Push-to-Talk

Introduction to Push-to-Talk

Push-to-Talk (PTT or P2T), originally introduced in the US by Nextel through its partnership with Motorola and its use of the iDEN technology is now poised to emerge as one of the premier voice-based VAS applications for many leading mobile communications service providers. Combining aspects of cellular mobile communications, presence detection, and walkie-talkie style communications, push to talk provides end-users with the ability to quickly find one another and engage in brief, burst-oriented style communication. Advances in market adoption and technology evolution of voice over wireless IP will enable improvements in Push-to-Talk (PTT).

Push to Talk Market

Rather then being a replacement of long, interactive communication, PTT is best suited for demands for quick communication among end-users. Due to the fact that PTT is provided in half-duplex mode (e.g. transmission occurs in both directions, but not at the same time – each party must wait to speak), the inability to interrupt lends itself to quick exchanges of information, as is the case with the market for business users that need to quickly exchange information and then get along with their business.
The market for PTT will continue to evolve and ultimately represent service opportunities for the more traditional markets (dispatch and mobile workforce users) as well as more mass market users such as the youth market, which is very community-of-interest oriented (e.g. staying in close with one’s close personal friends is very important) and will thus be very closely tied with other Unified Communications type services such as Mobile Instant Messaging and other Advanced Messaging Services, call management services, LBS, and others.
With a significant world-wide emphasis on Public Safety and Homeland Security, PTT will increasingly become important for government, public safety personnel and other officials as a communications tool (among other tools such as Wireless Emergency Service, Priority Service, etc.), serving the need for efficient communications during times of emergency, disaster, or threats.

Push to Talk Implementation and Operations

Implementing and operating PTT is not a simple issue as there are many issues that must be considered and ultimately resolved/managed for optimal success including:

Voice Quality: The use of IP technology for PTT inherently ads the issue of voice quality of service (QoS), just as QoS is an issue with VoIP on fixed networks

Call-Set-up Time: The duration of time from the instance of selecting a user to engage in a PTT session to the time that one is able to initiate a conversation.

PTT Interoperability: Currently, PTT implementations are strictly proprietary based, creating a situation in which there is little or no opportunity for interconnection between PTT systems and thus no inter-carrier PTT communication for end-users.

Numbering Issues: For example, one decision point is to use of a single number (for both normal cellular and PTT) or a separate number for PTT calling.

Technology Supporting Push to Talk

At the core of PTT is an IETP standardized protocol known as Session Initiation Protocol (SIP) used for IP communications and Wireless Softswitch network infrastructure.
Being that it uses IP as a transport/bearer, PTT is highly dependent on the roll-out, expansion and improvements of 2.5G and 3G technology and infrastructure.
The Open Mobile Alliance (OMA) is working to standardize Push-to-Talk over Cellular (PoC) – see PTT Standardization (below).

Benefits of Deploying and Operating Push to Talk

Incremental Revenue

PTT represents incremental revenue to the wireless carrier, as it is an additional service that does not replace normal cellular mobile communications service, but rather is a VAS add-on to existing service.

Differentiation

Being a VAS, PTT represents a significant differentiator for both carriers that implement and optimize early as well as those that find clever ways to integrate PTT with other VAS services in ways that maintain differentiation even after PTT is more mature (for example: even after inter-carrier PTT is in place and optimized).

Cost Savings

Perhaps one of the greatest benefits that wireless carriers enjoy from PTT is the network cost efficiencies that are realized in at least two ways. Use of the underlying IP-based network with half-duplex transmissions has the advantage of both requiring less bandwidth (e.g. network and facility savings) as well as avoiding interconnection to the PSTN (e.g. savings against interconnection charges).

The Future of Push to Talk Service and Technology

PTT Standardization

OMA is standardizing the infrastructure and processes supporting Push-to-Talk over Cellular (PoC), which is the evolution of PTT from proprietary approaches to a more open approach that would operated uniformly and seamlessly between and among technologies and service providers.
OMA is seeking to offer the following infrastructure network elements:
PoC Server: Contains the PoC server-side logic, providing the following functions: end-point for SIP signaling and voice bursts, handles participant lists distribution, reporting to the charging system, and media distribution.
IMS Core: Contains SIP proxies and SIP registers. The Ue access the IMS Core for purposes of SIP signaling to the PoC Server. The IMS Core also handles AAA functions and triggering of personal and group instant talk sessions.
Group/List Manager Server (GLMS): Responsible for management of contact lists, group lists, access lists, and permissions management such as the Do-Not-Disturb (DnD) flag.
User Equipment (Ue): Terminal equipment (mobile phone) containing the PoC application software
OMA is also seeking to standardize the following processes: roaming, identification, addressing, and modes of operation (session establishment and answering).

Inter-carrier PTT

The evolution of PTT to encompass the ability to offer inter-carrier PTT service (the ability for end-users to engage in a PTT session between different mobile network operators), will entail network and service optimization in many areas including the following:

Interoperability: There is a need for basic interoperability between PTT systems, including interface and protocol interoperability.
Clearing and Settlement: There is a need for an efficient clearing and settlement system for managing charges between mobile network operators as they charge different rates for PTT service (e.g. supporting for roaming and any service charge differentials for things like international PTT)

Integrated and Robust Presence Detection and Management

PTT will evolve to encompass robust Presence detection and controls such as availability management. The ability for people to be able to very easily manage their settings will become increasingly important, fostering the need for a Mobile Contact Manager – see below.

Integration of Location-based Services

As with presence and availability, integration of LBS with PTT will add a whole new dimension to the PTT communications experience, as members of a closed user group (e.g. a certain community of interest) will be able to engage in a much improved Unified Communications experience.

Multimedia Integration with PTT

Integration of MMS and other advanced messaging features with PTT service makes sense because both services are a VAS, but perhaps more so, because of the service synergy opportunities. For example, a user could (1) detect a friend (Presence), (2) find a friend (LBS), (3) talk to a friend (PTT) and/or message with a friend (MIM), and then (4) send multimedia messages (MMS) or engage in other Advanced Messaging Services with a friend.

Mobile Contact Manager

The above use case example illustrates the point that perhaps, even more so than MIM, PTT will spawn rapid expansion of Mobile Contact Manager (MCM) service. MCM represents a service (extension to PTT, MIM, and others) that allows for the management of contacts (personal, professional, and even ad-hoc) in terms of presence and availability, location, and contact details (phone number and other alias/addresses such as IM). The ability to quickly and efficiently manage the communications experience, such as add/modify/delete both pre-determined and ad hoc contacts will be of particular importance and synergy with PTT service.
Expansion of MCM will foster the further development and use of various community of interest VAS applications such as friend finder service, interactive mobile games (in the physical and virtual worlds), and more.

Downloadable PTT Client for the Cellular Phone

Even if the PTT client itself is not standardized, a more-or-less standardized method for downloading the client onto the mobile phone will be of great use for those that seek to try PTT very easily (no need to go to the mobile phone store), rapidly accelerating the adoption of PTT.

Push to Talk: Summary and Conclusion

Beneficiaries of PTT

The beneficiaries of PTT will be all major players involved in the deployment and operation of PTT service. Providers of Wireless Softswitch infrastructure and intermediation services will benefit as infrastructure is deployed and service evolution requires various support services such as billing, settlement, protocol conversion and transport required for PTT service. Wireless carriers will benefit from additional revenue generation, service offering differentiation, and cost reduction resulting from PTT operation.

Predictions for PTT

All tier-one carriers will offer their own differentiated PTT service offerings, which will evolve over time, but will also ultimately enable inter-carrier PTT.

Growth of PTT usage will further commoditize long distance service, especially as inter-carrier PTT service is commonplace and optimized.

Evolution of PTT will represent a leading VAS and will spawn the introduction and growth of various synergistic/complementary capabilities and services including Presence and LBS-based services, MCM, and other Unified Communications.Additional Resources:Books about: IP-based Communication
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