6- voip service

Kwangwoon Univ.http://netcom.kw.ac.kr

Wireless and Mobile Network Architectures

VoIP Service for Mobile NetworksVoIP Service for Mobile Networks

03, 05,06 03, 05,06 [email protected]@yahoo.co.kr

Network Computing LABNetwork Computing LAB김 응 도김 응 도

Chapter 16Chapter 16

mailto:[email protected]



VoIP is considered as a promising trend in telecommunicatiVoIP is considered as a promising trend in telecommunication.on.

Integrating mobile phone services with VoIP in particular haIntegrating mobile phone services with VoIP in particular has become an important issue.s become an important issue.

Telecommunications and Internet Protocol Harmonization oTelecommunications and Internet Protocol Harmonization over Network (TIPHON) specifies the mechanism (i.e. a mediver Network (TIPHON) specifies the mechanism (i.e. a mediation gatekeeper) to provide the service control functions fation gatekeeper) to provide the service control functions for convergence of IP networks, mobile networks, fixed wirelor convergence of IP networks, mobile networks, fixed wireless networks, and PSTN.ess networks, and PSTN.

Several scenario are defined in TIPHON to illustrate differenSeveral scenario are defined in TIPHON to illustrate different ways of integrating IP and mobile networks.t ways of integrating IP and mobile networks.

We use GSM as an example of mobile networks to describWe use GSM as an example of mobile networks to describe mobile/IP integration, where the mobile signaling protocoe mobile/IP integration, where the mobile signaling protocol is GSM MAPl is GSM MAP



TIPHON IP and mobile integration scenario.TIPHON IP and mobile integration scenario.

Signaling Gateway

MSCVLR

HLR

Gateway

(VLR)Mediation

Gatekeeper

Mobile Network

IP Network

BSC/BTS

BSC/BTS



contentscontents

GSM on the NetGSM on the Net

The iGSM Wireless VoIP SolutionThe iGSM Wireless VoIP Solution The H.323 Network The iGSM Architecture

iGSM Procedure and Message FlowsiGSM Procedure and Message Flows Registration Deregistration Call Delivery to the IP network

Implementation IssuesImplementation Issues Reducing GSM Tromboning Effect Misrouting Due to User Mobility



GSM on the NetGSM on the Net Based on a concept similar to TIPHON, Based on a concept similar to TIPHON,

Ericsson’s GSM on the Net utilizes a corporate Ericsson’s GSM on the Net utilizes a corporate intranet to integrate an enterprise intranet to integrate an enterprise communication network with the public GSM communication network with the public GSM networknetwork

This system supports both terminal mobility This system supports both terminal mobility and user 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 Each of the elements in the corporate network is connected to a switched Ethernet with is connected to a switched Ethernet with 10Mbps bandwidth.10Mbps bandwidth.

They communicate with each other using the They communicate with each other using the H.323 family of protocols.H.323 family of protocols.



GSM on the NetGSM on the Net

Servicenode

MSC

VLR

HLR

Gateway

Accessnode

GSM NetworkCorporate offices

GSM/BTS

BSC/BTSIntranet

IP Phone/PC



GSM on the NetGSM on the Net Service node 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 nodeAccess 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)



GSM/BTSGSM/BTS Provides wireless access for a GSM MS in the IP

network GatewayGateway

Provides interfaces between GSM on the Net and other networks (particularly the GSM network)

Consists of both voice and SS7 gateway functionality Terminal equipmentTerminal equipment

Can be an IP phone, PC, DECT phone, or GSM mobile station.



The iGSM Wireless VoIP soultionThe iGSM Wireless VoIP soultion

We proposes the iGSM service that realizes another TIPHWe proposes the iGSM service that realizes another TIPHON scenario supporting user mobility for GSM subscribers ON scenario supporting user mobility for GSM subscribers to access VoIP service.to access VoIP service.

GSM NetworkGSM Network 에서 에서 GSM GSM 서비스를 받던 사용자가 서비스를 받던 사용자가 GSM GSM MSMS 없이 없이 IP NetworkIP Network 으로 이동하여 자신의 으로 이동하여 자신의 MSISDN MSISDN 으로 으로 수신되는 전화를 받기 위해서 수신되는 전화를 받기 위해서 H.323 terminalH.323 terminal 을 사용할 을 사용할 수 있다수 있다 ..

iGSM solution is different from GSM on the NetiGSM solution is different from GSM on the Net Unlike GSM on the Net, iGSM is a value-added service to the pub

lic GSM Networks. iGSM network does not introduce wireless access equipment in th

e IP network; rather, iGSM service is implemented using standard platforms(general IP gateway / gatekeeper)



The iGSM Wireless VoIP soultionThe iGSM Wireless VoIP soultion

We describe the iGSM architecture and the protocols for We describe the iGSM architecture and the protocols for location update and call delivery.location update and call delivery.

We discuss how the tromboning effect in standard GSM We discuss how the tromboning effect in standard GSM systems can be avoided when accessing the IP Network.systems can be avoided when accessing the IP Network.

We investigate the problem of misrouting a call caused We investigate the problem of misrouting a call caused by user mobility.by user mobility.



H.323 NetworkH.323 Network

H.323Gatekeeper

H.323Gateway

H.323Multipoint

Control Unit

MC

MC

MC

MPMP

MP

MC

ISDNLANPSTN

H.323 Terminal (phone or PC)

The iGSM system consists of the GSM and H.323 (IP) networks.The iGSM system consists of the GSM and H.323 (IP) networks.

<H.323 Architecture><H.323 Architecture>

ITU-T H.323 covers the technical requirements for multimedia ITU-T H.323 covers the technical requirements for multimedia communicationscommunications

Over packet-based networks that may not provide a guaranteed Over packet-based networks that may not provide a guaranteed quality of servicequality of service



H.323 architectureH.323 architecture TerminalTerminal

Customer premises equipment (CPE) that provides audio, video, and data communications capability for point to point or multipoint conferences in the H.323 network

GatewayGateway Perform call control function and the communication protocol transl

ation mechanism between an H.323 endpoint and endpoint of a circuit-switched network, such as ISDN,PSTN

GatekeeperGatekeeper Optional in an H.323 network May be colocated with a terminal, gateway, or multipoint control unit Provide these functions that address translation, admissions contro

l, bandwidth control, and zone management.



H.323 architectureH.323 architecture

Multipoint control unit (MCU)Multipoint control unit (MCU) Utilizes multipoint controllers to support multipoint

conferences Multipoint controllerMultipoint controller

Provides control functions to support conferences between three or more endpoints in a multipoint conference.

Every MCU contains an MC. Multipoint process (MP)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



The iGSM ArchitectureThe iGSM Architecture iGSM gateway is implemented to perform two major functiiGSM gateway is implemented to perform two major functi

ons besides the standard H.323 mechanismsons besides the standard H.323 mechanisms GSM MAP and H.225 RAS (registration, admission, status) protoco

l translation. GSM/PSTN/IP call setup and release

An iGSM gatekeeper is implemented to serve as the VLR fAn iGSM gatekeeper is implemented to serve as the VLR for iGSM subscribers who visit the IP network.or iGSM subscribers who visit the IP network. Every iGSM gatekeeper is assigned an ISDN number that can be re

cognized 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.



iGSM architectureiGSM architecture

GSM

IP networkMSC

VLR

HLR

iGSMGateway

GatekeeperiGSM VLR

BTS/BSC

H.323 Terminal

MS



iGSM procedures and Message FlowsiGSM procedures and Message Flows

Every iGSM subscriber has a record in the datebase.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 I

P 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 th

e iGSM subscriber Presence indication of the iGSM subscriber in the IP network.



HLR 은 deregistration 을 oldVLR 에 알린다MAP_CANCEL_LOCATION을 oldVLR 로 전달 oldVLR 은 iGSM MS 의 기록을 지운다

RegistrationRegistration iGSM user moves from the GSM network to the IP network

H.323 terminal turn on MSISDN and password 입력Gatekeeper 로 RAS RRQ(MSISDN , passwd) 전송

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 끝낸다MAP_UPDATE_LOCATION_ack을 iGSM gateway 로 전달 iGSM Gateway 는 RFC(Registration Comfirm)를 gatekeeper 로 전달

H.323 terminal

GSM

IP networkMSC

VLR

HLR

iGSMGateway

GatekeeperiGSM VLR

BTS/BSC 1

24

7,8

MS

3

6 5

34

65



Message flow for iGSM registrationMessage flow for iGSM registrationH.323

terminal

Gatekeeper (new VLR)

Gateway HLR Old VLR

23 3

44

5

56

66

7

8

PRQ(MSISDN)IRQ

MAP_UPDATE_LOCATIONMAP_INSERT_SUBSCRIBERDATA

MAP_CANCEL_LOCATIONMAP_CANCEL_LOCATION_ackIRQ

IRR

MAP_INSERT_SUBSCRIBER_DATA_ack

MAP_UPDATE_LOCATION_ack

IRRRCF



deregistrationderegistration

H.323 terminalHLR Gatewa

y

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

11

1

In this case of the iGSM gatekeeper is the “OLD VLR”

iGSM subscriber moves from the IP Network to the GSM Network.



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_NUMBER) 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 설정iGSM subscriber 의 MSRN 을 수신한 gateway는 ARQ (Admission Request) and ACF (Admissions Confirm) exchange gatekeeper 로부터 MSRN 을 통해 terminal 의 call-signaling channel transport address 획득

Gateway sends the H.225(Q.931) Set-up msg를 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 terminal은 RAS Connect message 를 gateway 에 전달 SS7 ANM 로 변형되어 originating switch 에 전달대화 시작

Call delivery to the IP networkCall delivery to the IP networkH.323 terminal

GSMIP network

GatewayMSC

HLR

iGSMGateway

GatekeeperiGSM VLR

1

SwitchOriginating

PSTN

2 3

1

32

324

65

78

109

1211



Message flow for iGSM call setupMessage flow for iGSM call setup



Implementation IssuesImplementation Issues iGSMiGSM 을 구현함에 있어서 고려해야 할 두가지 이슈을 구현함에 있어서 고려해야 할 두가지 이슈

Reducing GSM Tromboning EffectReducing GSM Tromboning Effect

Investigating misrouting of user mobilityInvestigating misrouting of user mobility




Tromboning occurs when the caller and the called MS are iTromboning occurs when the caller and the called MS are in the same city but the GMSC is in another city.n the same city but the GMSC is in another city.

Both GSM MSCs and iGSM gateways can serve as GMSCs Both GSM MSCs and iGSM gateways can serve as GMSCs for iGSM subscribersfor iGSM subscribers If an iGSM subscriber is assigned a GSM MSC as his GMSC, call d

elivery 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



Reducing GSM Tromboning EffectReducing GSM Tromboning EffectPSTN iGSM IP network

SwitchiGSM

Gateway

GatekeeperiGSM VLR

12

caller

3 4

5iGSM user

IP Network iGSM IP network

iGSMGateway

GatekeeperiGSM VLR

1

2iGSM user

caller

Two kinds of subscribers are anticipated in iGSMTwo kinds of subscribers are anticipated in iGSM The GMSCs of the iGSM subscribers are standard GSM MSCs. I

n 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

<PSTN-to-IP Cal Setup> <IP-to-IP Cal Setup>




The first kind of subscribersThe first kind of subscribers call delivery follows the standard GSM procedure A subscriber visits the IP network, tromboning may occur as in t

raditional GSM networks The GSM operator would prefer this scenario if the iGSM gatewa

y and gatekeeper are owned by other ISPs. The second kind of subscribersThe 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



Misrouting Due to User MobilityMisrouting Due to User Mobility

To support user mobility, the subscriber To support user mobility, the subscriber needs to explicitly perform registration to needs to explicitly perform registration to inform the system in which location area he inform the system in which location area he resides when the terminal has been resides when the terminal has been changed.changed.

Missing Missing call deliveries may be misrouted call deliveries may be misrouted This problem can be eliminated if the This problem can be eliminated if the

subscriber always turns off the MS when he subscriber always turns off the MS when he moves to the H.323 terminalmoves to the H.323 terminal

The turn-off action results in a GSM detach The turn-off action results in a GSM detach message, which deregisters the MS.message, which deregisters the MS.



Misrouting Due to User MobilityMisrouting Due to User Mobility

GSM VoIP network

MSC GSMVoIP

Gateway

VLR B

HLR

p AVLR

Ap

IP Phone

HLR

p B

GSM MS

14

2

VLR A

VLR B

p

3

step1step1step2step2step3step3



Misrouting Due to User MobilityMisrouting Due to User Mobility The misrouting problem is avoided if the The misrouting problem is avoided if the

subscriber explicitly or implicitly registers subscriber explicitly or implicitly registers with the GSM MS step3.with the GSM MS step3.

Implicit registration occurs in two casesImplicit 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 Both case, after the HLR has modified the subscriber’s record, it also cancels the subscriber’s record, it also cancels the subscriber’s VLR record in VLR Bsubscriber’s VLR record in VLR B

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