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Introduction to Diameter The Evolution of Signaling

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Signaling has been an integral part of telecommunications from the beginning.

It is necessary for the establishment and control of a telecommunications circuit and the management of the network.

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Evolution of Signaling

As telecommunications networks have advanced, so have the signaling procedures.

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Evolution of Signaling

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Channel Associated Signaling

Common Channel Signaling

Signaling over IP NGN

Signaling over IP 4G

MF R1 R2

SS6 SS7

ISUP SCCP TCAP MAP

Circuit Related Non-Circuit Related

SIGTRAN SIP ENUM

M2UA M3UA SUA M2PA

DIAMETER SIP

Policy

Charging

Number Portability

Mobility

Supplementary Services

Intelligent Network

WATS

Call Setup

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Within the 3GPP defined architecture, the handling of the control signaling is separated from the user data traffic.

Allow independent scaling of control and user plane functions

Control data signaling tends to scale with the number of users

Data volumes may scale more dependent on new services and applications

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Signaling in 4G

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Diameter is an IETF defined protocol originally designed for Authentication, Authorization and Accounting (AAA) as an improvement over RADIUS supporting:

– Improved failure handling – More reliable message delivery – Bigger information elements – Improved security – Extensibility – More flexible discovery of other nodes

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Diameter in EPC / IMS

3GPP makes use of two signaling protocols:

– Session Initiation Protocol (SIP) used within the IMS for setting up sessions.

– Diameter used in both EPC and IMS for transactional events (requesting information).

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Relay Agent – Used to forward a message to the destination, depending on

information within the message. – Needs to understand base protocol, does not need to understand

the diameter application used.

Proxy Agent – Similar to relay agent, but can perform additional processing of

the diameter message. – Needs to understand the service being offered and diameter

application being used.

Redirect Agent – Performs routing function. Does not forward message towards

the destination. – Replies with another message to the node that sent the request

with information allowing the node to send message directly to the server.

Translation Agent – Performs translation between diameter and other protocols.

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IETF Defined Agents

Diameter agents assist in routing of a diameter command towards its final destination – the diameter server.

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Diameter Basics

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Client Relay Agent

Server

Peer connection Peer connection

Diameter session

Message Structure

Connections

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A diameter agent can act as a centralized routing entity by aggregating requests from different sources destined to the same destination realm.

Routing typically is performed based on the destination realm as well as the application identification.

The diameter nodes maintain a list of supported realms and known diameter peers and their capabilities.

The peer location as well as routing configuration is used when making routing decisions.

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Routing

HPMN

HSS HSS

vPCRF

VPMN

MME S6A

S6d

S9

GRX/IPX

hPCRF

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RFC 3588 specifies a few general Diameter messages called commands along with their AVP’s.

Extensions called Applications are created on top of Diameter base protocol.

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Extensions to Diameter

Diameter Base Protocol

NAS Application

(IETF)

Credit Control Application

(IETF)

S6a/S6d Application (3GPP Vendor

Specific)

Gx Application (3GPP Vendor

Specific)

etc….

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Network congestion becomes one of the biggest issues, highlighted by the popularity of smartphones and M2M.

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Increase in Diameter Traffic

(Source: Strategy Analytics& ABI Research)

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Increase in Diameter Traffic

It is critical for operators to have the ability to manage

this signaling traffic.

Signaling traffic is outpacing actual

mobile data traffic by 30 to 50 percent

due to:

Quantity of Re-attach Messaging

Always on Applications

Push Services

Battery saving Methodologies

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Users make constant queries as they move among cell sites to push email, access social networking tools and conduct other repetitive actions.

These always-on applications also rely on keep-alive messages.

A web-based IM user may send a message but then wait a couple of seconds between messages. To preserve battery life, the smartphone moves into idle mode. When the user pushes another message seconds later, the device has to set up a signaling path.

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Causes of Signaling Increase

There are an increased number of applications that send only a small amount of data, but the transmission frequency of the packets is relatively high.

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Fast Dormancy

– In order to keep UE power consumption low, UE sends Signaling Connection Release Indication (SCRI) to the RNC simulating a failure in the signaling connection.

Heartbeat for Always-on Application

– Heartbeat packets (keep-alive) between client and server end up being sent during the mobile device’s idle state, which in turn, triggers the device to continually switch between active and idle mode over short period time.

Constant Push Service

– Push messages may be sent while the device is on idle mode, which will trigger unnecessary signaling traffic, such as paging messages, network connection and release messages.

Network (Re-)Attachment

– Many mobile devices are designed to aggressively keep connecting to the broadband network as early as possible to ensure a good user experience.

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Common Smartphone Behaviors

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Need for Diameter Agents

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Need to concentrate and simplify the network connectivity to improve:

Maintainability/Provisioning

Congestion Management

Routing /Traffic Management

Need for operators to protect their networks:

Security Firewalls

Topology Hiding

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Need for Diameter Agents

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Need for Cost-Effective and Flexible Network Deployment

Scalability

Load Balancing

Session Routing and Control

Interoperability

Value-Added Services

Roaming Management

Roam Steering

Trusted non-3GPP

NonTrusted non-3GPP

P-GW

MME

Gxc

Gx

S6a

Gxa

S9

V-PCRF Gxb

S6d

AAA SWx

OCS

OFCS Gy

Gz

SWa

SWd

S6b

STa

Ro

Sh

P-CSCF Ro

Cx

Cx Rf

Rx

IMS

HPMN

VPMN

Non-3GPP

HSS

AS I-CSCF

S-CSCF

S6a

HSS

SGSN

MME

S-GW ePDG

3GPP AAA Proxy

H-PCRF H-

PCRF

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Diameter Agent Solutions

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Value Added Features

Roaming Management Steering of Roaming

H-PCRF

P-GW

MME

Gx

S6a

AAA

SWx

OCS

OFCS

Gy

Gz

S6b

Ro

Sh

P-CSCF Ro

Cx

Cx Rf

Rx

AS I-CSCF

S-CSCF

H-PCRF

HSS

OCS

HSS

DRA Load Balancer

SLF

HLR

Translation

DEA

Router

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