Introduction to CPL

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(No Transcript)
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Introduction to CPL

• Jonathan Rosenberg
• Chief Scientist

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CPL Problem Statement

• Would like to allow end users to
• Define new services
• GUI tools or web
• Hand edit
• Back and forth
• Customize vanilla services
• Have their services be enabled instantly
• Service providers require
• Platform independence
• Decouple service creation tool from execution
• Decouple service from signaling protocol
• Assurances on safety

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What are the Options?

• Web interfaces populate customer profile data
• Not cross platform
• Not flexible
• End users write Java applications and upload
• Moving between GUI tools and hand editing is
  impossible
• Safety issue still exists sandboxing helps but
  not completely
• BIG IDEA - Define an XML based Call Processing
  Language (CPL)

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Advantages of XML for call services

• Easily edited by hand or by GUI tools
• Cross platform
• Allows us to define our own language primitives
• Can engineer language to be safe
• Can make it easy to build many common services
• Can be manipulated by off the shelf XML tools
• Readily transported in HTTP, SIP, FTP, other
  means
• Small in size (compared to Java)
• Fast operation

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History of CPL

• Concept originated as end user uploading of
  service logic in SIP REGISTER
• JDR and HGS, 1997
• Proposed as one of main work items for new IP
  Telephony (iptel) working group when it was
  formed in Nov 1997
• Jonathan Lennox, Columbia U. took role as primary
  driver and author
• Framework and Requirements done first
• RFC2824 issued May 2000

• CPL specification
• First draft April 1999
• Submitted for consideration as RFC Dec. 2000
• Implementations
• First one by JDR, mid 1999 at Bell Labs
• Second by dynamicsoft
• Numerous ones exist or are in progress now
• Indigo Software
• Ubiquity
• Netcentrex

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CPL FAQ

• Where do CPLs get executed?
• In network elements
• SIP Proxies
• SIP Application Servers
• H.323 Gatekeepers
• Can be used in clients, not designed for it
• Who writes CPLs?
• Engineered for end users to write
• Can be written by administrators and third
  parties as well
• How do CPLs get into the network?
• Uploaded in REGISTER (next slide)

• Uploaded in http POST
• Sent through any other means
• Direct database writes
• FTP
• etc.
• What kinds of services are best suited for CPL?
• Call routing services
• Call screening services
• Call logging services

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Uploading CPL in REGISTER
REGISTER sipsip.example.com SIP/2.0 From Joe
User ltsipjoe_at_example.comgt To "J. User"
ltsipjoe_at_example.comgt CSeq 18 REGISTER Expires
1800 Call-ID 39485832_at_joespc.example.com Contact
sipjoe_at_joespc.example.com Accept
application/cplxml Authorization Basic
am9lOnBhc3N3b3JkAFBX Content-Type
application/cplxml Content-Length
137 Content-Disposition script Content-Action
add ltcplgt ltincominggt ltreject
status400/gt lt/incominggt lt/cplgt

• Include CPL in body of REGISTER message
• MIME type application/cplxml
• Content-Disposition Header
• Indicates purpose of bodies
• Indicates that content contains call logic
• Content-Action indicates what is desired
• Add the CPL to the server
• Delete CPL
• CPLs DO NOT get refreshed

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CPL Lifecycle
INV
INV

• CPL Execution starts on arrival of INVITE message
  at a proxy
• Governs operation of proxy for INVITE transaction
  ONLY
• When final response is sent, CPL execution
  terminates
• Does not stay in the call
• This is why CPL is good at pre-call services like
  routing and screening

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ACK
INV
600
ACK
600
CPL Lifecycle
Proxy
UA1
UA2
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Proxies and CPL
CPLs for called user
CPLs for caller

• SIP call setups traverse many paths
• Which ones does a user need to put their CPL on?
• CPL guides behavior of a single proxy
• Incoming calls, CPL is generally on proxy that
  accesses registrations for that user
• Outgoing calls, CPL is generally on local
  outbound proxy
• CPLs can be put anywhere else
• Up to user/system to decide where they need to go

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CPL Structure
lt?xml version"1.0" ?gt lt!DOCTYPE cpl PUBLIC
"-//IETF//DTD RFCxxxx CPL 1.0//EN"
"cpl.dtd"gt ltcplgt ltsubaction
id"voicemail"gt SOME STUFF HERE
lt/subactiongt ltsubaction idemailgt
SOME STUFF HERE lt/subactiongt
ltincominggt SOME STUFF HERE
lt/incominggt ltoutgoinggt SOME STUFF
HERE lt/outgoinggt lt/cplgt

• CPL represents a tree
• Trees have nodes and links
• Each corresponds to a tag in CPL
• Nodes
• Specify actions to take or decisions to make
• Links
• Specify results of actions
• Specify which decision was made
• CPL contains subroutines, each of which is a tree
• Incoming - tree to execute for incoming calls
• Outgoing - tree to execute for outgoing calls
• Subroutines - can be used by either incoming or
  outgoing

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Beginning a CPL
lt?xml version"1.0" ?gt lt!DOCTYPE cpl PUBLIC
"-//IETF//DTD RFCxxxx CPL 1.0//EN"
"cpl.dtd"gt ltcplgt ltsubaction
id"voicemail"gt SOME STUFF HERE
lt/subactiongt ltsubaction idemailgt
SOME STUFF HERE lt/subactiongt
ltincominggt SOME STUFF HERE
lt/incominggt ltoutgoinggt SOME STUFF
HERE lt/outgoinggt lt/cplgt

• First line Specifies XML version
• Next line Specifies DTD to be used for validation
• All CPLs then followed by CPL tag
• Within CPL tag, you can have
• subactions
• zero or one incoming
• zero or one outgoing

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Mapping Trees to CPLs
ltlookup sourceregistrationgt ltsuccessgt
ltproxy/gt lt/successgt ltotherwisegt
lttime-switchgt lttime dtstart20001001T000000
duration24H
freqweekly bydayMOgt
ltreject status400/gt lt/timegt
ltotherwisegt ltredirect/gt
lt/otherwisegt lt/time-switchgt
lt/otherwisegt lt/lookupgt
lookup
otherwise
success
What is the date?
proxy
Monday
otherwise
Reject
Redirect
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CPL Execution Model

• Processing begins at incoming or outgoing tag
• Depends on system
• Server traverses tree, making decisions or
  performing actions
• Implicit global variable - the list of locations
• Certain tags modify the location list
• location, lookup, location-filter
• Other tags use the location list
• proxy, redirect

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Available tags

• Signaling Actions
• proxy
• redirect
• reject
• Decisions
• address-switch
• string-switch
• time-switch
• priority-switch
• Other actions
• mail
• log

• Location modifiers
• location
• lookup
• remove-location
• Subroutine calls
• subaction
• sub

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Proxy tag

• Node
• Proxies to current location list
• Outputs are result of proxy
• busy (486)
• noanswer (408 or timeout)
• redirection (3xx)
• failure (4xx,5xx,6xx)
• Attributes
• timeout how long to try before giving up
• recurse whether to recurse or not
• ordering sequential, parallel, first-only

ltproxy recurseyesgt ltbusygt ltreject/gt
lt/busygt ltnoanswergt ltreject/gt
lt/noanswergt lt/proxygt
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Proxy tag Details

• Tried elements are removed from global location
  list
• for parallel and sequential, thats all sip URLs
• for first only, thats the top sip URL
• Default timeout
• 20s if a no-answer tag is present
• system defined otherwise
• why? If there is a no-answer, there is something
  else to do
• Default recurse is yes
• Default ordering is parallel

• Recursing
• Contacts from 3xx are adding to implicit global
  location list
• List is always kept in sorted order based on q
  value

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Redirect tag

• Node
• Redirects to the current location list
• Placed in Contact headers
• OK if there are no locations
• No outputs allowed script execution terminates
• Single attribute permanent
• yes or no
• Indicates whether redirection is a permanent or
  temporary condition
• For SIP, 301 in one case, 302 in other

ltlocation urlsipfoo_at_bargt ltredirect/gt lt/locat
iongt
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Reject tag

• Node
• Rejects the call
• Status code to use is provided as an attribute
• busy,notfound, reject, error
• SIP servers can also allow numeric codes
• optional reason phrase can also be used
• CPL processing terminates

ltreject statusbusy/gt
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Switch Statements

• Switch statements are the primary decision making
  components in CPL
• They support a common structure
• Start with X-switch, where X is the element to
  check
• Subtags are all called X, and each of them
  represents a link with a specific value of the
  element
• otherwise is defined as an allowed subtag of
  X-switch
• not-present as well - when element is not in the
  message

ltfoo-switchgt ltfoo ishellogt ltreject/gt
lt/foogt ltfoo isgoodbyegt ltredirect/gt
lt/foogt ltotherwisegt ltproxy/gt lt/otherwisegt
ltnot-presentgt ltlog/gt lt/not-presentgt lt/foo-s
witchgt
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Address-Switch

• Used to make decisions based on the value of
  address fields in the message
• Defines two attributes, field and subfield
• Field is
• origin (From field)
• original-destination (To field)
• destination (Request URI)
• Subfield defines component of the URI in the
  field
• address-type (scheme of URL)
• user

• Host
• port
• tel
• If its a tel URL, or a sip URL with a telephone
  number, this element is defined
• display
• display name undefined for request URI
• password

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Address

• Outputs of address-switch are address tags
• Singe attribute, which can be one of is,
  contains, subdomain-of
• is
• used for exact match
• case sensitivity depends on subfield
• contains
• substring match
• case sensitivity depends on subfield

• Subdomain-of
• only defined for tel and for host
• for host, it matches if the domain in the
  subfield is a subdomain of the listed domain
• for tel, it matches if the telephone number
  contains the listed number as a prefix

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Examples
ltaddress-switch fieldorigin
subfieldusergt ltaddress isruser/gt lt/address
-switchgt ltaddress-switch fielddestination
subfieldportgt ltaddress
is5060/gt lt/address-switchgt ltaddress-switch
fieldoriginal-destination
subfieldhostgt ltaddress subdomain-ofcom/gt lt
/address-switchgt ltaddress-switch fieldorigin
subfielddisplaygt ltaddress
containsFDisp/gt lt/address-switchgt

• The given address tags to the right all match
• Assume the request is

INVITE sipruser_at_rdomain.com SIP/2.0 From
FDisplay ltsipfuser_at_fdomain.comgt To TDisplay
ltsiptuser_at_tdomain.comgt
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Address-Switch motivations

• Older CPL drafts used string-switch for this
• Motivations for change
• Hard to match on specific fields through glob
  matching
• Glob matching was hard to implement
• Take advantage of inherent structure
• Didnt work for H.323

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String-Switch

• String matching on textual fields in request
• Mandatory attribute field indicates whats being
  matched
• subject
• user-agent
• organization
• language
• Subtags of string-switch are string
• String contains either is or contains for
  exact or substring matching

ltstring-switch fieldsubjectgt ltstring
isSalesgt ltlocation urlsipsales_at_foo.comgt
ltproxy/gt lt/locationgt lt/stringgt
ltstring containsmarketinggt ltlocation
urlsipmarketing_at_foo.comgt ltproxy/gt
lt/locationgt lt/stringgt ltotherwisegt
ltlocation urlsiprandom_at_foo.comgt
ltproxy/gt lt/locationgt lt/otherwisegt lt/string-s
witchgt
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String Switch Details

• Matching Issue
• Want case insensitive
• These fields are freeform UTF-8!
• Case insensitivity depends on language and locale
• Nearly impossible to do
• Solution is a new Compatibility Composition form
  defined for Unicode
• Language is Accept-Language header in SIP
• Good for routing to operator based on language of
  caller
• Only substring matching is useful
• Accept language has parameters, commas, etc.

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Priority-Switch

• Allows matching based on priority of request
• Subtags are priority tags, which have attribute
  less, equal, greater
• Comparisons are against defined SIP values of
  emergency, urgent, normal, non-urgent
• If nothing is in request, priority is normal
• unknown priorities mapped to normal for greater,
  less comparisons

ltpriority-switchgt ltpriority equalsnewpriority
gt ltlocation urlsipnew_at_foo.comgt
ltproxy/gt lt/locationgt lt/prioritygt
ltpriority lessnormalgt ltlocation
urlsipwhocares_at_foo.comgt ltproxy/gt
lt/locationgt lt/prioritygt ltpriority
greaterurgentgt ltlocation
urlsipemergency_at_foo.comgt ltproxy/gt
lt/locationgt lt/prioritygt lt/priority-switchgt
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Time Switch

• Significantly different and more complex than
  initial version
• Initially crontab based
• Now iCal based
• Why iCal?
• Makes integration with calendaring programs
  easier
• More complete, more modern
• -03 based on an iCal subset proven to be
  implementable in O(1) time!
• Powerful representation of repeating events
• Every third Tuesday in February and March
• First Monday of the month
• etc.

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Handling Timezones

• User and server may be in different timezone
• CPL times should refer to timezone of user
• How to indicate timezone of user?
• Offset from GMT not sufficient
• Want scripts to be valid for years
• Offset varies as DST comes and goes!!
• Solution
• time-switch contains either tzurl or tzid
• tzurl refers to an object that defines the
  timezone
• tzid refers to either a to-be-established
  registry, or a server specific name
• names are things like EST and CST
• Java has a standard set of names

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Time tags

• Time tags contain many attributes that define
  repeating events
• Basic event description
• dtstart event start date and time
• dtend event end time
• duration instead of dtend
• Defining repititions through periodicity
• freq frequency of occurrence
• daily, weekly, monthly, yearly
• interval how often recurrence repeats

• Limiting repititions
• until date/time when repititions end
• Defining exceptions
• byday List of days of the week
• bymonthday List of days of the month
• byyearday List of days of the year
• byweekno List of weeks of the year
• bymonth List of months of the year

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Exceptions

• Expansion
• If frequency is a greater unit than largest
  exception
• Adds more events
• Example freqyearly bymonthjan,feb defines
  an event that repeats twice a year - once in jan,
  once in feb
• Contraction
• If frequency is a smaller unit than largest
  exception
• Reduces number of events
• Example freqdaily bydayMO,WE defines only
  Mondays and Wednesdays

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Example time-switch
lttime-switch tzid"America/New-Yorkgt lttime
dtstart"20000703T090000" duration"8H"
freq"weekly" byday"MO,TU,WE,TH,FR"gt
ltlocation urlsipwork_at_foo.comgt ltproxy/gt
lt/locationgt lt/timegt lttime
dtstart20000703T170000
dtend20000703T210000 freqweekly
bydayMO,TU,WE,TH,FRgt ltlocation
urlsiphome-eve_at_foo.comgt ltproxy/gt
lt/locationgt lt/timegt lttime dtstart20000703T00
0000 duration24H freqweekly
bydaySA,SUgt ltreject reasonits the
weekend/gt lt/timegt lt/time-switchgt

• Time of day forwarding/screening application
• Proxy calls to work during 9-5 during the week
• Proxy calls to home during the evening of the
  week
• Reject calls on weekends

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Location Addition

• Location
• Defines a location to be added to the global
  location list
• Single attribute, URL, contains the URL to add to
  the list
• Lookup
• Obtains the URI to add through indirection
• source attribute specifies place to go to
• registration looks in registration DB
• if source is a URL, fetches the URL and that
  contains a document with just a URL to add
• success, failure, notfound outputs

ltlocation urlsipfoo_at_bargt ltredirect/gt lt/locat
iongt
ltlookup sourceregistrationgt ltsuccessgt
ltproxy/gt lt/successgt lt/lookupgt
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remove-location

• Allows for removal of locations from global
  location list
• Based on caller preferences specification
• Caller prefs
• Associates parameters with contacts
• Example mobilefixed, mediavideo
• INVITEs contain headers that ask to reach
  specific contacts by parameter

• Parameter filtering
• two main attributes, param and value
• both are comma separated lists
• param contains the name of a parameter (e.g.,
  mobile)
• value contains the value for that parameter
  (e.g., fixed)
• same number of elements in param and value lists
• causes matching contacts to be removed
• Address filtering
• location attribute contains a URL pattern to match

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Example Parameter filtering
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Mail tag

• Allows CPL to send email
• Single parameter, url, contains mailto URL to use
• CPL server will
• Set the From field to its own address
• Set the body to contain information about the
  call, unless a body is specified by CPL
• Set the Subject to something useful, unless
  subject is specified by CPL
• Caveats
• Ampersand must be with an entity!

ltmail urlmailtouser_at_host?subjectfoo
ampbodyhello20theregt
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Log tag

• Allows CPL to generate log output
• How output is logged is system dependent
• Two parameters
• name specifies name of log to use
• interpretation of name is system dependent
• comment text to place in log
• CPL should also generate time of day and other
  params in log

ltlog commentrejected callgt
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Subroutines
ltsubaction idvmailgt ltlocation
urlsipvmail_at_foo.comgt ltproxy/gt
lt/locationgt lt/subactiongt ltincominggt ltlookup
sourceregistrationgt ltsuccessgt
ltproxygt ltnotfoundgt ltsub
refvmail/gt lt/notfoundgt lt/proxygt
lt/successgt ltotherwisegt ltsub
refvmail/gt lt/otherwisegt
lt/lookupgt lt/incominggt

• CPL can call a subroutine defined by subaction
• Subactions have an id
• To call subroutine, use sub tag with that Id as
  the value of ref attribute
• Subroutines can only be called if they are
  physically above in the CPL
• Avoids loops!

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Default Actions

• What happens if a script reaches a point where
  there are no more tags?
• Default Action is taken
• Default action depends on how far script has
  gotten
• No signaling actions, no locations defined,
  location set empty
• lookup in database, proxy or redirect as normal
• No signaling actions, no locations, location set
  non-empty

• Happens for outgoing calls
• Proxy to location set
• locations or lookups performed, no signaling
• proxy or redirect there
• proxy action invoked, noanswer output not present
• let phone ring forever, or until system defined
  timeout
• proxy performed, responses received
• forward best response upstream

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CPL Extensions

• Uses XML namespaces
• Each extension defines its own namespace
• Will render DTD validation useless!
• General problem with namespaces

ltincominggt ltlookup sourceregistrationgt
ltsuccessgt ltproxy xmlnsfoohttp//bargt
ltfooscrewupgt ltsub refvmail/gt
lt/fooscrewupgt lt/proxygt
lt/successgt ltotherwisegt ltsub
refvmail/gt lt/otherwisegt
lt/lookupgt lt/incominggt
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Information Resource

• Jonathan Rosenberg
• jdrosen_at_dynamicsoft.com
• 1 973.952.5000