Delivering a Quality VoLTE Experience Depends on Policy

Virtualization Reality

Delivering a Quality VoLTE Experience Depends on Policy

By Frank Yue, Technical Marketing Manager  |  April 02, 2014

Service providers are working to roll out VoLTE services within the next couple of years.  They are being cautious with their deployment as they transition from circuit-switch based voice services to voice over the LTE (News - Alert) IP infrastructure.  The voice call will be sharing the same infrastructure as other Internet data communications within the S/Gi interface.  Service providers need to ensure that the voice calls receive the appropriate priorities and have policies applied to ensure that web browsing and video streaming services do not adversely affect the voice quality.

The LTE architecture brings significant changes to the signaling for voice communications.  Legacy circuit-switched protocols such as SS7 used in 2G/3G networks are making way for IP-based Diameter and SIP messaging.  It is essential to leverage the control plane messaging provided by Diameter signaling and SIP to gain insight into the subscriber intentions for the VoLTE call. That insight can then be used to define the appropriate policies through the policy and charging rules function (PCRF) and apply those policies through the policy and charging enforcement function (PCEF) or traffic detection function (TDF (News - Alert)) within the S/Gi network.

Before any kind of action can be taken to deliver QoS or manage the voice call itself, the service provider must understand the nature and importance of the call.  A call to my colleague has a different relative importance when compared to a call to the fire department or emergency services.  Other factors may be taken into effect when determining the priority and importance of a VoLTE call such as time of day, potential importance of caller and receiver, and network congestion. 

The service provider can gain insight into these parameters and others, by inspecting the Diameter and SIP messages associated with the call along with the monitoring of its network.  Based on the service provider’s understanding of the relative importance of the call, policies can be defined within the PCRF based on the subscriber profile.  Once the policy for the call has been established, it is now just a matter of applying that policy.

It is critical to leverage this information and the policy that has been created from it.  The bearer channel of the VoLTE call traverses the SGi interface in the LTE network using the RTP and RTSP IP protocols.  Since this traffic has to compete for SGi resources like bandwidth, firewall services, and VAS solution capacity, it becomes critical that the service provider apply appropriate policies to the data traffic to maintain the expected levels of quality that both the service provider and subscriber expect.

The application of the policy defined within the PCRF typically occurs at the PCEF and recently defined TDF.  Here, various data management tools are utilized, including rate limiting, application of QoS priority tags, and intelligent traffic steering to VAS solutions to optimize certain classes of traffic.  As an example, if there is congestion on the network, the service provider may apply a high priority QoS tag (News - Alert) on the VoLTE RTP communication stream to force the network infrastructure to drop lower priority traffic such as web surfing before the VoLTE call is affected.  In addition, the service provider can steer all streaming video traffic to a VAS solution that compresses and optimizes the video stream, making more valuable bandwidth available to VoLTE calls.

One of the questions that all service providers have is whether they can generate new revenue streams based on the new network architectures and shifting subscriber habits.  While it is critical that service providers deliver the quality and priority for VoLTE calls for emergency and other essential services, there is a lot of flexibility concerning the handling of all other calls that subscribers place.

Service providers may want to deliver tiered subscription plans that have differing levels of guaranteed quality for VoLTE calls based on the premium that the subscriber is willing to pay.  They may also look back at subscription models used in the past such as applying different rates for in-network calls vs. out-of-network calls. 

Ultimately, the service provider has the ability to create different service packages based on delivering tiered quality of experience plans for VoLTE to the subscriber.  They must understand how to extract policy from the control plane protocols and apply those policies in a meaningful manner to provide value to their subscribers.  When designed and implemented properly, VoLTE is a technology where everyone wins.

Frank Yue is technical marketing manager with F5 Networks (News - Alert) (

Frank Yue is the Technical Marketing Manager for the Service Provider vertical at F5 Networks. Mr. Yue has over 15 years of experience building large-scale networks and working with high performance application technologies, including deep packet inspection, network security, and application delivery. He is based in North Carolina and is a scuba diving instructor in his spare time.

Edited by Stefania Viscusi