Diameter is an authentication, authorization, and accounting protocol for computer networks. It evolved from the earlier RADIUS protocol. It belongs to the application layer protocols in the internet protocol suite.

1. By : MANJEET KAUR

2. Agenda
› Diameter Description
› Diameter Base Protocol
› Diameter Based Interfaces
S6a Interface
S13 Interface
SGd Interface
SLg Interface
Smp Interface
T6a Interface
› Messages Overview

3. DIAMETER
 Diameter is an Authorization,
Authentication and Accounting
protocol.
 Work within AAA Framework
 Provides an upgrade path from
RADIUS (Remote Authentication
Dial In User Service)
 It belongs to the Application layer
Protocols in internet protocol suite.
DIAMETER
SCTP
IP
L2
L1

4. DIAMETER
ARCHITECTURE
The DIAMETER is a working solution which is placed above the SCTP/TCP
layer. The Diameter protocol architecture consists of a base protocol and
a set of application protocols. An application protocol is intended to inherit
from the characteristics and specifications of the base protocol. The
Diameter base specification is defined to mainly include the common
functionality to be used by all application protocols developed on top of it
Diameter application is not a
software application, but a
protocol based on the
Diameter base protocol. Each
application is defined by an
application identifier and can
add new command codes
and/or new mandatory
AVPs.

5. DIAMETER BASED PROTOCOL
DIAMETER BASED PROTOCOL
Diameter Application
#1
Diameter Application
#2
Diameter Application
#3
….......
The Diameter base protocol defines a set of general messages and rules that
apply to all messages that are exchanged between Diameter nodes.
The SCTP port 3868 is assigned to the Diameter base protocol by IANA.

6. DIAMETER BASED INTERFACES
The S6a, S6d, S13, SGd, SLg and T6a interfaces are some of the interfaces
that are based on Diameter over Stream Control Transmission Protocol
(SCTP).
The Diameter based interfaces have additional messages defined by the
3GPP.
 S6a Interface
 S6d Interface
 S13 Interface
 SGd Interface
 SLg Interface
 T6a Interface

7. S6a Interface
The S6a interface connects the
MME to the HSS.
It enables transfer of
subscription and authentication
data for authenticating and
authorizing user access to the
EPS.
The MME also uses the S6a
interface to inform the HSS of
the MME service area in which
the subscriber is located.

8. S6d Interface
The S6d interface connects the
SGSN-MME to the HSS.
It enables transfer of
subscription and authentication
data for authenticating and
authorizing user access to the
EPS.
The SGSN-MME also uses the
S6d interface to inform the HSS
of the SGSN-MME service
area in which the subscriber is
located.

9. S13 Interface
The S13 interface connects the
MME to the Equipment
Identity Register (EIR).
It enables transfer of identity
data for identification of a
Mobile Equipment (ME) and
controlling the access for a
specific ME to the EPS.
This is enabled by the optional
licensed feature IMEI Check.

10. SGd Interface
The SGd interface is a
Diameter-based interface used
for signaling between the
MME and the SMS-
GMSC/SMS-IWMSC.
The main features of the SGd
interface :
1. Forwarding of MO short
messages
2. Forwarding of MT short
messages

11. SLg Interface
The SLg interface is a
Diameter-based interface used
for signaling between the
MME and the GMLC.
The main features of the SGd
interface is Control-Plane
Based Positioning
This feature enables external
clients to get UE location data
from the PLMN by connecting
to a Gateway Mobile Location
Center (GMLC).

12. T6a Interface
The T6a interface connects the
MME to the SCEF( Service
Capability Exposure Function)
The T6a interface provides the
following functions:
• The T6a interface supports
the Monitoring
Enhancements (MONTE)
function which allows for
MME-internal information
on specific events to be
made available to an
Application Server through
the SCEF.
• The T6a interface supports
the Non-IP Data Delivery
over SCEF function

13. DIAMETER message
Format
Diameter base protocol has
defined several types of
Diameter
messages, which are
identified by their command
code.
Comprises a fixed length
header part and a set
of Attribute Value Pairs
(AVP). The header contains
protocol-, command-, and
session-related information.

14. MESSAGES

15. MESSAGE Flow
 Transport connection (TCP/SCTP)
 Capabilities Exchange
 Messages(CCR/CCA , etc.)
 Watchdog
 Disconnect
 Transport Disconnect