-duplex IP telephony but enough for the half-duplex push-to-talk service.

For operators Push-To-Talk over Cellular is typically the first IP-based voice service i.e. their first step towards all-IP architecture.

While waiting for proper standards, the mobile phone and network manufacturers have launched pre-standard based solutions encouraged by the American success story of Nextel.

Depending on who you ask, the revenues are expected to grow fast or slowly like with WAP and MMS (Turner 2005).

In any case, the vendors, operators and service providers have a tough challenge to select their strategies.

3. Benefits

3.1 Benefits for end-users

The primary benefit for the user is the possibility to immediately contact a pre-defined person or a group without searching numbers and separately making connections through answering because there is an always-on connection between group members. PoC supports also text chat between active group members (Nokia 2005).

In the future combination with other applications like presence, picture sharing and video clips will make it still more attractive to consumers.

PoC enables calls over nationwide networks and across regional borders as provided by GSM/GPRS networks which remarkable advantage as compared with traditional two-way radio systems like Land Mobile radio or Professional Mobile Radio (Nokia 2005).

These benefits are valuable for various kinds of businesses and leisure groups where it is essential to

shortly communicate within a dedicated group of people to give guidance, orders or feeling of security (Nokia 2005).

However, for the time being the performance of PoC cannot be guaranteed in current cellular networks due to long cell-reselection times and possible network congestion. GPRS was not originally designed for real-time traffic. (Karvonen 2005).

3.2 Benefits for operators

PoC enables the cellular operators to compete with existing Push-To-Talk services on their own competence area by providing enhanced voice services and thus increasing the number of subscribers and Average Revenue per User (ARPU) (Nokia 2005).

PoC also provides for the future a platform for direct voice communication services using IP Multimedia applications (Nokia 2005).

Albeit the connection is always on, PoC is an efficient way of using the network resources by reserving them only for the duration of talk spurts. (Nokia 2005).

4. Technology Preview

The phone needs to include a PoC client and user interface (embedded or loaded), it also has to support SIP porotocol and VoIP features. The sendering phone sends packet data to a PoC server, as manifolded if it is a group call. The core network consists of PoC Call Processor and PoC Register network elements which are connected to GPRS or EDGE network.

Session Initiation (SIP) protocol is an application layer protocol for creating, modifying and terminating sessions with one or more participants. It also enables a terminal to register its currrent address to a proxy so that other users are able to reach it with a textual address; it includes also authentication and authorization. (RFC 3261).

The voice packets are transported with Real-time transport Protocol (RTP).

Internet Protocol Multimedia Subsystem (IMS) is a platform that may be used by operators to quickly develop and deploy multimedia services for 2.5G and 3G mobile networks. This platform contains a SIP application server on which mobile data services like Push-To-Talk over Cellular and telephone conferencing are based on in the future. The servers handle session and group control, VoIP streaming, stream control, provisioning and management of users and groups (Nokia FAQ 2005).

PoC is the first commercial application based on IMS which obviously makes large infrastucture vendors very interested in driving PTT into use (Northstream 2004).

Access to IMS requires IP connectivity from terminals, using IPv6 and expects underlying end-to-end quality of service for the traffic.

The key benefit of IMS is that it enables the users to access to the same services regardless of the terminal type. It also enables to transmit voice and data over the air simultaneously and in any combination. E.g. presence and messaging (immediate, session-based and deferred) services will be offered over IMS platform.

Current SIP-based PoC terminals for GPRS networks use Adaptive-MultiRate (AMR) audio coding schema, which are designed to tolerate transmission errors and packet losses. In GSM networks AMR is not yet commonly used.

5. Technology Competitors

Trunked radio systems (analog and digital) which allow automatic sharing of multiple radio channels, have replaced land mobile radios in professional use. They include Terrestrial Trunked Radio (TETRA) and Integrated Digital Enhanced Network (iDEN) which have became the basis for proprietary technology camps. The most successful PoC operator Nextel uses iDEN but the future of this technology seems to be problematic. (Rehbehn 2004) .

Due to Nextel´s high ARPU (about 15% higher than US competitors) and the need for new services, also other cellular operators and vendors woke up to find out ways to implement PTT.

Open Mobile Alliance (OMA) has been working since 2003 in order to agree a standard based on proposal made by Ericsson, Motorola, Nokia and Siemens. The pre-standard version describes how PTT can be implemented by using HTTP, SIP, RTP/RTCP and XML.

The current proprietary solutions are shown in Figure 1 by Rehbehn. In addition to the figure there is also a software based solution from Fastmobile called Fastchat. Kodiak Networks integrates packet-based presence function with circuit-switched voice transmission, so after setting up the call, the delays are like in normal call.

Kodiak has won some operator deals because its client is loadable to smart phones but it seems to stay temporary because circuit-switched PoC can be over six times more expensive than PoC over GPRS. (Northstream 2004).

Nextel is developing QChat compatible with iDEN for its CDMA networks.

From radio resource usage point of view, PoC over GPRS is five times more efficient and over EGPRS over 14 times more efficient than PoC over circuit-switched GSM. From core network view it is hard to say which one has favourable resource, scalability and cost figures. (Northstream 2004).

6. Substitutes

Depending on the strongest driving factor (from customer view), we can find some relevant substitutes for this functionality.

If the driver is talking to many by phone, one could use conference call which does not limit the phone type selection. If talking free of charge is the thing, one could take SKYPE with PDA and WLAN access to Internet or Push-To-Talk over Bluetooth (PoB).

Microsoft is adding PTT feature to its Messenger application used in computers. PoB is competitive on short range (100 meters with class 1) and even further if multihop communication is used. The main advantage from user´s view is that it is free of charge which probably would encourage its usage for gaming, folder sharing in addition to communication. It is also possible to create a hybrid service using PoB for reaching local members and PoC for reaching distant members. (Rönnholm 2005).

7. Standardization

One of the most critical success factors especially in consumer area is interoperability between different vendors, devices and operators and that is what Open Mobile Alliance (OMA) is working on. The lack of interoperability was one of the reasons provoking bad feelings of MMS. (Wieland 2005).

The dedicated standards are needed for defining how to reserve talk items in real time and how to optimize streaming for half duplex voice over GPRS.

OMA PoC builds on 3GPP IMS but with some concessions because IPv6 is not yet widely used and IMS has not passed trial phase even in existing 3G networks.

The standard is still under finalising and to be launched early this year according to OMA. (Wieland 2005).

You might ask if slow and delayed standardization is due to difficult issue or business political aspects.

8. PoC Performance

Latencies are remarkable here because the distance between terminals may be thousands of kilometers. OMA uses the Quality of Experience to describe user perceived quality of service but it is hard to find any independent studies on acceptable level ot it. So there is a doubt that OMA has selected quite high delay values only because GPRS network has not capacity for better (Karvonen 2005).

The voice quality requirement is on GSM level but bit error rate quite high. In practice the required performance of PoC cannot be guaranteed in all situations in GPRS but the true real-time services have to wait for EGPRS or UMTS. (Karvonen 2005).

The business users may find the delays more inconvinient than consumers.

Finally one must remember that the performance of packet based solution highly depends on how well the whole service delivery chain is tuned. (Northstream 2004).

9. Vendor strategies

Global technology vendors are divided into two camps: iDEN by Motorola, Siemens, SonyEricsson and TETRA by Nokia and Samsung. In China Huawei and ZTE have their own camps. Kodiak is in team with Lucent Technologies for CDMA networks. (Northstream 2004).

Although the biggest mobile phone vendors are working in OMA, they have also formed other groups beside. E.g. in the beginning of 2004 Siemens AG, Motorola Inc. ja Sony Ericsson Mobile Communications Ltd formed one group, Nokia and Samsung another. Then Nokia answered by announcing that it will use the prestandard immediately and promised to a offer a development route to the coming OMA standard. According to Nokia its products fully support both pre-OMA standard phones and the protocol preceding the optional standard by Ericsson, Motorola and Siemens. Reciprocally they expect the others to support Nokia phones already in the early phase. (Viitasaari 2004)

Most of the vendors have started trials with operators in order to test and push their own solutions. On the other hand, many operators have trials with several vendors to see the whole picture.

To enable diffusion of the service Nokia includes the feature into the most new phone models to be launched in 2005. Nokia has already launched new features for establishing temporary groups, using normal mobile phone numbers and checking the presence of desired callee (Nokia Press).

Including the PoC client also to the cheapest phone models is crucial if the the product is aimed to emerging markets (where the biggest growth will be in the next couple of years) as a cheaper alternative to voice call.

10. Operator Strategies

Worldwide over 35 operators are deploying pre-standard solutions until March 2005 but 14 of them are using Kodiak´s technology for 2G circuit-switched network and so threatening to cripple the whole market according to critics (Tanner 2005).

In Europe commercial PTT launches can be counted on one hand. The strategies are usually not published but some of them have stated to target the business customers first believing that PTT will be a better value proposition for closed user groups than for consumers. (Wieland 2005).

According to Motorola the operators need time to optimize their networks, target the right customers, work out tariffs and use vendors committed to interoperability. (Wieland 2005).

Proprietary PTT solutions may slow down the interoperability diffusion. Charging may require interconnection agreement between operators. These are necessary requirements in order to benefit from positive network effect on consumer market.

By using standardized solution the operators avoid being locked to one or few suppliers. (Northstream 2004).

In Europe the operators also face the challenge of lacking walkie-talkie culture, in US people are used to ‘asynchronous’ types of communication like walkie-talkies and pagers. (Wieland 2005).

The operators have several alternatives to select how they package this product, e.g. a cheap alternative to telephony, a voice complement to Instant Messaging, a voice messaging service or a standalone walkie-talkie. (Northstream 2004).

IMS core network would solve the quality problems beside its other benefits but investing into it requires

significant CAPEX, so there are no operators in Europe rolling out IMS now. (Wieland 2005).

From operator´s point of view the main issues are how use the network on the most efficient way and how to set prices high enough not to cannibalize existing business but low enough to increase network usage and to attract new customers.

11. Phone provision

In phones PoC service demands for integrated hands-free functionality, PoC software and user interface (Nokia Q&A).

Push-to-Talk feature is already available in many new mobile phones. It also possible to load it into many modern phone models free of charge but embedding it directly is seen as a prerequisite for wider service diffusion. (Northstream 2004).

12. Pricing

Although the call is data in IP network, it is meant to be charged as traditional voice calls by duration, not bit load. The OMA architecture supports both subscriber based and traffic based charging and each operator will be able to charge contracted online and offline participants independently. It is also possible to charge based on fixed monthly fee, active group membership (i.e. listened minutes), group creation or group attachment, session type, number of sent/received talk bursts. (OMA).

In US PTT is a subscription service with certain number of minutes included. (Northstream 2004).

In Australia the operator charges a double price compared to a normal call independent of the group size (Ouluexpo 2004).

Using simple pricing model so that the costs are predictable is reasonable.

Fragmentation of pricing policies due to different latencies in different networks may cause fragmentation of how the customers understand the service and the the pricing will be really difficult. (Wieland 2005).

Free local communication (PoB) may act as a driver for chargeable PoC or vice versa (Rönnholm 2005).

13. Regulation

In general the regulators seem to be quite late reacting to the change in transport media. The regulatory framework in Europe is better suited to deal with Internet-based services than in US. Regulation scope of VoIP services is under discussion on both continents.

In Europe European Regulators Group (ERG) is not willing strongly regulate VoIP but to promote its

penetration due to its lower infrastructure deployment cost and more efficient network utilization. “The approach focuses on the regulatory principles of objectivity, technological neutrality, transparency, non-discrimination and proportionality that would helpconsumers and service providers to make informed choices.” (EU 2005).

14. Conclusion

There seems to be a strong technology push to provide new services to mobile customers in order to replace the revenues disappearing due to the tough competition between mobile operators.

For some customer groups PoC clearly brings an opportunity to reduce their terminal count to one but the amount of those may be too small. Indeterminate groups like truck or taxi drivers on a certain area are now using open calls which is not possible with this service. Families and groups of friends may take this service if the pricing model is reasonable. However, they may find it difficult to get used to the half-duplex feature.

On the other hand, the feature differs so little from the normal voice service that the customers may find it useless to familiarize themselves with, at least before the enhanced functionalities (e.g. shared video) are available. For some vendors there is a risk to be locked out if the OMA standard is still delayed or it is not followed by those vendors having a significant market share before the launch.

The operators are presumably waiting for the standard both for PoC and IMS. Before that they cautiously protect their existing business models and formulate strategies used in case the competitors put the big belt on. In Europe and Asia the expected revenue may be too small compared with the cost of creating the market.

One possible driver to solicit customers using this kind of voice messaging service might be the congestion caused by SMS traffic in the networks albeit it gives the best revenue per volume at least in Finland.

References

Nokia 2005. Push To Talk over Cellular – Real-time always-on voice service. White paper. Referenced 4.3. 2005

Northstream AB. 2004. Overview and comparison of Push-to-Talk solutions. www.northstream.se

Karvonen, Tuukka. 2005. Design of Push To Talk Client for Performance Measurements. Master´s Thesis, TKK.

Rönnholm, Valter. 2005. Push-To-Talk over Bluetooth. Master´s Thesis, TKK.

Nokia Press. 2005. Nokia esittelee uusia tuotteita yhtenäistyviin palveluihin ja kehittyviin verkkoihin. Nokia Press 11.2. 2005.

China Daily. 2005. PoC phone service slow to take off. China Economic Net. Updated 21.1. 2005.

RFC 3261. IETF. www.ietf.org

OMA 2005. Open Mobile Alliance. http://www.openmobilealliance.org/release_program/PoC

Jukka Viitasaari. 2004. Siemens, Motorola ja Sony Ericsson push-to-talk –liittoon. IT-viikko.

Tanner, John C. 2005. Push to Talk struggles with standards. America´s Network, Duluth. Vol. 109, Iss 3. pp. 30-34.

Wieland, Ken 2005. A soft push on PTT. Telecommunications International. Norwood. Vol. 39, Iss. 2, pp. 20-22.

EU 2005. EU addresses VoIP Penetration in Europe. VoIP Newsletter. March 2005.

Rehbehn Ken. 2004. Push to Talk. Telecommunications Americas. Vol. 38, Iss. 3, pp. 22-23.

Ouluexpo 24.11. 2004. Interview of Marko Saarinen, Nokia. Referenced 9.3. 2005

Nokia Q&A. PoC – Questions & Answers. www.nokia.com. Referenced 4.3. 2005