Voice Over IP

1
Voice Over IP

• Bhaskaran Raman
• Sreedhar Mukkamalla
• Jimmy Shih

2
Outline

• Issues in designing Voice Over IP.
• Three groups working on Voice Over IP.
• (IETF, ETSI, ECTF)
• Three proposed architectures for Voice Over IP.
• (H.323, ECTF Architecture Framework, SIP)
• Three software APIs for CTI.
• (TAPI, TSAPI, JTAPI)

3
Issues in Designing Voice Over IP

• Naming User Location
• Signaling and Capabilities Exchange
• Media Transport and Flow Control
• Congestion Control
• Call Processing
• Gateway Location
• Thin Clients Support
• Multicast Support
• Scale to Wide Area

4
Three Groups Working on Voice Over IP

• Internet Engineering Task Force (IETF) IP
  Telephony (IPTEL) Working Group
• (http//www.ietf.org/html.charters/iptel-charter.
  html)
• European Telecommunications Standards Institute
  (ETSI) Telecommunications and Internet Protocol
  Harmonization Over Networks (TIPHON) Task Force
• (http//www.etsi.org/tiphon/)
• Enterprise Computer Telephony Forum (ECTF)
• (http//www.ectf.org/ectf/home.shtml)

5
IETF IPTEL

• Improve H.323 SIP
• Call processing framework (July 1998) and call
  processing syntax (October 1998)
• Users can use a scripting language to specify
  their preferences.
• Gateway discovery protocol
• Select a gateway based on client preferences,
  service provider preferences, gateway
  availability, and telephone destination.
• Centralized vs. Distributed protocol
• Client aware vs. Client unaware in the front end

6
ETSI TIPHON

• Improve H.323
• How to find appropriate gatekeepers and gateways?
• How to provide quality of service?
• How to find user location?
• How to support roaming?
• How to perform routing with cascaded
  heterogeneous networks?
• PSTN-gtIP-gtPSTN
• IP-gtPSTN-gtIP

7
ECTF

• Address the needs of the vendors
• Want to reach a technical implementation
  agreement.
• Similar to the agreement for making PC
  components.
• Different vendors can produce different
  components.
• Have a Voice Over IP architecture framework
  consists of application and telephone servers.
• Define the interface for connecting the servers.
• Define the components interfaces for implementing
  the servers.

8
Conclusion

• IETF focusing on improving H.323 and SIP.
• ETSI focusing on improving H.323.
• ECTF has its own architecture.

9
Additional Reference

• IETF IPTEL Working Group
• http//www.ietf.org/html.charters/iptel-charter.ht
  ml
• http//www.cs.columbia.edu/jdrosen/papers/ietf_ip
  tel_mar98.pdf
• http//www.bell-labs.com/mailing-lists/iptel/ietf_
  siptel95.pdf
• ESTI TIPHON Task Force
• http//www.bell-labs.com/mailing-lists/iptel/TIPHO
  N-rev4.3.ps
• ECTF Framework Architecture
• http//www.ectf.org/cgi-bin/ectf/docs.cgi?function
  GetDocfile_namearch_fr.

10
Session Initiation Protocol (SIP)
11
What is SIP?

• Spec of IETF MMUSIC working group
• Purpose
• to initiate multi-media (MM) sessions
• invite users to existing sessions
• (unicast as well as multicast sessions)
• Its the Internets signaling protocol

12
In the Context Of...

• SDP, SAP, SAP Security
• RTP, RTCP, RTSP
• SCCP
• RSVP
• SLP

These protocols address different issues that
need to be solved for MM on the Internet
13
Issues addressed

• Naming
• User location (personal mobility)
• User capability negotiation
• User availability
• Call Setup (ringing)
• Call handling (transfer termination)

14
Interoperation with H.323

• Using SIP, one can find that the user is
  reachable via H.323 use H.323 to establish a
  call
• Or, one can find that the user is reachable via
  PSTN use an Internet-to-PSTN gateway.

15
SIP Components

• SIP clients
• SIP proxy/redirect servers
• Registrar (co-located with SIP servers usually)
• Location servers

16
Naming in SIP

• SIP URLs are defined
• Examples
• bhaskar_at_cs.berkeley.edu
• sipbhaskar_at_cs.berkeley.edu
• sip1-510-642-90761234_at_gateway.berkeley.edu
• sipbhaskar_at_128.32.37.140
• sipbhaskar_at_cs.berkeley.edumaddr239.255.255.1

17
Locating a User

• Users register with Registrar
• Location servers can be used
• may use finger, rwhois, LDAP, multicast-based
  protocols etc.
• Note that the problem of user-location is not
  solved by SIP
• SIP servers operate in proxy or redirect mode

18
Redirect operation of a SIP server
19
Proxy operation of a SIP server
20
SIP methods

• INVITE, ACK, BYE, CANCEL
• OPTIONS (for capability negotiation)
• REGISTER (to register with the registrar)

21
Call processing in SIP

• Call forwarding at proxy server
• Call transfer yes
• Conference calling yes
• Call hold retrieve possible using SDP?
• Call waiting toggle to be handled at a higher
  layer

22
Call processing in SIP (contnd.)

• Generic call processing at proxy server
• Voice-mail, Voice-to-mail processing can be done
  at proxy server

23
SIP versus H.323

• Both address the same problem
• They have evolved from different backgrounds
• In terms of services/functionality, they are
  quite similar

24
Where SIP wins

• SIP is far less complex than H.323
• Extensibility similar to HTTP
• Scalability stateless servers
• Modularity - SIP is independent of the component
  protocols for MM on the internet

25
Where H.323 wins

• All components are well defined
• Industry support
• Microsoft support (Netmeeting)

26
References

• M.Handley, H.Schulzrinne, and E.Schooler, SIP
  session initiation protocol, Internet draft,
  IETF, May 1998, Work in progress.
• H. Schulzrinne, J. Rosenberg, A Comparison of
  SIP and H.323 for Internet Telephony, NOSSDAV,
  July 1998.
• Schulzrinne, H. A comprehensive multimedia
  control architecture for the Internet, NOSSDAV,
  May 1997. p.65-76.

27
Software APIs for CTI

• What is CTI (Computer Telephony Integration) ?
• First party vs. Third party Call Control
• TAPI
• TSAPI
• JTAPI

28
First Party vs. Third PartyCall Control

• First Party
• Individual user controls telephone call
• PC directly connected to telephone network
• applications such as enhanced personal
  organizers, sophisticated answering machines etc.

29
First Party vs. Third Party Call Control

• Third Party
• Network server acts as home base
• PC talks to server over the LAN
• Server controls the switch
• Logical link between PC and phone
• Example application Screen Pop

30
What is TAPI ?

• TAPI (Telephony API) is Microsofts API for
  application programs to talk to telephony
  hardware (such as analog PSTN, ISDN, PBXes,
  switches)
• Result of a joint initiative by Microsoft Intel
  in 1993
• Part of WOSA (Windows Open Sys. Arch.)
• similar to how Windows handles printers
• API (application programmers)
• SPI (Service Provider Interface equipment
  vendors)
• TAPI 1.4 shipped with Windows 95
• TAPI 3.0 being included with NT 5.0

31
Benefits of TAPI

• Achieves isolation between communications
  software and hardware
• Provides high level interface to application
  software for telephony services
• Allows more than one app to access device(?)
• Originally intended for first party call control
• TAPI 2.0 provides both First Party and Third
  Party Call Control
• TAPI 3.0 supports H.323 and IP multicast
  conferencing

32
TAPI 3.0 Architecture
Call control
Media control
Directory control
Terminal control
NTDS
LDAP
33
TSAPI

• TSAPI (Telephony Services API) is Novell ATTs
  standard for Computer Telephony Integration
• Mainly intended for Third Party Call Control
• Works on many platforms (unlike TAPI which is
  restricted to Windows)
• Could be more cost effective for large number of
  users

34
JTAPI

• Java Telephony API (JTAPI) is a Java based API
  for computer-telephony applications
• Advantage - Applications written using JTAPI will
  be portable across platforms
• Acts as a Java interface to existing telephony
  APIs such as TAPI, TSAPI
• Supports both First Party and Third Party
  (Desktop and Network configurations)

35
JTAPI configurations
Desktop Configuration
36
JTAPI configurations (..contd.)
Network Configuration