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Newsletter: Diameter Protocol Simulator Enhanced to Support Gy and Ro Interfaces

Welcome to another October 2015 issue of GL Communications' Newsletter providing information and insight into our enhanced MAPS™ Diameter Protocol Emulator - Scripted LTE Diameter S6a, S6d, Cx/Dx, Gx, Rx, Gy/Ro Interfaces Emulation.


The Diameter protocol is intended to provide a framework for Authentication, Authorization and Accounting (AAA) for applications such as network access, roaming, and IP mobility. The AAA protocols are used to determine whether the user is allowed to connect to the network (Authentication) and use a particular service (Authorization). It is also used to track network resources used by end-user for accurate billing (Accounting).

AAA protocols such as TACACS and RADIUS were initially deployed to provide dial-up PPP and terminal server access. Over time, with the growth of the Internet and the introduction of new access technologies, including wireless, DSL, Mobile IP and Ethernet, routers and network access servers (NAS) have increased in complexity and density, putting new demands on AAA protocols. As a result, the Diameter protocol has been chosen as the AAA protocol in all next generation fixed and mobile IP- based networks (IMS, LTE). The Diameter protocol is a considerably more sophisticated protocol for mobility management, policy and charging (online and offline) control. It is designed to support data, services, and applications with extreme flexibility and is expected to replace all legacy protocols such as MAP, LDAP, Radius, and others.

Functional Procedure

Within LTE-IMS network, MAPS™ Diameter can simulate S6a, S6d, Cx/Dx, Gx, and Rx Interfaces  to test LTE-IMS network elements such as the MME (Mobility Management Entity), HSS (Home Subscriber Server), CSCF (Call Session Control Function), SGSN (Serving GPRS Support Node), PDN GW (Packet Data Network Gateway), AF (Application Function) , PCRF (Policy and Charging Rules Function),CTF (Charging trigger Function) and OCS (Online Charging System).Recently MAPS™ Diameter has been enhanced to support simulation of Gy and Ro interfaces in addition to existing interfaces. The simulation of other interfaces (Rf, Dh, Gq, Zh, Zn, Wa, Wd, Wx, Wm, Wg, Pr) and elements will also be supported in near future.

The MAPS™ Diameter gives the users the unlimited ability to edit signalling messages to support various procedures listed below. MAPS™ Diameter supports both SCTP (Stream Control Transmission) and TCP (Transmission Control Protocol) transport protocol layers for PSTN signalling messages over IP networks.  

MAPS™ Diameter also supports an End-to-End 4G LTE Communications Network Lab with all components to simulate both E-UTRAN and EPC (Evolved Packet Core), allowing complete testing of the LTE-IMS network. 

Diameter over SCTP/TCP
Protocol Stack

Supported Protocols Standard / Specification Used
Diameter IETF RFC 3588
S6a & S6d - 3GPP TS 29.272 V10.3.0
Rx - 3GGP TS 29214-b10
Cx/Dx - 3GPP TS 29.228 & TS29.229
Gx - 3GPP TS 29.212 & TS 23.203 
Gy/Ro (DCCA)- 3GGP TS 32.225 , 3GPP TS 32.299 and IETF RFC 4006

S6a interface procedures Location Management, Subscriber Data Handling, Authentication, Fault Recovery, and Notification
Rx interface procedures AA-Request/Answer, Re-Auth-Request/Answer, Abort-Session-Request/Answer, and Session-Termination-Request/Answer
Gx interface procedures IPCAN Session Establishment and Modification
S13 interface procedures ME (Mobile Equipment) Identity Check procedure
Sh interface procedures User data handling procedures (User-Data-Update, Subscriber-Notification, User-Data-Pull)
Gy/Ro interface procedures Immediate Event Charging (IEC), Event Charging with Unit Reservation (ECUR), Session Charging with Unit Reservation (SCUR) 
CC-Request/Answer, Re-Auth-Request/Answer Procedures

Testing CTF and OCS entities in Gy/Ro interface

Both Gy and Ro interfaces define procedures for online charging in IMS & LTE networks. Ro interface is between IMS entity (CSCF) and Online Charging System (OCS) & Gy interface is between the PCEF (e.g., PDN GW) and the OCS. 

The PCEF node in LTE network, and CSCF node in IMS network perform the role of a Charging Trigger Function (CTF) entity to issue charging events to an Online Charging System (OCS). The charging events can be immediate (IEC), event-based (ECUR), or session-based (SCUR). An Online Charging System (OCS), is a functional architecture that provides support for all three levels (service level, subsystem level, and bearer level) of online charging as depicted in the image below.

As provided in the figure below, MAPS™ Diameter can be configured as CTF or OCS, while the other acting as the DUT in the network. If MAPS™ Diameter is configured as CTF, it tests the DUT (OCS) by initiating the messages towards OCS. Similarly, if MAPS™ Diameter is configured as OCS, it tests the DUT (CTF) by receiving the requests from CTF and sending responses back to the CTF (DUT).

MAPS™ Diameter as CTF and OCS (DUT)

MAPS™ configured as CTF in GY/RO interface (Session Based Charging)

Session Based Charging is a credit-control (CC) process that makes use of several interrogations: the first (INITIAL_REQUEST), a possible intermediate (UPDATE_REQUEST), and the final (TERMINATION_REQUEST). The first interrogation is used to reserve money from the user’s account and to initiate the process. The intermediate interrogations may be needed to request new quota while the service is being rendered. The final interrogation is used to exit the process.

The MAPS™ Diameter as CTF initiates a call by sending a CCR (Credit Control Request) message to the test the OCS. The CCA (Credit Control Answer) response message received back from the DUT (OCS) can be verified as shown in the message sequence window below.

Call Generation Diameter DCCA Interface for 
Session Based Charging

Diameter Gy/Ro Interface Session based 
Charging Procedure

MAPS™ configured as OCS in GY/Ro interface (Event Based Charging)

Event Based Charging is aone-time event charging process used when there is no need to maintain any state in the Diameter credit-control server; for example, enquiring about the price of the service, balance check, direct debiting, and refund. The use of a one-time event implies that the user has been authenticated and authorized beforehand. 

In CTF testing, MAPS™ Diameter is loaded with a set of inbuilt scripts to handle the incoming messages. MAPS™ Diameter acts as OCS and sends response to the one-time event based charging request as shown in the message sequence window below.

Call Reception Diameter DCCA Interface for 
Event Based Charging

Diameter Gy/Ro Interface Event based 
Charging Procedure

For comprehensive information on the application, please visit MAPS™ Diameter Protocol Emulator web page. 

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