With the advent of LTE and IMS, Voice and Video over LTE (VoLTE) is fast becoming a reality. Customers are turning to video services rapidly and data consumption is increasing exponentially.
Moreover, with multi-screen devices such as smart phones, tablets etc being churned out in millions – customers now own atleast 2 smart devices today. Customers also expect their applications to provide them with a uniform customer experience irrespective of the device form factor. This holds true for all applications, and it will also be a natural expectation from IMS and VoLTE applications.
Policy Control to the Rescue:
In contrast to OTT (Over the Top) internet traffic and OTT video applications, IMS video applications have a slight edge of policy control and enforcement.
As the form factor of the device increases (from a smart phone to a tablet for example), its data consumption requirements also increase due to the bigger screen size. Moreover, if the customer chooses to play HD content, the throughput requirements would further increase accordingly.
Hence, in order to preserve the customer experience of video applications on multiple screens, it is also important that a sufficient data pipe is provided to the application in order for it to perform uniformly. In addition to the data pipe, video playback latency and jitter control also need to be controlled over the air.
This becomes increasingly important, if we wish to deliver Live TV services and VoD services over IMS.
To mitigate this situation for IMS video applications, we can effectively use the IMS and LTE policy control framework.
The solution uses one of the most ‘ancient’ SIP headers defined by RFC 3261 in conjunction with the DIAMETER Rx interface.
The User-Agent header is defined in Section 20.41 of RFC 3261, and this header is used to provide ‘information’ on the user agent originating the SIP request. This header can be used by IMS User Equipment to provide details on the form factor of the device where the IMS client is executing. Moreover, it should also be possible to provide device pixel details (if available from the OS).
For example, on Android Operating System, the following Java code provides the screen display metrics which can be sent to the the IMS core by using the User-Agent SIP header:
DisplayMetrics dMetrics = new DisplayMetrics();
String str = “Display Metrics Are : “
+ ” x “
The P-CSCF in the IMS core network can extract the User-Agent header and use the device form factor details on the Rx interface. Based on the device form factor and resolution, the PCRF can enforce appropriate QCIs, UL Bandwidth and DL bandwidth for the specific device in question.
In addition, the P-CSCF also sends the codec information as received in the SDP (Session Description Protocol) to the PCRF. This information coupled with the device form factor and resolution can enable the PCRF to calculate a very accurate measure of the UL and DL bandwidth to enforce. Moreover, this information can also help the LTE network to provide bandwidth boost to premium customers or premium video content.
Discovering the Policy Enabled Architecture:
Policy control is a distinctive edge that the VoLTE architecture provides over traditional OTT video content. The ability of the LTE and the IMS network to accurately calibrate session QoS characteristics is a true differentiator as opposed to best effort video. By leveraging age old SIP headers in conjunction with the PCRF can lead to truely differentiated customer experience.
OTT video provides provide a lot of jitter control, echo cancellation and buffering techniques to enhance customer experience, especially compensating for poor RF conditions or congestion scenarios.
However, none of those techniques can match the realtime QoS enabled architecture of VoLTE, which can guarantee high throughput even in low converage areas of LTE.
This is because LTE radio coverage is not a decisive factor for calculating throughput for customers. Throughput depends on the number of empty resource blocks available in a given eNode-B cell. For a three sector LTE base station, there are 100 resource blocks per sector. This gives a total of 300 resource blocks per base station available for customers.
Throughput is a factor of the number of free resource blocks available for a given subscriber in the LTE cell at that time. Even if the coverage is poor (cell edge conditions), it is possible to provide high throughput to the customer through the policy control architecture.
Operators need to realize the power of the IMS and LTE architecture to truly exploit it and create differentiation in their services.
There are a lot of other hidden nuggets in the combined IMS and LTE network architecture, which I will leave for another discussion and for some other day. Hopefully, engineers from around the world will discover these hidden nuggets and construct innovative policy enabled services for consumers.