Diameter protocol | diameter interfaces | Diameter in LTE

What is diameter protocol?

Diameter protocol is the application layer protocol which provides  AAA functionality.  AAA means Authentication, Authorization and Accounting.  Diameter uses IP network for communication to its peer.  its uses SCTP or TCP as  transport layer on top of IP layer.
Diameter used in 3G , 4G and LTE for AAA. There are interfaces define in diameter in telecom network.
 Its base protocol is define on diameter rfc

https://tools.ietf.org/html/rfc6733.

                                                Diameter over SCTP:

                                                               

AAA Application

DIAMETER

SCTP

IP

         

                                                 Diameter over TCP:

                                                               

AAA Application

DIAMETER

TCP

IP

         

Radius vs diameter :

• ·         Diameter is the successor  of radius protocol this have following differences.
• ·         Radius runs on top of UDP , which is unreliable , while diameter runs on top of SCTP or TCP.
• ·         Radius does not define failover mechanism while diameter does.
• ·         Capability Negotiation is not supported in Radius while Diameter does.

Base Diameter supports following functionalities:

• ·         Delivery of AVPs
• ·         Capability Negotiation
• ·         Error Notification
• ·         Functionality to add new AVPs and Commands
• ·         Handling of user session etc.

       


Diameter Message Structure:
  
A diameter message is composed of diameter header and list of AVPs.

                       Diameter over SCTP example.

Diameter based rfc 6733

Diameter Interfaces:

Rf Interface: 
 This interface is used for offline charging. It is used between CTF and CDF. The CTE or Charging trigger function sends the charging events to Charging Data Function. The charging can be event based charging or session based charging.

Ro Interface:
 Ro Interface is used for online charging system. Online charging system is used for real time charging e.g call, sms or data charging in prepaid mobile connection. This can be even based, session based or immediate.

Gy Interface:
 Gy Interface is similar to Ro Interface, but it between PGW/GGSN and PCRF. PCRF is Online charging system.

S6a Interface:
 This interface is used between MME and HSS. This is used for Authentication, Location Update , Purge etc. On this interface MME downloads the subscriber APN profile configuration for accessing data network via PGW.

S6d Interface:
 This interface is used between SGSN and HSS. This is used for Authentication, Location Update , Purge etc. On this interface MME downloads the subscriber APN profile configuration for accessing data network via GGSN