## 2 The MMAS/IPTV-CS Architecture and the Registration Procedure  
In the MMAS/IPTV-CS architecture, the CSCF [(1) in Figure 1] is responsible for call control. The _Session Border Controller_ [SBC; (2) in Figure 1] supports the functions of topology hiding and _Network Address Translation_ (NAT)/firewall traversal. In our deployment, the CSCF is a _Nokia Siemens Networks_ (NSN) CFX-5000, the SBC is an ACME SD 4000. The Media Server [(5) in Figure 1] converts image files into base64 encoding format and text data into defined _Extensible Markup Language_ (XML) files for delivering contents to STBs/TVs [(11) in Figure 1] or UEs such as multimedia phones and mobile phones [(3) and (10) in Figure 1]. Equipped with both SIP and _HyperText Transfer Protocol_ (HTTP) signaling interfaces, the MMAS Server [(4) in Figure 1] provides the _IPTV Convergence Server_ [IPTV-CS; (7) in Figure 1] the access to the NGN core network. It also interacts with the Media Server to transfer the contents (voice, text, and images) from the content servers [e.g., Central Weather Bureau, Transportation Bureau, and so on; see (12) in Figure 1] to the UEs. The _Geographic Information System_ (GIS) Server [(6) in Figure 1] supports LBS. The IPTV-CS is a service agent and signal adapter between the UE and other application servers [(4) and (5) in Figure 1], which consists of four functional modules and a database system. The _Back-end Management Module_ [BMM; Figure 2(a)] performs service access control (including user authorization) and manages service related data for system notice and service configuration. The _Service Integration Module_ [SIM; Figure 2(b)] instructs the BMM to access the contents from the Media Server, and reorganizes various content types to be compatible with the STBs and the browsers. This module communicates with an STB through the HTTP proxy of the _MOD Service Delivery Platform_ [MOD-SDP; (9) in Figure 1]. Dispatched by the BMM, the _Message Push Module_ [MPM; Figure 2(c)] receives short messages or _Multimedia Messaging Service_ (MMS) messages from other application servers and forwards them to a subscriber's TV screen through the STB. The _Integrated Communication Module_ [ICM; Figure 2(d)] interacts with the MMAS Server to provide call control.  
Figure 2: The IPTV-CS Architecture.  
Before the UE can access the MMAS/IPTV-CS services, it must register to the NGN network (as illustrated in Figure 3):  
**Step 1:**: The UE (with the phone number +886233111111) sends a SIP REGISTER request to the CSCF with the domain name ims1.cht.com.tw. Therefore, the Request-URI of the SIP REGISTER is \(<\)sip: +[EMAIL_ADDRESS]\(>\).
**Step 2:**: When the CSCF receives this request, it selects the authentication vector [8] to challenge the UE. Then the CSCF sends the authentication vector to the UE through 401 Unauthorized message.
**Step 3:**: After receiving 401 Unauthorized message, the UE produces an authentication response, and sends it back to the CSCF through a SIP REGISTER message.
**Step 4:**: The CSCF compares the received response with the expected response. If they match, then the authentication is successful. The CSCF replies a positive SIP 200 OK response to the UE.  
After this registration procedure, the mobile user can access the MMAS/IPTV-CS services.