Wireless and Mobile AllIP Networks YiBing Lin linycsie
Wireless and Mobile All-IP Networks Yi-Bing Lin liny@csie. nctu. edu. tw 1
Contents [1/3] n n n Chapter 1: Short Message Service and IP Network Integration Chapter 2: Mobility Management for GPRS and UMTS Chapter 3: Session Management for Serving GPRS Support Node Chapter 4: Session Management for Gateway GPRS Support Node Chapter 5: Serving Radio Network Controller Relocation for UMTS 2
Contents [2/3] n n n n Chapter 6: UMTS and cdma 2000 Mobile Core Networks Chapter 7: UMTS Charging Protocol Chapter 8: Mobile All-IP Network Signaling Chapter 9: UMTS Security and Availability Issues Chapter 10: Vo. IP for the Non-All-IP Mobile Networks Chapter 11: Multicast for Mobile Multimedia Messaging Service Chapter 12: Session Initiation Protocol 3
Contents [3/3] n n n Chapter 13: Mobile Number Portability Chapter 14: Integration and WLAN and Cellular Networks Chapter 15: UMTS All-IP Network Chapter 16: Issues on IP Multimedia Core Network Subsystem Chapter 17: A Proxy-based Mobile Service Platform 4
Chapter 1: Short Message Service and IP Network Integration GSM SMS Network Architecture 5
SMS-IP Integration: SM-SC-based In most commercial implementations, SMS and IP networks are integrated through SM-SC. Mobile Network IP Network SM-SC Gateway 6
NCTU-SMS 7
i. SMS 8
Mobility and Session Management n n Three types of mobility: radio mobility, core network mobility and IP mobility n Radio mobility supports handoff of a mobile user during conversation n Core network mobility provides tunnel-related management for packet re-routing in the core network due to user movement n IP mobility allows the mobile user to change the access point of IP connectivity without losing ongoing sessions. Session management maintains the routing path for a communication session, and provides packet routing functions including IP address assignment and Qo. S setting. 9
Chapter 2: Mobility Management for GPRS and UMTS 10
LAs, RAs, URAs, and Cells 11
Chapter 3: Session Management for Serving GPRS Support Node 12
Chapter 4: Session Management for Gateway GPRS Support Node n n The GGSN plays the role as a gateway, which controls user data sessions and transfers the data packets between the UMTS network and the external PDN. The meta functions implemented in the GGSN are described as follows: network access control, packet routing and transfer, and mobility management. 13
Access Point Name (APN) 14
IP Address Allocation APN label INTERNET WAP ISP COMPANY Access mode Transparent Nontransparent IP address allocation GGSN/ DHCP/ RADIUS IP address type IPv 6/IPv 4 15
Chapter 5: Serving Radio Network Controller Relocation for UMTS Serving RNC Drift RNC Serving RNC 16
Lossless SRNC Relocation n In 3 GPP TS 23. 060, a lossless SRNC relocation procedure was proposed for non-real-time data services. 1. The source RNC first stops transmitting downlink packets to the UE, and then forwards the next packets to the target RNC via a GTP tunnel between the two RNCs. 2. The target RNC stores all IP packets forwarded from the source RNC. 3. After taking over the SRNC role, the target RNC restarts the downlink data transmission to the UE. No packet is lost during the SRNC switching period. Real-time data transmission is not supported because the IP data traffic will be suspended for a long time during SRNC switching. 17
Fast SRNC Relocation – Stage I n n n Stage I (the same as Stage I in SD) initiates SRNC relocation. The IP packets are delivered through the old path: UE Node B 2 target RNC source RNC SGSN 1 GGSN Steps 1 and 2: Source RNC initiates SRNC relocation by sending Relocation_ Required to SGSN 1. Step 3: SGSN 1 sends Forward_Relocation_ Request to request SGSN 2 to allocate the resources for the UE. Step 4: SGSN 2 send Relocation_Request with RAB parameters to the target RNC. After all necessary resources are allocated, the target RNC send Relocation_Request_ Acknowledge to SGSN 2. 18
Fast SRNC Relocation – Stage II n n n GGSN routes the downlink packets to the old path receiving Update_PDP_Context_ Request. After GGSN has received the message, the downlink packets are routed to the new path GGSN SGSN 2 target RNC. The “new” packets arriving at the target RNC are buffered until the target RNC takes over the SRNC role. Step 5: SGSN 2 sends Update_PDP_Context_ Request to GGSN updates the corresponding PDP context, and the downlink packet routing path is switched from the old path to the new path. Steps 6 -7: SGSN 2 informs SGSN 1 that all resources for the UE are allocated. SGSN 1 forwards this information to the source RNC. 19
Fast SRNC Relocation – Stage III n n The Iur link (i. e. , the old path) disconnected. The “old” downlink packets arriving at the source RNC later than Step 7 (Relocation_Command) are dropped. The SRNC role is switched from the source RNC to the target RNC. Step 8: The source RNC transfers SRNS context (e. g. , Qo. S profile) to the target RNC. Steps 9 and 10: The target RNC informs SGSN 2 that the target RNC will become the SRNC. At the same time, the target RNC triggers the UE to send the uplink IP packets to the target RNC. 20
Fast SRNC Relocation – Stage IV n n n The target RNC informs the source RNC that SRNC relocation is successfully performed. Then the source RNC releases the resources for the UE. Step 11: The target RNC indicates the completion of the relocation procedure to SGSN 2, and SGSN 2 forwards this information to SGSN 1. Step 12: SGSN 1 requests the source RNC to release the resources allocated for the old path. 21
Chapter 6: UMTS and cdma 2000 Mobile Core Networks n n n UMTS and cdma 2000 are two major standards for 3 G mobile telecommunication. Two important functionalities of mobile core network are mobility management and session management. This chapter describes these two functionalities for UMTS and cdma 2000, and compare the design guidelines for these two 3 G technologies. 22
cdma 2000 Architecture 23
cdma 2000 CS Domain n n BSC connects to the core network through the SDU. The SDU distributes the circuit switched traffic (e. g. , voice) to the MSC. A 1 interface supports call control and mobility management between MSC and BSC. A 2 and A 5 interfaces support user traffic and circuit switched data traffic between MSC and BSC. 24
cdma 2000 PS Domain n n The SDU distributes the packet switched traffic to PCF and then to the PDSN. Interfaces A 8 and A 9 support packet switched data and signaling between PCF and SDU, respectively. Interfaces A 10 and A 11 (R-P interface) support packet switched data and signaling between PCF and PDSN. n GRE tunnel is used for data routing in A 10 with standard IP Qo. S. n MIP is used for signaling routing in A 11. The R-P interface also supports PCF handoff (inter or intra PDSN). 25
PDSN n n n Maintaining link-layer sessions to the MSs Supporting packet compression and packet filtering before the packets are delivered through the air interface Providing IP functionality to the mobile network, which routes IP datagrams to the PDN with differentiated service support Interacting with AAA to provide IP authentication, authorization and accounting support Acting a MIP FA in the mobile network The interfaces among the PDN nodes (i. e. , PDSN, HA, AAA) follow the IETF standards. 26
cdma 2000 Control Plane 27
UMTS Control Plane 28
cdma 2000 User Plane 29
UMTS User Plane 30
Protocol Stacks [1/2] n n n The control plane carries out tasks for MM/SM/SMS. In cdma 2000, the mobility and session tasks are based on the same lower layer protocol (IP based protocols) for user data transportation. In UMTS, the lower layer protocols supporting MM/SM tasks in the control plane are different from the lower layer protocols in the user plane. n The signaling path between MS and SGSN consists of an RRC connection between MS and UTRAN, and an Iu connection between UTRAN and SGSN. 31
Protocol Stacks [2/2] n n n In UMTS, the PS domain services are supported by PDCP in the user plane. n PDCP contains compression methods, which provide better spectral efficiency for IP packets transmission over the radio. In cdma 2000, the header and payload compression mechanism is provided by PPP between MS and PDSN. Both UMTS RLC and cdma 2000 LAC provide segmentation and retransmission services for user and control data. n cdma 2000 LAC supports authentication functionality for wireless access, which is equivalent to GPRS transport layer authentication in UMTS. 32
PPP n n In both control and user planes for cdma 2000, PPP is carried over the LAC/MAC, and R-P tunnels are utilized to establish the connection between an MS and the PDSN. In cdma 2000, a PPP connection is equivalent to a packet data session, which is comparable to the UMTS PDP context. In the UMTS control plane, no PPP/IP connection is established between MS and SGSN. Signaling is carried over the RRC and Iu connections. UMTS user plane provides two alternatives for IP services. n IP is supported by non-PPP lower layer protocols. n IP is supported by PPP. n Dial-up application n Mobile IP is introduced to UMTS 33
Chapter 7: UMTS Charging Protocol n n The GTP’ protocol is used for communications between a GSN and a CG, which can be implemented over UDP/IP or TCP/IP. Above the GTP’ protocol, a Charging Agent (or CDR sender) is implemented in the GSN and a Charging Server is implemented in the CG. signaling and data a c b RNC f HLR Ga MS CG Node B d RNC MS g SGSN Gn GGSN e Gi PDN Node B UTRAN CG : Charging Gateway GGSN : Gateway GPRS Support Node HLR : Home Location Register MS : Mobile Station PDN : Packet Data Network Core Network UTRAN : UMTS Terrestrial Radio Access Network RNC : Radio Network Controller SGSN : Serving GPRS Support Node B : Base Station 34
The GTP’ Service Model n n n Our GTP’ service model follows the GSM Mobile Application Part (MAP) service model. A GSN communicates with a CG through a dialog by invoking GTP’ service primitives. A service primitive can be one of four types: n n Request (REQ) Indication (IND) Response (RSP) Confirm (CNF) 35
GTP’ Connection Setup Before a GSN can send CDRs to a CG, a GTP’ connection must be established between the charging agent in the GSN and the charging server in the CG. 36
GTP’ CDR Transfer The charging agent is responsible for CDR generation in a GSN. The CDRs are encoded using, for example, the ASN. 1 format defined in 3 GPP 32. 215. The charging server is responsible for decoding the CDRs and returns the processing results to the GSN. 37
GTP’ Failure Detection In a GSN, an entry in the CG list represents a GTP' connection to a CG. n n n n The CG Address attribute identifies the CG connected to the GSN. The Status attribute indicates if the connection is “active” or “inactive”. The Charging Packet Ack Wait Time Tr is the maximum elapsed time the GSN is allowed to wait for the acknowledgement of a charging packet. The Maximum Number of Charging Packet Tries L is the number of attempts (including the first attempt and the retries) the GSN is allowed to send a charging packet. The Maximum Number of Unsuccessful Deliveries K is the maximum number of consecutive failed deliveries that are attempted before the GSN considers a connection failure occurs. The Unsuccessful Delivery Counter NK attribute records the number of the consecutive failed delivery attempts. The Unacknowledged Buffer stores a copy of each GTP' message that has been sent to the CG but has not been acknowledged. n A record in the unacknowledged buffer consists of an Expiry Timestamp te , the Charging Packet Try Counter NL and an unacknowledged GTP' message. 38
Path Failure Detection Algorithm The Path Failure Detection Algorithm (PFDA) detects path failure between the GSN and the CG. PFDA works as follows: Step 1. After the connection setup procedure is complete, both NL and NK are set to 0, and the Status is set to “active”. At this point, the GSN can send GTP’ messages to the CG. Step 2. When a GTP’ message is sent from the GSN to the CG at time t , a copy of the message is stored in the unacknowledged buffer, where the expiry timestamp is set to te=t + Tr. Step 3. If the GSN has received the acknowledgement from the CG before te , both NL and NK are set to 0. Step 4. If the GSN has not received the acknowledgement from the CG before te , NL is incremented by 1. If NL =L, then the charging packet delivery is considered failed. NK is incremented by 1. Step 5. If NK =K, then the GTP’ connection is considered failed. The Status is set to “inactive”. 39
Chapter 8: Mobile All-IP Network Signaling n n Traditional SS 7 signaling is implemented in MTP-based network, which is utilized in the existing mobile networks including GSM and GPRS. In UMTS all-IP architecture, the SS 7 signaling will be carried by IP-based network. The low costs and the efficiencies for carriers to maintain a single, unified telecommunications network, guarantee that all telephony services will eventually be delivered over IP. This chapter describes design and implementation of the IPbased network signaling for mobile all-IP network. 40
SS 7 Architecture NETWORK 2 NETWORK 1 STP pair A-link SCP C-link D-link B-link A-link SSP E-link F-link A-link SSP Voice/Data Trunk SS 7 Signaling Link Trunk n n n Service Switching Point (SSP) is a telephony switch that performs call processing. Service Control Point (SCP) contains databases for providing enhanced services. Signal Transfer Point (STP) is a switch that relays SS 7 messages between SSPs and SCPs. 41
SS 7 Link Types n n n Access Links (A-links) connect the SSP/STP or the SCP/STP pairs. Bridge Links (B-links) connect STPs in different pairs. Cross Links (C-links) connect mated STPs in a pair. Diagonal Links (D-links) are the same as the B-links except that the connected STPs belong to different SS 7 networks. Extended Links (E-links) provide extra connectivity between an SSP and the STPs other than its home STP. Fully-Associated Links (F-links) connect SSPs directly. 42
SS 7 Protocol Stack OSI Model The SS 7 Layers OMAP Application ISUP TCAP Presentation Session Transport SCCP Network MTP 3 Data Link MTP 2 Physical MTP 1 43
SS 7 Protocol Stack: MTP & SCCP n Message Transfer Part (MTP) consists of three levels corresponding to the OSI physical layer, data link layer, and network layer, respectively. n n The MTP level 1 (MTP 1) defines the physical, electrical, and functional characteristics of the signaling links connecting SS 7 components. The MTP level 2 (MTP 2) provides reliable transfer of signaling messages between two directly connected signaling points. The MTP level 3 (MTP 3) provides the functions and procedures related to message routing and network management. Signaling Connection Control Part (SCCP) provides additional functions such as Global Title Translation (GTT) to the MTP. 44
SS 7 Protocol: ISUP, TCAP, MAP n n Integrated Services Digital Network User Part (ISUP) establishes circuit-switched network connections (e. g. , for call setup). Transaction Capabilities Application Part (TCAP) provides the capability to exchange information between applications using non-circuit-related signaling. Operations, Maintenance, and Administration Part (OMAP) is a TCAP application for network management. Mobile Application Part is a TCAP application that supports mobile roaming management. 45
Stream Control Transmission Protocol (SCTP) n n n IETF Signaling Transport (SIGTRAN) working group addresses the issues regarding the transport of packet-based SS 7 signaling over IP networks. SIGTRAN defines not only the architecture but also a suite of protocols, including the SCTP and a set of user adaptation layers (e. g. M 3 UA), which provides the same services of the lower layers of the traditional SS 7. Why not TCP ? n n n TCP provides strict order-of-transmission which causes head-of-line blocking problem. The TCP socket does not support multi-homing. TCP is vulnerable to blind Denial-of-Service (Do. S) attacks such as flooding SYN attacks. 46
SCTP Features n Like TCP n n n To provide reliable IP connection. To employ TCP-friendly congestion control (including slow-start, congestion avoidance, and fast retransmit) Unlike TCP n n To provide message-oriented data delivery service and new delivery options (ordered or unordered) To provide selective acknowledgments for packet loss recovery To use a four-way handshake procedure to establish an association (i. e. , a connection). To offer new features that are particularly for SS 7 signaling n n Multi-homing Multi-streaming 47
Chapter 11: Multicast for Mobile Multimedia Messaging Service n n n Short Message Service (SMS) allows mobile subscribers to send and receive simple text message in 2 G systems (e. g. GSM). Multimedia Message Service (MMS) is introduced to deliver messages of sizes ranging from 30 K bytes to 100 K bytes in 2. 5 G systems (e. g. GPRS) and 3 G systems (e. g. UMTS) The content of an MMS can be text (just like SMS), graphics (e. g. , graphs, tables, charts, diagrams, maps, sketches, plans and layouts), audio samples (e. g. , MP 3 files), images (e. g. , photos), video (e. g. , 30 -second video clips), and so on. 48
MMS Architecture [1/2] 49
MMS Architecture [2/2] n n n The MMS user agent (a) resides in a Mobile Station (MS) or an external device connected to the MS, which has an application layer function to receive the MMS. The MMS can be provided by the MMS value added service applications (b) connected to the mobile networks or by the external servers (d) (e. g. , email server, fax server) in the IP network. The MMS server (c) stores and processes incoming and outgoing multimedia messages. The MMS relay (e) transfers messages between different messaging systems, and adapts messages to the capabilities of the receiving devices. It also generates charging data for the billing purpose. The MMS server and the relay can be separated or combined. The MMS user database (f) contains user subscriber data and configuration information. The mobile network (g) can be a WAP (Wireless Application Protocol) based 2 G, 2. 5 G or 3 G system. Connectivity between different mobile networks is provided by the Internet protocol. 50
Short Message Multicast Architecture MCH (HLR) VLR 1 1 VLR 2 2 VLR 3 0 MCV (VLR 1) MCV (VLR 3) LA 5 0 LA 6 0 MCV (VLR 2) LA 1 0 LA 3 0 LA 2 1 LA 4 2 51
MMS Multicast [1/2] MCc (CBC) RA 1 0 RA 2 1 RA 3 0 RA 4 2 RA 5 0 RA 6 0 52
MMS Multicast [2/2] n n n Step 1. The multimedia message is first delivered from the message sender to the Cell Broadcast Entity (CBE). Step 2. The CBE forwards the message to the Cell Broadcast Center (CBC). Step 3. The CBC searches the multicast table MCC to identify the routing areas RAi where the multicast members currently reside (i. e. , MCC [RAi] > 0 in the CBC). In Figure 1. 7, i = 2 and 4. Step 4. The CBC sends the multicast message to the destination RNCs (i. e. , RNC 1 and RNC 2 in Figure 1. 7) through the Write Replace message defined in 3 GPP TS 23. 041. Step 5. The RNCs deliver the multimedia messages to the multicast members in the RAs following the standard UMTS cell broadcast procedure. Like SMS multicast, a multicast table MCC is implemented in the CBC to maintain the identities of the RAs and the numbers of the multicast members in these RAs. 53
Chapter 12: Session Initiation Protocol n n n SIP is an application-layer signaling protocol over the IP network. SIP is designed for creating, modifying and terminating multimedia sessions or calls. SIP message specifies the Real-Time Transport Protocol / Real-Time Transport Control Protocol (RTP/RTCP) that deliver the data in the multimedia sessions. n n RTP is a transport protocol on top of UDP, which detects packet loss and ensures ordered delivery. A RTP packet also indicates the packet sampling time from the source media stream. The destination application can use this timestamp to calculate delay and jitter. 54
Network Elements: User Agent n The user agent resides at SIP endpoints (or phones). A user agent contains both a User Agent Client (UAC) and a User Agent Server (UAS). n n The UAC (or calling user agent) is responsible for issuing SIP requests The UAS (or called user agent) receives the SIP request and responds to the request. (a) SIP UA Developed in the National Chiao Tung University (b) Windows Messenger 4. 7 -based SIP UA (with phone number 0944021500) 55
Network Elements: Network Servers n n n Registrar: A UA can periodically register its SIP URI and contact information (which includes the IP address and the transport accepting the SIP messages) to the registrar. Proxy Server: A proxy server processes the SIP requests. The proxy server either handles the request or forwards it to other servers, perhaps after performing some translation. Redirect Server: A redirect server accepts the INVITE requests from a UAC, and returns a new address to that UAC. 56
SIP Registration and Call Setup 57
Chapter 13: Mobile Number Portability n n Number Portability (NP) is a network function that allows a subscriber to keep a unique telephone number. NP is an important mechanism n n n to enhance fair competition among telecommunication operators and to improve customer service quality. Three types of NP are discussed: n n n location portability, service portability, and operator portability. 58
Terminologies n n Number range holder (NRH) network : the network which the number is assigned Subscription network: the network with which the customer’s mobile operator has a contract to implement services for a specific mobile phone number Donor (release) network: subscription network from which a number is ported in the porting process Recipient network: network that receives the number in the porting process 59
MDN vs MIN n An MS is associated with two number. n n n Mobile directory number (MDN) is dialed to reach the MS (e. g. , MSISDN in GSM). Mobile identification number (MIN) is a confidential number that uniquely identifies an MS in Mobile Network (e. g. , IMSI in GSM). When mobile number portability is introduced, a porting mobile user would keep the MSISDN (the ported number) while being issued a new IMSI in GSM. 60
Simplified GSM Call Termination Procedure without NP Step 1: After calling party dials the MSISDN of MS 2, the call route to the GMSC of MS 2. Step 2: GMSC query HLR to query the location of MS 2. Step 3: The call is routed to the destination MSC and eventually set up. 61
Call Routing Mechanism with NP n In 3 GPP TS 23. 066, two approaches are proposed to support number portability call routing: n n n Signaling Relay Function (SRF)-based solution, and Intelligent Network (IN)-based solution. Both approaches utilize the Number Portability Database (NPDB) that stores the recodes for the ported numbers. 62
SRF-based Approach n n The SRF node is typically implemented on the Signal Transfer Point (STP). Three call setup scenarios have been proposed for SRF-based approach: direct routing (DR) and indirect routing (IR). n DR: The mobile number portability query is performed in the originating network. n IR: The mobile number portability query is performed in the NRH. 63
DR Call Setup Scenario 1 Step 1: After calling party dials the MSISDN of MS 2, the call is routed to the GMSC of the originating network. Step 2: The GMSC queries SRF for the subscription network information of MS 2. Step 3: By consulting the NPDB, the SRF obtains the subscription network information, and forwards it to the originating GMSC. Step 4: The originating GMSC routes the call to the subscription GMSC (i. e. , GMSC of MS 2). The call is then set up following the standard GSM procedure. 64
DR Call Setup Scenario 2 Step 1: After calling party dials the MSISDN of MS 2, the call is routed to the GMSC of the originating network. Step 2: The GMSC queries SRF for the subscription network information of MS 2. Step 3: By consulting the NPDB, the SRF obtains the subscription network information. If the originating network is the subscription network of MS 2, then SRF forward message to query HLR to obtain the routing information of MS 2. Step 4: The information will then be returned to the originating GMSC. Then call is set up following the standard GSM procedure. 65
Chapter 14: Integration and WLAN and Cellular Networks n n n n UMTS: Universal Mobile telecommunication System UTRAN: UMTS Terrestrial Radio Access Network RNC: Radio Network Controller SGSN: Serving GPRS Support Node GGSN: Gateway GPRS Support Node Service aspects Access control aspects Security aspects Roaming aspects Terminal aspects Naming and address aspects Charging and billing aspects HLR: Home Location Register PDN: Packet Data Network WGSN: WLAN-based GPRS Support Node AP: Access MS: Mobile Station 66
WLAN/Cellular Integration Scenarios Service Capabilities Scenario 1 2 3 4 5 6 Common Billing ○ ○ ○ Common Customer Care ○ ○ ○ Cellular-based Access Control ╳ ○ ○ ○ Cellular-based Access Charging ╳ ○ ○ ○ Access to Mobile PS Services ╳ ╳ ○ ○ Service Continuity ╳ ╳ ╳ ○ ○ ○ Seamless Service Continuity ╳ ╳ ○ ○ Access to Mobile CS Service with Seamless Mobility ╳ ╳ ╳ ○ 67
The MS Architecture Perform MS Attach and detach procedure. (The authentication action is included in the attach procedure. ) Set up network Configuration. Retrieve the SIM information. 68
The WGSN Node Architecture 69
Chapter 15: UMTS All-IP Network n Mobile system history n The advantages of evolution from UMTS R 99 to all-IP network n n n Mobile network will benefit from all existing Internet applications. The telecommunications operators will deploy a command backbone for all type of access, and thus to reduce capital and operating cost. New applications will be developed in an all-IP environment, which guarantees optimal synergy between the mobile network and Internet. 70
All-IP Architecture n Option 1 n n Support PS-domain multimedia and data service. Option 2 n Extend option 1 network by accommodating CSdomain voice service over a packet switched core network. 71
All-IP Architecture (option 1) 72
All-IP Architecture (option 1) n Radio Network n n Home Subscriber Server n n Support mobility management and session management. IP Multimedia Core Network Subsystem n n Act as master database containing all 3 G user-related subscriber data. GPRS Network n n Can be GERAN or UTRAN. Provide mobility management and session management. Application and Service Networks n Support flexible services through service plateform. 73
Call Session Control Function (CSCF) n Function n Communicate with HSS for location information Handle control-layer functions related to application level registration and SIP-based multimedia session. Logical components n Incoming Call Gateway n n Communicate with HSS to perform routing of incoming calls. Call Control Function n Handle call setup and call-event report for billing and auditing. 74
CSCF (cont. ) n Serving Profile Database n n Address Handing n n Interact with HSS in the home network to obtain profile information. Analyze, translate, and may modify address. Three types of CSCF n P-CSCF n n n I-CSCF n n n Be assigned to a UE while it attaches to the network. Forward the requests to the I-CSCF at home network. Contact point for the home network of the destination UE. Route the request towards the S-CSCF n n Be assigned to a UE after successful application level registration. Support signing interactions with the UE for call setup and supplementary services control. 75
HSS, BGCF, and MGCF n Home Subscriber Server (HSS) Keep a list of features and services associated with users, and maintain the location of the users. Provide the HLR functionality required by the PC and CS domain, and the IM functionality required by the IMS. n n n Breakout Gateway Control Function (BGCF) n n Select appropriate PSTN breakout point (another BGCF or an MGCF). Media Gateway Control Function (MGCF) n n Acts as the media gateway controller in a Vo. IP network. Control the media channels in an MGW. 76
T-SGW, MRF, and MGW n Transport Signaling Gateway Function (T-SGW) n n Media Resource Function (MRF) n n Map call related signing from/to the PSTN on an IP bearer and send it to/from the MGCF. Perform multiparty call, multimedia conference, tones and announcements functionalities. Media Gateway (MGW) n n Provide user plane data transport between UMTS core network and PSTN. Interact with MGCF for resource control. 77
All-IP Architecture (option 2) Two control elements are introduced: MSC server and GMSC server. n n Support Media Gateway Control Protocol (MGCP) or H. 248 to handle control layer functions related to CS domain. MSC server + MGW = MSC (in UMTS R 99) Control plane User plane 78
Application Level Registration Step 1. UE sends SIP REGISTER to P-CSCF. Step 2. P-CSCF performs address translation of UE’s home domain name to find I-CSCF address. Step 3. I-CSCF determines the HSS address, and queries the HSS about the registration status of the UE. Step 4. I-CSCF obtains the required S -CSCF capability information and selects an appropriate S-CSCF. Step 5. I-CSCF forwards SIP REGISTER to S-CSCF. Step 6. S-CSCF presents its name and subscriber identity to HSS. Step 7. S-CSCF obtains the UE’s subscriber data from HSS. Step 8. SIP 200 OK is replied. Step 9. P-CSCF stores the home contact name and forwards SIP 200 OK. 79
Author Biography n n Yi-Bing Lin is Chair Professor of College of Computer Science, National Chiao Tung University. His current research interests include mobile computing and cellular telecommunications services. Dr. Lin has published over 200 journal articles and more than 200 conference papers. He is the co-author of the books Wireless and Mobile Network Architecture (with Imrich Chlamtac; published by Wiley, 2001) and Wireless and Mobile All-IP Networks (with Ai-Chun Pang; published by Wiley, 2005). Dr. Lin is an IEEE Fellow, ACM Fellow, AAAS Fellow, and IEE Fellow. 80
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