1. B2BUA – A New Type of SIP Server Name: Stephen Cipolli Title: System Architect Date: Feb. 12, 2004

2. PSTNIP VoIP Networks SIPH.323 MEGACOMGCP

3. IP-PBX  What is an IP-PBX?  Multiple definitions Traditional PBX + VoIP Gateway PBX supporting IP-based Phones Decoupled Signaling and Media Server components for Peer-to-Peer Call Control Back-2-Back User Agent (B2BUA)

4. IP-PBX Traditional PBX + Gateway PBX MG SIP Gateway RTP

5. IP-PBX PBX supporting IP-based Phones PBX MG SIP PSTN RTP

6. IP PBX IP-based Phones/Decoupled Media IP PBX MG SIP RTP SIP

7. Analog IP-PBX Decoupled Media + Proxy/Gateway IP-PBX/Proxy MG SIP RTP SIP PSTN Gateway B-Channels D-Channels

8. Peer-to-Peer Call Control User Agent 2 IP User Agent 1 Proxy Invite Location DB

9. B2BUA ?

10. Types of IP-PBXs  Stimulus-based Signaling  Client/Server model  Intelligence is in the PBX  Phones are “dumb” devices  Centralized Call Control  Maps easily to Traditional PBX model  Session-based Signaling  True Peer-to-Peer Model (e.g. “Pure” SIP)  Centralized Control Model (e.g. SIP B2BUA)

11. Stimulus-based Signaling  Protocols  MGCP & MEGACO/H.248  Phones  Send events to PBX (e.g. Hook-state, button state, etc.)  Play tones on command from PBX (e.g. ring, busy, etc.)  Create/modify/destroy Media connections on command from PBX  PBXs  Manages Call state based on Phone events  Commands Phones to ring, play dial tone, etc.  Commands Phones to create/modify/destroy media connections

12. IP PBX Stimulus-based Signaling IP PBX MG MGCP Off-Hook Digits Play Dialtone Create Media RTP

13. Session-based Signaling: Peer-to-Peer  Protocols  SIP & H.323  Phones  Implement call control  Implement services (e.g. Transfer, Forward, …)  Implement Presence  “PBXs” are SIP Server components such as:  Proxy Server  Redirect Server  Registrar  Event Server/Presence Server

14. SIP Servers  The SIP specification defines a SIP server as “a network element that receives requests in order to service them and sends back responses to those requests”  Examples of SIP Servers:  Registrar Server– accepts user location messages (registrations) and updates a location DB  Proxy Server– forwards requests and responses Similar to a router, but at the SIP level  Redirect Server– returns “contact this address” response  SIP Events Server – Handles subscription requests (i.e. Presence) from watchers and notifies them of status change.

15. SIP Proxy User Agent 2 IP User Agent 1 Proxy Invite Location DB

16. SIP Redirect User Agent 2 IP User Agent 1 Redirect Server Invite “Contact this address” Location DB

17. Session-based Signaling: Centralized Control (B2BUA)  Protocols  SIP (H.323 has a similar capability)  Centralized Call Control  Similar to traditional PBX call control  Enables traditional (& non traditional) PBX services Transfer Conference Forwarding Etc…  Allows Third Party Call Control (3PCC)  Enables PBX to manage and track calls from beginning to end  Allows interworking with other networks (e.g. H.323)

18. SIP B2BUA  Back-to-back user agent (B2BUA)  Takes what is traditionally a SIP end-to-end call and mediates it through a central SIP server for the entire length of the call.

19. SIP Servers at Work Back-2-Back UA Transparent User Agent 2 Response IP User Agent 1 SIP Request Request Response B2BUA UAS Dialog created UAC Dialog created

20. SIP Back-2-Back UA at Work – Third Party Call Control User Agent 1 200 no media IP User Agent 2 INV no media B2BUA B2BUA acts as 3PCC to create call between UA1 & UA2 INV no SDP 200 SDP1 INV SDP1 200 SDP2 ACK SDP2 ACK Call between UA1 & UA2 connected RTP ACK

21. SIP B2BUA Uses  Call Center  Connecting inbound/outbound calls to free agent allowing monitoring, agent training and recording.  Prepaid  Allows third party to play mid-call announcements.  Allows third party to disconnect call  Create value added services  Call recording  Send a song/recorded message  Dating – IM/MMS -> call creation  Etc…  Traversal of NAT  Policy Servers (QoS)

22. Stimulus-based Signaling (MGCP & MEGACO/H.248)  Advantages  Simpler to Implement Phones Add feature  Model closer to traditional PBX model  Smaller footprint  Lower cost  Third-party Call Control  Disadvantages  Can’t be used end-to-end to phones not on PBX (need Peer-to-Peer protocols anyway)  Can’t take advantage of standardized advanced VoIP concepts Presence Instant Messaging

23. Session-based Signaling: Peer-to-Peer Model  Disadvantages  Complex to Implement Phones Add Features  Phones typically have larger footprints  No Third Party Call Control (3PCC) Support  Advantages  Advanced standardized end-to-end features Presence Instant Messaging Integration with Internet applications Proxy/redirect behavior Forking Etc.  Phones operate independently of centralized call control. Simplifies “PBX”

24. Session-based Signaling: Centralized Control Model (B2BUA)  Disadvantages  Complex to Implement Phones Implement PBX  Phones typically have larger footprints  Breaks end-to-end services of SIP  End-to-end security (S/MIME) will not work  Single point of failure  Introduces more load on the network B2BUA MUST stay in call signaling path Call statefulness requires more memory  Advantages  May take advantage of standardized features Presence Instant Messaging Integration with Internet applications Proxy/redirect behavior Forking  Third Party Call Control  Centralized Control of Services

25. Summary  There are many Roads to IP-PBX  Choices range from the traditional to the leading- edge  Different solutions provide different services and challenges  Standards-based solutions are well-defined across the range of choices

26. Thank You www.radvision.com scipolli@radvision.com