CAMEL in GPRS prepaid service

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CAMEL in GPRS prepaid service

• ghlee_at_alumni.csie.nctu.edu.tw

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Outline

• Evolution of IN
• GPRS overview
• CAMEL in GPRS
• Discussion

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Plain Old Telephone Service

• Service logic were hardwired in switching
  systems.
• Network operators discuss services customers
  required with switch vendors. (no standard)
• Once services were implemented, they were not
  easily modified.

service logic hardwired
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Stored Program Control

• In the mid-1960s, stored program control (SPC)
  switching systems were introduced.
• As a result, it was easier to introduce new
  services.
• Service logic was not modular.

service logic programmable
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Common Channel Signaling

• In the mid-1970s, common channel signaling
  network (CCSN) was introduced.
• Signaling system number 7 (SS7) is the protocol
  that runs over the CCSN.
• SS7 network separates the call setup information
  and talk path from the common trunk that runs
  between switching systems.

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SS7 network components

• signal switching points (SSPs)SSPs are telephone
  switches equipped with SS7-capable software and
  terminating signaling links. They generally
  originate, terminate, or switch calls.
• signal transfer points (STPs)STPs are the packet
  switches of the SS7 network. They receive and
  route incoming signaling messages to destination.
  
• signal control points (SCPs)SCPs are databases
  providing information necessary for advanced
  call-processing capabilities

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SS7 network
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The Introduction of IN

• During the mid-1980s, Telcordia Technologies
  responded to RBOCss request and developed the
  concept of Intelligent Network 1 (IN/1).
• Service logic splits from switching system, now
  resides in service control points (SCP).

service logic now here
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Call Model

• PICs represent switching system states that a
  call goes through from origination to
  termination.
• SSPs check TDPs to see if there are any active
  triggers.
• If an active trigger is detected, normal
  switching system call processing is suspended
  until the SSP and SCP complete communications.

SSP suspended,and ask SCP what to do in next step
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GPRS logical architecture
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Transmission plane in 2.5G
Multiplexing layer
Radio indep
Radio dep
Frame relay
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Signaling plane in 2.5G
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Multiplexing of network protocols
IP/X.25
Transmission plane
Signaling plane
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User plane in 3G
ATM
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Control plane in 3G
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CAMEL architecture
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MAP/CAP protocol stack

• CAP has the same underlying protocol stack as
  MAP.
• Ge interface is first defined in 3G, but didnt
  appear in 2.5G.

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Overall CAMEL Architecture
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Detection Points (DPs)

• GPRS events maybe made visible to gsmSCF. DPs are
  points at which these events are detected.
• DPs can be armed to notify gsmSCF GPRS event was
  encountered, and to allow gsmSCF to influence
  subsequent handling of GPRS session/PDP Context.
• If DP isnt armed, processing entity continues
  processing without gsmSCF involvement at the DP.

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Detection Points (DPs)

• 3 different types of DP
• Trigger Detection Point-Request (TDP-R)
• Event Detection Point-Request (EDP-R)
• Event Detection Point-Notification (EDP-N)

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Detection Points (DPs)

• TDP-R
• Statically armed, initiate a CAMEL control
  relationship
• When GPRS event is encountered, processing is
  suspended
• EDP-R
• Dynamically armed within CAMEL control
  relationship
• When GPRS event is encountered, processing is
  suspended and gprsSSF waits for inst from gsmSCF
• EDP-N
• Dynamically armed within CAMEL control
  relationship
• When GPRS event is encountered, processing is not
  suspended.

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GPRS Attach/Detach State Model

• 3 DPs are defined
• DP Attach
• DP Change of Position GPRS session
• DP Detach

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GPRS PDP Context State Model

• 4 DPs are defined
• DP PDP Context Establishment
• DP PDP Context Establishment Ack
• DP PDP Context Disconnection
• DP Change of Position Context

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GPRS CAMEL Scenarios

• 2 scenarios for CAMEL control of GPRS
• Scenario 1
• Allows CAMEL control of GPRS session and of
  multiple PDP contexts within 1 GPRS dialogue
• Scenario 2
• Allows CAMEL control of a single PDP contexts
• Multiple PDP contexts are controlled via multiple
  GPRS dialogues.
• Scenario 1 and scenario 2 are mutually exclusive.

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GPRS CAMEL Scenario 1

• Involves Attach/Detach state model
• Uses less resource (tcap dialogue)
• More complicated when implementation

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GPRS CAMEL Scenario 2

• Doesnt involves Attach/Detach state model
• Uses more resource (tcap dialogue)
• Simpler when implementation

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GPRS Attach

• The message sequence chart is too large to fit in
  this slide. Please see the supplementary document
  from 3GPP 23060 spec.
• Notice the Insert subscriber data procedure,
  GPRS-CSI (CAMEL Subscription Information) is sent
  from HLR to SGSN.
• 2.5G HLR does not keep GPRS-CSI, nor does it send
  GPRS-CSI to SGSN.
• 3G HLR could keep GPRS-CSI, also it sends
  GPRS-CSI when doing Insert subscriber data
  procedure.

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GPRS-CSI

• GPRS-CSI contains following information
• gsmSCF Address
• Service Key
• Default GPRS Handling
• TDP List
• CAMEL Capability Handling
• CSI state
• Notification flag
• gsmSCF address list for CSI

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PDP Context Activation in 2.5G

• C1 DP for CAMEL_GPRS_PDP_Context_Establishment
• C2 DP for CAMEL_GPRS_PDP_Context_Establishment_Ac
  knowledgement

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PDP Context Activation in 3G

• C1 DP for CAMEL_GPRS_PDP_Context_Establishment.
  
• C2 DP for CAMEL_GPRS_PDP_Context_Establishment_Ac
  knowledgement

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CAMEL procedures for charging activities
Procedure ssf -gt scf scf -gtssf
ApplyChargingGPRS -
ApplyChargingReportGPRS -
InitialDPGPRS -
ContinueGPRS -
EventReportGPRS -
RequestReportGPRSEvent -
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Discussion