The Role of IMS in Global Roaming for 3G Networks

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The Role of IMS in Global Roaming for 3G Networks

• Omar Faruk
• 9th March 2007

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Outline

• What is IMS ?
• Layered View of IMS
• Functional Components of IMS
• Roaming in 3G Networks
• IMS Roaming Scenarios
• Present Role of IMS in Global Roaming
• Possible Area of Improvements for IMS
• References

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What is IMS (IP-Multimedia Subsystem)?

• Defined by the 3GPP and 3GPP2 wireless working
  groups
• A new IP based architecture that enables
  convergence of -
• Data
• Voice
• Mobile Network Technology
• Fill the gap between -
• Traditional telecommunications technology and
• Internet technology
• IMS offers both -
• Service convergence
• Network convergence
• Service convergence
• Common set of services across different networks
• Network convergence
• Ability of a service provider to support a
  single, IP-based infrastructure

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Layered View of IMS (1)
Figure 1
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Layered View of IMS (2)

• IMS core network specifies a collection of
  logical functions which be classified into three
  layers
• Access and Transport Layer
• Session Control Layer
• Application Layer
• Common Application layer while reusing Access and
  Session control layers
• To provide multiple services to users
• Across multiple access networks
• Access Transport Layer
• Signaling, Routing Control bearer traffic
• Media Gateway, Media Resource Function Processor,
  Endpoints
• Session Control Layer
• Call or session control, authentication,
  charging, mobility management
• Call Session Control Function, Policy Decision
  Function etc.
• Application Layer
• Consists of Database, Application content
  Servers

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Functional Components of IMS (1)
Figure 2
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Functional Components of IMS (2)

• P-CSCF (Proxy-CSCF)
• Entry point to IMS for devices ( Both Home
  Visited )
• Forward SIP messages to the S-CSCF
• I-CSCF (Interrogating-CSCF)
• Entry point to IMS from other networks
• S-CSCF (Serving-CSCF)
• Provides Session control services for the IMS
  client
• Maintains a session state as needed by the
  network operator
• HSS (Home Subscriber Service)
• Information about the end users and the services
• BGCF (Breakout gateway control function)
• Selects the network in case of PSTN breakout
• Selects a MGCF, for inter-working with the PSTN

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Roaming in 3G Networks (1)

• Roaming
• Use a mobile terminal in networks other than the
  home network
• Provide services independently from their
  physical location
• Two types of roaming - National Roaming,
  International Roaming
• GPRS Roaming
• Use of the Gateway GPRS support node (GGSN) in
  the home network
• Using GGSN in the visited network
• Interconnecting network (GRX) between the GPRS
  networks

Figure 3
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Roaming in 3G Networks (2)

• IMS Roaming
• IMS subscriber in home GPRS/IMS networks access
  IMS services through a home GGSN
• While roaming users either uses a visited network
  Access Point or a home network Access Point
• In The 1st phase of IMS deployment, 3GPP assumes
  always using GGSN of home network
• P-CSCF and GGSN are always located in the same
  network either visited or home network
• All other IMS core elements are always located at
  the home network
• Roaming between IMS and the circuit-switched
  domain refers to inter-domain roaming between IMS
  and CS
• Both the CS domain and the IMS domain have their
  own services which are not accessible from
  another domain

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IMS Roaming Scenarios
Figure 4 Service platform in home network
Figure 5 Service platform in external network
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Present Role of IMS in Global Roaming

• Ensuring Session Mobility
• SIP supports personal mobility where a user can
  be found independent of location and network
  device
• Also supports Session mobility which allows a
  user to continue a media session even while
  changing terminals
• Services with Seamless Blending
• Services offered to visiting users are not
  limited by the home network services only
• Third-party service platform can be employed to
  offer services to a roaming user
• Controlled Billing and Charging
• Interoperability with IP versions (IPv4/IPv6)
• Visited Network IPv4 Home Network IPv6
• Interoperability with CS and PS networks
• Communicating with PSTN while roaming is ensured
  by transport level inter-working scheme

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Possible Area of Improvements for IMS

• Interoperability Issues with SIP
• SIP specification describes both optional and
  required behaviors
• Implementers choose different options or
  overlook some requirements for their SIP entities
• Ex. A signaling port number is optional in a SIP
  request. 14
• Application adds the default port number, but the
  SIP server does not forward the default port
  number
• Minimizing the number of implementation options
  in future standards to reduce the number of
  interoperability issues
• SIP Message Compression
• Amount of SIP messages transferred varies from
  service to service
• Presence information generates significant load
  on the network even when there is no application
  bearer traffic 15
• In case of global roaming this will be a critical
  issue
• Security and Authentication Scheme 16
• Testing and Simulation Environment

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References (1)

• 1 T. Zahariadis, K. Vaxevanakis, C.P.
  Tsantilas, N.A. Zervos, N. Nikolaou, "Global
  roaming in next-generation networks," IEEE
  Communications Magazine 40 (2) (2002) 145-151
• 2 "IMS is Hot But What is it ?" Last Visited -
  Feb 2007, http//www.itbusinessedge.com/item/?ci1
  9903
• 3 "GSM Roaming," Last Visited - Feb 2007,
• http//www.gsmworld.com/roaming/index.shtml
• 4 Dupyo Choi, Christine Fischer, Anne Y. Lee,
  E-Ling Lou, Chung-Zin Liu, Hsien-Chuen Yu,
  "Transition to IPv6 and support for IPv4/IPv6
  interoperability in IMS," Bell Labs Technical
  Journal 10(4) 261-270 (2006)
• 5 "IP Multimedia Subsystem (IMS)," 3GPP TS
  23.228
• Last Visited - Feb 2007
• http//www.3gpp.org/ftp/Specs/html-info/23228.htm
  
• 6 "Network architecture" 3GPP TS 23.002 Last
  Visited - Feb 2007
• http//www.3gpp.org/ftp/Specs/html-info/23002.htm
  
• 7 Anders Ross, Magnus Hartman, and Stephen
  Dutnell, "Critical Issues for Roaming in 3G" IEEE
  Wireless Communications, February 2003.
• 8 "IMS Roaming Interworking Guidelines IR 65
  3.6,
• Last Visited - Feb 2007
• http//www.gsmworld.com/documents/ireg/ir65_36.pd
  f

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References (2)

• 9 Miikka Poikselka, Georg Mayer, Hisham
  Khartabil, and Aki Niemi, "The IMS IP Multimedia
  Concepts and Services in the Mobile Domain". John
  Wiley Sons, 2004
• 10 H. Schulzrinne and E. Wedlund,
  "Application-layer mobility using sip," in
  Service Portability and Virtual Customer
  Environments. IEEE, December 2000, pp. 29-36.
• 11 Mohammad Torabi, "A shift in the mobile
  network service provisioning paradigm," Bell Labs
  Technical Journal 5(3) 112-129 (2000)
• 12 Nick J. Mazzarella, "Advantages of
  harmonized IMS-based charging architecture in
  different access technologies." Bell Labs
  Technical Journal 10(4)109-115 (2006)
• 13 "Interworking aspects and migration
  scenarios for IPv4-based IP Multimedia Subsystem
  (IMS) implementations," 3GPP TS 23.981,
• Last Visited - Feb 2007
• http//www.3gpp.org/ftp/Specs/html-info/23981.htm
  
• 14 Willem A. Romijn, Dirk-Jaap Plas, Dennis
  Bijwaard, Erik Meeuwissen, Gijs van Ooijen
  "Mobility management for SIP sessions in a
  heterogeneous network environment." Bell Labs
  Technical Journal 9(3) 237-253 (2004)
• 15 Carlos Urrutia-Valdés, Amit Mukhopadhyay,
  Mohamed El-Sayed, "Presence and availability with
  IMS Applications architecture, traffic analysis,
  and capacity impacts." Bell Labs Technical
  Journal 10(4) 101-107 (2006)
• 16 Erik E. Anderlind, David W. Faucher, Eric H.
  Grosse, Daniel N. Heer, Andrew R. McGee, David P.
  Strand, Robert J. Thornberry Jr., "IMS security."
  Bell Labs Technical Journal 11(1) 37-58 (2006)

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Questions ???
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Thank You