IMS核心元素

对于IMS架构

其中的：

• 核心元素和简介
  • AS=Application Server=应用服务器
    • Executes service logic associated with value-added services
    • Provides enhanced and intelligent services to subscribers
  • CSCF=Call Session Control Function=调用会话控制功能
    • P-CSCF=Proxy CSCF
      • is the first point of contact and the control point for the User Equipment (UE) within the Service Provider network. It forwards session requests from the UE to the S-CSCF
    • S-CSCF=Serving CSCF
      • has access to the user subscription data and actually handles the session request
    • I-CSCF=Interrogating CSCF
      • is the first contact point within a Service Provider network for all incoming session requests from another Service Provider
  • BGCF=Breakout Gateway Control Function
    • Identifies the network that will be used for connecting IP sessions to the PSTN
  • HSS=Home Subscriber Server=归属用户服务器=HSS用户数据库
    • Stores all the static and dynamic information for a subscriber
    • Maintains a list of features and services associated with a user, and also the location and means of access to the user
    • Provides user profile information
  • SLF=Subscription Locator Function
    • Queried during Registration and Session Setup to get the name of the HSS containing the required subscriber specific data
  • MGCF=Media Gateway Control Function
    • Controls the parts of the call state that pertain to connection control for media channels in a T-MGF MGW
    • Selects the CSCF depending on the routing number for incoming calls from legacy networks
    • Performs protocol conversion between ISUP and call control protocols (e.g., SIP) and maintains call states
  • MRF
    • MRFC=Multimedia Resource Function Controller
      • Controls the media stream resources in the MRFP under direction from an S-CSCF or Application Server
      • Interprets information coming from an AS or S-CSCF (e.g., session identifier) and controls MRFP accordingly
    • MRFP=Multimedia Resource Function Processor
      • Provides media resources under the direction of MRFC
      • May generate media streams (e.g., multimedia announcements), mix incoming media streams for multiple parties, or process media streams (e.g., audio trans-coding, media analysis)
  • PDF=Policy Decision Function
    • Provides management of network QoS resources, authorization of resource allocations, and makes policy decisions with regard to use of network QoS resources
    • SPDF=Service Policy Decision Function
  • T-MGF=Trunk Media Gateway Function
    • Terminates bearer channels from a switched circuit network and media streams from a packet network (e.g., RTP streams in an IP network)
    • Establishes and releases connections between these channels under control of the MGCF in support of calls between PSTN and IP network
  • SGF=Signaling Gateway Function
    • Acts as a gateway between the IP call/session control signaling and the SS7-based PSTN signaling
    • May provide signaling translation, for example between SIP and SS7 or simply signaling transport conversion e.g., SS7 over IP to SS7 over TDM
  • A-BGF=Access Border Gateway Function
    • Packet gateway between an access network and a core network used to mask a service provider’s network from access networks, through which UE accessing packet-based services (e.g., IMS, Internet)
    • Functions may include Opening and closing gate, Traffic classification and marking, Traffic policing and shaping, Network address and port translation, and Usage information
    • Under control of the PDF
  • I-BGF=Interconnection Border Gateway Function
    • Packet gateway used to interconnect a service provider’s core network with another service provider’s core network supporting the packet-based services
    • Functions may be the same as that of the A-BGF
  • I-BCF=Interconnection Border Control Function
    • Controls I-BGF to interwork with other packet-based networks
    • May support the following functions (not limited to)
      • Inter-domain protocol normalization and/or repair
      • Inter-domain protocol interworking
      • Interaction with PDF for resource reservation, resource allocation, and/or other resource related information
  • MRB=Media Resource Broker
    • Assigns specific media server resources to incoming calls at the request of service applications (i.e., an AS)
    • Acquires knowledge of media server resources utilization and reservation requests that it can use to help decide which media server resources to assign to resource requests from applications
    • Employs methods/algorithms to determine media server resource assignment