LTE is rapidly changing the way mobile services are used. It is spurring development of rich new broadband services, and triggering the deployment of new handset features such as higher screen resolution and better battery technologies through increased capacity. Traditional services like SMS and MMS are morphing into rich communication services to include features such as real-time video calling.
While these advances are great for the end-user, service providers require their network to support a variety of applications not traditionally seen on mobile phones -- like advanced web surfing, streaming video, peer-to-peer networking, and machine-to-machine communications that consume large amounts of bandwidth for longer durations. Smartphones and increased backhaul traffic have already created nightmare scenarios for carriers, including the need to regulate the traffic flows and the need to monetize new services. Moving forward, LTE will be available for notebooks, ultra-portables, cameras, camcorders, mobile broadband routers, and other devices that would benefit from mobile broadband.
With this surge, mobile services providers are not only faced with finding ways to optimize the performance of their networks, but simultaneously creating billing structures that drives revenue for these enhanced services. Should the person who is streaming HD movies from Netflix be billed at a different rate than someone simply sending out text messages? Most service providers believe so, since downloading a YouTube video uses 100x more bandwidth than voice, and not to mention that the average iPhone uses 400MB of data per month. Solutions must not only recognize the applications and services each individual is using, but also decipher their different billing plans based on a variety of criteria. This can be a huge challenge when you consider the millions of concurrent mobile users any one network has at any given time.
As LTE starts meeting key 4G capacity requirements, infrastructures will be designed simply for easier deployment and operation, while at the same time becoming flexible enough to adapt to frequency band constraints. In order to maintain profitability in a climate of ever-increasing backhaul network costs, operators will need to move beyond a flat data rate model.
The Role of the Evolved Packet Core
As such, providers’ best option is to validate and optimize the performance and accuracy of the charging system components of the evolved packet core (EPC). The EPC is the all-IP mobile core network for LTE, allowing the convergence of packet-based real-time and non-real-time services. It not only provides a simpler, flatter, and cheaper network infrastructure, but also adheres 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.
Components of Validating the EPC
Measurements are essential to assessing the quality and performance of the EPC. They must be rich, flexible, visual, complete, and represent an accurate real-time view of the network or device being tested. Service providers must remember a few key areas in their test and validation methodology, in order to get the insight they will need to optimize performance and accuracy:
- 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.
By creating a high number of subscribers and their behavior, and stepping through a sequence of events that trigger charging data records (CDR), operators can successfully validate the EPC billing system. These events can include 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 dozens of 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. By comparing the emulated event counts to the records in the OCF/OFCS the accuracy of the charging system can be determined.
Closing the Loop – Preparing for LTE Billing
The deployment of LTE wireless networks and the required interoperability with legacy technologies creates new levels of network complexity. Fortunately, through a full EPC evaluation using test tools for all mobile network elements from layer 2-7, service providers can meet the high demands of LTE while simultaneously generating revenue. The ability to decipher an average text message user versus the avid YouTube video watcher will not only allow service providers to create a realistic billing model, but also charge according to usage. Deep insight into their networks will equip service providers with the necessary information to tackle these new LTE infrastructures head on.
About the Author
Joseph Zeto, serves as a senior market development manager within Ixia's marketing organization. He has over 17 years of experience in wireless and IP networking, both from the engineering and marketing sides. Joe has extensive knowledge and a global prospective of the networking market and the test and measurement industry. Prior to joining Ixia, Joe was Director of Product Marketing at Spirent Communications running Enterprise Switching, Storage Networking, and Wireless Infrastructure product lines. Joe holds a Juris Doctorate from Loyola Law School, Los Angeles, CA.