1. ngn architecture

1. NGN Architecture
Application Servers (AS)

ISC-Interface (SIP)

Home Subscriber Server (HSS)
Diameter


SIP
Session Controller

H.248

SIP

Media Gateway Controller


PSTN/PLMN
Media Gateway




other

Broadband Access

IP Network
Access SBC

1. 
   SBC
   

IP Network

Figure 3: NGN architecture (Source: SBR, based on Darvishan et al.)
The main elements of this generalized NGN architecture are:

• 
  Home subscriber server (HSS): The HSS is the database of all subscribers and service data, which includes user profile, roaming profile, authentication parameters and service information.
  
• 
  Session controller: This functionality is responsible for registering the users and providing the services to them. It performs routing and translation, provides billing information to mediation systems, maintains session timers, and interrogates the HSS to retrieve authorization, service triggering information and user profile.
  
• 
  Media_gateway_controller'>Media gateway controller: This is the function that performs call control protocol conversion between SIP and ISUP and interfaces with the signalling gateway over SCTP. It also controls the resources in MGW across an H.248 interface.
  
• 
  Media gateway (MGW): This is the function that interfaces with circuit switched network, terminates bearer channels from circuit switched networks and packet switches media streams, and handles DSP resources such as codecs, transcoder etc.
  
• 
  Application server (AS): AS include enhanced service logic and can make use of the session control.
  

• 
  Broadband access: Broadband access can be based on different technologies. Broadband access also provides NASS functionality. This is the function that provides registration at access level and initialization of user equipment for access to services. NASS provides network-level identification and authentication, manages the IP address space of the access network, and authenticates access sessions.
  
• 
  Session border controller (SBC): The SBC provides the border to other IP networks. Access SBC and Interconnection SBC can be distinguished. The Access SBC usually includes the RACS functionality. SBC have evolved to address a wide range of issues like security and DOS prevention, policy enforcement and QoS control, firewall and NAT traversal.