SIP-based Mobilityin a future NGN-based Core Network

for TETRA-PMR-Systems Selected results of an R&D project funded by the Federal Ministry of Economics and Technology (BMWi), Germany

Rohde & Schwarz Professional Mobile Radio GmbHResearch Group IP-based Communications Systems, Ostfalia University of Applied Sciences

Daniel Hartmann, Xing Cao, Mark Stephan, Diederich Wermser

3rd NGN Workshop, TNO, DelftNovember 02, 2011 - November 03, 2011

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Research Group IP-based Communication SystemsVoice over IP, Multimedia over IPSession Initiation Protocol (SIP)Presence Service

NGN: IMS (IP Multimedia Subsystem), TISPANSoft-PBX: SipXecs, eZuce, Asterisk, FreeSWITCH

Quality-of-Service-Mechanisms (QoS)IntServ, DiffServ, MPLS, IPv6Routing, NAT„VoIP-Readiness“ AnalysisSecurity in VoIP-Systems

Testing of IP-based Communication SystemsConformity Tests, TTCN-3Interoperability TestsStress Tests

Development and Integration of Open Source SoftwareSelf developed Open Source Soft PBX Askozia®Adaption of Open-Source-Components for Embedded-Hardware-Solutions

Overview

1. Initial Situation - Today‘s TETRA

2. Approach for an NGN-based Core Network

3. Proof-of-Concept Implementation with SIPfoundry‘s sipXecs

4. Example for a TETRA-specific Feature: Push-to-Talk Group Call

5. Selected Aspects of Mobility Support

6. Conclusion

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TETRA Professional Mobile Radio System

Terrestrial Trunked Radio

Initial Situation

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Today‘s TETRA Architecture (simplified)

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BS: Base StationTDM: Time Division MultiplexLR: Location RegisterPSTN: Public Switched Telephone NetworkT-MS: TETRA Mobile Station

Approach for an NGN-based Core Network using VoIP

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Aspects of using other radio access networks (e.g. LTE)

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● Extend the coverage or provide redundancy

● Much higher bitrate on the air interface

● Challenge: Seamless handovers between both access networks

Quelle: Dahlman, Erik et al.: 3G Evolution.

„new“ TETRAcore network

??

Proof-of-Concept Implementation

Open Source SIP Service Orientated Architecture (SSOA)

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IMS Architecture (simplified)

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AS: Application ServerHSS: Home Subscriber ServerCSCF: Call Session Control FunctionMRF: Media Resource FunctionSG/MGCF: Signalling/Media Gateway Control FunctionMGW: Media Gateway

sipXecs as a Set of Building Blocks for the Core Network

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Source: Schumacher, Jan; Wermser, Diederich: VoIP-TK-Anlagen auf Basis von Open Source.

HSS CSCF

MRFMGW

AS

TETRA Group Call

An essential TETRA-Feature – Implemented as an Application Server

Push-to-Talk over Cellular (PoC)

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Examples to implement Floor Control:

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● Talk Burst Control Protocol (TBCP): In-band signalling

● Alternative: Floor Control with SIP-Mechanisms

Source: Lescuyer, Pierre; Lucidarme, Thierry: Evolved packet Systems (EPS).

Group Call Server Concept

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Application Server

Mobility Support

Selected Aspects

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Examples for Handover Scenarios

● handover w/o (1) or w/ (2) changing the Cluster Controller.

● „concurrent“ handover of severalmobile devices (3)

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IP-Layer Mobility in UMTS Release 5

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Source: Trick, Ulrich; Weber, Frank: SIP, TCP/IP und Telekommunikationsnetze.

TETRA-MS has noIP-stack, so mobilityhas to implementedon a different layer.

SIP-Layer Mobility for TETRA Core Networt (Concept)

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Before HandoverAfter Handover

Terminal Mobility in Idle Mode (Concept)

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Session Mobility (Concept)

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INVITE Replace (RFC 3891)

Outlook:Analysis of Interaction between Group Calls and Mobility Support

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Before HandoverAfter Handover

Conclusion

… and outlook.

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Conclusion and Outlook

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● Extend base stations with a gateway between the TETRA air-interface andthe new NGN-core.

● Mobility for TETRA mobiles can be provided by application layer mobilityusing SIP-based methods (SIP Presence, INVITE Replace).

● TETRA-specific features and services can be implemented by additional application servers ( IMS).

● Detailed Tests:– Performance, scalability, stress tests, high availability and redundancy.

● Integration of LTE into TETRA has to be investigated:– SRVCC (Single Radio Voice Call Continuity) „seamless“ Handover

Thank You!

Any Questions?

Contact:Daniel Hartmann Prof. Diederich Wermserd.hartmann@ostfalia.de d.wermser@ostfalia.de

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