IMS Network Element - RACS+NASS (TISPAN)

IMS Network Element - RACS+NASS (TISPAN) (Study Note)

NASS = Network Attachment Subsystem
CLF = Connectivity session Location and repository Function
NACF = Network Access Configuration Function
UAAF = User Access Authorization Function
PDBF = Profile Data Base Function
CNGCF = CNG Configuration Function

RACS = Resource Admission Control Subsystem
A-RACF= Access-Resource and Admission Control Function
SPDF = Service-based Policy Decision Function

AF = Application Function
CNG = Customer Network Gateway
ARF = Access Relay Function
AMF = Access Management Function
RCEF = Resource Control Emulation Function
BGF = Border Gateway Function
BTF = Basic Transport Functions

NASS Function OV:
- CLF holds a number of records representing active sessions. These records contain information received from the NACF and the UAAF/PDBF, and additional statically configured data. CLF registers the association between network location information received from the NACF and geographical location information.
- NACF is the extension of existing DHCP component and is responsible for the IP address allocation to the UE.
- PDBF contains NASS User authentication data and the NASS User network profile related to the required network access configuration as a Policy Server which is responsible for mapping the subscriber’s services
- UAAF is the extension of existing Radius Server component and performs NASS User authentication, as well as authorization checking, and retrieves authentication data and access authorization information from the NASS User network profile information contained in the PDBF.
- CNGCF is used during initialization and update of the CNG

RACS Function OV:
- A-RACF performs admission control, Subscriber access profile-based checking and Resource admission control depending on the operator's policy, for the access and aggregation segment.
- SPDF acts as a final Policy Decision Point for Service-Based Policy control (SBP) and makes policy decisions by using service policy rules defined by the network operator, and hides the underlying network topology from applications and from interconnected SPDFs.

Further Information: https://docs.google.com/fileview?id=F.6000c46a-184d-406c-a1d0-1ffa4bf8d82b&hl=en

IMS Network Element - P-/I-/S-CSCF Overview (IMS Core)

IMS Network Element - P-/I-/S-CSCF Overview (IMS Core)

Three flavors of CSCFs
- Proxy CSCF (P-CSCF) - Entry point to IMS for devices
- Interrogating CSCF (I-CSCF) - Entry point to IMS from other networks
- Serving CSCF (S-CSCF) - Session control entity for endpoint devices

P-CSCF (Proxy-CSCF):
- Entry point to IMS from any access network
- Performs integrity protection
- Local outbound stateful proxy for all SIP requests/responses, ensuring all signalling is sent via the home network
- Includes a Policy Decision Function (PDF) that authorizes bearer resources

I-CSCF (Interrogating-CSCF):
- First contact point in home network
- Selects assigned S-CSCF
- Performs network hiding (THIG)

S-CSCF (Serving-CSCF):
- Stateful proxy that provides session control
- Performs subscriber authentication
- Acts as SIP registrar
- Invokes the AS’ (Application Servers) based on IFC (Initial Filter Criteria)

Further Information: https://docs.google.com/fileview?id=F.8b4bc0e6-cb99-415b-8848-165f3b548ba6

IMS Network Element - AGCF Overview (TISPAN IMS-Based PES)

IMS Network Element - AGCF Overview (TISPAN IMS-Based PES) (Study Note)

Discussion: CS-Based PES, IMS-Based PES and IMS PSS

AGCF Function OV:
- AGCF appears as a P-CSCF to the other CSCFs
- Act as an MGC for controlling media gateways functions
- The first point of contact for residential and access media gateways
- Perform signalling interworking between SIP and analog signalling via the P1 reference point.
- Act as a SIP User Agent
- Delivering the appropriate dialtone pattern;
- Processing mid-call events

AGCF to interact with the resource control subsystem (SPDF in RACS) for the following purposes:
- authorization of QoS resources;
- resource reservation;
- gate control (including NAPT binding information relay)

e2 supports information transfer between the P-CSCF or the AGCF and the CLF of Network Attachment Subsystem.
- AGCF may require to control residential or access media gateways
- Receipt of an off-hook or flash-hook event from MG, AGCF shall autonomously request the MG to play a dial tone, or aware of dial tone changes in case some specific supplementary services are activated, or Special dial tone if using service code
- etc.

Further Information: https://docs.google.com/fileview?id=F.c094cbfe-f59d-4d0c-87eb-2fe62d24f562

IMS Network Element - IP-SM-GW (for Short Message)

IMS Network Element - IP-SM-GW (for Short Message) (Study Note)

General functions of IP-SM-GW:
- Determine the domain (CS/PS or IMS)
- Connect to the SMS‑GMSC or SMS-IWMSC or HSS via interfaces
- Acquire and maintain knowledge of the association between the MSISDN, IMSI and the address of the S‑CSCF serving of the user;
- Act as an AS towards the IMS core;
- For terminating procedures, to map the recipient’s address from an MSISDN/IMSI to TEL URI format
- Perform domain selection to choose the appropriate domain to deliver a message from the HSS
- Check that it has a valid address in SMS for the sender as well as the recipient when receiving an IMS message for an SMS user
- etc.

Two Mechanisms:
- Transport-level interworking is done by carrying encapsulated Short Messages into IMS messages
- Service-level interworking is done between Short Messages and Instant Messages in IMS

Further Information: https://docs.google.com/fileview?id=F.b6e7cac8-17fa-4aa2-a11e-c7fef781b452

IMS Network Element - Emergency Service (E-CSCF+LRF)

IMS Network Element - Emergency Service (E-CSCF+LRF) Overview

UE (SIP: UA)
- Initiates e-calls, if necessary also e-registration
- May receive callbacks from PSAP

P-CSCF (SIP: Outbound Proxy)
- Detects whether call is subject to emergecny treatment
- Rejects e-calls if UE should e.g. use CS domain
- Allow and Forwards e-calls to the E-CSCF

E-CSCF
- Routing to PSAP (based on e-URN, location information, etc.)
- Query LRF (Location Function in 3G network) for user location information

MGCF / MGW (Interworking between IMS / CS)
- No additional requirements due to e-calls
- Based on the local policy if an incoming call from the PSTN is for the purpose of PSAP call-back

LRF (PS: Le is used between an AS and a GMLC on LCS)
- Consist of a RDF and a LS
- provide the correct PSAP destination address to the E‑CSCF for routing the emergency request
- Responsible for retrieving the location information of the UE
- Information provided by the LRF to the E‑CSCF (includes the routing information and other parameters like ESQK, ESRN, LRO in NA, or location number, PSAP SIP‑URI or TEL‑URI in EU)

PSAP: No 3GPP specific requirements

S-CSCF (SIP: Registrar, Home Service Proxy)
- Registration of the user and always locates in users home network
- Call-backs from PSAP take place via home network

P.S. E-SCC AS (TBD Later)

Furthr Information: https://docs.google.com/fileview?id=F.309cf55c-be6a-4557-931a-2e8e50138ea7

IMS Network Element - HSS Overview

IMS Network Element - HSS Overview (study Note)

HSS Overview
- A FE in Core Network (CN) in IMS, its role similar to HLR of the PS & CS domains
- Subscriber database for IMS network, Master database of subscriber information.

HSS (Home Subscriber Server) - Master database of subscriber information:
- User identification, numbering and addressing
- User security: network access control for authentication and authorization
- User location information at inter-system level
- User profile

IMS HSS Function
- Provide Filter Criteria to S-CSCF
- I-CSCF will assign S-CSCF to UE during IMS registration, HSS will provide these information to I-CSCF
- Provide S-CSCF address to I-CSCF for INVITE
- Cancellation of S-CSCF (due to change in subscription of Subscriber)
- Store Information
- Before Registration à Subscriber Profile
- After Registration à Serving-CSCF address/name & Subscriber Profile

HSS stores information required by:
- S-CSCFs (downloaded via Cx interface) Data model and abstract syntax notation in 3GPP TS 29.228;
- IM-SSF Application Servers (downloaded via Si interface);
- Application Servers (downloaded via Sh interface).

Further Information: https://docs.google.com/fileview?id=F.60e80214-c355-44a0-8161-f5283a851bc2

IMS Network Element - SLF Overview

IMS Network Element - SLF Overview (for HSS) (Study Note)

Subscription Locator Function (SLF)
- To retrieve the address of the UPSF (HSS) which holds the subscription for a given user
- To query the SLF from I‑CSCF, S‑CSCF or AS
- Response to provide the HSS name towards the I‑CSCF, S‑CSCF or AS

The SLF is accessed via the Dx interface or via the Dh interface.
- The Dx interface is the standard interface between the CSCF and the SLF
- The Dh interface is the standard interface between the AS and the SLF.
- The synchronisation between the SLF and the different HSSs is an O&M issue.
- The SLF may not be required. These interfaces are not required in a single UPSF environment. An example for a single UPSF environment is a server farm architecture.

DX_SLF_Query from
- I‑CSCF receives a REGISTER request from P-SCSCF
- S‑CSCF receives a REGISTER request from I-SCSCF
- I‑CSCF receives a (UE) INVITE request from x-SCSCF
- AS queries the SLF to identify the HSS to access
- SLF determination of unknown user

Further Information: https://docs.google.com/fileview?id=F.0eaba5e5-8ed5-433e-bed4-f0a0d0e657e1

IMS Newtork Element - BGCF Overview

IMS Newtork Element - BGCF Overview (Study Note)

BGCF Function OV:
- Selects the network to use for PSTN/PLMN interworking in which breakout is to occur and within that network
- Selects Media Gateway Control Function (MGCF)
- Provides security through authorization of peer networks
- BGCF of a peer network can be selected to hand-off routing
- BGCF determines the next hop for routing the SIP message
- Generation of CDRs
- Location of the PSTN address
- Local policies and business agreements between the peer network
- Minimize path distance
- Least cost path

Interfaces bewteen BGCF and other NEs:
- between CSCF and BGCF (Mi),
- between BGCF and MGCF (Mj),
- between BGCF/IMS ALG and BGCF (Mk)
- between BGCF/CSCF and IBCF (Mx).

Further Information: https://docs.google.com/fileview?id=F.66ad2c67-fa6d-42d0-9d6d-493ca7232881

IMS Network Element - BCF (IBCF+ALG+THIG+TrGW) Overview

IMS Network Element - BCF (IBCF+ALG+THIG+TrGW) Overview (Study Note)

IBCF acts as an entry point for this network (instead of the I‑CSCF), and also acts as an exit point for this network.
- IBCF may perform transit routing functions
- IBCF can detect whether an IWF needs to be added in the SIP signalling path
- IBCF can filter all SIP signalling information based on source / destination and operator policy
- IBCF for Generation of CDRs;

- IMS ALG provides the necessary application function for SIP/SDP protocol stack in order to establish communication between IPv6 and IPv4 SIP applications.
- THIG provides network configuration hiding to restrict the following information from being passed outside of an operator's network
- TrGW is located within the media path and controlled by an IBCF, and provides network address/port translation and IPv4/IPv6 protocol translation, and supports proactive and reactive transcoding

BCF (border control function) may be applied between two IM CN subsystem networks or between an IM CN subsystem network and other SIP based multimedia network (R6: ALG à R7: IBCF)

Further Information: https://docs.google.com/fileview?id=F.5bb947aa-ea7f-4e85-b178-9a1d32c0c681&hl=en

IMS Network Element - MRF (MRFC+MRFP) Overview

IMS Network Element - MRF (MRFC+MRFP) Overview Study Note












The MRF is made of two functional blocks:
- MRFC: MRF Controller part
- MRFP: MRF Processor part

1). Between MRFC & MRFP:
- (Mp) H.248

2). Application interaction (through Mr)
- SIP-Based
- NETANN RFC4240
- MSCML
- AMSML (XML based)

3A). MRFC:
- Manages the availability of MRFP resources
- Hides to the AS for the MRFP resources
- A SIP proxy only involved into initial INVITE
- etc

3B). MRFP
- Interprets & processes the commands sent by the AS
- Manages the media stream
- Performs the media processing
- etc

MRF Features Supporting:
- Announcement playback Voice/video Recording
- DTMF user interactivity
- Conferencing
- Tromboning
- Announcements management
- VoiceXML scripts facility
- etc

Audio and Video Codecs
Supported: TBC later

Further Information: https://docs.google.com/fileview?id=F.12eb8edc-376f-4332-a95d-ead553c4b63f&hl=en

IMS Network Element - MRB Study Note

IMS Network Element - MRB Study Note

MRB Ovreview:
- Supply appropriate MRF (MS) information to consuming entities such as the AS.
- Collection of appropriate published MRF information
- Acquire knowledge of MS resources utilization and reservation requests
- Assign resources to services from a common sharing pool of Media Servers,
- Assign specific suitable MRF resource based on MRF attributes specified by the applications
- Employ methods/algorithms to determine MS resource assignment
- Performs load distribution and site management functions, as well as resource brokering

Deployment Arch:
- In-Line or
- Query Modes

Further Information: https://docs.google.com/fileview?id=F.a5edb08d-e202-41f5-80cc-7737c2b7328d