LESS effort, more services

1
LESS effort, more services

• Xiaotao Wu
• Henning Schulzrinne
• Dept. of Computer Science
• Columbia University

2
The Language for End System Services (LESS)

• Simple
• Based on CPL enhancement and extension
• Four kinds of elements trigger, switch, action,
  modifier
• Tree-like structure simplifies feature
  interaction analysis
• Safe
• Type safety XML-based, no user defined variables
• Control flow safety tree-like structure without
  back-reference
• No direct memory access
• Default behavior for every tree branch
• Handle user interactions and media operations
• Beyond call control
• presence, IM, Web, mid-call handling, location

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Supported services

• Services in ITU Q.1211
• ABD, ACB, CFC, CHA, QUE, CRG, OCS,
• Services in 5ESS switches
• Attendant camp-on, Automatic recall,
• Services in CSTA Phase III
• defined as signaling actions in LESS, e.g.,
  mediaupdate
• Location-based services
• location-switch
• Event-based services
• approve, deny, subscribe, notify
• Mid-call handling
• transfer, update media attributes
• Call queuing
• Other Internet services
• - mail, send IM

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LESS triggers

• incoming incoming call handling
• timer timer triggered actions
• UIcommand user interaction commands
• IMmessage incoming instant messaging
• Eventsubscription incoming subscription
• Eventnotification incoming notification

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LESS switches

• time-switch make decisions based on time
• address-switch make decisions based on caller,
  callee
• priority-switch make decisions based on call
  priority
• string-switch make decisions based on subject,
• language-switch make decisions based on
  languages
• status-switch make decisions based on users
  status (remote user or local user, status
  includes presence, activity, mood, , as listed
  in RPID)
• Eventevent-switch check values in event
  notifications
• LOCwhere-switch check users physical location
  information (remote or local user)
• LOCwhere-relation-switch check relative
  physical locations between two people

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LESS actions

• accept accept an incoming call
• reject reject an incoming call
• redirect redirect an incoming call
• authenticate authenticate an incoming request
• call make an outgoing call
• terminate disconnect a call
• wait wait for a certain time before next action
• mail send email
• log log request handling process
• Mediamediaupdate update media attributes
• Midcalltransfer transfer a call

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LESS actions

• Midcallmerge merge multiple calls
• UIalert alert user
• UIgetinput get user input
• IMsendmsg send an instant message
• Eventapprove approve subscription
• Eventdeny deny event subscription
• Eventdefer defer the decision on event
  subscription
• Eventsubscribe send subscription out
• Eventnotify send notification out
• Queueenqueue put a call and its context into a
  queue
• Queuedequeue get a call and its context from a
  queue

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LESS modifiers

• location to which a request to be directed
• lookup lookup locations from a source
• remove-location remove locations from location
  set
• Mediamedia provide media attributes

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Timer triggered outgoing call

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltless xmlns"urnietfparamsxmlnsless
• xmlnsIM"urnietfparamsxmlnslessim
• xmlnsxsi" xsischemaLocation"gt
• lttimer dtstart"20050307T110000Z"gt
• ltstatus-switch uri"sipbob_at_example.com"
• status-name"presenc
  e"gt
• ltstatus is"open"gt
• ltlocation url"sipbob_at_example.com"gt
• ltcallgt
• ltbusygt
• ltlocation url"sipbob_at_example.com"gt
• ltIMsendmsggt
• Hi, please call me back. I am in
  office
• lt/IMsendmsggt
• lt/locationgt
• .

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Automatic Call Back (ACB)

• ltless xmlns"urnietfparamsxmlnsless
• xmlnsEvent"urnietfparamsxmlnslessevent
• xmlnsQueue"urnietfparamsxmlnslessqueue
• xmlnsxsi.
• xsischemaLocation"gt
• ltincominggt
• ltstatus-switch
• status-nameactivitygt
• ltstatus ison-the-phone"gt
• ltreject reasonbusygt
• ltnextgt
• ltQueueenqueue
• queue"callback"/gt
• lt/nextgt
• lt/rejectgt
• lt/statusgt
• lt/status-switchgt
• lt/incominggt

Use Event and Queue extension
In ITU Q.1211 This feature allows the called
party to automatically call back the calling
party of the last call directed to the called
party.
Check my activity for an incoming call
If I am on-the-phone Reject and enqueue
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Automatic Call Back (ACB) (cont.)
A event notification for myself
ltEventnotificationgt ltaddress-switch
field"origin"gt ltaddress uri"agent.uri"gt
ltEventevent-switchgt
ltEventevent packagepresence"
nameactivity" isnormal"gt
ltQueuedequeue
queue"callback"gt ltQueuesuccessgt
ltcall/gt
lt/Queuesuccessgt lt/Queuedequeuegt
lt/Eventeventgt lt/Eventevent-switchgt
lt/addressgt lt/address-switchgt
lt/Eventnotificationgt lt/lessgt
I am available
Dequeue and make a call
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Feature Interaction handling

• Syntax correct, semantic warnings
• e.g., parent switch and child switch mutually
  exclusive
• By-product of modularity
• Focusing on current needs when creating services
• FI handling between multiple CPL/LESS scripts
• Action conflict tables
• Tree merging algorithm
• Multi-component feature interactions
• e.g., parallel forking with all end systems
  automatically accept an incoming call need to
  check presence
• Translate to formal languages (e.g., LOTOS) to
  check FI with other complex services

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Open issues

• Can we use LESS for B2BUA?
• lookup from database
• coordinate multiple sessions
• multi-user feature interaction handling
• No loop and no user-defined variables is
  sufficient for commonly used services?
• Based on our exercises, yes
• But, what about unknown new services?
• Whats the impact on feature interaction handling

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Some links

• Spec http//www.ietf.org/internet-drafts/draft-wu
  -iptel-less-00.txt
• Service examples http//www.cs.columbia.edu/libr
  ary/TR-repository/reports/reports-2004/cucs-048-04
  .pdf
• Feature interaction handling
• http//www.cs.columbia.edu/xiaotaow/rer/Research/
  Paper/fiw.pdf
• Computer Networks (Elsevier), Volume 45, Issue 5

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Service partition
Available anytime, anywhere More bandwidth More
computation power If possible, put services
in the network
BUT
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Service creation
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Help users to find out services

• Service learning
• Users do not know what they can do
• Users not aware of available services
• Help users, not bypass users
• CPL/LESS tree-like structure
• Decision tree learning
• Incremental Tree Induction (ITI) algorithm
• Service risk management (beyond LESS)
• connection, privacy, money, attention
• possibility and impact
• risk avoidance, transfer, reduction, and
  contingency plan