By Yang Hong
OTTs are now providing voice services; to compete, carriers must secure user loyalty by providing a better voice service experience. Fortunately, carriers have network resources at hand. Optimization of the EPC network can turn VoLTE commercialization into a historic success.
OTT challenge and VoLTE opportunity
Mobile voice services have evolved from 2G to 3G to LTE. With the development of mobile broadband, over-the-top (OTT) voice services keep emerging, causing a huge impact on carrier voice revenue. In the LTE era, all carrier services will be IP-based. The circuit switched (CS) network will gradually die out and the CS voice service will be ultimately replaced by voice over LTE (VoLTE).
This means that the evolved packet core (EPC) network of LTE has to bear not only traditional data services such as web browsing, video and apps, but also the most important service to carriers – voice. OTT voice services will also be supported on the EPC network. It is critical that carriers prioritize their VoLTE services over OTT voice services.
Leveraging network advantages and focusing on user experience
User experience is the key factor of competitiveness. Carriers must deliver better user experience to maintain user loyalty. With the proper network optimization, carriers' VoLTE service experience cannot be matched by OTTs.
Adjust EPC architecture to improve VoLTE experience
The EPC network has evolved from the packet switched (PS) core network, which was designed only for data services. The PS networks of most carriers are centralized. The serving GPRS support node (SGSN) and the gateway GPRS support node (GGSN) are deployed in the centralized room. For example, most Chinese carriers' provincial PS devices are deployed in the primary provincial equipment room to provide province-wide services. After evolution to LTE, the mobility management entity (MME) and system architecture evolution gateway (SAE-GW), which are upgraded from the SGSN and GGSN, are still deployed in a centralized equipment room.
According to CS voice statistics, 80% of calls are initiated and ended locally. Based on the current network structure, 80% of VoLTE traffic needs to be transmitted by the SAE-GW deployed in the centralized equipment room, causing two problems: First, 80% of these transmission network resources are wasted. Second, longer transmission distance causes longer latency. Unlike data services, voice service depends heavily on low transmission latency; if end-to-end latency exceeds 300ms, user experience is substantially degraded. By adjusting the current EPC network architecture and deploying gateways locally, 80% of VoLTE traffic will be transmitted locally, saving bandwidth resources and latency.
Deploy special voice gateways to improve VoLTE service processing efficiency
According to 3GPP, all VoLTE and data service traffic goes through the SAE-GW. However, the sharing of the gateway leads to poor network efficiency due to the inherent differences between voice and data services.
Carriers can deploy special VoLTE gateways locally to process local users' VoLTE services. Since the VoLTE gateway does not need service awareness (SA) functionality to distinguish VoLTE from data services, the user capacity and signaling processing capability of each card would be in full play. VoLTE services do not require high throughput; few cards are needed for a gateway, so cost is minimal. VoLTE is also less demanding on the policy and charging rules function (PCRF), which can be conveniently integrated on the VoLTE gateway. As a result, networking cost is reduced. Since signaling interaction between network elements (NEs) is performed by the VoLTE voice gateway, signaling processing is efficient. In addition, voice packets are small and stable compared with other data service packets. The special VoLTE voice gateway can provide transmission and scheduling efficiency optimization for small packets, while improving VoLTE service processing efficiency.
Prioritize VoLTE signal processing for E2E QoS
Compared with OTT players, carriers have a big advantage in network resources. Leveraging the EPC network, they can realize guaranteed bitrate (GBR) and thereby ensure E2E QoS for VoLTE services. A bitrate of 23.85kbps with less than 100ms transmission delay ensures HD voice experience for VoLTE users. In comparison, OTT voice services are supported by whatever is available, so they cannot guarantee QoS absolutely.
The EPC network can prioritize scheduling of VoLTE packets by configuring the differentiated service code point (DSCP) of the packets. In addition, carriers can perform optimization for VoLTE access and paging signaling to ensure VoLTE prioritization. Special network resources can also be reserved to ensure high-quality VoLTE services.
Provide reliable voice solutions to ensure 100% VoLTE availability
The CS network ensures 99.999% network reliability for voice services. Carriers can ensure availability for voice services in almost all scenarios. In the VoLTE era, the EPC network can also implement targeted VoLTE service optimization to ensure near-100% VoLTE availability.
While users can tolerate some data service delay, they are much less tolerant when it comes to voice service. Most data services are initiated by users themselves while voice calls are typically between a caller and a receiver (who could be anywhere). Therefore, reliable storage of user location information must be guaranteed to ensure call availability, even when faults occur in the mobility management entity (MME) and the gateway. By backing up user location information between MMEs deployed with the MME Pool mechanism, carriers can ensure 100% call availability even when user location information on one MME is lost; 1+1 hot backup is also implemented for the special voice gateway.
First-time call success rate and drop rate are KPIs unique to voice. The EPC network can be optimized in a variety of scenarios to guarantee smooth VoLTE services. For example, in case of a handover scenario, EPC can be optimized to avoid call initiation during handover. If the network is congested, EPC should reserve special resources and prioritize scheduling of VoLTE services. Even some of the network resources for data services can be used for VoLTE to ensure first-time call success.
Simplify VoLTE O&M through E2E KPI visualization
Carriers accumulated a lot of valuable experience in voice service operation and maintenance (O&M) during the 2G/3G era. The entire KPI system was designed for voice services. These KPIs must be adapted for VoLTE O&M. VoLTE operation and management aims at visibility, intelligence, and automation. As the VoLTE bearer network, the EPC network allows for effective analysis of VoLTE signaling and data traffic. Service visualization is required for effective VoLTE O&M. The EPC network provides visualized KPI reports that indicate VoLTE service status. The KPIs include call success and drop rates as well as packet latency and jitter.
Intelligent VoLTE O&M helps O&M personnel identify and locate service faults quickly. The EPC is the best element to locate the faults involving specific NEs based on abnormal KPIs and to locate faults involving specific modules through fault replay. Quick fault location ensures timely problem solving.
Automated VoLTE O&M significantly boosts the work efficiency of O&M personnel. For example, the EPC analyzes the call success and drop rates in different areas to direct the O&M personnel to conduct targeted network optimization, ensuring consistent service experience in all areas. The EPC can also provide voice quality analysis reports based on different types of terminals, which is useful for terminal device marketing.
EPC: Key to VoLTE success
In summary, the EPC network is not only a VoLTE bearer network. For carriers, it is the key to differentiating VoLTE services from OTT voice services. To enhance user loyalty, carriers must provide a service experience that OTTs cannot match.
Voice services are the key to carriers' survival. If carriers optimize EPC to establish absolute advantages over OTT, they can succeed once again in the VoLTE era as they did in the 2G/3G eras.