1. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures VoIP Service for Mobile Networks 03, 05,06 winthory@yahoo.co.kr Network Computing LAB 김 응 도 Chapter 16

2. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures  VoIP is considered as a promising trend in telecommunication.  Integrating mobile phone services with VoIP in particular has become an important issue.  Telecommunications and Internet Protocol Harmonization over Network (TIPHON) specifies the mechanism (i.e. a mediation gatekeeper) to provide the service control functions for convergence of IP networks, mobile networks, fixed wireless networks, and PSTN.  Several scenario are defined in TIPHON to illustrate different ways of integrating IP and mobile networks.  We use GSM as an example of mobile networks to describe mobile/IP integration, where the mobile signaling protocol is GSM MAP

3. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures TIPHON IP and mobile integration scenario. Signaling Gateway MSC VLR HLR Gateway (VLR) Mediation Gatekeeper Mobile Network IP Network BSC/BTS

4. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures contents  GSM on the Net  The iGSM Wireless VoIP Solution  The H.323 Network  The iGSM Architecture  iGSM Procedure and Message Flows  Registration  Deregistration  Call Delivery to the IP network  Implementation Issues  Reducing GSM Tromboning Effect  Misrouting Due to User Mobility

5. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures GSM on the Net  Based on a concept similar to TIPHON, Ericsson’s GSM on the Net utilizes a corporate intranet to integrate an enterprise communication network with the public GSM network  This system supports both terminal mobility and user mobility.  Terminal mobility : whereby a terminal can be moved around the service area without losing contact with the system  User mobility : whereby, using various types of terminals, a user can move around the service area without losing contact with the system  Each of the elements in the corporate network is connected to a switched Ethernet with 10Mbps bandwidth.  They communicate with each other using the H.323 family of protocols.

6. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures GSM on the Net Service node MSC VLR HLR Gateway Access node GSM Network Corporate offices GSM/BTS BSC/BTS Intranet IP Phone/PC

7. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures GSM on the Net  Service node  Enables user mobility.  Controls calls among different types of terminals.  Translates addresses between PSTN and GSM on the Net.  Provides authentication, resource management, least-cost routing, and administration for user identity and service profile.  Access node  Resembles the MSC, VLR, and BSC to manage connection, mobility, and radio resources.  Does not provide trunks; instead, controls only the communication between the endpoints.  Consist of network access controller (NAC), and the radio network server (RNS)

8. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures  GSM/BTS  Provides wireless access for a GSM MS in the IP network  Gateway  Provides interfaces between GSM on the Net and other networks (particularly the GSM network)  Consists of both voice and SS7 gateway functionality  Terminal equipment  Can be an IP phone, PC, DECT phone, or GSM mobile station.

9. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures The iGSM Wireless VoIP soultion  We proposes the iGSM service that realizes another TIPHON scenario supporting user mobility for GSM subscribers to access VoIP service.  GSM Network 에서 GSM 서비스를 받던 사용자가 GSM MS 없이 IP Network 으로 이동하여 자신의 MSISDN 으로 수신되는 전화를 받기 위해서 H.323 terminal 을 사용할 수 있다.  iGSM solution is different from GSM on the Net  Unlike GSM on the Net, iGSM is a value-added service to the public GSM Networks.  iGSM network does not introduce wireless access equipment in the IP network; rather, iGSM service is implemented using standard platforms(general IP gateway / gatekeeper)

10. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures The iGSM Wireless VoIP soultion  We describe the iGSM architecture and the protocols for location update and call delivery.  We discuss how the tromboning effect in standard GSM systems can be avoided when accessing the IP Network.  We investigate the problem of misrouting a call caused by user mobility.

11. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures H.323 Network H.323 Gatekeeper H.323 Gateway H.323 Multipoint Control Unit MC MP MC ISDN LAN PSTN H.323 Terminal (phone or PC) The iGSM system consists of the GSM and H.323 (IP) networks. ITU-T H.323 covers the technical requirements for multimedia communications Over packet-based networks that may not provide a guaranteed quality of service Over packet-based networks that may not provide a guaranteed quality of service

12. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures H.323 architecture  Terminal  Customer premises equipment (CPE) that provides audio, video, and data communications capability for point to point or multipoint conferences in the H.323 network  Gateway  Perform call control function and the communication protocol translation mechanism between an H.323 endpoint and endpoint of a circuit-switched network, such as ISDN,PSTN  Gatekeeper  Optional in an H.323 network  May be colocated with a terminal, gateway, or multipoint control unit  Provide these functions that address translation, admissions control, bandwidth control, and zone management.

13. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures H.323 architecture  Multipoint control unit (MCU)  Utilizes multipoint controllers to support multipoint conferences  Multipoint controller  Provides control functions to support conferences between three or more endpoints in a multipoint conference.  Every MCU contains an MC.  Multipoint process (MP)  Receives audio, video, and data streams from the endpoints involved in a multipoint conference.  An MP is optionally included in a gateway, gatekeeper, or MCU

14. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures The iGSM Architecture  iGSM gateway is implemented to perform two major functions besides the standard H.323 mechanisms  GSM MAP and H.225 RAS (registration, admission, status) protocol translation.  GSM/PSTN/IP call setup and release  An iGSM gatekeeper is implemented to serve as the VLR for iGSM subscribers who visit the IP network.  Every iGSM gatekeeper is assigned an ISDN number that can be recognized by the HLR.  The iGSM gatekeeper maintains a list of all iGSM subscribers.  Based on this list, the gatekeeper performs MSISDN-to- transport address translation and GSM roaming management procedures for the iGSM subscribers.

15. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures iGSM architecture GSM IP network MSC VLR HLR iGSM Gateway Gatekeeper iGSM VLR BTS/BSC H.323 Terminal MS

16. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures iGSM procedures and Message Flows  Every iGSM subscriber has a record in the datebase.  MSISDN of the MS  Transport address of the H.323 terminal for the subscriber in the IP network.  Password of the iGSM subscriber  HLR address of the iGSM subscriber  IMSI of the MS  User profile which indicates the service features and restrictions the iGSM subscriber  Presence indication of the iGSM subscriber in the IP network.

17. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures iGSM user moves from the GSM network to the IP network H.323 terminal turn on  MSISDN and password 입력  Gatekeeper 로 RAS RRQ(MSISDN, passwd) 전 송 Pass 를 통해 validate 검사  IRQ(UpdateLoc, IMSI, VLR, MSC num) 을 iGSM gateway 로 전달  Gateway GSM MAP 으로 변환 HLR 로 MAP_UPDATE_LOCATION(IMSI, VLR, MSC num) 전송 수신된 IMSI 를 통해 HLR 은 user profile 수정  MAP_INSERT_SUBSCRIBER_DATA (user profile) 을 iGSM gateway 로 전달  iGSM Gateway IRR(InsSubsData, user profile) 을 gatekeeper 로 전송 iGSM gatekeeper 는 user profile 을 기록  IRQ(InsSubDataAck) 을 iGSM gateway 로 전달  iGSM Gateway 는 ACK 를 HLR 로 전송 HLR 은 registration 과정을 끝낸다  MAP_UPDATE_LOCATION_ack 을 iGSM gateway 로 전달  iGSM Gateway 는 RFC(Registration Comfirm) 를 gatekeeper 로 전달 HLR 은 deregistration 을 oldVLR 에 알린다  MAP_CANCEL_LOCATION 을 oldVLR 로 전달  oldVLR 은 iGSM MS 의 기록을 지운다 Registration H.323 terminal GSM IP network MSC VLR HLR iGSM Gateway Gatekeeper iGSM VLR BTS/BSC 1 2 4 7,8 MS 3 65 3 4 6 5

18. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures Message flow for iGSM registration H.323 terminal Gatekeeper (new VLR) Gateway HLROld VLR 2 3 3 4 4 5 5 6 6 6 7 8 PRQ(MSISDN) IRQ MAP_UPDATE_LOCATIO N MAP_INSERT_SUBSCRIBERDATA MAP_CANCEL_LOCATIO N MAP_CANCEL_LOCATION_ac k IRQ IRR MAP_INSERT_SUBSCRIBER_DATA_ac k MAP_UPDATE_LOCATION_ack IRR RCF

19. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures deregistration H.323 terminal HLRGateway Gatekeeper (old VLR) MAP_CANCEL_LOCATION(IMSI) MAP_CANCEL_LOCATION_ack IRR (CanLoc, IMSI) IACK (CanLocAck) URQ(unregister Request) UCF(Unregister Confirmation) 2 2 2 1 1 1  In this case of the iGSM gatekeeper is the “OLD VLR”  iGSM subscriber moves from the IP Network to the GSM Network.

20. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures iGSM 가입자의 MSISDN 입력 (0-936105401)  0 : special digit, 936 : GMSC  Originating switch send SS7 IAM message to GMSC GMSC query the location of iGSM subscriber to HLR  MSISDN 을 통해 HLR 은 가입자가 IP network 에 있음을 확인  HLR send iGSM gateway(MAP_PROVIDE_ROAMING_NUMBE R)  Gateway LRQ(Location Request) 를 Gatekeeper 에 전달. Getekeeper 는 Gateway 와 terminal 의 주소를 통해 MSRN 생성  RAS LCF(Location Confirm) 를 gateway 로 전달  gateway 는 MAP_PROVIDE_ROAMING_NUMBER_ack with MSRN 을 HLR 에 전달  HLR 은 GMSC 에 MAP_SEND_ROUTING_INFORMATION_ack 얻은 MSRN 을 통해 GMSC 는 IAM message 를 통하여 Gateway 와 trunk 설정 iGSM subscriber 의 MSRN 을 수신한 gateway 는 ARQ (Admission Request) and ACF (Admissions Confirm) exchange  gatekeeper 로부터 MSRN 을 통해 terminal 의 call-signaling channel transport address 획 득 Gateway sends the H.225(Q.931) Set-up msg 를 H.323 terminal 에 전달  Call Proceeding ( 충분한 routing 정보를 받았다 ) message reply H.323 terminal 은 gatekeeper 와 ARQ and ACF message 를 교환 ( 이때 ARJ(Admission Reject) 수신 가능 Ringing tone is generated at the H.323 terminal  H.225 Alerting message is sent to gateway  gateway 는 Alerting message 를 SS7 ACM message 로 변형하여 GMSC 에 전달 iGSM subscriber 가 수신하면, H.323 terminal 은 RAS Connect message 를 gateway 에 전달  SS7 ANM 로 변형되어 originating switch 에 전 달  대화 시작 Call delivery to the IP network H.323 terminal GSM IP network Gateway MSC HLR iGSM Gateway Gatekeeper iGSM VLR 1 Switch Originating PSTN 2 3 1 3 2 3 2 4 6 5 7 8 10 9 12 11

21. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures Message flow for iGSM call setup

22. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures Implementation Issues  iGSM 을 구현함에 있어서 고려해야 할 두가지 이슈  Reducing GSM Tromboning Effect  Investigating misrouting of user mobility

23. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures Reducing GSM Tromboning Effect  Tromboning occurs when the caller and the called MS are in the same city but the GMSC is in another city.  Both GSM MSCs and iGSM gateways can serve as GMSCs for iGSM subscribers  If an iGSM subscriber is assigned a GSM MSC as his GMSC, call delivery follows the procedure iGSM call delivery and tromboning occurs.  If an iGSM subscriber is assigned a iGSM gateway as his GMSC, call delivery tromboning can be avoided

24. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures Reducing GSM Tromboning Effect PSTN iGSM IP network Switch iGSM Gateway Gatekeeper iGSM VLR 1 2 caller 34 5 iGSM user IP Network iGSM IP network iGSM Gateway Gatekeeper iGSM VLR 1 2 iGSM user calle r  Two kinds of subscribers are anticipated in iGSM  The GMSCs of the iGSM subscribers are standard GSM MSCs. In this case, the subscibers typically subscribe to the standard GSM services at the beginning, and determine to include the iGSM service later  The GMSC of the subscribers is the iGSM gateway. In this case, the subscribers typically subscribe to the iGSM service from the beginning

25. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures Reducing GSM Tromboning Effect  The first kind of subscribers  call delivery follows the standard GSM procedure  A subscriber visits the IP network, tromboning may occur as in traditional GSM networks  The GSM operator would prefer this scenario if the iGSM gateway and gatekeeper are owned by other ISPs.  The second kind of subscribers  Call-delivery tromboning avoided when the subscriber visits the IP network.  The GSM operator is likely to own the iGSM gateway and gatekeeper

26. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures Misrouting Due to User Mobility  To support user mobility, the subscriber needs to explicitly perform registration to inform the system in which location area he resides when the terminal has been changed.  Missing  call deliveries may be misrouted  This problem can be eliminated if the subscriber always turns off the MS when he moves to the H.323 terminal  The turn-off action results in a GSM detach message, which deregisters the MS.

27. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures Misrouting Due to User Mobility GSM VoIP network MSC GSM VoIP Gateway VLR B HLR p A VLR A p IP Phone HLR p B GSM MS 1 4 2 VLR A VLR B p 3 step1 step2step3

28. Kwangwoon Univ. http://netcom.kw.ac.kr Wireless and Mobile Network Architectures Misrouting Due to User Mobility  The misrouting problem is avoided if the subscriber explicitly or implicitly registers with the GSM MS step3.  Implicit registration occurs in two cases  The subscriber originates a call. In this case, VLR A finds that the VLR record for the subscriber does not exit. VLR A will ask the MS to perform a registration operation, as described in the VLR failure restoration procedure  The subscriber moves to another LA in the GSM network. Registration is automatically initiated by the GSM MS.  Both case, after the HLR has modified the subscriber’s record, it also cancels the subscriber’s VLR record in VLR B