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3G vs. 4G LTE Charging: The Vital Differences


Mary ClarkBy Mary Clark

As mobile network operators uncover LTE’s impacts to their operational processes, it's becoming evident that the complexities of the new charging mechanisms required to support 4G roaming are much more abundant than in a 3G environment. This often-misunderstood topic can lead to both retail and wholesale billing disputes if left unaddressed, so it is vital to grasp new accounting flows to ensure customers are billed correctly and wholesale transactions are accurately cleared and settled.

Here is an explanation of these technical charging principles that mobile operators need to know:

Prepaid Charging — The CAMEL standard, which enables prepaid services in 3G, is not supported in LTE; therefore, prepaid customer information must be routed back to the home network as opposed to being handled by the local visited network. As a result, operators must rely on new accounting flows to access prepaid customer data, such as through their P-Gateways in both IMS and non-IMS environments or via their CSCF in an IMS environment.

Postpaid Charging (TAP) — Postpaid data-usage charging works the same in LTE as it does in 3G, using versions TAP 3.11 or 3.12. With local breakout of IMS services, TAP 3.12 is required.

Local Breakout — In local breakout scenarios, operators do not have the same amount of visibility into subscriber activities as they do in home-routing scenarios because subscriber-data sessions are kept within the visited network; therefore, in order for the home operator to capture real-time information on both pre- and postpaid customers, it must establish a Diameter interface between charging systems and the visited network’s P-Gateway.

Local Breakout of IMS Services — In this highly complicated scenario, the visited network creates call detail records (CDRs) from the S-Gateway(s); however, these CDRs do not contain all of the information required to create a TAP 3.12 mobile session or messaging event record for the service usage. As a result, operators must correlate the core data network CDRs with the IMS CDRs to create TAP records. Operators can access real-time charging of both pre- and postpaid customers through its S-CSCF or Diameter messages.

LTE: 101

  • IMS Services: IP multimedia services built on top of the core IP data network like VoLTE, video conferencing and other advanced services
  • Non-IMS Services: Legacy services like voice and messaging that rely solely on SS7 networks or on the core IP data network
  • P-Gateway: Packet (data network) Gateway, the equivalent to the GGSN or HA for 2G/3G
  • S-Gateway: Serving Gateway, the equivalent to the SGSN or FA for 2G/3G
  • CSCF: Call Session Control Function, a network element that controls IMS services
  • TAP: Transferred Account Procedure, method for sending billing records of roaming subscribers from the visited network to their respective home network
  • P-CSCF: Proxy CSCF, an IMSI node controlling the IMS session in the visited network
  • S-CSCF: Serving CSCF, an IMSI node controlling the IMS session in the home network

While there are new hurdles to overcome, understanding these elements now is critical for operators looking to deliver the reach that subscribers have come to expect from legacy technologies in the world of LTE.

Mary Clark joined Syniverse in June 2009 and serves as senior vice president, Roaming. Prior to joining Syniverse, she served in a number of executive-level positions at MACH. She also has experience working for both mobile technology providers and for mobile operators, having spent time with CTIA-The Wireless Association, Cibernet and CellularOne.


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