PSTN and IP INTERWORKING PINT

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PSTN and IP INTERWORKING ( PINT)

• Ravishankar Krishnan

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Vision Voice, Application in Data Networks
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Reality Voice Services in PSTN Today
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What is PINT ?

• Desire to invoke certain telephone call
  services from the Internet
• PINT is a complete transaction, starting with the
  sending of a request from an IP client and
  including the telephone call itself
• PINT always involves two separate networks
• IP Network to request placement of a call
• Global Switched Telephone Network (GSTN) to
  execute the actual call

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Intelligent Network Center of Convergence
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Need for IP to PSTN Control
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PINT History

• By end 1996, several prototypes ( from ATT-NS,
  Siemens, HP and IBM) emerged, which were
  providing the PSTN customer with the combination
  of the Internet and traditional telephony
  services
• Industry was positive about PSTN-IP Interworking
  though economic justification was questioned
• It was clear that the IN was a natural mechanism
  for building such a hybrid
• Following the initial proposal and PINT BOF, the
  IETF chartered PINT as a working group in the
  Transport Area in the Summer of 1997

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Glossary of PINT Terms

• Requestor An internet host from which a request
  for service originates
• PINT Service A service invoked within a phone
  system in response to a request received from a
  PINT Client
• PINT Client An internet host that sends
  requests for invocation of a PINT service
• PINT Gateway An internet host that accepts
  requests for PINT service and dispatches them
  towards a telephone network
• Executive System- A system that interfaces to a
  PINT server and to a telephone network
• Requesting User The initiator of a request for
  service
• Party a person who is involved in a telephone
  network call that results from the execution of a
  PINT service request

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PINT Milestone Services

• The original motivation for PINT was the desire
• invoke the following three services
• Request to Call IP host sends request and
  causes a phone call to be made
• Request to Fax Content IP host sends request
  and causes a fax to be sent to a fax machine
• Request to Speak/Send/Play Content A request is
  sent from an IP host that causes a phone call to
  be made to user A, and for some sort of content
  to be spoken out.

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PINT Functional Architecture
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PINT Architecture (contd.)

• PINT clients and servers are SIP clients and
  servers
• SIP used to carry the request over the IP network
  to the correct PINT server
• SDP is used to describe the telephone network
  session
• A PINT gateway relays requests in to a
  telephone system and receives acknowledgement
• The system of PINT servers is represented as a
  cloud since a single PINT request might pass
  through a series of location servers, proxy
  servers and redirect servers
• PINT Gateway might be connected to the telephone
  network directly or through an Executive System

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SDP Operation in PINT

• The SDP payload contains a description of the
  particular
• telephone network session. This includes
• Telephone network address, i.e. Telephone Number
• Indication of the media type (audio/video/text/ima
  ge/application)
• An indication of the information to be
  transported via voice,fax , or pager transport
• The following enhancements are made to SDP
• A new network type TN and address type
  RFC2543
• New media types text/image/application

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SIP The Protocol of Choice

• Why SIP?
• SIP supports essential supplementary services
  such as call forwarding, address translation,
  personal mobility, conferencing, etc.
• SIP embeds standard HTTP security features
• SIP runs on anything (provides own reliability
  mechanism)
• SIP addresses are expressed as URLs, which can
  represent any numbering scheme(e.g. E.164)

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PINT enhancements to SIP

• Multipart MIME payloads
• Mandatory support for Warning Headers
• Subscribe,Unsubscribe and Notify requests
• Require Headers
• Format for PINT URLs with a PINT request
• Telephone network parameters within PINT URLs

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Other Extensions in PINT

• Specification of Telephone Service Provider(TSP)
  and/or phone-context URL-parameters
• Data objects as session media
• Protocol Transport formats to indicate treatment
  of media within GSTN
• Implicit media streams
• In-Line data objects using multipart/mime

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Request to a call center from anonymous user to
receive a phone call

• INVITE sipR2C_at_pint.mailorder.com SIP/2.0
• Via SIP/2.0/UDP169.130.12.5
• From sipanon-1827631872_at_chinet.net To sip1
• 201-456-7890_at_iron.orguserphone
• Call-ID19971205T234505.56.78_at_pager.com
• CSeq 4711 INVITE
• Subject Sale on Ironing Boards
• Content-type application/sdp
• Content-Length 174
• v0
• o- 2353687637 2353687637 IN IP4 128.3.4.5
• sR2C
• iIroning Board Promotion
• eanon-827631872_at_chinet.net
• t2353687637 0
• maudio 1 voice
• cTN RFC2543 1-201-406-4090

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A request from a non anonymous customer(John
Jones) to receive a phone call from aparticular
sales agent (Mary James)concerning the defective
ironing board that was purchased

• INVITE sipmarketing_at_pint.mailorder.com SIP/2.0
• Via SIP/2.0/UDP 169.130.12.5
• From sipjohn.jones.3_at_chinet.net
• To sipmary.james_at_mailorder.com
• Call-ID 19971205T234505.56.78_at_pager.com
• CSeq 4712 INVITE
• Subject Defective Ironing Board - want refund
• Content-type application/sdp
• Content-Length 150
• v0
• o- 2353687640 2353687640 IN IP4 128.3.4.5
• smarketing
• ejohn.jones.3_at_chinet.net
• c TN RFC2543 1-201-406-4090
• t2353687640 0
• maudio 1 voice -

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Sports Headlines sent to your Pager

• INVITE sipR2FB_at_pint.wwos.skynet.com SIP/2.0
• Via SIP/2.0/UDP 169.130.12.5
• To sip1-900-123-456-7_at_wwos.skynet.comuserphone
  phone-context1
• From sipfred.football.fan_at_skynet.com
• Call-ID 19971205T234505.56.78_at_chinet.net
• CSeq 4723 INVITE
• Subject Wonderful World Of Sports NFL Final
  Scores
• Content-type application/sdp
• Content-Length 219
• v0
• o- 2353687840 2353687840 IN IP4 128.3.4.5
• sR2FB
• iNFL Final Scores
• efred.football.fan_at_skynet.com
• cTN RFC2543 44-1794-8331015
• t2353687840 0
• mtext 1 pager x-pay
• afmtpx-pay oprmci.com/md5

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Basic Principles of PINT Use

• Responsibility for Service Requests
• Request may specify an incorrect telephone/fax
  number
• Purposeful wrong Numbers
• Request Interception and alteration
• All of these may constitute harassment of called
  party
• GSTN Operators dont want to be liable!!
• In general, operators must act only on requests
  that they
• believe are correct. PINT Service providers may
  require that the
• identity of the Requestor be confirmed, otherwise
  they may be
• forced not to provide service

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Basic Principles of PINT Use

• Authority to Make Requests
• When GSTN is used to provide PINT service,
  payment may
• be made either by requestor or another party(e.g.
  collectcall)
• or on a subscription basis
• However, whichever model is chosen, there may be
  a
• Requirement that the authority of a requestor to
  make a
• PINT request is confirmed
• If the confirmation is not available, the PINT
  gateway and
• Executive System may choose not to provide service

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Basic Principles of PINT Use

• Privacy
• The request from the user may be corrupted,
  maliciously
• altered or even replaced in transit between the
  requestor
• and the PINT Gateway
• Information on the authority issuing request is
  also carried in it. An eavesdropper can use this
  within his own requests
• Certificates used for secure transactions on the
  Internet may not be used in GSTN since they store
  only an account code and PIN
• Hence, requests SHOULD be encrypted

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REGISTRATION PROCEDURES

• Any number of PINT Gateways may register to
  provide the same service e.g. service providers
  supporting Request-to-Fax service
• A request may specify the Gateway name explicitly
• If not, an Intervening Proxy(or Broker.com) that
  acts on a Registration database is in a position
  to select the various gateways using a suitable
  algorithm
• This opens up an avenue for attack The Rouge
  Gateway Operator
• Hence, all registrations by PINT Gateways must be
  authenticated(includes new/replacement
  registrations and cancellations)

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Security Implications in PINT

• PINT carries sensitive data items
• PINT is based on SIP and SDP. PINT messages must
  be protected, so PINT implementations MUST
  support SIP Security
• Clients, Servers and Gateways may utilize network
  / transport/ physical level security. Manual
  configuration is required in such cases
• In a network level approach, the intervening
  proxies must be capable of examining the contents
  of the IP datagrams
• If transport level security is used, TCP will
  have to be used.This is different from Default
  SIP(Try UDP, then try TCP if that fails)

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Web Front End to PINT

• Due to the high numbers of available Web browsers
  and servers, some PINT systems will use HTML/HTTP
  as the front end
• HTTP is used over a connection from the
  Requesting Users Web Browser(WC) to an
  Intermediate Web Server(WS)
• This is closely associated with a PINT Client
• The PINT client represents the Requesting User to
  the PINT gateway, and thus to the Executive System

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Summary

• A step on the way to the NextGen Network vision
  Service Integration of the PSTN and Internet
• Intelligent Network is a natural PSTN platform to
  support such integration
• PINT made the first step in this direction for
  standardization. PINT uses SIP on the Internet
  side of the PSTN Gateway and Intelligent Network
  Application Protocol on the PSTN side
• Success of PINT depends, among other factors on
  the cooperation of IETF and ITU-T

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Further..

• PINT Management Information Base
• ( MIB)
• Request for Conference

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References

• RFC 2848 The PINT Service Protocol Extensions
  to SIP and SDP for IP Access to Telephone Call
  Services
• RFC 2458 Toward the PSTN/Internet
  Inter-Networking
• Lawrence Conroy's presentation from 43rd IETF
  (Dec 8, 1998) PINT Meeting