1. Siptrex Scalable IP Centrex http://www.siptrex.net Elias C. Efstathiou, efstath@aueb.gr Joint work with Rob Dupuis, Usman Arshad and Alejandro Flores at Department of Computer Science, University College London, 2001.

2. Siptrex.net Motivations VoIP maturity –Codec standardisation –Converged carriers Popularity of service outsourcing –ASP model –Centrex services

3. Siptrex.net Overview Platform for IP telephony services –Distributed –Scalable –Fault tolerant Enabling technology –Session Initiation Protocol (SIP) –Java API for Integrated Networks (JAIN)

4. Siptrex.net Objectives To utilise commodity components –Standard PCs running Windows / Linux –Cheap commodity Ethernet infrastructure To design and implement a scalable architecture –Load balanced –Fault tolerant –“Hot Pluggable” –Versatile

5. Siptrex.net Objectives (cont’d) To provide a Java API for service development –Low level API for fine grained control –Higher level API for rapid service deployment To develop telephony services –Traditional –Innovative

6. SIP – RFC 2543 Text-based signaling protocol (it does not care about things like RTP and it does lot more than just VoIP). Similar to HTTP. May also use UDP as transport. Defines the SIP URL notion: –sip:efstath@aueb.gr –Elias Efstathiou –Only one SIP URL per person? What about private numbers? SIP Messages = SIP-Requests | SIP-Responses

7. JAIN SIP API “Standard” Java Interfaces to SIP. Protocol-level API. SIP transaction-oriented (not call-oriented). The Siptrex stack implemented most of it. Lies between the stack and apps such as SIP servers and UAs. Nice way to look at SIP. Streamlines things - especially the headers. The Siptrex stack reuses the NIST SIP Parser Current JAIN SIP version has design flaws. Siptrex solved several.

8. Siptrex.net Call API Our own “higher-level” interface. The Siptrex UA uses it. Call-oriented API, similar to JTAPI and JAIN SIP Lite. Lies between JAIN SIP API and the Siptrex User Agent. Makes it easier to construct JAIN SIP Messages. Makes it easier to use services. Core notions: CallProvider, CallListener. Defines a CallProvider state model and a call state model. Siptrex Call API implementation uses JMF for RTP.

9. Layered Depiction of the Siptrex.net Components Siptrex Stack MessageCentre Siptrex JAIN SIP implementation Siptrex Call API implementation Siptrex UdpNetworkCentre Load Balancing Component UA registration SIP User Agent (UA) Application JAIN SIP API Siptrex Call API

10. Siptrex.net 2001 PBX Services Siptrex.net 2001 supports: –Two-party calls (call, talk, hang-up) –Call waiting –Call hold/unhold –Presence information (through a buddy-list) Siptrex.net 2002 will support: –Call Transfer –Conference Calls –Call Pickup –Call Forwarding

11. Siptrex.net Issues Forking made the stack a bit more complicated. Load balancing affects basic operation? Hotmail-like road-warrior applet-usage scenario unrealistic? Gateway to the PSTN: –Use Cisco’s SIP Gateway? –Support SIP-to-SIP intra-domain and inter-domain calls, support PSTN-to-SIP calls, support SIP-to-PSTN calls. Logging and Billing. Scalability, Voice QoS and Security?

12. Thank You – Useful Links www.siptrex.net www.cs.columbia.edu/~hgs/sip/ www.dynamicsoft.com www.ubiquity.net www.sipcenter.com www.sipforum.org www.vovida.org/vocal/