LTE Quality of service, charging and policy control (PCC)

What is PCC in LTE?

The purpose of PCC in LTE is policy and charging control. Policy control is a very generic term and in a network there are many different policies that could be implemented, for example, policies related to security, mobility, use of access technologies etc. When discussing policies, it is thus important to understand the context of those policies. When it comes to PCC, policy control refers to the two functions gating control and QoS control:1.

Gating control is the capability to block or to allow IP packets belonging to IP flow(s) for a certain service. The PCRF makes the gating decisions which are then enforced by the PCEF. The PCRF could, for example, make gating decisions based on session events (start/stop of service) reported by the AF via the Rx reference point.2.

QoS control

QoS control allows the PCRF to provide the PCEF with the authorized QoS for the IP flow(s). The authorized QoS may, for example, include the authorized QoS class and the authorized bit rates. The PCEF or BBERF enforces the QoS control decisions by setting up the appropriate bearers. The PCEF also performs bit rate enforcement to ensure that a certain service session does not exceed its authorized QoS.

Charging Control

Charging Control includes means for both offline and online charging. The PCRF makes the decision on whether online or offline charging shall apply for a certain service session, and the PCEF enforces that decision by collecting charging data and interact with the charging systems. The PCRF also controls what measurement method applies, that is, whether data volume, duration, combined volume/duration or event-based measurement is used. Again it is the PCEF that enforces the decision by performing the appropriate measurements on the IP traffic passing through the PCEF.

With online charging, the charging information can affect, in real-time, the services being used and therefore a direct interaction of the charging mechanism with the control of network resource usage is required. The online credit management allows an operator to control access to services based on credit status. For example, there has to be enough credit left with the subscription in order for the service session to start or an ongoing service session to continue. The OCS may authorize access to individual services or to a group of services by granting credits for authorized IP flows. Usage of resources is granted in different forms. The OCS may, for example, grant credit in the form of certain amount of time, traffic volume or chargeable events. If a user is not authorized to access a certain service, for example, in case the pre-paid account is empty, then the OCS may deny credit requests and additionally instruct the PCEF to redirect the service request to a specified destination that allows the user to re-fill the subscription.

PCC also incorporates service-based offline charging. With offline charging, the charging information is collected by the network for later processing and billing. Therefore, the charging information does not affect, in real-time, the service being used. Since billing is taking place after the service session has completed, for example, via a monthly bill, this functionality does not provide any means for access control in itself. Instead policy control must be used to restrict access and then service-specific usage may be reported using offline charging.

Online and offline charging may be used at the same time. For example, even for billed (offline charged) subscriptions, the online charging system may be used for functionality such as Advice of Charge. Conversely, for prepaid subscribers, the offline charging data generation may be used for accounting and statistics.

LTE Quality of service, charging and policy control (PCC)

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PLMN: What is a Public Land Mobile Network ?

A public land mobile network (PLMN) is any wireless communications system intended for use by terrestrial subscribers in vehicles or on foot. Such a system can stand alone, but often it is interconnected with a fixed system such as the public switched telephone network (PSTN). The most familiar example of a Public Land Mobile Network end user is a person with a cell phone. However, mobile and portable Internet use is also becoming common.

Public Land Mobile Network (PLMN)

PLMN code

A Public Land Mobile Network is identified by a globally unique PLMN code, which consists of a MCC (Mobile Country Code) and MNC (Mobile Network Code). Hence, it is a five- to six-digit number identifying a country, and a mobile network operator in that country, usually represented in the form 001-01 or 001-001.

A PLMN is part of a:

  • Location Area Identity (LAI) ( Public Land Mobile Network and Location Area Code)
  • Cell Global Identity (CGI) (LAI and Cell Identifier)
  • IMSI (see PLMN code and IMSI)

PLMN code and IMSI

The IMSI, which identifies a SIM or USIM for one subscriber, typically starts with the Public Land Mobile Network code. For example, an IMSI belonging to the PLMN 262-33 would look like 262330000000001. Mobile phones use this to detect Roaming, so that a mobile phone subscribed on a network with a Public Land Mobile Network code that mismatches the start of the USIM’s IMSI will typically display an “R” on the icon that indicates connection strength.

PLMN services

A Public Land Mobile Network typically offers the following services to a mobile subscriber:

The availability, quality and bandwidth of these services strongly depends on the particular technology used to implement a Public Land Mobile Network.

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Diameter Protocol in 4G LTE

What is Diameter in LTE?

Diameter is an AAA (Authorization, Authentication and Accounting ) protocol which works at the application layer in OSI model over TCP/SCTP or TLS/DTLS (for security) protocol. Diameter is the successor of RADIUS (Remote Remote Authentication Dial In User Service) protocol that runs over UDP.

This AAA technology is a message based protocol, where AAA nodes exchange messages and receive Positive or Negative acknowledgment for each message exchanged between nodes. For message exchange it internally uses the TCP and SCTP which makes diameter reliable. Its technical specifications are given in RFC-6733 Diameter Base Protocol. (Please refer to this link to RFC-6733 for the original definition)

Advantages of Diameter compared to Radius

This AAA technology has following improvements over RADIUS:   

a) More Reliable
b) Transport Layer Security                   
c) Fail-over Mechanism
d) Server Initiated Messages
e) Agent Support
f) Audit-ability
g) Transition Support
h) Capability Negotiation
i) Roaming Support
j) Peer Discovery & Configuration

Defaults Ports                      

The default port is 3868 for TCP/SCTP and 5868 for TLS/DTLS.

More details on AAA in LTE

LTE Evolved Packet Core (EPC) generally have 5 nodes:

1) Mobility Management Entity (MME)
2) Home Subscriber Server (HSS)
3) Serving Gateway (S-GW)
4) PDN Gateway (P-GW)
5) Policy and Charging control entity/Function (PCRF)

These nodes interact then uses diameter based interfaces. Please see the diagram below for more detailed information on this topic:

Diameter Protocol in LTE

The Dark Lines in the diagram show the major Interfaces in the LTE EPC (Evolved Packet Core). Sometimes the CSS data is not stored at HSS then S7a interface is used to communicate with the MME. S7a is also a diameter based interface.

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Build Private LTE 4G & 5G Networks

Private LTE brings major benefits compared to Public LTE networks. A Private LTE network connects people/things belonging to an enterprise (normally across a campus or site), and where data needs to be kept totally secure by avoiding transmitting it through the core network of a mobile operator.  Full private ownership of the whole LTE network – including Base Stations and Core – has several advantages.

Major Benefits of Private LTE

The many benefits of a Private LTE network can include:

  • Guaranteeing coverage and capacity in the target coverage area. Organisations can design, engineer and update the RAN to meet their specific performance demands, including for coverage, configuring uplink and downlink, set usage policy, determine which users connect, how traffic is prioritised, and other key parameters.
  • Optimising parameters in the LTE radio to operate in challenging physical environments (e.g., warehouse or oil/gas facility with lots of metal). This can include fast recovery from failure, or optimizations for reliability, and for latency. This is not possible when connecting to a public network, where such parameters are under control of the operator, not the user.
  • Retaining control of critical data: In private networks, the organization controls its own security and can ensure that sensitive information does not leave the network; this is an essential requirement for many types of businesses and security-focused organisations. Another benefit of keeping data and the core network on the private LTE network is the risk of service disruption due to a WAN link outage is eliminated.
  • Dedicated coverage and capacity of high speed 4G network with the ability to customise performance to enterprise needs
  • High speed, high capacity, reliable and secure mobile broadband communication layer for mission-critical and business-critical people, machines and applications
  • A fast route to digital transformation and IoT, bringing intelligent insights for more efficient operation, agility, quality and innovation
  • LTE mobility – the use of advanced applications on mobile platforms (vehicles, robots, etc) and transparent hand-over to public LTE networks outside of private LTE network coverage
  • In mining and minerals, private LTE can be used to automate remote facilities and enhance security
  • Enabling IoT applications which can run over a Private LTE network

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