Diameter Protocol Overview

1. Diameter
Beny Haddad

2. Agenda
• Origin of Diameter
• Main Features of Diameter
o Diameter Base protocol
o Type of Diameter Nodes
• Main Applications
• Messages Overview
Company Confidential 2

3. Why did we need
Diameter?
• Diameter is an
Authentication, Authorization
and Accounting protocol
(AAA) for computer
networks, and an alternative
to RADIUS.
• Diameter provides an
upgrade path for the “old”
RADIUS (Remote
Authentication Dial In User
Service) and solves several
limitations.
In the early 1990s, Radius has
been developed to control
Dial-in access

4. AAA
• Authenticate users or devices before granting them
access to a network
• Authorize those users or devices for certain network
services
• Account for usage of those services
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5. DIAMETER = 2 *
RADIUS
RADIUS DIAMETER
Reliable
transport
No (uses UDP) TCP, SCTP
Failover Not defined by
standard
Failover is defined for
network errors and actions
Security Not mandatory and not
end to end
Mandatory and end to end
Agent roles Not defined (other
then client and server)
Defines many (such as
proxy, relay and redirect)
Transactions ID up to 255, other
implicit methods
End to end and node by
node each 2^32 range
Vendor specific Not explicit Through negotiation
Dynamic
configuration
No Defined in the standard
5

6. Main features of
Diameter
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7. Diameter - Basic Functionality
Diameter
Client Application
Session Management
Diameter Tutorial - IETF67
Diameter Server Node at otherrealm.com
Diameter
Server Application
Routing Management
Connection
Management
Session Management
Routing Management
Connection
Management
Diameter Client Node at somerealm.com
Base Protocol Base Protocol

8. Diameter - Basic Functionality
• Base Protocol
– Connectivity: Peering and Routing
– Application support: Application session management
• Applications
– Purpose specific: Gx, Gy, etc
– Identified by application Id
• Every application MUST have an IANA-assigned application
identifier
• Used also for diameter message routing
- Define the Commands (e.g. CCR/CCA, RAR/RAA)
- Defines the AVP (Attribute/Value Pair) fields (e.g. Origin-Host)
Diameter Tutorial - IETF67

9. Diameter – Message Format
• Diameter Message:
Diameter Header AVP AVP AVP
Version, Diameter Header = Length, Flags, Code, AppId, H2H Id, E2E Id
AVP Header = Code, Flag, Length, Vendor-Id (Opt)
Diameter Tutorial - IETF67
AVP Header AVP Data
• Each message must be defined using an ABNF grammar
• Pre-defined AVP data types (Integer32, Float, OctetString etc.)

10. Diameter ABNF Conventions
Symbol Example Meaning Occurrences
<XXX> ::= <X, F> <CER> ::= <
Diameter Header:
257, REQ >
Diameter Tutorial - IETF67
Command Code, Flags 1
< AVP > < Session-Id > Required AVP
At this place (first)
1
{ AVP } { Origin-Host } Required AVP 1
1* { AVP } 1* { Host-IP-Address
}
Required AVP,Can
appear more than once
1+
[ AVP ] [ Origin-State-Id ] Optional AVP 0,1
*[ AVP ] * [ Supported-
Vendor-Id ]
Optional AVP, Can
appear more than once
0+

11. Diameter ABNF Example
<CER> ::= < Diameter Header: 257, REQ > /* Command Code, Flags */
< Session-Id > /* Required AVP, Occurrence: 1 At this place
(first) */
{ Origin-Host } /* Required AVP, Occurrence: 1 */
{ Origin-Realm }
1* { Host-IP-Address } /* Required AVP, Occurrence: 1+ */
{ Vendor-Id }
{ Product-Name }
[ Origin-State-Id ] /* Optional AVP, Occurrence: 0 or 1 */
* [ Supported-Vendor-Id ] /* Optional AVP, Occurrence: 0+ */
* [ Auth-Application-Id ]
* [ Inband-Security-Id ]
* [ Acct-Application-Id ]
* [ Vendor-Specific-Application-Id ]
[ Firmware-Revision ]
* [ AVP ]
Diameter Tutorial - IETF67
Note: /* */ is not part of ABNF

12. Capabilities Exchange
• Capabilities Exchange
– Use of Capabilities-Exchange (CER/CEA) messages
– Message exchange advertises:
• Peer Identity
• Security schemes – Indicates the use of TLS
• SCTP host addresses if used
– CER/CEA may or may not be protected
• Peer Table Creation
– Lists all peers that passes capabilities negotiation
– Indicates the connection status of each peers
– Also used for message routing
Diameter Tutorial - IETF67

13. Diameter Sessions – definitions
• What is a session?
o A session is a related progression of events devoted to a
particular activity
• Applications provide guidelines as to when a
session begins and ends
• Sessions are identified by Session-Id
o Globally and eternally unique
<DiameterIdentity>;<high 32 bits>;<low 32 bits>[;<optional value>]
• DiameterIdentity: Senders identity in FQDN
• High and Low 32 bits: Decimal representation of a 64-bit value,
monotonically increased
• Optional value: Implementation specific, i.e. MAC address, timestamp
etc
Diameter Tutorial - IETF67

14. Types of Diameter Nodes
• Diameter Clients and Servers
– Request and Answer Originators
• Where application normally reside
– Advertises supported applications only
• Diameter Agents
– Request and Answer forwarders
– Adds routing information to the message
– Relay Agents
• Provides basic message forwarding
• Does not inspect content of the message other than Destination-
Host and/or Realm and AppIds
• Advertises support all applications
Diameter Tutorial - IETF67

15. Types of Diameter Nodes – (cont.)
– Proxy Agents
• Inspects and possibly modifies contents of the request or answer it is
forwarding.
– Useful in scenarios such policy enforcement, admission control,
provisioning etc
– Can maintain session state
• Examples: Translation agents, RADIUS<->DIAMETER
– Re-Direct Agents
• Does not forward messages but notifies the previous hop of the new
next-hop to use
• Advertises support all applications
Diameter Tutorial - IETF67

16. Types of Diameter Nodes
Relay/Proxy
Agent
realmA.com realmB.com
Diameter Tutorial - IETF67
Redirect
Agent
Client
2. Request 3. Redirect Notification
1. Request
4. Request
6. Answer 5. Answer
Request/Answer Path:
• Normal Relay or Proxy: 1, 4, 5, 6
• Re-directed Agent: 1, 2, 3, 4, 5, 6
Server

17. Main Applications
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18. Main Applications in 3gpp
Policy:
- Gx
- Rx
- S9
- Sd
Charging:
- Gy
- Gz (Rf)
- Sy
Subscriber Info:
- Sh
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19. Gx/Rx Application
• Gx:
o Interface between the PCEF (Policy and Charging Enforcement Function)
and the PCRF (Policy Control and Charging Rule Function)
o PCRF provides PCC rules (QoS and Charging rules) to PCEF at session
establishment
o PCRF can push PCC Rules for new bearers creation
• Rx:
o Interface between the AF (Application Function) and the PCRF
o Enables 3rd party applications (IMS, SBC, etc) to create dynamically
bearers
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20. Gy/Gz Application
• Gy:
o Diameter Credit Control Application (DCCA)
o Online Charging
o OCS (Online Charging) Allocates Quotas to PCEF
• Gz:
o Offline Charging
o Also known as Rf
o Report usage to OFCS (Offline Charging)
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21. Messages overview
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22. Message Flow
• Transport (TCP/SCTP)
• Capabilities Exchange
• Messages (CCR/CCA, etc)
• Watch Dog
• Disconnect
• Transport Disconnect
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23. Messages
Message name Abbreviation Command code
Capabilities-Exchanging-Request CER 257
Capabilities-Exchanging-Answer CEA 257
Device-Watchdog-Request DWR 280
Device-Watchdog-Answer DWA 280
Credit-Control-Request CCR 272
Credit-Control-Answer CCA 272
Re-Auth-Request RAR 258
Re-Auth-Answer RAA 258
Session-Termination-Request STR 275
Session-Termination-Answer STA 275
Disconnect-Peer-Request DPR 282
Disconnect-Peer-Answer DPA 282
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24. Gx Interface
Rx
AF
Policy and Charging
Rules Function
(PCRF)
Gx
PCEF
GW
Online Charging System (OCS)
Subscription Profile
Service Data Flow
Based
Credit Control
CAMEL
SCP
Repository
(SPR)
Gy
Gz
Sp
Offline
Charging
System
(OFCS)
Company Confidential 24

25. Gx Messages - CCR
• CCR command: sent by the PCEF to PCRF for 2
purposes:
o To request from PCRF for PCC rules for a bearer
o To indicate bearer or PCC rule related events or the termination of the IP
CAN bearer and/or session
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26. Gx Messages - CCR
<CCR> ::= < Diameter Header: 272, REQ, PXY >
< Session-Id >
{ Auth-Application-Id }
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ CC-Request-Type }
{ CC-Request-Number }
[ Destination-Host ]
[ CC-Subsession-Id ]
[ Origin-State-Id ]
*[ Subscription-Id ]
[ Framed-IP-Address ]
*[ Framed-IPv6-Prefix ]
[ 3GPP-RAT-Type ]
[ Termination-Cause ]
[ User-Equipment-Info ]
{ 3GPP-GPRS-Negotiated-QoS-Profile }
[ 3GPP-SGSN-MCC-MNC ]
[ 3GPP-SGSN-Address ]
[ 3GPP-SGSN-IPv6-Address ]
[ Called-Station-ID ]
[ Bearer-Usage ]
[ TFT-Packet-Filter-Information ]
* [ Proxy-Info ]
* [ Route-Record ]
*[ AVP ]
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27. Gx Messages - CCA
• The CCA command is sent from the PCRF to PCEF
as a response to a CCR command.
• It provides the PCEF with
o PCC rules and event triggers for the bearer/session
o Selected bearer control mode for the IP-CAN session
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28. Gx Messages – CCA (cont)
<CCA> ::= < Diameter Header: 272, PXY >
< Session-Id >
{ Auth-Application-Id }
{ Origin-Host }
{ Origin-Realm }
[ Result-Code ]
[ Experimental-Result ]
[ CC-Request-Type ]
[ CC-Request-Number ]
[ CC-Sub-Session-Id ]
*[ Event-Trigger ]
[ Origin-State-Id ]
*[ Charging-Rule-Remove ]
*[ Charging-Rule-Install ]
[ Primary-CCF-Address ]
[ Secondary-CCF-Address ]
[ Primary-OCS-Address ]
[ Secondary-OCS-Address ]
[ Error-Message]
[ Error-Reporting-Host ]
*[ Failed-AVP ]
*[ Proxy-Info ]
*[ Route-Record ]
*[ AVP ]
Charging-Rule-Install ::= < AVP Header: 1001 >
*[ Charging-Rule-Definition ]
*[ Charging-Rule-Name ]
*[ Charging-Rule-Base-Name ]
[ Bearer-Identifier ]
[ Rule-Activation-Time ]
[ Rule-Deactivation-Time ]
[ Resource-Allocation-Notification ]
[ Charging-Correlation-Indicator ]
*[ AVP ]
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29. Gx Messages – CCA (cont)
Flow-Information ::= < AVP Header: 1058 >
[ Flow-Description ]
[ Packet-Filter-Identifier ]
[ Packet-Filter-Usage ]
[ ToS-Traffic-Class ]
[ Security-Parameter-Index ]
[ Flow-Label ]
[ Flow-Direction ]
*[ AVP ]
QoS-Information ::= < AVP Header: 1016 >
[ QoS-Class-Identifier ]
[ Max-Requested-Bandwidth-UL ]
[ Max-Requested-Bandwidth-DL ]
[ Guaranteed-Bitrate-UL ]
[ Guaranteed-Bitrate-DL ]
[ Bearer-Identifier ]
[ Allocation-Retention-Priority]
[ APN-Aggregate-Max-Bitrate-UL]
[ APN-Aggregate-Max-Bitrate-DL]
* [AVP]
Charging-Rule-Definition ::= < AVP Header: 1003 >
{ Charging-Rule-Name }
[ Service-Identifier ]
[ Rating-Group ]
* [ Flow-Information ]
[ Flow-Status ]
[ QoS-Information ]
[ Reporting-Level ]
[ Online ]
[ Offline ]
[ Metering-Method ]
[ Precedence ]
[ AF-Charging-Identifier ]
* [ Flows ]
[ Monitoring-Key]
[ AF-Signalling-Protocol ]
* [ AVP ]
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30. Gx Messages - RAR
• The RAR command: sent by the PCRF to the PCEF in
order to provision PCC rules and event triggers using
the PUSH procedure to initiate the provision of
unsolicited PCC rules.
o NOTE: If the RAR command is received by the PCEF without providing any
operation on PCC rules or any QoS information, the PCEF will respond with
a CCR command requesting PCC rules.
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31. Gx Message - RAR
<RA-Request> ::= < Diameter Header: 258, REQ, PXY >
< Session-Id >
{ Auth-Application-Id }
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ Destination-Host }
{ Re-Auth-Request-Type }
[ Origin-State-Id ]
*[ Event-Trigger ]
*[ Charging-Rule-Remove ]
*[ Charging-Rule-Install ]
*[ QoS-Information ]
*[ Proxy-Info ]
*[ Route-Record ]
*[ AVP]
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32. Gx Messages - RAA
• The RAA command: sent by the PCEF to the PCRF in
response to the RAR command.
<RA-Answer> ::= < Diameter Header: 258, PXY >
< Session-Id >
{ Origin-Host }
{ Origin-Realm }
[ Result-Code ]
[ Experimental-Result ]
[ Origin-State-Id ]
[ Event-Trigger ]
*[ Charging-Rule-Report]
[ Access-Network-Charging-Address ]
*[ Access-Network-Charging-Identifier-Gx ]
[ Bearer-Identifier ]
[ Error-Message ]
[ Error-Reporting-Host ]
*[ Failed-AVP ]
*[ Proxy-Info ]
*[ AVP ]
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33. Rx Interface
Rx
AF
Policy and Charging
Rules Function
(PCRF)
Gx
PCEF
GW
Online Charging System (OCS)
Subscription Profile
Service Data Flow
Based
Credit Control
CAMEL
SCP
Repository
(SPR)
Gy
Gz
Sp
Offline
Charging
System
(OFCS)
Company Confidential 33

34. Event Triggers (examples)
• SGSN_CHANGE (0)
• QOS_CHANGE (1)
• RAT_CHANGE (2)
• TFT_CHANGE (3)
• PLMN_CHANGE (4)
• LOSS_OF_BEARER (5)
• RECOVERY_OF_BEARER (6)
• IP-CAN_CHANGE (7)
• QOS_CHANGE_EXCEEDING_AU
THORIZATION (11)
• UE_IP_ADDRESS_ALLOCATE (18)
• UE_IP_ADDRESS_RELEASE (19)
• UE_TIME_ZONE_CHANGE (25)
• USAGE_REPORT (26)
• RAI_CHANGE (12)
• USER_LOCATION_CHANGE (13)
• OUT_OF_CREDIT (15)
• REALLOCATION_OF_CREDIT (16)
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35. Rx Messages
• AAR: sent by an AF to the PCRF in order to provide it
with the Session Information
• AAA: sent by the PCRF to the AF in response to the AAR
command
• RAR: (Re Authentication Request): sent by the PCRF to
the AF in order to indicate an Rx specific action
• RAA: sent by the AF to the PCRF in response to the RAR
command
• STR (Session Termination Req): sent by the AF to inform
the PCRF that an established session shall be terminated
• STA: sent by the PCRF to the AF in response to the STR
command.
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36. Rx Messages - AAR
• <AA-Request> ::= < Diameter Header: 265, REQ, PXY >
• < Session-Id >
• { Auth-Application-Id }
• { Origin-Host }
• { Origin-Realm }
• { Destination-Realm }
• [ Destination-Host ]
• [ AF-Application-Identifier ]
• *[ Media-Component-Description ]
• [Service-Info-Status ]
• [ AF-Charging-Identifier ]
• [ SIP-Forking-Indication ]
• *[ Specific-Action ]
• *[ Subscription-ID ]
• [ Reservation-Priority ]
• [ Framed-IP-Address ]
• [ Framed-IPv6-Prefix ]
• [ Service-URN ]
• [ Origin-State-Id ]
• *[ Proxy-Info ]
• *[ Route-Record ]
• *[ AVP ]
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37. Rx Messages – Media
Component AVP
• Media-Component-Description ::= < AVP Header: 517 >
• { Media-Component-Number } ; Ordinal number of the media comp.
• *[ Media-Sub-Component ] ; Set of flows for one flow identifier
• [ AF-Application-Identifier ]
• [ Media-Type ] ; Video, Audio, Data , applucation, Control, text, message, other
• [ Max-Requested-Bandwidth-UL ]
• [ Max-Requested-Bandwidth-DL ]
• [ Flow-Status ] ; enable DL, enable UL, enable All, Remove All
• [ Reservation-priority ]
• [ RS-Bandwidth ]
• [ RR-Bandwidth ]
• *[ Codec-Data ]
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38. Rx Messages - AAA
• <AA-Answer> ::= < Diameter Header: 265, PXY >
• < Session-Id >
• { Auth-Application-Id }
• { Origin-Host }
• { Origin-Realm }
• [ Result-Code ]
• [ Experimental-Result ]
• *[ Access-Network-Charging-Identifier ]
• [ Access-Network-Charging-Address ]
• [Acceptable-Service-Info ]
• [ IP-CAN-Type ]
• [ 3GPP-RAT-Type ]
• [ Error-Message ]
• [ Error-Reporting-Host ]
• *[ Failed-AVP ]
• [ Origin-State-Id ]
• *[ Redirect-Host ]
• [ Redirect-Host-Usage ]
• [ Redirect-Max-Cache-Time ]
• *[ Proxy-Info ]
• *[ AVP ]
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39. Rx Messages - RAR
• <RA-Request> ::= < Diameter Header: 258, REQ, PXY >
• < Session-Id >
• { Origin-Host }
• { Origin-Realm }
• { Destination-Realm }
• { Destination-Host }
• { Auth-Application-Id }
• { Specific-Action }
• *[ Access-Network-Charging-Identifier ]
• [ Access-Network-Charging-Address ]
• *[ Flows ]
• *[ Subscription-ID ]
• [ Abort-Cause ]
• [ IP-CAN-Type ]
• [ 3GPP-RAT-Type ]
• [ Origin-State-Id ]
• *[ Proxy-Info ]
• *[ Route-Record ]
• *[ AVP ]
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40. Rx Messages - RAA
• <RA-Answer> ::= < Diameter Header: 258, PXY >
• < Session-Id >
• { Origin-Host }
• { Origin-Realm }
• [ Result-Code ]
• [ Experimental-Result ]
• *[ Media-Component-Description ]
• [ Service-URN ]
• [ Origin-State-Id ]
• [ Error-Message ]
• [ Error-Reporting-Host ]
• *[ Failed-AVP ]
• *[ Proxy-Info ]
• *[ AVP ]
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41. Specs
• Diameter Base Protocol: RFC 3588
• 3GPP TS 23.203: "Policy and charging control
architecture":
o http://www.3gpp.org/ftp/Specs/html-info/23203.htm
• 3GPP TS 29.212: “Gx Interface”:
o http://www.3gpp.org/ftp/Specs/html-info/29212.htm
• 3GPP TS 29.211: “Rx Interface”:
o http://www.3gpp.org/ftp/Specs/html-info/29211.htm
• 3GPP TS 32.29: “Gy interface”
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42. Questions?
42

43. Thank You
43