b2bua – a new type of sip server
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
B2BUA – A New Type of SIP Server
Name: Stephen Cipolli
Title: System Architect
Date: Feb. 12, 2004
PSTN IP
VoIP NetworksVoIP Networks
SIPH.323
MEGACO MGCP
IP-PBXIP-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)
IP-PBXTraditional PBX + Gateway
IP-PBXTraditional PBX + Gateway
PBX
MG
SIP
SIPGateway
RTP
IP-PBXPBX supporting IP-based Phones
IP-PBXPBX supporting IP-based Phones
PBX
MG
SIP
PSTN
RTP
IP PBXIP-based Phones/Decoupled Media
IP PBXIP-based Phones/Decoupled Media
IP PBX
MG
SIP RTP
SIP
Analog
IP-PBXDecoupled Media + Proxy/Gateway
IP-PBXDecoupled Media + Proxy/Gateway
IP-PBX/Proxy
MG
SIPRTP
SIP
PSTN
Gateway
B-Channels
D-Channels
Peer-to-Peer Call ControlPeer-to-Peer Call Control
User Agent 2
IP
User Agent 1
ProxyInviteInvite
LocationDB
B2BUAB2BUA
?
Types of IP-PBXsTypes 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)
Stimulus-based SignalingStimulus-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
IP PBXStimulus-based Signaling
IP PBXStimulus-based Signaling
IP PBX
MG
MGCP
Off-Hook
Digits
Play Dialtone
Create Media
RTP
Session-based Signaling: Peer-to-Peer
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
SIP ServersSIP 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.
SIP ProxySIP Proxy
User Agent 2
IP
User Agent 1
ProxyInviteInvite
LocationDB
SIP RedirectSIP Redirect
User Agent 2
IP
User Agent 1
Redirect
Server
Invite
Invite
“Contact this address”
LocationDB
Session-based Signaling:Centralized Control (B2BUA)
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)
SIP B2BUASIP 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.
SIP Servers at WorkBack-2-Back UA Transparent
SIP Servers at WorkBack-2-Back UA Transparent
User Agent 2
Response
IP
User Agent 1
SIP
Requ
est
Request
Resp
onse
B2BUA
UAS Dialog created
UAC Dialog created
SIP Back-2-Back UA at Work – Third Party Call Control
SIP Back-2-Back UA at Work – Third Party Call Control
User Agent 1
200 no media
IP
User Agent 2
INV no mediaB2BUA
B2BUA acts as 3PCC to create
call between UA1 & UA2
INV no SDP
200 SDP1INV SDP1
200 SDP2ACK SDP2
ACK
Call between
UA1 & UA2 connected
RTP
ACK
SIP B2BUA UsesSIP 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)
Stimulus-based Signaling(MGCP & MEGACO/H.248)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
Session-based Signaling:Peer-to-Peer Model
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”
Session-based Signaling:Centralized Control Model (B2BUA)
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
SummarySummary
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