An Application Component Architecture

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An Application Component Architecture for SIP
Jonathan Rosenberg Chief Scientist
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Building Complex Applications is Hard

• Auto-Conference Application
• Procedure
• Enter email addresses into a web form (1)
• Application subscribes to users (2)
• Notifications come as users come and go
• When all online, application sends each an IM
• For PSTN only users, it calls them and asks if
  now is OK
• Users indicate if now is OK
• Web click for PC users
• Say yes for phone users
• If now is good with everyone, the users are
  dropped into a conference call (3,4)

Conference Server
4
Application Server
2
Presence Server
1
3
3
Why is this hard?

• Many components
• Call control
• Conferencing
• IVR
• Messaging
• Web
• Instant Messaging
• Presence
• Database
• Different expertise domains for each component
• Varying end device capabilities
• Web enabled
• Voice enabled
• Small display

Web Setup
Authorize Service
Presence of Participants
Ask if its OK (IM, IVR)
Accept/Reject (Web, IVR)
Conference call
4
Big Idea I Components are Coarse Grained

• Coarse Grained Components
• Concrete start and stop
• Internal details not important
• Application dependent outputs
• Acceptance of conference call start
• Web form with email/phones of participants
• Authorization success/failure
• Some components are UI
• Define inputs/outputs independent of how
  component works
• UI Independence!!

Web Setup
addresses
Authorize Service
Yes/no
Presence of Participants
available
Ask if its OK
Accept/Reject
OK/No
Conference call
5
Big Idea II Isolate the Essence of the
Application

• Essence of the application
• Sequence of components
• Input/Output of each component
• Isolate this into a coordinator
• Application starts here
• Invokes components as needed
• Provides input to components
• Receives outputs of components
• Benefits
• Easy to completely change UI just invoke
  different component
• Easy to break application into pieces
• Each piece handles interaction with a component
• Servlets!

Web Setup
addresses
Authorize
Yes/no
Participant Presence
available
Coordinator
IM if OK?
Web Yes/No
OK/No
Conference call
6
Big Idea III Model Components as Resources

• Transactional Resources
• Short duration
• No prior establishment
• Discrete data in, discrete operation, discrete
  data out
• DB Authorization
• Session Resources
• Long duration
• Must be established and torn down
• Continuous interaction
• May have side channel for getting back results
  of interaction
• IVR, Conference servers
• Resources are identified by URIs
• HTTP for transactional resources
• SIP for session resources

C
S
C
S
7
Big Idea IV Third Party Control

• Problem
• Session Resources have a continuous interaction
  between entities
• Session resources accessed by controller
• But controller is not the entity in the
  continuous interaction!
• Solution Third Party Call Control
• Controller initiates session
• SDP in initiation is that of the device that
  needs to interact with the resource
• Allows controller to have any component
  continuously interact with any other!

INVITE
C
S
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Putting it All Together

• Components themselves can be controllers!
• Same interface between client and controller and
  controller and components
• Result an application component hierarchy
• Controllers use 3pcc to connect session resources
  to clients or other components
• HTTP critical for data input and output to
  components

Controller
Media Server
Conf. Server
Conf. Server
Media Server
HTTP
SIP
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Its Decomposition!

• What about MGCP/megaco?
• Alternate model
• Master Slave
• Differences
• Tight vendor and provider coupling
• Cant say no
• MS/Conf. Server USELESS by themselves
• No longer modular
• AS knows nitty details of all component functions
• Limited to voice and black phones that do DTMF
• Application and UI tightly integrated
• Difficult to reuse components
• Significantly more messaging!

Media Server
Conf. Server
Softswitch
MGCP
AS
Media Server
Conf. Server
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Media Server Component

• Media Server provides a dialog with an entity
• How can we specify the dialog?
• VoiceXML!!!
• What is it?
• XML based dialog language,
• Voice equivalent of HTML
• Dialog modeled as filling a form
• Form results HTTP POSTed
• Response to HTTP POST is next VoiceXML to run

lt?xml version"1.0"?gtltvxml version"1.0"gtltformgt
ltfield name"drink"gtltpromptgtWould you like
coffee, tea, milk, or nothing?lt/promptgtltgrammar
src"drink.gram" type"application/x-jsgf"/gtlt/fie
ldgtltblockgtltsubmit next"http//www.drink.example
/drink2.asp"/gtlt/blockgtlt/formgtlt/vxmlgt
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SIP, VoiceXML and HTTP the Eternal Golden Braid

• Controller INVITEs MS w/ SDP of user to interact
  with MS
• R-URI contains HTTP URL for VoiceXML script
• HTTP URL fetched back from AS
• Provides initial VoiceXML script to start dialog
• Voice form is filled out
• MS sends HTTP POST back to AS with result of form
• Same as if form filled out by web browser
• AS returns next VoiceXML script
• AS sends BYE when done

INVITE/200/ACK
RTP
HTTP GET
VoiceXML Doc
HTTP POST
VoiceXML Doc
BYE/200
AS
MS
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Conferencing Server Component

• Conference server provides a generic mixing
  service
• How do we know which devices to mix?
• Mixer is represented as a resource with a URI
• All calls to same URI are mixed
• Mixer context exists as long as calls are active
  for that URI
• More complex applications built by placing logic
  on the controller

INV/200/ACK sipa
Context created
X/-
INV/200/ACK sipa
Y/X
X/Y
BYE/200
BYE/200
Context destroyed
X
Y
Conf. Srvr
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Auto-Conference Once More
Media Server

• Web form with users POSTED to controller

Conference Server

• Controller initiates SUBSCRIBE session with
  presence server

• On NOTIFYs update presence

Application Server
Presence Server

• When all online
• Send IM to some with HTTP URL for accept

• Use 3pcc to connect others to MS

• MS fetches VoiceXML from AS

• HTTP POST of each accept/reject

Presence HTTP IM SIP Call

• Use 3pcc to connect each to same conference URL

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Information Resource

• Jonathan Rosenberg
• Chief Scientist
• 1 973.952.5060
• jdrosen_at_dynamicsoft.com

draft-rosenberg-sip-app-components-00.txt