Dsr

Diameter Signaling Router (DSR) Application HandbookThe exclusive guide for orchestrating and interworking services in multi-vendor, multi-technology networks

Improve the performance of your IMS and LTE networks

About Tekelec

Tekelec, the broadband data management company, enables billions of people and devices to surf, talk, and text. Our solutions allow service providers to give consumers a consistent and tailored broadband experience. We handle network complexity with a portfolio that manages and capitalizes on the exponential growth in data applications and traffic. Tekelec has more than 25 offices around the world serving customers in more than 100 countries.

For more information please call 888.628.5521 or +1.919.460.5500Visit our web site at www.tekelec.com

The information presented is for demonstration purposes only and is not intended to represent any particular company. Any similarities are purely coincidental. Actual performance results depend on particular network configurations, capacity and other technical requirements.

Introduction

Mobile data traffic is skyrocketing, fueled by the introduction of smartphones, laptop dongles, flat-rate plans, social networking and compelling applications like mobile video. And, there is no slowdown in sight. ABI Research (9 August 2009) predicts that by 2014 the mobile data traffic registered per month will equal the total data traffic logged during 2008.

Operators have realized that their 3G networks are not equipped to sustain this high level of traffic growth. They are looking to all-Internet protocol (IP) networks such as long term evolution (LTE) and IP multimedia subsystem (IMS) to provide the bandwidth required to support data-hungry devices and applications.

The Diameter protocol, using stream control transmission protocol (SCTP) for transport, is used widely in the all- IP, service-oriented IMS and LTE architectures. Within the IMS control and service planes, Diameter plays a central role in policy, charging, authentication and mobility management. In the absence of a Diameter signaling

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Table of Contents

Introduction 3

Diameter Signaling Router Overview 5

Use Case 1: Centralized Routing 7

Use Case 2: LTE Roaming 10

Use Case 3: HSS Address Resolution 13

Use Case 4: LTE-to-2G/3G Roaming 15

Use Case 5: Centralized/Integrated Monitoring 17

Use Case 6: PCRF Binding 20

About Tekelec 22

Appendix: Acronyms 23

core implemented by Diameter relay/proxy agents, endpoints such as mobility management entities (MMEs) and home subscriber servers (HSSs) would need to utilize direct signaling connections to each other, forming a mesh-like network architecture. They would also need to handle all session-related tasks such as routing, traffic management, redundancy and service implementation. Initially, implementing an IMS or LTE network without a signaling core may be sufficient, but as traffic levels swell, the lack of a capable signaling infrastructure poses a number of challenges, some of which are already being seen today in 3G networks. These include:

• Scalability: Each endpoint must maintain a separate SCTP association with all of its Diameter peers as well as the status of each, placing a heavy burden on the endpoints as the number of nodes grows.

• Congestion control: Diameter lacks the well-defined congestion control mechanisms found in other protocols such as signaling system 7 (SS7).

For example, if an HSS has multiple Diameter front ends, the lack of sufficient congestion control increases the risk of a cascading HSS failure.

• Network interconnect: A fully meshed network is completely unworkable when dealing with connections to other networks because there is no central interconnect point, which also exposes the operator’s network topology to other operators and can lead to security breaches.

• Interoperability testing (IOT): Protocol interworking becomes unmanageable as the number of devices supplied by multiple vendors increases. With no separate signaling or session framework, IOTs must be performed at every existing node when a new node or software load is placed in service. IOT activities require a considerable amount of operator time and resources, with costs increasing in proportion to the number of tests that must be performed.

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• Support for both SCTP- and transmission control protocol (TCP)-based implementations: SCTP-based elements cannot communicate with TCP-based elements unless they are upgraded or all of the elements support both protocol stacks.

• Subscriber to HSS mapping: When there are multiple HSSs in the network, subscribers may be homed on different platforms. Therefore, there must be some function in the network that maps subscriber identities to HSSs. With no separate Diameter signaling infrastructure, that task could be handled by the HSS. This approach wastes HSS and possible MME (or call session control function [CSCF]) processing, can add unnecessary delays, and may even result in the need for more HSSs than would otherwise be necessary.

• Policy and charging rules function (PCRF) binding: When multiple PCRFs are required in the network, there must be a way to ensure that all messages associated with a user’s particular IP connectivity access network (IP-CAN) session are processed by the same PCRF.

Diameter Signaling Router Overview

Tekelec’s Diameter Signaling Router (DSR) creates a centralized core Diameter signaling layer that relieves LTE and IMS endpoints of routing, traffic management and load balancing tasks and provides a single interconnect point to other networks. Each endpoint only needs one connection to a DSR to gain access to all other Diameter destinations reachable by the DSR. This approach eliminates the Diameter/SCTP (or TCP) mesh that is created by having direct signaling connections between each network element. Having one or more SCTP hubs that centralize the SCTP connection to all end nodes simplifies interoperability between different network elements and enhances network scalability. The resulting architecture, which reduces the cost and complexity of the core network, enables IP networks to grow incrementally to support increasing service and traffic demands. It also facilitates network monitoring by providing a centralized vantage point in the signaling network.

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Benefits

• Improves signaling performance and scalability by alleviating issues related to the limited signaling capacity of MMEs, HSSs, CSCFs and other Diameter endpoints

• Simplifies network expansion because routing configuration changes for new endpoints are performed only on the DSR

• Increases reliability by providing geographic redundancy

• Provides mediation of Diameter variants to support interoperability between multi-vendor endpoints

• Creates a gateway to other networks to support roaming, security and topology hiding

• Reduces provisioning, maintenance and interoperability testing costs associated with adding new network nodes

• Enables HSS routing flexibility with integrated HSS address resolution function

• Creates a centralized monitoring and network intelligence data collection point to isolate problems and track key performance indicators (KPIs)

• Provides network wide PCRF binding to ensure that all messages associated with a user’s particular IP-CAN session are processed by the same PCRF

This handbook explores six use cases that demonstrate the applications and associated benefits of Tekelec’s DSR in IMS and LTE networks:

• Centralized Routing

• LTE Roaming

• HSS Address Resolution

• LTE-to-2G/3G Roaming

• Centralized/Integrated Monitoring

• PCRF Binding

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USE CASE 1: CeNTRAlIzeD ROuTINg

Problem Operator A, a large mobile operator, deployed an LTE network to increase bandwidth, lower costs and improve performance of data-enabled applications. The operator has experienced significant growth in its subscriber base and needs to expand its network with new MMEs and HSS front ends. The addition of the new resources is presenting a challenge. Diameter protocol,

which uses SCTP for transport, interconnects many of the network elements in the operator’s evolved packet core (EPC). Each Diameter-based element must have a direct SCTP association with every element to which it is connected, creating a logical mesh network. As a result, the addition of new resources requires configuration and routing updates at each and every network element.

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vSGSN

vS4-SGSN

Foreign LTE Domain Foreign GPRS Domain

Home LTE/IMS Domain

OFCF

OCF

ABMF

RFMME PCRF

P-CSCF I/S-CSCF

AF

IP-SM-GW

DiameterAgent

vPCRFvMMESS7

DiameterAgent

DSR

FIguRe 1. Centralized Routing

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SolutionWith Tekelec’s DSR, Operator A can decrease the cost and complexity of its core LTE network. The DSR serves as a Diameter relay, thereby reducing the number of SCTP associations in the network and offloading Diameter routing tables and routing-status maintenance from the end nodes. The MMEs connect to a mated pair of DSRs, which interface to the HSS front ends and to other networks. When Operator F deploys new MMEs or HSS front ends, routing updates are required only at the DSR.

Benefits:• Reduces the complexity and improves the scalability

of the core LTE network

• Lowers OPEX by simplifying provisioning and updates

• Creates a more flexible architecture


USE CASE 2: lTe ROAmINg

Problem Operator B, a global operator, has encountered a problem when its LTE subscribers roam into foreign LTE networks. Because the LTE network has no core routing layer, there is no centralized interoperability point from which to manage the handoffs to other networks, and the endpoints must take on all traffic and routing management tasks. This set-up not only burdens the endpoints, but also creates potential security threats. Because there is no network demarcation point, the operator has no way to hide its topology or effectively secure the network.

SolutionBy deploying Tekelec’s DSR, Operator B can create a single interconnect point to other networks. The DSR consolidates all incoming and outgoing network traffic and handles the management tasks associated with roaming handoffs. As the first point of contact at the network’s edge, the DSR provides a centralized vantage point from which the operator can defend against potential overloads or attacks.

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HSS FE HSS FE

MME MME MME

Roaming HubProvider

Operator_N

MME

Operator_3

MME

Operator_N+1

MME

Operator_2

MME

DSR

DSR

DSR

DSR

DSR

HSS FE HSS FE

HSS FE HSS FEHSS FE HSS FE

DSR

FIguRe 2. lTe Roaming


Benefits• Increases network security and hides

network topology

• Simplifies routing and interconnection to other networks


USE CASE 3HSS ADDReSS ReSOluTION

ProblemOperator C plans to deploy new HSSs in its LTE network but has encountered an issue. With the addition of new HSSs, the operator’s subscribers will be homed on different platforms. Unlike IMS, there is no subscription locator function (SLF) in the LTE architecture that maps subscribers to HSSs. As a result, Operator C must find a cost-effective solution to provide and maintain those associations.

SolutionThe DSR centralizes routing data and provides the mapping between a subscriber identity (e.g., MSISDN, IMSI) and an HSS. This flexibility enables Operator C to easily move subscribers from one HSS to another. With the DSR, subscriber number ranges can be split over different HSSs and individual subscriber numbers can be assigned to any HSS.


DSRMME

Benefits• Simplifies HSS provisioning by centralizing

routing data

• Enables dynamic updates as new HSS are placed in service

FIguRe 3. HSS Address Resolution


USE CASE 4 lTe-TO-2g/3g ROAmINg

ProblemOperator D deployed an LTE network and provided its subscribers with multi-mode handsets. Since many of its roaming partners have not deployed LTE, Operator D’s subscribers are encountering problems when they roam in 2G/3G networks because of the disparity in protocols used to manage mobility. Mobile application part (MAP) protocol is used in

2G/3G networks as the interface between nodes such as serving GPRS support nodes (SGSNs) and home location registers (HLRs) for mobility management and authentication. In LTE, MAP has been replaced with the Diameter protocol. To support seamless roaming and handoffs between LTE and 2G/3G networks, Operator D needs a function to interwork the two protocols.


SolutionThe DSR, serving as a gateway to other networks, provides the Diameter/MAP interworking function to enable seamless subscriber roaming. Along with message mapping, the DSR provides mapping between SS7 addresses/point codes and diameter node IDs. This allows Operator D to support seamless roaming and handoff between LTE and 2G/3G networks.

Benefits• Simplifies network migration to LTE

• Supports seamless 2G/3G roaming

IPSS7

DiameterUpdateLocation

vSGSN

MAPUpdateLocation

DSR

FIguRe 4. lTe - to - 2g/3g Roaming


USE CASE 5CeNTRAlIzeD/INTegRATeD mONITORINg

Problem After launching an LTE network, Operator E has discovered that the shift from delivering low- bandwidth voice services to advanced data applications has dramatically heightened the complexity of network management. Tracking which subscribers use the network and what services

they are accessing is much more complicated than in the circuit-switched domain. The operator’s legacy monitoring system does not have the flexibility to provide real-time subscriber and service data or the end-to-end transaction visibility required to pinpoint anomalies and understand the customer experience.


LTE

eNodeBX2

S16

Sv, SGs

S4

S2

S8

Iu

MSC

PLMNS

S4SGSN

MMEEIR

— Diameter signaling— User data path— Control plane only • Probe based interfaces

S11S10

eNodeB

S1-US12

IMS

WLAN GPRS/EDGE 3G/UMTS

ePDG

DSR

PDN GW

GRX/IPX

PCRF

AAAServer

SWa

Gb

S1-C

Serving GW

Gy

GzGy, Gz, Gx

Rx,Cx,Dx,Sh,S9Gx,Rx,S9

SWx,SWa,SWm

S6SWx

S13

IP Networks

SGi

S3S6dSWm

S5

S6a,S13

FIguRe 5. Centralized/Integrated monitoring


SolutionBecause Tekelec’s DSR consolidates incoming and outgoing Diameter signaling traffic, it provides the perfect vantage point from which Operator E can collect network traffic and subscriber data for troubleshooting, managing traffic, roamers, services and revenue. By coupling the DSR with Tekelec’s Performance Intelligence Center (PIC) the operator has a complete multiprotocol, network-wide monitoring solution that collects and filters real-time network, service and subscriber data and converts it into useful business intelligence. The tight integration between the DSR and PIC simplifies provisioning and system use. Any modifications made to the DSR, such as the addition of new endpoints, automatically flow through and are configured in the PIC.

Benefits• Improves quality of experience (QoE) and QoS

• Prevents fraud and revenue loss

• Provides a single platform for collecting data from virtually every network type, including: VoIP, UMTS/WCDMA, WiMAX/LTE, GPRS, Internet, GSM and TDM

• Supplies real-time and historical network data usage that can be used for trending, tracking, tracing, surveillance and performance management


SolutionThe Tekelec DSR provides the diameter routing agent (DRA) proxy function defined for policy by 3GPP. It supports static binding or dynamic load sharing across PCRFs when IP-CAN sessions are first established. The DSR will ensure that subsequent messages over the Gx, S9, Gxx or Rx reference points are sent to the same PCRF. Additionally, the DSR will extend this functionality across multiple DSRs in Operator F’s network, which communicate with each other to act like a single, logical DRA.

USE CASE 6PCRF BINDINg

Problem Operator F is planning to deploy multiple policy and charging rules function (PCRF) elements in its network for scalability reasons. Operator F needs a way to balance the assignments of user IP connectivity access network (IP-CAN) sessions to PCRFs and to make sure subsequent messages are handled by the same PCRF. These messages can arrive on different interfaces (for example Gx and Rx) and may be identified by different elements, such as IMSI and IP address.


PCRF

To/From OtherNetworks

MME

IPX

GatewayDSR

MME

PCRF

S6S6

DSR

S6 S6

DSR

P-CSCF

PGW/HSGW

Gx.Gxx

Rx

Gx.Gxx

Rx

DSR

DRA

DSR

DRA

P-CSCF

PGW/HSGW

DRMA

Region1

Region 2

FIguRe 6. PCRF Binding


Benefits• Enables PCRF scalability

• Solves network-wide PCRF binding problem

• Can be integrated with other, non-policy proxies and core and/or edge relay agents

About TekelecTekelec, the broadband data management company, enables billions of people and devices to surf, talk, and text. Our solutions allow service providers to give consumers a consistent and tailored broadband experience. We handle network complexity with a portfolio that manages and capitalizes on the exponential growth in data applications and traffic. Tekelec has more than 25 offices around the world serving customers in more than 100 countries.


Appendix: Acronyms used in this document

3GPP Third Generation Partnership Project

CSCF Call session control function

DRA Diameter routing agent

DSR Diameter signaling router

EIR Equipment identity register

ENUM E164 number mapping

EPC Evolved packet core

GPRS General packet radio service

GSM Global system for mobile communications

HLR Home location register

HSS Home subscriber server

IMS Internet protocol multimedia subsystem

IMSI International mobile subscriber identity

IOT Interoperability testing

IP Internet protocol

LTE Long term evolution

MAP Mobile application part

MME Mobility management entity

MSISDN Mobile subscriber integrated services digital network

PCRF Policy and charging rules function

PIC Performance Intelligence Center

QoE Quality of experience

QoS Quality of service

RAN Radio access network

S-CSCF Serving call session control function

SGSN Serving GPRS support node

SLF Subscription locator function

SCTP Stream control transmission protocol

SSR SIP signaling router

TCP Transmission control protocol

TDM Time division multiplexing

UMTS Universal mobile telecommunications system

WCDMA Wideband code division multiple access

WiMAX Worldwide interoperability for microwave access

© 2010 Tekelec. All rights reserved. Printed in U.S.A. TKLC-HB-004-07-2010

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