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B2BUA – A New Type of SIP Server

B2BUA – A New Type of SIP Server. Name: Stephen Cipolli Title: System Architect Date: Feb. 12, 2004. PSTN. IP. VoIP Networks. H.323. SIP. MEGACO. MGCP. IP-PBX. What is an IP-PBX? Multiple definitions Traditional PBX + VoIP Gateway PBX supporting IP-based Phones

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B2BUA – A New Type of SIP Server

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

  2. PSTN IP VoIP Networks H.323 SIP MEGACO MGCP

  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. SIP IP-PBXTraditional PBX + Gateway PBX SIP Gateway RTP MG

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

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

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

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

  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 PBXStimulus-based Signaling IP PBX Create Media Digits Play Dialtone Off-Hook MGCP RTP MG

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

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

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

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

  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. 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 Stimulus-based Signaling(MGCP & MEGACO/H.248)

  23. 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” Session-based Signaling:Peer-to-Peer Model

  24. 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 Session-based Signaling:Centralized Control Model (B2BUA)

  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

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