SIP Signaling Router (SSR) Use Cases · sion control layer at the core of the NGN. From a signaling...

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APPLICATION GUIDE

Signaling Router (SSR) Use Cases SIP Using SIP to improve network performance and deliver advanced services

This document is for informational purposes only, and Tekelec reserves the right to change any

This application guide discusses how operators can use a SIP Signaling Router (SSR) to solve many of their next-gen network challenges.

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aspect of the products, features or functionality described in this document without notice. Please contact Tekelec for additional information and updates. Solutions and examples are provided for illustration only. Actual implementation of these solutions may vary based on individual needs and circumstances. © 2009 Tekelec. All rights reserved. The Tekelec logo is a registered trademark of Tekelec. All other trademarks are the property of their respective owners. TKLC-AG-001-NA-01-2009

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Table of Contents Introduction.............................................................................................................................................1

.............................1

.............................1

1

Use Case 2: SIP Trunking........................................................................................................................4

6

.............................7

.............................9

Summary................................................................................................................................................11

About Tekelec........................................................................................................................................11

Appendix – 1: Acronyms used in this document.................................................................................12

The Challenge.............................................................................................................

Session Initiation Protocol (SIP) Signaling Router ...................................................

Use Case 1: Enhanced Application Server .............................................................................................

Use Case 3: SIP Number Portability.......................................................................................................

Use Case 4: Centralized SIP Routing .........................................................................

Use Case 5: Specialized SIP Proxy..............................................................................

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SIP Signaling Router (SSR) Use CasesUsing SIP to improve network performance and deliver advanced services 1

Introduction The appeal of next-generation, voice over Internet protocol (VoIP) networks is compelling for oDeployments cut across all types of telecom operators – from the largest incumbents to the smallProviders see VoIP and session initiation protocol (SIP)-based services as an opportunity to cut thand boost their bottom line with new rev

perators worldwide. est regional players.

eir operating expenses enue. Delivering VoIP and SIP services to consumer and enterprise customers

enables providers to expand their subscriber base. And, SIP facilitates the interworking of real-time applications with

etwork to support it. Many operators are discovering that their current next-generation networks (NGNs) are based on an outdated, voice-

architecture, which does not support multimedia services, access independence, backward network

, which are hierarchical, sion control layer at the core of the NGN. From a signaling perspective, each

tasks such as routing, traffic management, redundancy and service implementation. All possible routes must be defined at each node, creating a logical mesh-

d signaling tasks

itiation Protocol (SIP) Signaling Router reates a signaling and

twork. The SSR enhances on management duties.

emand for VoIP and

es with 3rd Generation Partnership Project (3GPP) specifications and offers adaptations for GPP-compliant IP environments. It provides seamless interworking and creates an evolution

gies such as IMS, long term evolution (LTE) and WiMAX.

e applications and associated benefits of deploying Tekelec’s GN networks. They include:

SIP proxy

Use Case 1: Enhanced Application Server Problem

voice and video to create new, multimedia services.

However, as VoIP and SIP traffic and applications grow, so do the requirements placed on the n

centric, softswitchcompatibility or network growth.

The Challenge Unlike signaling system 7 (SS7) and Internet protocol multimedia subsystem (IMS) networksthere is no separate signaling and sesNGN network element must handle all application-layer related

network, routing architecture. Expanding the NGN without a framework that offloads session anfrom the edge elements is complex and costly.

Session InTekelec’s SIP Signaling Router (SSR) solution, a SIP proxy with enhanced routing capabilities, csession control framework for NGNs by implementing SIP routing functionality in the core nerouting capabilities and increases service and network flexibility by relieving endpoints of sessiThe resulting architecture allows the NGN to grow systematically in response to increasing dmultimedia services.

The SSR solution compliinterworking with non-3path to future technolo

This paper explores five use cases that demonstrate thSSR in N

Enhanced application server selection SIP trunking SIP number portability Centralized SIP routing Specialized

:

The operator, DanTel, provides VoIP services to small enterprise customers, using a SIP enterprise application server (AS) and SIP phones. The SIP AS provides voice features such as “find-me, follow-me” and simultaneous ring. Each subscriber must be identified and registered on the SIP AS platform. Prior to shipping, DanTel configures each SIP phone with the address of the SIP AS, which is “voipsvc.dantel.com.” The SIP phone uses this address for registration and to make voice calls.

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Application Guide - © 2009 Tekelec, Inc.

VoIP ASVoIP ASHosting SubscriberA through Z

Address =voipsvc.dantel.com

DanTel IP Network

voipsvc.dantel.com

voipsvc.dantel.com

voipsvc.dantel.com

voipsvc.dantel.com

voipsvc.dantel.com

voipsvc.dantel.com

voipsvc.dantel.com

voipsvc.dantel.com

voipsvc.dantel.com

voipsvc.dantel.com

voipsvc.dantel.com

voipsvc.dantel.com

Figure 1: Subscribers are identified a

nd registered on the SIP AS platform.

DanTel has developed a solid reputation for its service quality, and its subscriber numbers have grown significantly. To support current and future growth, the company deploys three additional application servers, each with its own address. Subscribers are now distributed among four application servers.

Sub A - FSub A - F

voipsvc1.dantel.com

Sub G - MSub G - M

voipsvc2.dantel.com

Sub N - SSub N - S

voipsvc3.dantel.com

Sub T - ZSub T - Z

voipsvc4.dantel.com

DanTel IP NetworkDanTel IP Network

Figure 2: How can DanTel easily map subscribers to the application servers?

This new configuration poses a number of problems. With four application servers in the network, how does the SIP phone know which AS to request? And, since the SIP AS address is configured on the SIP phone, each time a customer is assigned to another application server, the address programmed on the SIP phone must be reconfigured.

From a technical perspective, the problem is the result of a “tight” coupling between the SIP endpoints – the SIP phones – and the SIP AS. Any changes to the physical network, such as adding a new application server, have a direct impact on the way the SIP phones access a service. As a result, complex provisioning is increasing operational costs, and quality of service is being impacted by service disruptions due to provisioning errors. DanTel needs a solution that will allow the company to:


Manage growth without sacrificing quality of service. Make changes to its application server assignments without reconfiguring the phones that are already in

service.

Solution:

DanTel deploys the SSR solution in its network to shield the endpoints from changes in the pa process called “abstraction,” the phones are decoupled from direct knowledge of the complenetwork. The SIP phones jus

hysical network. Through x and changing

t have to be configured with a single abstract address – “voip.dantel.com.” Endpoints P AS platform and routes

Since the endpoint only deals with an “abstract view” of the network, it is not impacted by changes in the physical network such as adding a new application server. Regardless of changes in the SIP AS topology, the address on the SIP phone remains the same, and no re-configuration is necessary.

send requests to the SSR, which resolves the “voip.dantel.com” address to the appropriate SIthe request to that platform.

Sub A - FSub A - F

voipsvc1.dantel.com

Sub G - MSub G - M

voipsvc2.dantel.com

Sub N - SSub N - S

voipsvc3.dantel.com

Sub T - ZSub T - Z

voipsvc4.dantel.com

Request to “voip.dantel.com”

Consult internal routing policy – A number

directed routing

Forward the request to correct AS platform

where Nick is assigned

Nick

SSRSSRSSRSSR

in the physical network.

Benefits:

Figure 3: Endpoints are shielded from changes

By deploying the SSR solution, DanTel:

Creates a flexible architecture free of endpoint constraints. Saves capital costs by simplifying subscriber management and maximizing the efficiency of application servers

through load sharing and flexible subscriber management. Can explore different business models such as using third-party, hosted services. Creates a foundation for multimedia services.

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Use Case 2: SIP Trunking Problem:

LinTel is a long-distance (LD) operator that provides service to local phone companies. The comppoints of presence (POPs) conveniently located near the networks it serves.

any has a number of The local phone companies provide service

to ent rprise customers via primary rate interfaces (PRIs) to private branch exchanges (PBXs).

.

s directly to enterprise the “middle men,” the local phone companies. With

SIP trunking, LinTel can enable business customers with IP PBXs to use their Internet connection to provide “off-net” ia services to its

Provide enterprise voice service imme ately while laying the foundation for future multimedia SIP services. Maintain low start-up cost without co romising the long-term plan.

The company could implement a softswitch-based solution, but that alternative has a number of disadvantages. Since it is based on a “per connection” cost model, the approach can become costly very quickly. The softswitch-based model is voice centric and may not be suited to delivering multimedia services. Softswitch implementations usually are deployed with the switch vendor’s choice of application server, so it is difficult to gain the economy of a “best-of-breed” solution.

e

Figure 4: LinTel provides service to local phone companies

With deregulation, LinTel decides to enter the local service market and offer fixed-line servicecustomers. LinTel can deliver substantial savings by cutting out

service. In addition to voice services, LinTel wants to create a foundation for delivering multimedenterprise customers in the future.

LinTel faces several challenges and needs a solution that will enable the company to:

dimp


or “off-net” services. Figure 5. SIP trunking enables enterprise customers to use their Internet connection f

Solution:

By implementing Tekelec’s SSR solution, LinTel can use a session-based approach, which balances cost and flexibility. The SSR creates a SIP signaling and session control layer that routes on-net calls (IP PBX to IP PBX) over the VoIP network, off-net local calls (IP PBX to local numbers), and off-net long-distance calls (IP PBX to long-distance numbers). A PSTN gateway handles IP PBX to public switched telephone network (PSTN) calls.

Figure 6: SSR creates a SIP signaling and session layer to route on- and off-net calls.

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In the process, the company also creates a framework that complies with Internet Engineer3GPP standards for the delivery of multimedia services. The solution enables Lin

ing Task Force (IETF) and Tel to create a volume-based cost

re and reduces costs by allowing the company to select “best-of-breed” application servers. structu

Benefits:

With the SSR solution, LinTel can compete with local telephone companies by offering SIP trunking to enterprise

Saving money by maximizing the capacity of application servers through load sharing and flexible subscriber

Creating a SIP peering point to interconnect with other VoIP providers.

customers. The company receives additional benefits that include:

Laying the foundation for multimedia services.

management.

Use Case 3: SIP Number Portability Problem:

LinTel, an LD operator, entered the local calling service market by deploying Tekelec’s SSR solutitrunking infrastructure. LinTel is an operator in the call routing sequence immediately prior to operator. So, it’s customary for LinTel to perform number portability, or NP service, for VoIP calls from theitrunking service. The company could simply “dump” calls onto the PSTN gateway and use its exi

on to build a SIP the terminating

r SIP-sting time division

multiplexing (TDM)-based, number portability solution to route calls to the correct network. However, to do so, there must be adequate intelligent network capacity to handle the increased traffic, and the terminating network must be TDM If the terminating number is an IP PBX or belongs to another VoIP provider, the call must be shuttled from VoIP to TDM and back to VoIP again. Running pure VoIP calls over the TDM network to perform NP wastes capacity on the PST gateway and degrades voice quality.

Figure 7: Calls destined for a VoIP provider or IP PBX must be routed over the TDM network.

Solution:

.

N

LinTel could replicate an NP solution in its SIP domain, but that is an expensive approach. A more cost-effective and efficient method is to make the TDM-NP solution available to the SIP network. The TDM-NP database can be accessed using the SSR’s SS7 access feature. This capability allows the SSR to augment its routing capabilities with data from the SS7 domain. The SSR provides NP services to the SIP domain in one of three ways:


Number portability corrected forwarding proxy: The SSR receives a request from an ori(UA) such as an IP PBX. The

ginating user agent SSR performs the NP function and then forwards the request to the appropriate

SSR, which performs e SSR then sends a SIP redirect message to the UA

that instructs the UA to forward the request to the appropriate destination. Number portability corrected forwarding application server: After receiving a request from the originating UA,

t with the destination ion and sends it back to the originating UA. The UA the appropriate SIP

Figure 8: SSR accesses TDM-NP database using SS7 access feature.

Benefits:

SIP endpoint for call completion. Number portability corrected redirect server: The originating UA sends a request to the

the NP function to determine the endpoint destination. Th

the SSR performs the NP processing to locate the called number. It modifies the requesinformat n proxies the call to the endpoint.

Since NP is deployed through a standard SIP framework, the approach can be used in the next-gen network

arency is maintained, so the NP solution can be applied to voice service AND any

ased applications like

outing m:

as well as a future IMS network. End-to-end media transp

other type of multimedia service such as a video or IPTV. The SS7-access feature used for the NP application also supports access to other SS7-b

calling name, toll-free and message-waiting indicator.

Use Case 4: Centralized SIP RProble

ators. The company ts. Softswitches, which

hout Southeast Asia in a fully meshed framework. Every switch must be defined in the translation table of every other switch.

AsiaTel, a hub provider, offers voice transit and signaling services to fixed-line and mobile operdeployed softswitch technology to take advantage of lower Internet protocol (IP) transport cosserve as POPs, are installed throug

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POP

SIP ClientTDM Client

TDM Client

TDM Client

TDM Client

TDM Client

TDM Client

TDM Client

TDM Client

TDM Client

AsiaTel Network

Voice

Multi-media

Text

SSSSPOP

SSSSPOP

SSSSPOP SSSSPOP POPSSSS

POPSSSS

POPSSSS

POPSSSS POPSSSSPOPSSSS POPSSSS

Figure 9: Softswitches, serving as POPs, form a fully meshed architecture.

so plans to enhance its d, it would like to provide SIP

ing the network s complex as each new piece of

s for all of the existing softswitches. And, the existing r the new equipment. Since routing is based on pre-defined

complex as the network expands. Service and subscriber data are ew applications uniformly.

eep network operation costs low. Offer voice and non-voice services AND reduce capital costs.

deploy multiple, “point” solutions, which increase long-term CAPEX and OPEX. However, if AsiaTel took a holistic view of the network, they would see that they are, in fact, all related. A piecemeal approach will not address the challenges because solving one problem likely exacerbates another.

Solution:

AsiaTel would like to expand its network to serve other Asian markets. The company alportfolio by offering transit services for text messaging and multimedia applications. Anpeering as an alternative to TDM to other VoIP providers.

The new business plan presents a number of issues for the meshed, softswitch network. Expandrequires the addition of new softswitches to increase capacity. Provisioning iequipment must be provisioned with the routing entriesoftswitches must be updated with the routing entries foSIP trunks, route management becomes increasinglytightly coupled with the softswitch, making it difficult to change an existing service or add n

AsiaTel must address several complex issues related to growing its network, including how to:

Expand its network AND k

Prevent degradation as media flows through its network.

Like many operators, AsiaTel views these as three, unrelated challenges. As a result, they

AsiaTel creates a SIP-based reference architecture over it existing network by deploying the SSR as a SIP proxy. With this approach, all calls are routed by default from the softswitch to the SSR. The SSR makes layer-5 SIP routing decisions based on advanced routing algorithms and forwards the request to the appropriate SIP destination.


POPSSSS

SIP Client

TDM Client

TDM Client

TDM Client

TDM Client

TDM Client

TDM Client

TDM Client

TDM Client

POPSSSS

SIP ClientSIP Client

POP

POP

POPSSSS

SIP Signaling

RouterSSSSPOP

SSSSPOP

SSSSPOP

TDM Client

POPSSSS

SIP Signaling

Router

POPSSSS POPSSSS

AsiaTel Network

rchitecture. Figure 10: SSR creates a SIP-based reference a

Benefits:

The company now has a centralized SIP signaling and session control framework that:

Acts as a route manager for all of the softswitches, relieving them of routing functions. here is no longer a need to provision translation tables on each and every

switch. Maintains end-to-end media transparency so the endpoints can communicate using any media – voice, text,

k.

Use Case 5: Specialized SIP Proxy Problem:

Eliminates the mesh network, so t

video, or data streaming. Preserves media quality because there is no decoding/encoding required in the networ

EuroTel is a provider of fixed and mobile services. The company maintains its operation as two, separate businesses – EuroTel Telecom and EuroTel Mobile. The fixed and mobile networks are loosely coupled through TDM peering. Each netw k “views” the other as a foreign network.

Figure 11: EuroTel’s network before consolidation.

or

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EuroTel wants to consolidate the networks and create a single operating entity – EuroTel – to rcosts. The company also plans to expand its offerin

educe its operating gs with integrated mobile and fixed services, mobility solutions for

e the opportunity to an lower the cost of

timedia services. EuroTel’s plan is to cap its existing TDM-based mobile switching centers (MSCs) and begin deploying SIP-capable mobile softswitches. Its strategy is to interconnect the mobile softswitches with the existing wireline SIP softswitches.

fixed-line enterprise customers and future multimedia services.

Since EuroTel already has some SIP deployments in its fixed-line network, it has decided to takupgrade its underlying wireless network technology to SIP as well. By doing so, the company cnetwork integration and create a future path for mul

MobileSoftswitch

Softswitch

MSC SMSC Switch

SCPSCPSCPSCP

VMVMVMVM

EuroTel

technology.

bile and landline t SIP implementations.

lem, but they gladly will provide a

EuroTel is caught in a situation called “vendor lock-in.” As long as the company deploys equipment from a single ere is no problem. But, when it introduces equipment from another vendor, interoperability problems arise.

f money for a “customized rced to purchase all of its equipment from a single vendor?

er vendors

Solution:

Figure 12: EuroTel connects mobile and wireline softswitches with SIP

However, EuroTel faces a problem common to many operators: different vendors supply the mosoftswitches. The softswitches are unable to establish sessions because the vendors use differenThe two vendors refuse to recognize the interoperability issue as a prob“customized solution” to EuroTel - if the company is willing to pay for it.

vendor, thThis situation creates significant challenges for the company.

How can it solve the interoperability issue without spending an excessive amount osolution” or being fo

How can the company avoid the same problem in the future as it brings new elements from othinto the network?

EuroTel deploys the Tekelec SSR as a protocol mediation point between the different vendor products. This approach creates an architectural solution that is indepe dent of the endpoints and eliminates interoperability problems. The SSR solution, which is deployed in the signaling layer, can be implemented in one of two ways: as an internal SSR feature or as an external application.

With the SSR solution, EuroTel creates a SIP-based, NGN reference architecture over its existing network. In this role, the SSR acts as a proxy server to route SIP traffic between the mobile and landline softswitches. It also forms a mediation point that “fixes” protocol variations on-the-fly between the softswitches.

n


between them.

Figure 13: SSR acts as a mediation point between softswitches and routes traffic

Benefits:

EuroTel now has the SIP signaling and session control framework that solves its immediate interoperability needs and:

undation for a multi-vendor environment and future multimedia services.

its expansion capabilities. ale network architecture.

t for fairly small session framework

ession framework that off-loads the various signaling and session tasks from the edge NGN elements orks to expand efficiently and avoids the pitfalls created by a point-to-point, virtual-mesh routing

P routing capability ent tasks at the

tically to support VoIP re technologies and

About Tekelec Found at the heart of most global networks, Tekelec’s market-leading, mission-critical, high-performance network solutions enable the secure and instant delivery of calls and text messages for more than one billion mobile and fixed-line subscribers. The company’s session management solutions allow telecom operators to manage the diverse applications, devices, technologies and protocols, across existing and evolving networks, to meet the demands of today’s consumer. Tekelec uniquely ensures telecom operators have a clear migration path to SIP-based IP networks, and whatever comes next, with the flexibility to deploy solutions at a pace dictated by their business needs. For more information, please visit www.tekelec.com.

Creates the fo Enables the company to choose “best-of-breed” products, avoiding vendor lock-in. Provides a centralized SIP monitoring point.

Summary The current NGN architecture has no core signaling/session framework, which greatly limitsHistory shows that the signaling and session control layer is critically important to any large-scHaving softswitches and other endpoints perform layer-5 session management may be sufficiendeployments and simple management tasks. But, as the network expands, the lack of a capable introduces a host of network issues.

A suitable senables NGN netwnetwork. Just as core routers are used to minimize the routing burden on IP endpoints, layer-5 SIcan be used to reduce the routing burden on NGN endpoints by centralizing session managemnetwork core instead of at each endpoint. The resulting architecture can expand systemasubscriber growth, deliver advanced multimedia services and create the foundation for futuservices.

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tion Partnership Program

e

ystem

otocol

rivate branch exchange

g center

on network

ence

erface

initiation protocol

SSR – SIP signaling router

TDM – Time division multiplexing

UA – User agent

VoIP – Voice over Internet protocol

Appendix – 1: Acronyms used in this document 3GPP – 3rd Genera

AS – Application server

IETF – Internet Engineering Task Forc

IMS – Internet protocol multimedia subs

IP – Internet pr

IP PBX – Internet protocol p

LD – Long distance

MSC – Mobile switchin

NGN – Next generati

NP – Number portability

POP – Point of pres

PRI – Primary rate int

SIP – Session

SS7 – Signaling session 7

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