IP Multimedia Subsystem FAQs

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Do I need to set up a partnership with AT&T to distribute my applications for AT&T's IMS platform?

You will have to have a business relationship with AT&T in order to use our APIs, but you can distribute your application or service yourself.

Updated: 8/25/2014 20:45:24
Created: 10/17/2013 07:17:40

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What elements are responsible for billing services?

Charging Trigger Function (CTF), Charging Data Function (CDF), and Charging Gateway Function (CGF) are the billing service elements.

Updated: 8/25/2014 20:47:5
Created: 10/17/2013 07:17:40

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Is this difference based on the number of PDP contexts available?

Not necessarily. A single PDP context can accommodate different media applications.

Updated: 8/25/2014 20:47:12
Created: 10/17/2013 07:17:40

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How do you see IMS services being offered to prepaid subscribers?

IMS is capable of handling both prepaid and postpaid offers. The functionality offered by this new service includes 3G, 2.5G, and 2G network technology.

Updated: 8/25/2014 20:51:7
Created: 10/17/2013 07:17:40

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Will IMS make data transfer over wireless and wired networks easier, faster, or less expensive?

No, IMS will not provide that sort of impact; rather, quality of service mechanisms may improve the user experience.

Updated: 8/25/2014 20:46:56
Created: 10/17/2013 07:17:40

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What are the IP Multimedia Subsystem quality of service goals?

IMS has defined the Geologic Quadrangle (Gq) interface to specify quality of service (QoS). To date, four levels of QoS, ranging from conversational voice down to best effort, have been defined in the 3GPP standards.

Updated: 8/25/2014 20:46:52
Created: 10/17/2013 07:17:40

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What are your plans for interoperability between wireless carriers?

GSM World of which AT&T is a member, is sponsoring interoperability tests between carriers to address interoperability issues while IMS is in its infancy. AT&T is actively participating in these interoperability tests.

Updated: 8/25/2014 20:45:33
Created: 10/17/2013 07:17:40

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How many different types of communications can occur within a single session simultaneously?

There is a theoretical limit, we have written applications using up to eight sessions.

Updated: 8/25/2014 20:47:10
Created: 10/17/2013 07:17:40

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Why is Open Mobile Alliance (OMA) on the standards list? Doesn't that go against 3GPP IMS?

3GPP has transitioned the standardization of specific applications to OMA to ensure that different vendors' products can work together. OMA is working on applications of IMS such as push-to-talk, instant messaging, and presence enablers.

Updated: 8/25/2014 20:45:39
Created: 10/17/2013 07:17:40

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What extensions are necessary to support IMS?

The main difference between Session Initiation Protocol (SIP)and the International Steering Committee (ISC) interface is that the ISC interface uses SIP as its foundation.

Updated: 8/25/2014 20:47:2
Created: 10/17/2013 07:17:40

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What is AT&T's view on market requirements for Unlicensed Mobile Access vs. IMS for future services?

Unlicensed Mobile Access (UMA) is much more limited in functionality. AT&T has decided that, although it may take longer to launch services, in the long run IMS will be more beneficial than UMA.

Updated: 8/25/2014 20:47:25
Created: 10/17/2013 07:17:40

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Will I have to modify my SNPP, SMTP, or SMS code to be compatible with IMS?

If you have a system that uses Simple Network Paging Protocol (SNPP), Simple Mail Transfer Protocol (SMTP), or Short Message Service (SMS) to send messages to users, you will not have to modify your code to be compatible with IMS. If you need to send a message using IMS, you will not have to write a SIP message.

You may choose to modify your application to integrate new media and new features that IMS will make possible, but you won't have to change your current application if such enhancements are not planned.

Updated: 8/27/2014 20:52:30
Created: 10/17/2013 07:17:40

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How does AT&T view the end-user presentation of multiple applications on mobile devices?

We expect it will depend on the types of terminal and applications. On terminals with rich user interfaces, such as WWAN-enabled PCs, we can imagine a robust dashboard for communication across multiple types of media. Handhelds can also handle these types of media, but developers will need to pay close attention to delivering simple, intuitive UIs on these types of devices. SIP will help these be standard.

Updated: 8/27/2014 20:36:34
Created: 10/17/2013 07:17:40

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How do the phones and the network handle load balancing over multiple SIP connections?

The quality of the user experience does not degrade elegantly in each session, meaning that the voice quality does not suffer as a user opens multiple video streams.

The PDF is responsible for taking into account the various user requirements in order to provide sufficient quality of service.

Updated: 8/27/2014 20:36:49
Created: 10/17/2013 07:17:40

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What interfaces are available to work with legacy Intelligent Network (IN)-based call logic?

There is an element within the IMS architecture called the IM-SSF which handles interworking legacy IN applications (CAMEL) and the IMS network. 3GPP TS 23.002 (3rd Generation Partnership Project Technical Specification) provides additional explanation of this architecture.

Updated: 8/27/2014 21:25:21
Created: 10/17/2013 07:17:40

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What is AT&T's view on the maturity of JAIN/JSLEE?

We have been following and participating in Java APIs for Integrated Networks (JAIN) and Java Service Logic Execution Environment (JSLEE) development. We have not fully defined how we will use it, but we are investigating it. We believe several implementations of JAIN/JSLEE are ready for prime time.