– Joe Zeto, Director of Product Marketing for Ixia, says:

Thanks to LTE, consumers have access to new services, including real-time video calling, but service providers are faced with supporting a variety of applications not traditionally seen on mobile phones, such as web surfing, streaming video, peer-to-peer networking, and machine-to-machine communications, all of which consume large amounts of bandwidth for longer durations. As such, providers are tasked with creating billing structures that drive revenue for these enhanced services as well as optimize network performance.

Smartphones have already created nightmare scenarios for carriers through increased backhaul traffic. For example, downloading a YouTube video uses 100x more bandwidth than voice, and the average iPhone uses 400MB of data per month. But does this mean that the person who streams HD movies should be billed at a different rate than your average person who simply sends a few texts? There are millions of concurrent mobile users on any one network at any given time, and most service providers believe solutions should be able to recognize the applications and services each individual is using, and also decipher their different billing plans based on a variety of criteria.

To achieve this, operators need to move past a flat data rate model in order to maintain profitability in a climate of ever-increasing backhaul network costs. Infrastructures will also need to be designed simply for easier deployment and operation, while simultaneously becoming flexible enough to adapt to frequency band constraints.

Evaluating the Evolved Packet Core for Proper Billing

The best option for service providers to create accurate billing structures is to validate and optimize the performance and accuracy of the all-IP mobile core network for LTE, the evolved packet core (EPC). The charging system components of the EPC allows the convergence of packet-based real-time and non-real-time services to provide a simpler, flatter, and cheaper network infrastructure, and the ability to adhere to new, stringent LTE requirements for high bandwidth, reduced latency, and 2G/3G interoperability. Therefore, the enforcement of quality of service (QoS)-related parameters, such as jitter and delay, is critical. EPC components include the serving gateway (SGW), packet data network gateway (PDN-GW), and the online (OCS) and offline charging systems (OFCS). The important component definitions you need to know here are: 


Serving Gateway (SGW)

The SGW is a user-plane node providing data paths between eNodeBs and the PDN gateway. One of the essential functionalities of the SGW, beside routing and forwarding packets, is as a local mobility anchor point for inter-eNodeB handovers, as well as managing mobility between the LTE, 2G/GSM, and 3G/UMTS networks. The SGW also provides charging for user equipment, PDN, and service classes.

Packet Data Network Gateway (PDN-GW)

The PDN-GW is the termination point of the packet data interface. It provides the anchoring function for sessions with external packet data networks. A critical function of the PDN-GW is enforcement of per-user-based packet filtering, allowing gating and rate enforcement policies as well as service level charging.

Online Charging System (OCS)

The OCS allows service providers to charge their customers based on service usage – in real time. It is applicable to all subscriber types and service types, offers unified online charging and online control capabilities, and can be used as a unified charging engine for all network services, which makes it a core basis for convergent billing in the network.

Offline Charging System (OFCS)

The OFCS allows for the collection of network resource charging information concurrently with that resource usage. The OFCS enables the aggregation and correlation of the charging information from multiple sources and delivers it to a Billing System.

The Components of Measurement

In order to validate the quality and performance of the EPC, measurements must be rich, flexible, visual, complete, and represent an accurate real-time view of the network or device being tested. In order to get the insight they will need to optimize performance and accuracy, service providers must remember a few key areas in their test and validation methodology:

  • Quality of Service (QoS). The quality of service, expressed in jitter, latency, packets dropped, and other measurements, is a key performance indicator in an all-IP network. QoS testing measures the degradation of a guaranteed bit rate flow, such as a voice call, when a sudden data surge occurs. QoS imbalances should be measured on a per service data flow, per-subscriber, and node level basis using triple-play and video-rich traffic.
  • Quality of Experience (QoE). QoE tests validate the perceived quality of a voice or video stream.  Based on well-established standards, QoE tests are essential to assess the overall quality of the network from the user’s view, and they are especially effective as end-to-end measurements conducted between mobile equipment and the edge of the IP core network.
  • Deep Packet Inspection (DPI). DPI is a cornerstone capability of the PDN-GW, since QoS enforcement is performed by inspecting and regulating ingress and egress traffic. Using DPI to simulate PDN behavior and to observe and report traffic violations, the EPC can certify service level agreements (SLAs). Triple-play and video-rich traffic is essential for testing node functions that enforce QoS, such as DPI.
  • Subscriber behavior. Subscriber modeling emulates the mix, volume, and variability of mobile user communities. It is only by using rich traffic profiles, including video, file transfer, instant messaging, email, torrents, etc., that the EPC core network can be fully battle-tested.
  • Charging. LTE charging occurs mostly in the PDN-GW and SGW. Interfaces have been defined for offline and online charging. A crucial EPC charging test involves checks and balances between the generated traffic trigger events and the measured charging events.
The EPC billing system can be successfully validated through simulating massive-scale, real-world mobile user behavior. To meet billing needs, operators can follow a sequence of events that trigger charging data records (CDR), including establishment of dedicated bearers for VoLTE services or a conversational video session, roaming, access to a specific external network (APN), and many other events. In fact, there are several  events that a particular operator may choose to monetize, each of which can trigger CDRs to be generated by the S-GW or P-GW and sent on to the OCS or OFCS.  The accuracy of the charging system can be determined by comparing the emulated event counts to the records in the OCF/OFCS.

Are You Ready for LTE Billing?

Service providers will be able to capitalize on the promises of LTE through a full EPC evaluation using test tools for all mobile network elements from layer 2-7. The ability to generate a realistic billing model and charge according to usage will be imperative for service providers. They can achieve this through interpreting an average text message user versus the avid YouTube video watcher. Deep, actionable-insight into service providers’ networks will allow them to capitalize on new LTE infrastructures.