EAB-05:006037 Uen Rev A ... [e-mail]

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IMS Interfaces and Protocols

• Gonzalo.Camarillo_at_ericsson.com

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Contents

• Interfaces
• The Cx and Dx interfaces
• DIAMETER
• The Sh and Si interfaces
• The Mw and ISC interfaces
• The Go interface
• COPS
• The Mi, Mj, Mk, Mm, Mr, Mg and Mc interfaces
• The Ut interface

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Interfacesof IMS
SIP Application Servers
OSA Application Server
CSE(SCP)
Home IMS Network
ISC
Sh
OSA-SCS
Sh
ISC
ISC
Cx
HSS
Cx
Mi
Mw
Mw
Mr
Mg
Gi
Mw
MGW
Gi
ISUP/BICC
Visited IMS Network
Visited Access Network
GGSN
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Cx Interface

• I-CSCF or S-CSCF to HSS
• Allocation of S-CSCF, authentication, retrieval
  of subscriber information
• Diameter protocol, with a specific application
  Diameter Multimedia Application

SIP Application Servers
OSA Application Server
OSA-SCS
IM-SSF
SLF
HSS
P-CSCF
S-CSCF
I-CSCF
GGSN
MRF
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Dx Interface

• I-CSCF or S-CSCF to SLF
• Used to find the HSS, either by
• CSCF queries SLF, and SLF returns HSS address or
• CSCF sends Cx request to SLF which proxies the
  request on to the relevant HSS
• Diameter protocol, with a specific application
  Diameter Multimedia Application

HSS
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DIAMETER protocol

• The RADIUS protocol (Remote Access Dial In User
  Services) has been widely and successfully
  deployed to provide authentication,
  authorization, and accounting (AAA) services in
  the internet. However, inherent shortcomings of
  the RADIUS protocol have limited its ability to
  adapt to the ever-increasing capabilities of
  routers and network access servers, and the
  ever-expanding set of desired AAA services. A
  number of requirements for AAA protocols were
  identified and these requirements drove the
  design of the Diameter protocol.
• Below are listed some characteristics of the
  Diameter Protocol
• It is a Query-Response type protocol so, it could
  be used for retrieving user or service
  information.
• Diameter operates over TCP (Transmission Control
  Protocol) or SCTP (Stream Control Transmission
  Protocol). TCP and SCTP are connection-oriented
  transport protocols with flow control and
  congestion avoidance mechanisms.
• Diameter includes support for capability
  negotiation so, although clients and servers are
  not aware of each other's capabilities, they
  may be able to successfully negotiate a mutually
  acceptable service.
• It is capable of transporting of user
  authentication information, transporting of
  service specific authorization information,exchang
  ing resource usage information,relaying, proxying
  and redirecting of Diameter messages through a
  server hierarchy.
• Diameter is a peer- to-peer protocol so any node
  can initiate a request.

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Sh and Si Interfaces

• Sh Interface
• AS to HSS
• Read from or write to HSS records
• DIAMETER
• Si Interface
• HSS to IM-SSF
• Query CAMEL subscription information from HSS
• DIAMETER

Sh
Si
HSS
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Mw and ISC Interfaces

• Mw Interface
• CSCF to CSCF
• Communication between CSCFs. Considered as a
  proxy from the SIP point of view
• SIP
• ISC Interface
• S-CSCF to AS
• ISC IMS Service Control. Needs to carry
  charging information.
• SIP

ISC
HSS
Mw
Mw
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Go Interface

• PDF to GGSN
• QoS Authorisation
• COPS

HSS
Gi
Go
P-CSCF
PDF
Go
Gi
GGSN
PEP
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COPS protocol

• It is a simple query and response protocol that
  can be used to exchange policy information
  between a policy server (Policy Decision
  Point-PDP) and its clients (Policy Enforcement
  Points-PEP). In 3GPP, the client (Policy
  Enforcement Points) is the GGSN and the server
  (Policy Decision Point) in the PDF residing in
  the P-CSCF.
• The characteristics of the COPS protocol are
• The protocol employs a client/server model where
  the PEP sends requests, updates, and deletes to
  the remote PDP and the PDP returns decisions back
  to the PEP.
• The protocol uses TCP as its transport protocol
  for reliable exchange of messages between policy
  clients and a server.Therefore, no additional
  mechanisms are necessary for reliable
  communication between a server and its clients.
• It allows the server to push configuration
  information to the client, and then allows the
  server to remove such state from the client when
  it is no longer applicable.
• The PEP is responsible for initiating a
  persistent TCP connection to a PDP. The PEP uses
  this TCP connection to send requests to and
  receive decisions from the remote PDP.
  Communication between the PEP and remote PDP is
  mainly in the form of a stateful request/decision
  exchange, though the remote PDP may occasionally
  send unsolicited decisions to the PEP to force
  changes in previously approved request states.
  The PEP also has the capacity to report to the
  remote PDP that it has successfully completed
  performing the PDP's decision locally, useful for
  accounting and monitoring purposes. The PEP is
  responsible for notifying the PDP when a request
  state has changed on the PEP. Finally, the PEP is
  responsible for the deletion of any state that is
  no longer applicable due to events at the client
  or decisions issued by the server.

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Mi,Mj,Mk,Mm,Mr, Mg Mc reference points

• Mr Interface
• CSCF to MRFC
• SIP
• Mg Interface
• MGCF to CSCF
• SIP
• Mc Interface
• MGCF to MGW
• Megaco (H.248)
• Mp interface
• MRFC to MRFP
• Megaco (H.248)

• Mi Interface
• CSCF to BGCF
• SIP
• Mj Interface
• MGCF to BGCF
• SIP
• Mk Interface
• BGCF to BGCF
• SIP
• Mm Interface
• CSCF to Other SIP
• SIP

HSS
Mi
Mr
Mg
Mj
Mc
Mp
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The Ut interface

• UE to AS interface
• Available in Release 6
• Used to do data manipulation, such as
• Configuration of presence list
• Configuration of conference participants
• Configuration of watcher access
• This interface is not used for traffic.
• The protocols are HTTP and XCAP

HSS