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TelecommunicationNetworks and Services

Simon ZNATY, EFORTznaty@efort.com

http://www.efort.com

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A Telecommunication NetworkOperator

AccessNetwork

ADSL, xDSLISDN,

GSM, AMPSetc.

Switching NetworkCircuit Switching, Packet Switching,

Frame Switching, Cell Switching

Transmission NetworkPDH, SDH, D-WDM

Signaling NetworkSS7

Intelligent NetworkManagement Network = OSS

Business Information System = BSSCustomer Care, Billing, SLA Management, etc.

Transport Network

OSS : Operation Support SystemBSS : Business Support SystemSLA : Service Level AgreementPDH : Plesiochronous Digital HierarchySDH : Synchronous Digital HierarchyD-WDM : Dense Wavelength Division Multiplexing

A Telecommunication network consists in two parts:• the “network” (transmission, switching, access, signaling, mobile, intelligent network)• the “business and technical information system” (OSS, BSS).The transmission network enables carrying all kinds of traffic (voice, video, data). It consists in nodes calledmultiplexers and links among multiplexers. The goal of the multiplexer is to multiplex/demultiplex traffic onto/from thelink. There exists three multiplexing techn ologies : PDH, SDH and D-WDM. The link technology is generally optic fiberbut may also be coax, radio, etc. A transmission network generally consists in hundreds of multiplexers and tens ofthousands of kilometers of optic fiber.The switching network enables switching the traffic from the sender to the appropriate destination. A switchingnetwork consists in switches. All switches rely on the transmission network. A switch receives traffic from thetransmission network at input ports, applies the switching function that forwards the traffic to output port. Then, theswitch relies on the transmission network to send the traffic to adjacent switches.There exists 4 switching networks, each providing specific services.:• circuit switching (e.g., PSTN) that provides voice services.• Packet switching (e.g., X.25) that provides data services at low bitrate (less than 64 kbit/s).• Frame Switching (e.g., frame relay) that provides data services at higher data rates (between 64 kbit/s and 2 Mbit/s,in fact multiple of 64 kbit/s).• Cell switching (e.g., ATM) that provides a large variety of services (data, voice, video, etc.) at various bit rates.All the switching networks operate in a connection oriented mode. That means that prior to enabling users exchangingdata, there is a need of reserving resources on the path between the sender/caller and the receiver/callee. To reserveresources, all switches on the path exchange signaling information. Signaling information is data. In case ofpacket/frame/cell switching, adjacent switches exchange user and signaling data. This is in-band signaling. In thecase of circuit switching, signaling data is carried over a separate network called Signaling System 7. This is out-of-band signaling.The intelligent network is used in the voice network for the provisioning of services cuch as freephone, premium rate,virtual private network, account cart calling, etc. It consists of a set of application servers containing service logic andservice data.The OSS (Operation Support System) is the management of the network and the services. The BSS (Business SupportSystem) is the interface to and the management of the customer.The access network is the network that enables attaching the user equipment to the switching/transmission network.The bandwidth at the access is increasingly higher (DSL, HDSL, ADSL, Wireless IP, WLL, etc).The mobile network is considered as an access network because it always interfaces to the switching network.

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GSM Network

Management Network

Signaling System 7

SCP

Switching Network

Signaling Network

Intelligent NetworkCAMEL

OMC : Operation and Maintenance CenterR : Radio; S : SwitchingOSS : Operations Support systemBSS : Base Station SubsystemSCP : Service Control PointNSS : Network SubSystem

Transmission Network

GSM RadioAccess Network

(BSS)

GSM Network (Circuit Mode)(NSS) PSTN

OMC-R OMC-S

OSS

BSS

Transmission Network

The GSM network is a voice network. As for PSTN, it has a switching planewhere Mobile switching Centers (MSCs) may be found. The switching part withMSCs is called NSS (Network Subsystem). For example Orange Franceconsists in 145 MSCs, for 17 Millions of subscribers. The attachment of themobile terminals to the network is handled by a radio access network calledBSS (Base Station Subsystem) which consists in antennas and controllers ofantennas.The MSCs of the GSM network interface with the PSTN network to enablecommunication between mobile and fixed terminals.Since the GSM network is a voice network, SS7 is used for the transport ofsignaling information between BSS and NSS and between MSCs within NSSand between NSS and PSTN.The Intelligent Network is called CAMEL (Customized Application MobileNetwork Enhanced Logic). GSM provides terminal mobility and CAMELprovides service mobility. CAMEL provides services such as call screening,VPN and Mobile prepaid. With CAMEL, the user may access to its services inhis home network or from visited networks when roaming to those networks.The management of BSS is handled by OMC-R (OMC Radio). Themanagement of the MSCs is handled by OMC-S (Switching). OMC-R andOMC-S are supplied by telecom vendors with the equipement those OMCshave to manage.A network operator builds its OSS and BSS that interface with these OMCs.

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GSM, GPRS and UMTS Networks

GPRS Network (Packet Mode)X.25

Internet

GSM Network (Circuit Mode) PSTN

GSM+GPRSRadio Access

Network(BSS)

UMTS RadioAccess Network

(UTRAN)

UTRAN : UMTS Terrestrial Radio Access NetworkBSS : Base Station SubsystemUMTS : Universal Mobile Telecommunications SystemGPRS : General Packet Radio ServiceD : Data

SCPOMC-R OMC-S

OSS

BSS

OMC-D

GSM provides voice services. GPRS reuses the existing GSMinfrastructure to provide end-to-end packet-switched services, i.e., dataservices.While a voice communication requires 12 kbit/s at the radio access, GPRSenables access to data services (e.g., WAP) at a bitrate that may be 20 to30 kbit/s on the downlink (from the network to the user terminal) and 10kbit/s on the uplink (from the user terminal to the network). Moreover thecost of the call is not related to the duration of the call but related to thevolume of data exchanged.GPRS provides interfaces to X.25 or Internet networks.GPRS does not impact the GSM BSS (Base Station Station). This isimportant because 2/3 of the cost of a mobile network resides in the BSSwhile the other 1/3 is the cost of the mobile switches.CAMEL is also used to provide value added services. For example, acustomer may have a mobile prepaid card that he/she may use for a voicecommunication (GSM) or data session (GPRS).UMTS provides a new radio interface called UTRAN (UMTS TerrestrialRadio Access Network). It will provide 100 kbit/s per user. A voicecommunication with UMTS requires 12,2 kbit/s. A data session may usethe available bandwidth, e.g., 100 kbit/s.UMTS radio interface attaches to the GSM network and GPRS network.However, since the cost of the mobile network is the radio interface, thedeployment of UMTS will be expensive.

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The four important values of anetwork operator

● 1. Customers● 2. Staff● 3. Information System (technical and business)● 4. Network

The four main important values of a network operator are :1. Its customers2. Its staff. The staff should be highly qualified to operate the business andthe network.3. Information System. A Network operator cannot differentiate from othernetwork operators only by means of the network. The reason is that allnetwork operators have more or less the same network. Indeedequipments come from the same telecom suppliers.The differentiating factor is the Information System (i.e., OSS and BSS). Itenables :• Planning and provisioning services and networks (fulfilment)• Monitoring faults and performance (assurance)• Rating and discounting, Billing.• Handling the relationship with the customer (customer care)4. The network with its transmission/switching/signaling planes.

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PLAN● 1. Today ’s telecommunication Network

● 1.1. Transmission Network● 1.2. Circuit switching Network● 1.3. Signaling Network● 1.4. Intelligent Network (Wired, Mobile)● 1.5. Mobile Network : GSM, GPRS, UMTS● 1.6. Information System : OSS and BSS● 1.7. Data Networks (Packet, Frame, Cell)● 1.8. Access Network

● 1.9. Tomorrow ’s Telecommunication Network : NextGeneration Network and IP Telephony

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1.1. Transmission Network

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Transmission Network : PDH

● PDH : Plesiochronous Digital Hierarchy● Point-to-point link● In Europe

● E1 : 2,048 Mb/s (32 * 64 kb/s)● E2 : 8,448 Mb/s (4 * E1)● E3 : 34,368 Mb/s (4 * E2)● E4 : 139,264 Mb/s (4 * E3)● E5 : 564,992 Mb/s (4 * E4)

● In U.S.A.● T1 : 1,544 Mb/s (24 * 64 kbit/s))● T2 : 6,312 Mb/s (4 * T1)● T3 : 44,736 Mb/s (7 * T2)● T4 : 274,176 Mb/s(6 * T3)

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PDH Multiplexing

E1

E2

E3E4

E3

E2E1

2 Mbit/s

8 Mbit/s

34 Mbit/s140 Mbit/s

34 Mbit/s

8 Mbit/s

2 Mbit/s

PDH Multiplexing Function

PDH Multiplexer 140 Mb/s PDH Multiplexer 140 Mb/s

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Transmission Network : SDH● SDH : Synchronous Digital Hierarchy● SDH network topology is generally a double ring● SDH data rates :

● STM-1 : 155 Mb/s (STM : Synchronous Transport Module)● STM-4 : 622 Mb/s● STM-16 : 2,49 Gb/s● STM-64 : 10 Gb/s

● D-WDM : Dense - Wavelength Division Multiplexing● 40 Gb/s, 160 Gb/s, .., terabit/s

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SDH Network Elements

● Terminal Multiplexer : used to combine PDH and SDH trafficinto STM-N SDH traffic.

● Add/Drop multiplexer (ADM) : enables inserting (Add) andremoving (Drop) bandwidth.

● Repeater : Amplifies the SDH signal.

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SDH network configuration Example

STM-4

Customer siteSTM-4 (622 Mb/s)

STM-1 (155 Mb/s)E4 (140 Mb/s)E1 (2 Mb/s)

ADM

TM

E4E1 E1

STM-1

ATM Switch

ADME4

E4 E1 E1

ADM : Add/Drop MultiplexerTM : Terminal Multiplexer

ADM TME4E1E1

STM-1

STM-1

PDH : Plesiochronous Digital HierarchyPoint-to-point link• In Europe

E1 : 2,048 Mb/s; E2 : 8,448 Mb/s; E3 : 34,368 Mb/sE4 : 139,264 Mb/s; E5 : 564,992 Mb/s

• In U.S.A.T1 : 1,544 Mb/s; T2 : 6,312 Mb/s; T3 : 44,736 Mb/s;T4 : 274,176 Mb/s

SDH : Synchronous Digital HierarchySDH network topology is generally a double ringSDH data rates :• STM-1 : 155 Mb/s (STM : Synchronous Transport Module)• STM-4 : 622 Mb/s• STM-16 : 2,49 Gb/s• STM-64 : 10 Gb/sTerminal Multiplexer : used to combine PDH and SDH traffic into STM-N SDH traffic.Add/Drop multiplexer (ADM) : enables inserting (Add) and removing (Drop) bandwidth.Repeater : Amplifies the SDH signal.

D-WDM : Dense - Wavelength Division Multiplexing• 40 Gb/s, 160 Gb/s, .., terabit/s

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Main Transmission EquipmentVendors

● ALCATEL● NORTEL● SIEMENS● LUCENT● ERICSSON

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1.2. PSTN :Circuit Switching Network

PSTN : Public Switched Telephone Network

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France Telecom PSTN

AccessSwitches

SecondaryTransit

Switches

PrimaryTransit

Switches

InternationalTransit

Switches

InternationalNetwork

Class 4 Switch

Class 5 Switch

Class 4 Switch

The circuit switching network is called PSTN (Public Switched Telephone Network).It consists in a hierarchy of switches.Access switches are called Class 5 switches. They are also called LocalExchanges.Transit switches are called Class 4 switches.France Telecom PSTN consists in 4 levels of switches as shown on the diagram.British Telecom PSTN= 2 levels. Deutsche Telecom PSTN = 2 levels. AT&T PSTN= 5 levels.Number of Switches at France Telecom:• Access Switches = Class 5 Switches = 600• Secondary Transit Switches = Class 4 Switches = 65• Primary Transit Switches = Class 4 Switches = 10• International Transit switches = Class 4 Switches = 5.The number of customers of France Telecom PSTN is currently 36 millions.A Class 5 switch is able to attach 100.000 user lines. The performance of a Class 4switch is expressed in BHCA (Busy Hour Call Attempts). It represents the numberof calls a Class 4 switch is able to attempt during a busy hour (includingunsuccessful calls because the callee is absent or busy). A Class 4 switch is able tohandle 1 to 2 Millions of BHCA.The PSTN network of a given operator consists in switches of two to three vendors.France Telecom PSTN consists of Alcatel E10 and Ericsson AXE10 switches.Deutsche Telekom PSTN consists of Alcatel S12 and Siemens EWSD switches.British Telecom PSTN consists of Nortel DMS100 and Ericsson AXE switches.

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Main suppliers of Voice switches

Vendor Switch Name Nb Ports % Total Millions

Alcatel E10,S12Lucent 5ESSNortel DMS100Siemens EWSDEricsson AXENEC NEAX 61Fujitsu FETEX 150All others

278.7 17.6%271.3 17.2%223.6 14.2%219.3 13.9%165.4 10.5%79.6 5.0%55.7 3.5%285,9 18,1%

1 579.5 100.0%

Top 7 Suppliers – Installed Base Worldwide Market Share (April 2001 Digital Port Count [in millions] – Wireline & Wireless)

The table lists the 7 main vendors of voice switches (Both Wireline andWireless). The criterion used is the number of telephone lines attached.ALCATEL E10 is mainly sold in Africa and France, while ALCATEL S12 isdeployed in China and in most european countries except in France. Thebusiness generated by the S12 is more than twice that of the E10. E10 isbuilt in France; S12 is built in Belgium and Germany.ALCATEL has sold 16000 switch worldwide.5ESS is originally from AT&T and now offered by LUCENT.EWSD from SIEMENS stands for Elektronisches WählSystem Digital.AXE-10 From ERICSSON is also called System Y in UK.NEAX has been specified by the Nippon Telegraph Telephone (NTT) andimplemented by NEC.A Class 4 switch costs between 1,7 and 4 millions of dollars depending onthe features included in the switch (e.g., presence or absence of an STP,presence or absence of an SSP, etc.).

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Switching/Transmission

ADM

ADM

ADM

ADM ADM : Add and Drop Multiplexer

Class 5 Switch

Class 4 Switch

Class 4 Switch Voice circuit

Transmission Ring

The figure above shows the relationship between the switching plane andthe transport plane.Multiplexors attach PSTN switches.Each voice circuit available between two adjacent switches is a 64 kbit/sdata rate that is reserved within the optic fiber. The multiplexor isresponsible of multiplexing and demultiplexing a large number of voicecircuits.

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1.3. SS7 : Signaling Network

SS7 : Signaling System 7

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PSTN : Out-of-band Signaling

Customer lineVoice circuitSignaling Link

Switch 1 SS7: Signaling System N°7

SignalingSystem 7

(SS7)

Switch 2Switch 4

Switch 3

CIC= 2

CIC= 2

CIC= 4

CIC= 4

User AUser B

CIC : Circuit Identification Code

In telecommunications, switching networks always operate in a connection orientedmode. This means that prior to the exchange of user information, a network path(connection) should be reserved between the caller and the callee. The establishmentof this connection is performed through exchange of signaling information among thevarious switches on the route.Thus, in PSTN, adjacent switches need to exchange signaling information to reservevoice circuits among them. The circuit switching network is not adapted to transportdata but voice, while signaling is data. To ensure fast transfer of signaling information,a parallel data network has been introduced.That means that in the PSTN, signaling is carried out-of-band. The signaling networkis called SS7 (Signaling System 7) or CCS7 (Common Channel Signaling 7) or C7(Channel 7).Assume Call establishment between User A and user B :User A picks up the phone and dials destination number. Signaling information isreceived by the Class 5 switch that attaches user A. Based on destination number,Switch 1 identifies the next switch on the route to reach user B. It is switch 2. Switch 1share with Switch 2 a set of voice circuits identified at both ends by the same CIC(Circuit Identification Code). Switch 1 selects and reserve a CIC corresponding to avoice circuit in the idle state (CIC = 2). Switch 1 sends on the signaling link a signalingmessage to Switch 2 to ask Switch 2 to reserve CIC=2. The signaling network routesthe signaling message to Switch2. Switch 2 receives the signaling message whichcontains the destination number and CIC parameters. It reserves the CIC and basedon destination number, identifies the next switch on the route to the destination (Switch4). It reserves a CIC corresponding to a voice circuit it shares with Switch 4 and sendsa signaling message to Switch 4 containing this CIC and the destination number. Uponreception, Switch 4 reserves the same CIC and finds out that the destination is directlyattached to it. It alerts this destination (User B).

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Interface between the circuitswitching network and the signalingnetwork

PSTN Switch PSTN Switch

Voice Circuits

Signaling Links

ControlUnit

SignalingPoint

Control Unit

Fabric

SignalingSystem 7

Fabric

SignalingPoint

A PSTN switch has two interfaces :• switching interface that consists in a set of trunks that multiplex voicecircuits that operate at 64 kbit/s in Europe and 56 kbit/s in the U.S. Everytrunk is represented physical in the switch by a card. If the transmissiontechnology is PDH which is generally the case, then E1 cards (in the US,T1 cards) are embedded in the switch. E1 = 2 Mbit/s; T1 = 1,544 Mbit/s. Ifthe transmission technology is SDH, then STM-1 cards are embedded.STM-1 = 155 Mbit/s. The voice circuit carries voice traffic. The switchingplane occurs when the call has been established by signaling. Everyswitch has one or several fabric that switch the traffic from an input voicecircuit termination (CIC) to an output voice circuit termination (CIC).• Signaling interface that consists in a set of signaling links that alsooperate at 64 kbit/s in Europe and 56 kbit/s in the U.S. The signaling linkcarries signaling traffic, e.g., messages for the establishment and releaseof voice circuits. It is the signaling point which is a function within theswitch that generates and receives signaling messages.

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SS7, Associated Mode

SP

Fabric

SP

Fabric

Signaling LinkSLC (Signaling Link Code)

Voice CircuitsCIC (Circuit Identification Code)

PSTN Switch PSTN Switch

Switch 1

Switch 2Switch 4

User AUser B

Signaling LinkVoice circuit

SP : Signaling Point

The most basic mode to setup a signaling network is called associatedmode.With this mode, the signaling link, which is parallel to the voice circuit,enables exchange of signaling data between adjacent switches calledSignaling Points (SP) in the signaling plane.The signaling link must be set up between two SPs.Obviously this mode is not ideal since it requires a signaling link betweena given SP and all the other SPs. The signaling messages and the voicego the same way but over different media (channels).This mode is interesting and optimal if the number of switches of thePSTN network is small (less than 12). If the number of switches is large,then it is more appropriate considering the quasi-associated mode whereSTPs are introduced.Both the voice circuit and the signaling link operate at 64 kbit/s in Europeand 56 kbit/s in the U.S. IN Japan, the signaling link may operate at 4,8kbit/s.

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SS7, Quasi-Associated Mode

STP STP

STP STP

Switch 1

Switch 2Switch 4

Switch 3

User AUser B

Sign

alin

g lin

k

Voice circuit

STP : Signaling Transfer PointSP : Signaling Point

Voice CircuitSignaling Link

SP

SP

SP SP

SS7

In the quasi-associated mode, The SS7 network architecture consists inSTPs and SPs.Signaling Transfer Points (STPs) are switches that relay signalingmessages between PSTN switches. Their main function is to route SS7messages to the correct outgoing signaling link. STPs are normallyprovisioned in matted pairs. In the failure of individual components, thisduplication allows signaling traffic to be automatically diverted to analternate resource, minimizing the impact on service.An STP may be a function integrated within a Class 4 Switch or astandalone equipment. Most of the telecommunications vendors include itwithin their class 4 switch.The main vendors of standalone STPs are Tekelek with the Eagle STP,Alcatel with the INFusion STP and Siemens.An STP is able to route 5000 to 10000 signaling packets per second. Themaximum size of a packet is 272 octets. Moreover, 1024 signaling linksmay connect to an STP while a maximum of 32 signaling links may beused to connect an SP to a pair of STPs.

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ISUP : ISDN-User Part

ISUP is used to set up and tear down all circuits used for voice or datacalls in the PSTN. In addition to its usage in the PSTN, it can be found inwireless networks for establishing trunk connections between MSCs. It isa call related protocol while MAP and INAP are call unrelated protocols.

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Call establishment with ISUPSP

Fabric

SP

Fabric

SP

Fabric

SP

Fabric

Voice circuits

ISUP IAM

x x

ISUP IAM

x x

ISUP IAM

x x

SP

Fabric

SP

Fabric

SP

Fabric

SP

Fabric

ISUP ACM

Voice circuitsx x

x xx x

SP

Fabric

SP

Fabric

SP

Fabric

SP

Fabric Voice circuitsx x

x xx x

SetupSetup

ISUP ACMISUP ACMAlerting

Alerting

ISUP ANM ISUP ANM ISUP ANMConnect

Connect

Switch A Switch B Switch C Switch D

When a call is placed to a remote destination, the originating switch Athrough its SP function transmits an ISUP initial address message (IAM)to reserve an idle voice circuit portion from the originating switch anintermedia switch B. The IAM includes the circuit identification code,dialed digits and, optionally, the calling party number. The IAM is routedvia the STP of the originating switch A to the intermediate switch B.

Switch B identifies next hop as beingswitch C and exchange with switch A an ISUP IAM message for thereservation of a shared voice circuit portion. Switch C does the same withswitch D.

The destination switch (D) examines the dialed number, determines that itserves the called party, and that the line is available for ringing. Thedestination switch rings the called party line and transmits an ISUPaddress complete message (ACM) to switch C (intermediate switch) (viaits STP) to indicate that the remote end of the voice circuit has beenreserved. The STP routes the ACM to the intermediate switch C. Switch Cdoes the same with the switch B that performs the same procedure withthe originating switch A. This latter rings the calling party's line andconnects it to the voice circuit portion to complete the voice circuit fromthe calling party to the called party.

When the called party picks up the phone, the destination switchterminates the ringing tone and transmits an ISUP answer message(ANM) to the intermediate switch C via its STP. The STP routes the ANMto the intermediate switch C. Switch C sends an ANM message to switchB. Switch B sends an ANM message to switch A. Switch A which verifiesthat the calling party's line is connected to the reserved voice circuitportion and, if so, initiates billing.

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Call Release with ISUP

FabricFabricFabricFabric

Voice circuits

x xx x

x xDisc

Disc

ISUP REL ISUP REL ISUP RELISUP RLC ISUP RLC ISUP RLCSP SPSP

STPSTP

SP

SS7STPSTP

ISUP : ISDN User Part C5 : Class 5 SwitchREL : Release C4 : Class 4 SwitchRLC : Release complete

Switch A (C5) Switch B (C4) Switch C (C4) Switch D (C5)

If the calling party hangs-up first, the originating switch sends an ISUPrelease message (REL) to release the voice circuit portion it hasestablished with Switch B. The STP routes the REL to the next hop,switch B. Switch B releases the share voice circuit portion with Switch C.Switch C does the same with switch D.

If the called party hangs up first, or if the line is busy, the destinationswitch sends an REL to the originating switch through the intermediateswitches indicating the release cause (e.g., normal release or busy).

Upon receiving the REL, the destination switch disconnects the voicecircuit portion from the called party's line, sets the voice circuit portionstate to idle, and transmits an ISUP release complete message (RLC) tothe originating switch to acknowledge the release of the remote end ofvoice circuit portion. When the originating switch receives (or generates)the RLC, it terminates the billing cycle and sets the voice circuit portionstate to idle in preparation for the next call.

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ISUP Supplementary Services

● Supplementary services supplied by ISUP :● Calling line identification presentation (CLIP)● Calling line identification restriction (CLIR)● Call forwarding busy (CFB)● Call forwarding no reply (CFnR)● Call forwarding unconditional (CFU)● Malicious Call Identification● Explicit Call Transfer● Call Waiting (CW)● Completion of calls to busy subscriber (CCBS)● etc.

● Supplementary services are always handled by Class 5switches.

The supplementary services are handled by the class 5 switches with theISUP protocol.All subscribers attached to a class 5 switch are declared within the switchdatabase by means of a database record. This record contains all the dataabout the supplementary services subscribed by the correspondingcustomer and his profile.Assume the called party has subscribed to CLIP. When an ISUP IAMmessage is received by the destination switch, this switch first checkswhich services the called party has subscribed to. Since the callee hassubscribed to the CLIP service, his Class 5 switch shows the calling partynumber (this parameter is within the ISUP IAM message).Assume the called party has subscribed to CLIP and the calling party toCLIR. The Originating switch receives a call establishment request from acaller. It checks the customer record in its database to identify theservices this customer has subscribed to. Since he has subscribed toCLIR, the originating switch will encapsulate within the generated ISUPIAM message the calling party number with two bits positionned to 1 toinform that the divulgation of this number is restricted. When thedestination switch receives this ISUP IAM message, it checks the calledparty record in its database. Since the called party has subscribed toCLIP, the calling party number should be presented. However, since thecalling party number has the two bits positionned to the value 1, thisnumber will not be presented.

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1.4. IN : Intelligent Network

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Intelligent NetworkSRP : Specialized Resource PointSCP : Service Control PointSSP : Service Switching PointSTP : Signaling Transfer PointSP : Signaling Point

STP STP

Switch 1

Switch 2Switch 4

Switch 3

User AUser B

Sign

alin

g lin

k

Voice circuit

Voice circuitSignaling Link

SSP

SP

SSP

SRP

SP

SCP SCP

STP STP

SS7

The IN architecture mainly consists in three entities :•The Service Control Point (SCP) that contains service logic and service data and isresponsible for executing the service.•The SSP (Service Switching Point) which is an interface within the switch and is responsiblefor executing the service.•The SRP (Specialized Resource Point) that is responsible for plying announcements.In the intelligent network (IN) architecture, the SCP is the master, whereas the switches(SSP) are slaves. This centralized architecture seems to fit in well with services that rely ononly one database.Moreover, when a new service is introduced, only the SCP needs to be updated. When aFreephone service is launched, the following stages are performed: a person picks up thephone to dial a Freephone number (e.g., 0800 25 26 27), the SSP detects the prefix (0800)and decides to stop the natural process for the call, and asks for the SCP to returninstructions. The SCP then looks in its tables for the correct physical number (correspondingto 25 26 27) in order to redirect the call if it also matches with other criteria such as the dayof the week, the hour of the day, the calling party location, etc. Once the number is found, theSCP informs the SSP that he has to establish a connection with the physical number (e.g., 0143 55 46 56) and that the charges for the call are for the called party. The SSP receives andexecutes these orders from the SCP and follows handling call processing.The performance of an SCP is expressed in transactions per second (tps) or calls persecond. For an SCP the common performance is 200 to 300 calls per second where a call toa service translates into 4 to 5 transactions.Because of the cost of SSP, only Class 4 switches generally include this SSP. FranceTelecom PSTN contains 12 SSPs and 30 STPs.The protocol that enables SSP, SCP and SRP to interact for service execution is INAP(Intelligent Network Application Part).

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Intelligent Network

STP STP

Switch 1

Switch 2Switch 4

Switch 3

User AUser B

Sign

alin

g lin

k

Voice circuit

SSP

SP

SSP

SRP

SP

SCP SCP

STP STP

SS7

SMP

SCEP

SDP

SMP : Service Management PointSCEP : Service Creation Environment PointSDP : Service Data Point

X.25/IP

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Televoting

SMP

0801-121O1--> C1 = C1+1O2--> C2 = C2+1O3--> C3 = C3+1

Caller1

2, 6 3, 11, 13

Thanks for calling.Your vote has been taken into account

The service subscriber queries the service results

PSTN

SCP

Switch

Switch

SSP

4, 12

7, 9

8, 10

SS7

SCEP

SCEP : Service Creation Environment PointSMP : Service Management PointSRP : Specialized Resource PointSSP : Service Switching PointSCP : Service Control Point

5

SRP

Assume the televoting service execution :1. Setup (ISDN). The user dials the destination number announced by the TV show to vote byphone.2. Initial_DP (call identifier, televoting number) (INAP). The class 5 / Class 4 switch receives theuser request for call establishment and identifies a request for a televoting service. It sends aINAP transaction to launch the service within the SCP.3. Connect_to_resource.Req (SCP requests SSP to connect SRP with user) (INAP). The SCPneeds to get the user vote. The first step is to establish a voice circuit between the user and theSRP. The SRP contains the announcement and is able to play it and collect user data while theSCP is just an application server without any voice circuit. The SCP requests this voice circuitestablishment to the SSP.4. ISUP IAM (SSP connects IP with user by means of ISDN or ISUP messages) (ISUP). TheClass 5/Class 4 switch sends an ISUP IAM message to establish a voice circuit with the SRP.5. ISUP Connect (ISUP). The SRP acknowledges to the SSP the reservation of the circuit.6. Connect_to_resource.Conf (SSP confirms the connection of IP with user to SCP) (INAP). TheSSP attaches the two circuit portions (one towards the SRP and one towards the user) andacknowledges circuit establishment to the SCP.7. Prompt and Collect User Information (SCP request SRP to play an announcement to the userand to collect user information) (INAP)8. Collected User Information (SRP returns to SCP collected user data)(INAP)The SCP then increases the value of the corresponding counter.; it corresponds to a local actionperformed by SCP.9. Play announcement.Req (to thank the caller) (INAP)10. Specialized Resource Report (Confirmation that the announcement has been played) (INAP)11. Disconnect Forward Connection (INAP)12. Release (ISDN)13. Release Call (INAP)

31Copyright - EFORT

Freephone Service at France Telecom

PSTN

SCP

Class 5 Switch

SS7

Class 5 Switch

Class 5 SwitchSSP

SSP : Service Switching PointSCP : Service Control Point

IPIVR

1. Q.931 SETUP2. ISUP IAM3. INAP InitialDP4. INAP Connect5. ISUP IAM6. Q.931 SETUP7. Q.931 Connect8. ISUP Connect9. ISUP Connect

1

6

7

3 4

2

xx

x 5

x

8

9

Assume the following example when considering a PSTN such as that of France Telecom:1. The caller dials a freephone number (e.g., 0800 23 24 26).2. The Class 5 switch contains a switching table that tells it that the next switch on the routingto the destination is a class 4 switch having an SSP function. Therefore, the Class 5 switchsends an ISUPIAM message for the establishment of a voice circuit with an adjacent class 4switch.3. The class 4 switch having this SSP function is able to activate the service by sending anINAP message to the appropriate SCP.4. The SCP runs the service (translation of the freephone number into a physical number)and returns this physical number to the SSP. This number may correspond to anannouncement server (IVR) that is attached to the same class 5 switch as the caller (This willgenerally be the case to minimize the cost of the call for the callee that must pay for that call).5. The Class 4 switch sends an ISUP IAM message to the Class 5 switch.6. The Class 5 switch sends an Q.931 message (ISDN signaling) to the IVR for theestablishment of the call.7. The IVR returns a confirmation.8. The Class 5 switch return an ISUP connects to the class 5 switch as a response to themessage 5.9. The Class 4 switch returns an ISUP connect as a response to the message 2.When an announcement is played by the IVR to the caller, the announcement is sent overthe voice circuit to the class 5 switch that switches that announcement to the voice circuit itshares with the Class 4 switch, that switches it to the voice circuit that it shares with theClass 5 switch that forwards it to the caller.In this example, two voice circuits have been established due to the fact that the Class 5switch that attaches the caller has no SSP function.

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IN Vendors

● ALCATEL � SCP based on COMPAQ workstation +SS7 Stack + SS7 board. ALCATEL adds the SLEE, SCEand SMP.

● SIEMENS �SCP based on SUN workstation + ULTICOMSS7 Stack + ULTICOM board. SIEMENS adds the SLEE,SCE and SMP.

● NOKIA � IN Solution is that of HP.

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1.5. GSM, GPRS, UMTS :Mobile Network

GSM : Global System for Mobile CommunicationsGPRS : General Packet Radio ServiceUMTS : Universal Mobile Telecommunications System

34Copyright - EFORT

GSMMS : Mobile StationBTS : Base Transceiver StationBSC : Base Station ControllerMSC : Mobile Switching CenterGMSC : Gateway MSCVLR : Visitor Location Register HLR : Home Location RegisterSMSC : Short Message Service Center

MS BSCBTS

BTS

BTS

BTS

BTS

BTS

BTS

MSC

BSC

MSC

BSC

Signaling linkVoice circuit

PSTN

GMSC

SMSCSS7

VLR

VLR

HLR

A GSM network is made up of many cells which are areas that each have a cellular base station called BTS(Based Transceiver Station) that communicates with the cell phones currently located in that cell. When a cellphone is turned on, it finds the nearest BTS to it and establishes a communications link in a process calledregistration. A BTS is able to handle between 20 and 40 simultaneous communications.A BSC (Base Station Controller) is a controller of BTS. It is in fact a small switch with a substantialcomputational capability. A typical BSC consists of one or two rack and can manage some tens of BTS (up to128) .In GSM vocabulary, a BSS (Base Station Subsystem) means the set of one BSC and all the BTS s under itscontrol.MSCs (Mobile Switching Centers) are the brains of the GSM network. A GSM network contains several of theseMSCs each of which handles communications with a cluster of BSSs. The main function of an MSC is tocoordinate setting-up of calls to and from GSM users. The MSC has interfaces with the BSS on one site andwith the external networks on the other.Besides MSCs, The Network Subsystem (NSS) includes databases. Subscriber information relevant to theprovision of telecommunications services is held on the infrastructure side in the HLR (Home Location Register)independently of the actual location of the subscriber. The HLR also includes some information related to thecurrent location of the subscriber.An HLR is typically an independent computer that is able to handle amaximum of 1 Million subscribers (records). An HLR may be based on a specific hardware (e.g., ALCATEL,Nokia) or on UNIX (e.g., Lucent).The second database function identified in GSM is the VLR (Visitor Location Register) integrated in each MSCand in charge of temporarily storing subscription data for those subscribers currently situated in the service areaof the corresponding MSC as well as holding data on their location at a more precise level than the HLR.In order to setup a call towards a GSM user, this call is first routed to a GSMC (Gateway MSC), without anyknowledge of the whereabouts of the subscriber. The GMSC is in charge of fetching the location informationand of routing the call towards the MSC through the subscriber can obtain service at this instant. To do this, theGMSC must first find the right HLR and then interrogate it. The GMSC is a function that is generally in the samemachine as the MSC function.The SMSCs are typically implemented on high-speed server platforms (HP 9000 Stations, SUN Sparc Stationsor Compaq Alpha server).Example of GSM network configuration : BTS = 10000; BSC = 200; MSC/VLR = 80; STP = 6; HLR = 20.Number of subscriber : 6 Millions.

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Signaling Network in GSM context

MSC

GMSC

Quasi-Associated Mode

Associated Mode

STP STP

STP STP

Class 5 SwitchVoice circuitSignaling link

SP

BSC

BSC

VLR SPSP

HLRHLR

The signaling link between the BSC and MSC are fully associated. Thismeans that there is no STP for the routing of the SS7 signaling trafficbetween the BSC and the MSC.In the core mobile network called NSS (Network Subsystem), there arealways STP. Generally most GSM mobile network operators deploy 2, 4, 6or 8 STPs to enalble exchange of MAP transactions between the VLR andHLR and between the GSMC and the HLR. Moreover the short messagesare transported over SS7 STPs between the SMSC and the MSC thatattaches the destination mobile station. To obtain the identification of thedestination MSC, the SMSC interrogates through the MAP protocol theHLR.Orange France has 8 STPs for 145 MSCs.SFR has 6 STPs for 90 MSCs.The HLR, VLR, SMSC and GMSC interface with the STP through acertain number of signaling links.

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Fixed Versus Mobile Network

CM Protocol

SubscriberDatabase

MM Protocol

FixedNetwork

MobileNetwork CM Protocol

CM : Connection ManagementMM : Mobility ManagementVLR : Visitor Location RegisterMSC : Mobile Switching Center

VLR

MSC

Class 5 Switch

In the fixed network, the telephone line is always attached to the sameaccess switch (Class 5 switch). This switch contains a customer table withone record per customer to describe the customer profile. It particularlycontains the supplementary services subscribed by the customer and itstelephone line. Such table may contain 100 000 records.The user may use a connection management (CM) protocol toestablish and release calls. For example, if the user has an ISDN line,then its sends the setup message for call establishment.

In the mobile environment, a mobile phone is not always attached to thesame switch. That is the reason the mobile phone has to regularly informthe network about its current location. The MSC (Mobile switching Center)is the switch that attaches the mobile phones. It contains a table called theVLR (Visitor Location Register) that may consist of 100 000 records.Every time the mobile phone is switched on by the user, it has to attach tothe network by informing the switch that controls the area the mobilephone is in, of its current location.To perform this action, the mobile phone uses a mobility management(MM) protocol. When the user wants to establish a call, it uses then aconnection management protocol. This latter looks similar to the ISDNsignaling protocol (setup, alerting, connect, etc).

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Mobile Station

● To every subscriber is associated :● An MSISDN Identity (Mobile station ISDN number) that enables this

subscriber to be called● An IMSI Identity (International Mobile Subscriber Identity) use by the

network to locate the subscriber● An equipment is identified by an IMEI (International Mobile

Equipment Identity)

IMSI = 208 01 435624

MSISDN =33 6 11 23 24 25IMSI =208 01 435624GSM

Network SIM Card

IMEI =435654450565430

When registering for service with a mobile network operator, eachsubscriber receives a unique identifier, the IMSI. This IMSI is stored in theSIM card. A mobile station can only be operated if a SIM with a valid IMSIis inserted into an equipment since this is the only way to correctly bill theassociated subscriber. The IMSI is a GSM-specific addressing conceptand is different from the ISDN numbering plan.The IMSI is unknown to the GSM user and is used by the GSM networksonly.The IMSI starts with a digit that defines a continent (Europe = 2), then twodigits that define the country (France = 08), then two digits that identify theoperator within the country (Orange France = 01) and finally a maximumof 10 digits to define the subscriber number. An IMSI example is : 2 08 01435624.The real telephone number of a mobile station is the MSISDN. AnMSISDN example is : 33 6 11 90 24 50. It enables being called.33 identifies the country. 611 identifies the operator within the country(SFR in France). 902450 is the identification of the subscriber.The IMEI uniquely identifies mobile stations internationally. It is a kind of aserial number. The IMEI is allocated by the equipment manufacturer.

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Additional identifiers

● LAI : Location Area Identification● TMSI : Temporary IMSI● MSRN : Mobile Station roaming Number

The MSRN (Mobile Station Roaming Number) is the routing number thatidentifies the current location of the called MS. MSRN is a temporarynetwork identity assigned during the call establishment to a mobilesubscriber.An MSC area is partitioned into several location areas (Las). Every LAconsists of several BTSs.Because the IMSI should be kept secret, it is necessary to assign anotheridentification to the mobile user so that it cause update its location withouthaving to send its IMSI over the air interface. This additional identificationis called a TMSI (Temporary IMSI).

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GSM Mobility Management● There are two aspects of mobility in a PLMN (Public Land

Mobile Network):● Handover (also called handoff in U.S. or automatic link transfer) : When

a mobile user is engaged in conversation, the MS is connected to a BTSvia a radio channel. If the mobile user moves to the coverage area ofanother BTS, the radio channel of the old BTS is eventuallydisconnected, and a radio channel to the new BTS should be establishedto continue the conversation. This process is referred as handover.

● Roaming : When a user moves from one location to another location, thesystem should be informed of the current location of the user. Otherwise,it would be impossible to deliver the services to the mobile user.

● The two basic operations in roaming management are :● registration (or location update) which is the process whereby the MS informs

the system of its current location● location tracking, the process during which the system locates the MS.

Location tracking is required when the network attempts to deliver a call tothe mobile user.

● Roaming management makes use of the HLR and VLR databases.

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Attachment to the GSM Network(MM Procedure)

BSC

BSC

LA1

LA2MSC

SS7VLR1

1.1.

1.

2.

IMSI LAI TMSIxxx LA1 yyy

VLR Table

IMSI MSISDN VLR SupSxxx zzzz 1 CFB

HLR Table

3.

MSISDN SupSzzzz CFB

4.

4.

LA1

Voice circuitSignaling link

HLR

In GSM, registration or location update occurs when an MS moves fromone LA to another LA or when the mobile is turned on.All BTS permanently broadcast the identification of the location area thereare in. When the MS attaches to the network, it receives an LAI if it iswithin an area covered by a BTS.1. A location update message is sent from the MS to the MSC through theBTS and the BSC. This message includes the address of the visited LA,and the IMSI (We assume it is the first attachment to the network; newuser). The MSC forwards these information to the VLR.2. The VLR creates a record with fields (IMSI, LAI) and assigns a TMSI tothis mobile station (MS). It sends a location-update request to the HLR(message 2) which contains the IMSI of the registering MS and the VLRthat attaches this MS (VLR1).3. The HLR updates the field VLR (VLR = 1) of the corresponding entry(key = IMSI) and returns the information about the MSISDN and thesupplementary services.The VLR1 receiving these information enhances the corresponding recordand return to the MSC the TMSI assigned to the MS.4. This MSC forwards the TMSI to the BSC/BTS/MS. The MS stores thisTMSI into its SIM card.The IMSI will not be used anymore when the MS has to register of updateits location.

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GSM location update : Inter- VLRMovement (MM Procedure)

BSC

BSC

LA1

LA2MSC

SS7VLR1

1.

1.1.

IMSI LAI TMSIxxx LA1 yyy

VLR1 Table

IMSI MSISDN VLR SupSxxx zzzz 1 CFB

HLR Table

MSISDN SupSzzzz CFB

LA2

Voice circuitSignaling link

VLR2

2.3.

IMSI LAI TMSI LA2 yyy

VLR2 Table

MSISDN SupSzzzz CFB

6.7.

4. 5.

8.

8.

2

xxx

HLR

The two LAs belong to MSCs connected to different VLRs, as illustrated in the figure.The Inter-VLR location update procedure consists of the following steps :1. The location update request is sent from the MS to the VLR (through the BSC andMSC). This message contains the new LA (LA2), the old LA (LA1) and the TMSI ofthe MS.2. Since the MS moves from VLR1 to VLR2, VLR2 does not have a VLR record of theMS, and the IMSI of the MS is not known. This IMSI is mandatory to enable the VLRinforming the HLR about the new VLR that handles this MS. The HLR uses as key ofall its records the IMSI and not the TMSI which is a purely local identifier handled bythe VLR. Hopefully the VLR does not receive only LA2 but also LA1. From the LA1,the VLR is able to identify the address of the previous VLR (VLR1). VLR2 sends amessage to VLR1 that contains the TMSI of the MS.3. VLR1 returns the corresponding IMSI.4. VLR2 enhances the MS record and sends a registration message to update theHLR. The HLR updates the record of the MS (VLR field contains now value VLR2).5. An acknowledgment is sent back to VLR2 that contains the IMSI and thesupplementary services of the MS.6. The HLR request VLR1 to delete the record of the MS that changed of locationarea supplying to the VLR1 the corresponding IMSI.7. The VLR1 acknowledges this deletion to the HLR.8. VLR2 generates a new TMSI and sends it to the MS through MSC, BSC and BTS.In GSM, the TMSI is changed from time to time to avoid fraudulent usage.

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Handover

3

BTS

BTS

BTS

BTS

1a

1b

2a

2b

1

2

3a

3b

4a

4b

MSC A

4

BSC 3

4

1

2

34

5

6

7

8

BSC 2

BSC 4

BSC 1

MSC B

MSC C

PSTN

BTS

BTS

BTS

BTS

Handover : When the mobile user is engaged in conversation, the MS isconnected to a BTS via a radio link. If the mobile user moves to thecoverage area of another BS, the radio link to the old BTS is eventuallydisconnected, and a radio link to the new BTS should be established tocontinue the conversation. This process is referred to as automatic linktransfer, handover or handoff.

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Handover types with GSM

● 4 types of handover are possible with GSM :● Intra-cell Handover : same cell.● Intra-BSC Handover: Different cells, same BSC. The BSC

assigns a new radio channel in the new cell and releases theold radio channel (Typical handover).

● Intra-MSC Handover : The MSC performs the handoverbetween cells controlled by different BSCs.

● Inter-MSC Handover : The two MSCs performs thehandover.

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Incoming call

MSC

GMSC

HLR2 MSISDN 3 IMSI

4 MSRN5 MSRN

6MSRN

MSRN : Mobile Station Roaming NumberIMSI : International Mobile Subscriber IdentityMSISDN : Mobile Station ISDN NumberLAI : Location Area IdentifierTMSI : Temporary IMSIHLR : Home Location RegisterVLR : Visitor Location RegisterUm : Air InterfaceMS : Mobile Station

VLR1

MSISDNPSTN

MSRN 78

LAITMSI

Um 9

MS

IMSI MSISDN VLR SupSxxx zzzz 1 CFB

HLR TableIMSI LAI TMSIxxx LA1 yyy

VLR TableMSISDN SupSzzzz CFB

MSRNtttt

1. The MSISDN (e.g., in France 06 11 87 65 66) is dialed by the caller.The call is routed by the PSTN (Class 5 switch) to the closest GMSC ofthe appropriate mobile network operator. In our example 11 correspondsto SFR mobile network operator.2. The GMSC interrogates the HLR to know the MSC which the GSMSCshould forward the call to.3. The HLR translates the MSSDN into an IMSI and interrogates the VLRof the mobile callee using the IMSI.4. The VLR assigns an MSRN to the mobile station and returns thisMSRN to the HLR.5. The HLR receiving this MSRN passes it to the GMSC.6. The GMSC establishes the call towards the MSC of the mobile userusing the MSRN.7. and 8. The MSC interrogates the VLR to translate the MSRN into anLAI and a TMSI.9. The MSC passes the call to the BSC of the corresponding LAI. TheBSC broadcasts the call indicating the TMSI. The mobile stationrecognizing its TMSI handles the call.

45Copyright - EFORT

Outgoing Mobile-to-Mobile Call

1

2MSC1 3

HLR

GMSC

5MSISDN

6 IMSI

7MSRN

MSRN8

12

9 MSRN

MSC2

MSRN10

TMSI,LAI 11

4MSISDN

Caller

Callee

VLR 1u1u2u3...

VLR 2u1u2u3...

46Copyright - EFORT

Call termination by the mobileterminal

RTC VLR MSC MS1. CM Disconnect

2. ISUP RELEASE

3. RELEASE COMPLETE4. CM Release

5. CM Release Complete6. MAP RegisterCharging Info7. MAP RegisterCharging Info Ack.

MSC/VLR and GMSC produce the CDRs (Call Detail Records)

47Copyright - EFORT

Roaming :International Call Setup Procedure

HLR

GMSC ISC

GMSC : Gateway MSCHLR : Home Location RegisterISC : Interational Switching CenterMSC : Mobile Switching Center VLR : Visitor Location Register

1Paris

LondonISC

2

Class 5Switch

MSC

3.1

3.21.2

1.1

1.3

4.1

3.3 3.4

3.5

3.63.7

4.2

4.3

4.4

4.5

A

B

VLR

1. A dials destination number of B1.1. The Class 5 Switch generates an ISUP message and sends it to anInternational Switching Center (Class 4 Switch) of BT that sends it to anISC of France Telecom (1.2) that forwards it to the GMSC of the mobilenetwork the destination party belongs to (1.3).2. GMSC interrogates the HLR to get an MSRN (Mobile Station RoamingNumber).3.1. HLR interrogates the VLR that controls the area destination party(user B) is in. The interrogation is forwarded to the France Telecom ISC(3.1) that forwards it to BT ISC (3.2) that forwards it to the VLR (3.3)3.4. The VLR returns the MSRN (3.4.) forwarded to the HLR (3.5. and3.6.) that passes it to the GMSC (3.7.).4.1., 4.2. et 4.3. The GMSC uses ISUP to establish a voice circuit with theMSC the user B is attached to.A pays the call from London to Paris and B pays the call from Paris toLondon.

48Copyright - EFORT

Call Forwarding UnconditionalClass 5 SwitchGMSC

Exchange of informationincluding CFU and the CallForwarding Number

(Home) (MSC)

Send Routing InfoSetup

VLRHLR

ISUP IAM

SetupVoice circuit

49Copyright - EFORT

Short Message Service

Internet/Intranet

OperatorPortal

MS

BTS

BTS

BSC

SMSC : Short Message Service Center

STP STP

STP STP

MSC

VLR

MSC

VLR

23

SMSC4

1

HLR

Elements involved in SMS are the mobile station (MS), mobile switching center (MSC), visitor location register(VLR), home location register (HLR) and short message service center (SMSC). The MS can either originate orterminate SMS messages.A SMSC operates in a store-and-forward methodology. When the destination MS is not available, for whateverreason, to accept the SMS delivery from the SMSC, the SMSC must store the message until the destination MSbecomes available for SMS delivery. Notification procedures are defined that allow a mobile network, the HLRin particular, to notify the SMSC when the MS becomes available for accepting SMS messages.The main vendors of SMSCs are :CMG, Sema, Logica, Nokia, Ericsson• CMG and Sema SMSC rely on Compaq Alpha server + Compaq SS7• Nokia and Logica SMSC rely on HP 9000 Server + SS7 HP OpenCallIn the example of the figure, an Internet user is sending a text message to a mobile subscriber, MS A, who isbeing served by his home network.1. A request is received by the SMSC via the Internet. This request contains the message content as well asthe destination mobile identification number.2. The SMSC makes an attempt to deliver the message received from the Internet to MS A. An SMSrequestmessage is sent from the SMSC to the HLR, via a STP, so that the serving MSC of the MS A can be located..3. The HLR performs database functions to find the serving MSC of MS A. Once the information is found, theserving MSC address is returned to the SMSC. Note: If MS A is inactive or not available, the HLR will return anegative indication to the SMSC. This negative indication allows the SMSC to retain the message for laterdelivery..4. The SMSC originates a request containing the short message via MAP/SS7 toward the serving MSC 1 of MSA, based on the routing information passed to it by the HLR. The MSC 1 delivers the SMS message to MS A viathe Radio Access Network. MS A acknowledges that it has successfully received the SMS message byinforming the SMSC, via MSC 1.

50Copyright - EFORT

Subscription management

SIM Card

IMSI MSISDN VLR SupSxxx zzzz CFB

HLR Table

HLRCustomer databaseContract databaseBilling database

Business SupportSystem

IMSI

51Copyright - EFORT

Prepaid Service

BSC

BTS

BTS

MSC

SSP

SS7

SCP

1

1

2

3

45

6

7

8 9

10

11

12

14

17

16

15

13

BTS : Base Transceiver StationBSC : Base Station ControllerMSC : Mobile Switching Center

SRP

PSTN

52Copyright - EFORT

● 1. SETUP (GSM CM)● 2. IntialDP (INAP)● 3. ConnectToResource.Req + RRBE (O_Answer, O_Disconnect) (INAP)● 4. ISUP IAM ou Q.931 SETUP (Q.931 ou ISUP)● 5. ISUP CONNECT ou Q.931 CONNECT (Q.931 ou ISUP)● 6. ConnectToResource.Conf (INAP)● 7. Play Announcement (INAP)● 8. Specialized Resource Report (INAP)● 9. DisconnectForwardConnection (INAP)● 10. ISUP ou Q.931 Release (Q.931 ou ISUP)● 11. Connect (INAP)● 12. IAM (ISUP)● 13. ANM or Connect (ISUP)● 14. EventReportBCSM (O-Answer) (INAP)● 15. Release (GSM CM)● 16. EventReportBCSM (O-Disconnect) (INAP)● 17. Release (ISUP)

RRBE : Request Report BCSM Event

Information flows for the Prepaidservice

53Copyright - EFORT

Prepaid Card recharge

BSC

BTS

BTSMSC

SSP

SS7

SCP

1

1

2

3

456

710 9

10

BTS : Base Transceiver StationBSC : Base Station ControllerMSC : Mobile Switching Center

9 8

11

12

13

14

15

16

SRP

54Copyright - EFORT

Prepaid card recharge informationflows

● 1. SETUP (GSM CM)● 2. IntialDP (INAP)● 3. ConnectToResource.Req (INAP)● 4. ISUP IAM ou Q.931 SETUP (Q.931 ou ISUP)● 5. ISUP CONNECT ou Q.931 CONNECT (Q.931 ou ISUP)● 6. ConnectToResource.Conf (INAP)● 7. Prompt and Collect User Information (INAP)● 8. Envoi d’un message vocal par le SRP à l’abonné sur le circuit de parole● 9. L’abonné introduit son code PIN et les informations pour la recharge● 10. Collected User Information (INAP)● 11.Play announcement (INAP)● 12. Envoi du crédit sur le compte de carte à l’abonné● 13. Specialized Resource Report (INAP)● 14. Release (INAP)● 15. ISUP RELEASE ou Q.931 DISCONNECT (ISUP ou Q.931)● 16. ISUP RELEASE COMPLETE ou DISC.Conf (ISUP ou Q.931)

55Copyright - EFORT

GPRSMS : Mobile StationBTS : Base Transceiver StationBSC : Base Station ControllerMSC : Mobile Switching CenterPCU : Packet control UnitVLR : Visitor Location Register HLR : Home Location RegisterSGSN : Serving GPRS Support NodeGGSN : Gateway GPRS Support Node

MS BSCBTS

BTS

BTS

BTS

BTSMSC

BSC

Signaling linkVoice circuitFrame Relay Link

PSTN

SS7VLR

PCU

PCU FrameRelay

IPSGSN

GGSN

Internet X.25

HLR

In early 2000, only a small portion of GSM subscribers used data services,because existing GSM systems do not support easy access, high datarate and attractive prices. GSM operators must offer better services tostimulate the demand. The solution is General Packet Radio Service(GPRS).GPRS reuses the existing GSM infrastructure to provide end-to-endpacket-switched services.Two kinds of GSN (GPRS Support Nodes) are introduced in GPRS: Aserving GSN (SGSN) and a Gateway GSN (GGSN).The functionality of SGSN and GGSN can be combined in a physical node(e.g., Ericsson solution) or distributed in separate nodes (e.g., Nortel andAlcatel solutions).The SGSN is the GPRS equivalent to the MSC. Most vendors developedtheir SGSN based on existing multiple processor system products. LucentSGSN supports 40000 attached users and 4000 simultaneous activeGPRS data sessions. Nortel SGSN supports 50000 attached users andthe number of simultaneous active sessions is 20000.The GGSN provides interworking with external packet-switched networksand is connected with SGSNs via an IP-based GPRS backbone network.The GGSN is primarily provisioned by a router. For example, AlcatelGGSN is based on the Cisco 7200 series router. Nortel GGSN is basedon Bay Networks CES 4500.

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GPRS Impact on GSM

Add new nodes : SGSN, GGSN.

Entity Software Hardware

MS Upgrade required Upgrade required

BTS Upgrade required No change

BSC Upgrade required PCU Interface

MSC/VLR Upgrade required No change

HLR Upgrade required No change

By reusing the GSM infrastructure, most GPRS implementation costs inexisting GSM nodes are software related. The major hardware impact onthe GSM network is limited to the addition of a PCU-model to the BSC,and the introduction of two new node types, SGSN and GGSN.A GPRS software upgrade can be performed efficiently. In many vendorsolutions, GPRS software can be remotely downloaded to BTSs, so thatno site visits are needed.

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GPRS charging

BTS

BTS BSC

FrameRelay

SGSN

GGSN

Internet X.25

PCU Intra-PLMNIP Backbone

CGF

Billing CenterSun Enterprise Server, e.g. E250

Charging Gateway Function

Biling Record• Duration of the session• Nb octets received• Nb octets sent• Nb packets received• Nb packets sent• etc.

58Copyright - EFORT

Short Message Service with GPRS

BTS

BTS

BSC

FrameRelay Intra-PLMN

IP BackboneSGSN

GGSN

Internet X.25

PCU

SS7 SMSC1

23

4

Signaling LinkVoice CircuitFrame Relay Link

HLR

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UMTS

RNC

MS BSCBTS

BTS

BTSMSC

Signaling linkVoice circuitFrame Relay LinkATM Link

PSTN

HLR

SS7VLR

PCU

FrameRelay

IPSGSN

GGSN

Internet X.25

Node B

UMTS : Universal Mobile Telecommunications SystemRNC : Radio Network controller

ATM

UMTS (Universal Mobile Telecommunications System) introduces a new radio interfacecalled UTRAN (UMTS Terrestrial Radio Access Network). UTRAN will enable mobileterminal to be able to run multimedia sessions at 100 kbit/s in practice.The basic functional blocks of the UTRAN architecture are the node B and the radionetwork controller (RNC). The node B can be said to be roughly equivalent to the GSMBTS in linking the antenna site to the network.The RNC is roughly equivalent at a peer level to the GSM BSC. It is responsible forcontrolling the resources associated with a number of nodes B, and for negotiating withthe core network for aspects such as bearers and quality of service (QoS).The Node B interfaces with its RNC by means of ATM. The RNC interfaces with theMSC and the SGSN also using ATM connectivity.Those network operators who already have GSM/GPRS networks have two basicchoices for the UMTS launch architecture — an integrated solution or an overlaysolution.The integrated solution sees the current GSM/GPRS core network aspects upgradedand reused with the same switching (MSC) and routing (GSN) elements used for bothGSM and UMTS radio. The new UTRAN is connected to this network using the ATMinterface. This approach allows the re-application of common O&M systems, service-delivery mechanisms, switch sites, and platforms; however, the capacity, performanceand network growth impacts of connecting relatively new and unproven UMTS radioaccess technology to a live, service-providing network need careful assessment.The overlay solution relies upon operators using a different (overlay) network ofswitching (MSC) and routing (GSN) elements to support the UMTS radio. The overlaysolution enables a parallel independent development of the UMTS access with lowerrisks to the live GSM/GPRS network.

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Fixed and Mobile NumberPortability

Number portability is a network function that allows a subscriber to keep a“unique” telephone number. Number portability is an important mechanismto enhance fair competition among telecommunication operators and toimprove customer service quality.Two kinds of number portability exist :• location portability,• operator portability.With location portability, a subscriber may move from one location toanother location without changing his or her telephone number. This typeof portability is already implied in mobile phone service.With operator portability, a subscriber may switch operators or serviceproviders without changing his or her telephone number.In most countries, location portability is ignored and only operatorportability is implemented in a fixed network.The reason is twofold : First, operator portability is considered essentialfor fair competition among operators, while location portability is typicallytreated as a value added service; second, the implementation andoperation costs can be significantly reduced if we ignore locationportability.

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Fixed-Network Number Portability

Caller

0143567898 1. ISUP IAM

0143567898

2. ISUP IAM

Call Forwarding0711234567

Class 5 Switch Class 5 Switch Class 5 Switch

7211234567Call Forwarding

Caller

01435678981. ISUP IAM0143567898

2. ISUP RELcause = ported number

3. INAP Initial_DP4. INAP Connect

5. ISUP IAM7211234567

SCP

Query-on-Release

Caller

0143567898

1. INAP Initial_DP

3. ISUP IAM7211234567

SCP

All-Call-Query

2. INAP Connect

Class 5 Switch

Class 5 Switch

Class 5 Switch

NP databaseNP database

ON DN RN

ONDN

RN

ON

RN

ON : Originating Network DN : Donor Network RN : Recipient Network

Several solutions are possible to support fixed-network number portability: call forwarding,query-on-release, all-call-query.Call forwarding solution :1. The originating switch routes the call to the donor switch that according to the dialledtelephone number.2. If the dialler number has been ported, the donor switch forwards the call to the recipientswitch. For a nonported number, the recipient switch is the donor switch in this step, andno forwarding action is performed.Query on release solution :1. As in call forwarding, the originating switch sets up a voice circuit to the donor switchusing an ISUP IAM message.2. If the dialed number has been ported, the donor switch replies with an SS7 ISUP RELwith the cause value.3. And 4. When the originating switch receives the REL message, the trunk to the donorswitch is released. Since the cause value indicates that the called party number is ported,the originating switch sends a TCAP or INAP message to query the number portabilitydatabase for the routing address of the recipient switch.4. The originating switch sets up the voice circuit to the recipient switch based on theobtained routing information.All call query solution :1. and 2. The originating switch sends a TCAP or INAP message to query the numberportability database for the routing address of the recipient switch.3. The originating switch sets up the voice circuit to the recipient switch based on theobtained routing information.

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Mobile Number Portability :Signaling Relay Approach (1)

GMSC

1. ISUP IAM0611905252

PSTN

SignalingRelay

Function

2. MAP_SEND_ROUTING_INFORMATION (MSISDN)

3. MAP_SEND_ROUTING_INFORMATION (MSISDN)

6. MAP_SEND_ROUTING_INFORMATION_ack (MSRN)

VLR

4. MAP_PROVIDE_ROAMING_NUMBER (IMSI)

5. MAP_PROVIDE_ROAMING_NUMBER_ack (MSRN)

7. MAP_SEND_ROUTING_INFORMATION_ack (MSRN)

8. ISUP IAMMSRN

0611905252 � 0608132456

MSCPb : The GMSC of the recipient networkis not involved in call establishment

HLR

HLRON DN

RN

Signaling Relay Approach 1 utilizes a signaling relay function (SRF)mechanism to provide routing information for ported numbers. The callsetup procedure consists of the following steps :1. The originating switch routes the incoming call to the donor GMSC ofthe ported Mobile Station (MS).2. The donor GMSC sends the MSRN query message to the SRF.3. The SRF determines the HLR of the destination MS. If the MS is notported, the original HLR is queried. If the MS is ported, the recipient HLRis queried.Upon receipt of the MSRN, the donor GMSC routes the call to the servingMSC.The approach does not meet the following restriction : The GMSC must bein the call path for the provision of special features and services, as wellas for billing; that is, the GMSC of the recipient network is not in the callpath.

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Mobile Number Portability :Signaling Relay Approach (2)

GMSC

1. ISUP IAM0611905252

PSTN

SignalingRelay

Function

2. MAP_SEND_ROUTING_INFORMATION (MSISDN)

3. MAP_SEND_ROUTING_INFORMATION (MSISDN)

4. MAP_SEND_ROUTING_INFORMATION_ack (IRN)

VLR

5. MAP_SEND_ROUTING_INFORMATION_ack (IRN)

0611905252 � 0608132456

MSC

GMSC

6. ISUP IAM (IRN)

7. MAP_SEND_ROUTING_INFORMATION (IRN)

10. MAP_SEND_ROUTING_INFORMATION_Ack (MSRN)8. IMSI

9. MSRN

IRN : Intermediate Routing Number

11. ISUP IAM (MSRN)

HLR

HLR DN

RN

ON

Signaling Relay Approach 2 makes sure that the recipient GMSC is in thecall path for call termination to a ported number. The call setup procedureis described as follows:1. The originating switch routes the incoming call to the donor GMSC ofthe ported Mobile Station (MS).2. The donor GMSC sends the MSRN query message to the SRF.3., 4. and 5. If the MS is ported, then the SRF queries the recipient HLR.IN this case, the recipient HLR returns an intermediate routing number(IRN) instead of the MSRN. IN the UK, the IRN consists of the called partynumber with a prefix that indicates the recipient GMSC.6. Upon receipt of the MSRN, the donor GMSC routes the call to therecipient GMSC.7. The GMSC requests an MSRN to the HLR.8. and 9. The HLR requests the MSRN to the VLR that returns it.10. The HLR returns the MSRN to the recipient GMSC.11. The recipient GMSC routes the call using the standard GSM calltermination procedure.

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Mobile Number Portability :All-Call-Query Approach

Appelant

0611905252

1. INAP Initial_DP

SCP

2. INAP Connect (IRN)

Class 5 Switch

VLR

MSC

GMSC

4. MAP_SEND_ROUTING_INFORMATION (IRN)

7. MAP_SEND_ROUTING_INFORMATION_Ack (MSRN)5. IMSI

6. MSRN8. ISUP IAM (MSRN)

3. ISUP IAM (IRN)

Number Portability Number

HLR

ON

RN

ON : Originating NetworkRN : Recipient Network

All Call Query Approach utilizes the existing fixed network, all-call-querymechanism to route the calls to a ported MS.1 and 2. The originating switch queries the mobile number portabilitydatabase to obtain the IRN (Intermediate routing number) of the recipientGMSC.3. The originating switch sets up the voice circuit to the recipient GMSC.4. The GMSC requests an MSRN to the HLR.5. and 6. The HLR requests the MSRN to the VLR that returns it.7. The HLR returns the MSRN to the recipient GMSC.8. The recipient GMSC routes the call using the standard GSM calltermination procedure.

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1.6. OSS and BSS :Information System

OSS : Operation Support SystemBSS : Business Support System

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Service Provider Processes andInformation

● The main groups of processes that are performed by theService Operator are:

● Planning and Administration; to plan, design and administrate the services.● Multi-Service Provisioning; to activate instances of services for particular

customers.● Service Operations and Assurance; to monitor and uphold the quality of the

delivered services.● Accounting and Billing; to charge for the services.

● The service operator has also several databases :● customer database that contains all data about the customers and the services

subscribed by the customer.● Workforce database that contains all data about the service administrators of the

service operator● Inventory database that contains all data about the services subscribed by a

given subscriber.● Service assurance that contains logs about service incidents and service QoS

degradations.● Product portfolio that is the service catalogue of the service operator.

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A simplified view of service providers

Design service

Plan work

Receive orders

Configure service

Activate service

Operate service

Collect usage data

Bill service

Customers

Product Portfiolo

Inventory

Workforce

ServiceAssurance

The main groups of processes that are performed by the Service Operator are:• Planning and Administration; to plan, design and administrate the services.• Multi-Service Provisioning; to activate instances of services for particular customers.• Service Operations and Assurance; to monitor and uphold the quality of the delivered services.• Accounting and Billing; to charge for the services.Planning means designing the service and planning the work to introduce this service within thenetwork.Provisioning means receive orders from customers and configuring the service for the customerplus activating the service.Service operations means operating or monitoring the service (fault and performance).Accounting and Billing means collecting usage data for a given service and billing that service.The service operator has also several databases :• customer database that contains all data about the customers and the services subscribed by thecustomer.• Workforce database that contains all data about the service administrators of the service operator• Inventory database that contains all data about the services subscribed by a given subscriber.• Service assurance that contains logs about service incidents and service QoS degradations.• Product portfolio that is the service catalogue of the service operator.The Customer Care is the system of the network operator to provide an interface to the customersfor all issues related to sales, ordering, problem handling and billing of the services.

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A simplified view of networkproviders

Design the network

Plan work

Provision network

Operate network

Collect usage data

ProductPortfolio

NetworkInventory

Workforce

NetworkAssurance

The main groups of processes that are performed by the NetworkOperator are:• Planning and Administration; to plan, design and administrate thenetwork.• Multi-Service Provisioning; to provision network resources to supportservices for particular customers.• Network Operation; to monitor the faults that may occur within thenetwork and the performance level supplied by the network.• Accounting : Collect usage data about use of network resources.The network operator has also several databases :• customer database that contains all data about the customers and theservices subscribed by the customer.• Workforce database that contains all data about the networkadministrators responsible for the management of the network• Inventory database that contains all data about the network resourcesthat support services.• Network assurance that contains logs about network faults and networkperformance degradations.• Product portfolio : Network services that the network business unitsupplies to the internal clients (i.e., business unit that handles residentialcustomers, business unit that handles corporate customers, etc.).

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Operator Information System :OSS and BSS

Network Element Management Processes

I mn af no am ga et mi eo nn t

S py rs ot ce em s s e s

Physical Network

Order HandlingSales

Problem Handling

Siebel, Vantive, Clarify Scopus, Gaïa

Invoicing/

DiscountingRating and

Collection

Arbor B.P Portal

GenevaBSCS

Network DataManagementMETRICA

TTIEHPT

Service Quality

Management

Customer QoS

ManagementMETRICA

SLAQuallaby Proviso

Service Problem

Resolution

NetworkMaintenance& Restoration

HP OpenviewCOMPAQ Temip, IBM Tivoli, etc.

Configuration

Network Inventory

Management

NetworkProvisioning

Service Planning/

Development

Network Planning/

Development

IronmanDimension

Graniteetc.

Service

A good overview of what the OSS and BSS worlds really are intended to cover is provided by theorganization TMForum, via the process overview Telecom Operations Map (TOM). It contains adetailed description of the most important processes involved in running a Network Operatoroperation.What is TOM?• Customer Focused• A Map of ‘end to end’ Operational Processes for Management Automation• A Framework for gaining industry consensus• An Enabler of common understanding• A Tool to identify requirements and position solutionsOn the above diagram, some de-facto solutions are mapped into the TOM process map. We find :• Planning tools that cover the service planning/development and network planning/ developmentprocesses.• Provisioning tools that cover the network provisioning, Network inventory management and serviceconfiguration processes. Some tools handle both planning and provisioning.• Supervision tools that cover network maintenance and restoration and service problem resolutionprocesses.• Performance monitoring and mediation tools that cover the network data management process.• Billing tools that cover rating and discounting and invoicing/collection processes• SLA management tools that covers service Quality management and Customer QoS management.• Customer care tools that cover sales, order handling and problem handling processes.

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1.7. Data Networks

Packet Switching (X.25),Frame Switching (Frame Relay),

Cell Switching (ATM)

ATM : Asynchronous Transfer Mode

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Data Networks

● Data networks consist of a set of switches.● X.25 provides data services at low bit rates (less than 64

kbits/s).● Framed Relay provides data services at bit rates

comprised between 64 kbit/s and 2 Mbit/s (multiple of 64kbit/s).

● ATM is a multiservice network technology that providesvoice, video and data services at various bit rates.

● IP network consists in a set of routers because IPoperates in the connectioless mode.

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Services types supplied by datanetwork

● With data networks such as X.25, Frame Relay andATM, two types of services may be offered :

● PVC (Permanent Virtual Circuit) : Circuit established bymanagement using provisioning tools.

● SVC (Switched Virtual Circuit) : Circuit established bysignaling; switches exchange signaling messages forestablishing/releasing calls. Switches switch both thesignaling traffic and user traffic.

● In fact, Frame Relay does not operate with signaling, whichmeans that Frame Relay services are provisioned bymanagement.

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IP / Frame Relay / ATM

Router with an equipmentto access the Frame Relay network

LAN1

LAN : Local Area NetworkUNI : User to Network Interface

LAN3

UNIUNI

Frame Relay Switchwith an equipmentto access an ATM network

ATMBackbone

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1.8. Access Network

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Broadband access network

● A recent interest to increase bandwidth in the accessnetwork.

● Must benefit from the recent advances in transmissiontechnologies.

● Target services :● interactive TV and TV distribution● Video on Demand● Broadband Internet● Tele-shopping● Tele-working

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Broadband over customer linesTechnology Data ratge (Mbits/s) Distances (Km)

DSL 0.16 5.4

HDSL 1.5 - 2 4

ADSL 1.5 - 2 5.4

6 3.6

VDSL 13-14 1.5

26-28 1

52-56 0.3

DSL : Digital Subscriber Line• Used for the basic ISDN access• Corresponds to 2B+D channels• Throughput reached = 160 kbit/s• Distance = 5.4 Km

HDSL : High Speed Digital Subscriber Line• Primary rate access to ISDN

•T1 (1.544 Mbits/s)•E1(2 Mbits/s)

• For applications that require symmetric bit rates :•Typically professional access

ADSL : Asymmetric Digital Subscriber Line• Broadband and Asymmetric bitrate

Very High Bit-Rate Digital Subscriber Line - VDSL• Short distance but very high bitrate• Currently being defined• Same principles as ADSL : asymmetric

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ADSL

Ethernet Card

Modem+Splitter

Telephone line

Home

DSLAM

DSLAM : DSL Access MultiplexerISP : Internet Service Provider

ATM

Central office

ISP

Class 5 Switch

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2. Next Generation Networkand IP Telephony

Many changes have occurred in recent years that have caused the traditional 64 kbit/sbased Time Division Multiplexing (TDM) networks (e.g., PSTN, GSM) and networkarchitecture to become more and more unsuitable for today's and tomorrow's servicerequirements. TDM networks have failed to overcome the 64 kbit/s limitation.Moreover, while technology has reduced the bandwidth required for voice to wellbelow 64 kbit/s, it still has to be carried in a full 64 kbit/s channel. GSM showed thisreduction clearly. Voice compression to 16 kbit/s and lower is no longer a problem.However, transcoders had to be introduced at both sides of the cellular accessnetwork to convert speech to and from 64 kbit/s and A-or µ-law, for transport overTDM networks, introducing an unnecessary loss of quality for mobile-to-mobile calls.TDM efficiency is lost entirely when one starts introducing asymmetrical, bursty orvariable bitrate services.All these limitations can be overcome by packet networks based on the InternetProtocol (IP) or Asynchronous Transfer Mode (ATM), for example.While TDM was starting to lose this battle, computers and computer-connectivity weregrowing dramatically in importance, causing the operators’ data networks to boom.The volume of data traffic is rapidly overtaking the amount of voice traffic in someparts of the world, and the clear trend is for more and more bandwidth to be requiredfor data, while voice can be handled with the same or even less bandwidth.Owners of both a voice and a data network are using this argument to startconsolidating the two networks. Taking the above reasoning on limitations in the TDMnetwork into account, it is clear that the data network will survive; the TDM networkhas to go.

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Next Generation Network : Drivers

DRIVERS:ServicesTime to marketCost

ENABLER:Technologíes (Hardware andSoftware)

mono-service network

PSTN

Mob

ile N

e tw

o rk

Dat

a N

etw

ork

multi-service networkNGN

Application LayerControl Layer

Transport Layer

Adaptation LayerAccess Layer

MANAGEMENTTerminal Layer

NGN Architecture consists in five layers :• Terminal Layer : It contains all terminals enabling making and receiving calls.• Access Layer : Links the users to the network• Transport Layer : Transports the traffic to the destination• Adaptation Layer : Adapts the traffic for its transfer by the network. For example,the voice traffic is encoded into ATM cells or IP packets.• Control Layer : Contains the call intelligence. This layer decides which service auser will receive. It controls other lower layer network elements to indicate themwhich treatment to perform on the traffic.• Application Layer : Provides supplementary and value added services.• Management is transversal to the set of layers.The NGN Advantages are:• There is a unique multi-service backbone to operate and manage• It uses a transport based on IP or ATM ignoring the limitations of TDM (TimeDivision Multiplexing) networks (PSTN network).• It’s an open topology which may transport voice-based services as well as dataservices.• It dissociates the control and transport parts, enabling them to evolve separatelyand breaking the monolithic communication structure.• It uses open interfaces between all elements, allowing a network operator to buythe best products from the best manufacturers for each part of its NGN network.

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NGN : A Layered Structure● Terminal Layer : It contains all terminals enabling making

and receiving calls.● Access Layer : Links the users to the network● Transport Layer : Transports the traffic to the destination● Adaptation Layer : Adapts the traffic for its transfer by the

network. For example, the voice traffic is encoded into ATMcells or IP packets.

● Control Layer : Contains the call intelligence. This layerdecides which service a user will receive. It controls otherlower layer network elements to indicate them whichtreatment to perform on the traffic.

● Application Layer : Provides supplementary and valueadded services.

● Management is transversal to the set of layers.

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PSTN versus NGN

SP

Fabric

SP SP

Fabric Fabric

ISUP ISUPSP

Fabric

ISUPPSTN

NGN

SP : Signaling PointMGW : Media GatewayMGC : Media Gateway Controller

Voice circuits

SP SP

IP/ATMATM

SP

Voice circuit Voice circuitMGW MGWFabric

Fabric Fabric

Fabric

ISUP

x x x

ISUP

x

PSTN versus NGNFrom the fixed telecommunications circuit-switched network perspective anumber of developments are ongoing to give operator’s greater flexibilityin the deployment of networks. Distributed processing has enabled theseparation of pure switch/routing functionality away from the controlmechanisms. The separation of contemporary switch mechanisms intomedia gateways (MGWs) (containing switching, transcoding and user-plane transmission aspects) and media gateway control functions (MGCs)(containing switch and service control functionality), connected viastandard interfaces (e.g. H.248/Megaco), will enable operators to increasethe service delivery and control parts of their networks in relative isolationto the growth of the user traffic parts of the network. The above figureillustrates the concept behind the distributed processing and switchingmechanisms offered by H.248/Megaco. This approach also enablesprocurement towards distributed networks with controller and gatewayprocured from separate suppliers, enabling a real progression towards callserver ‘farms’ connected to ‘pools’ of resource control and switching.

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NGN Advantages● NGN Advantages:

● It’s a unique multiservice network to manage.● Uses a transport based on IP or ATM ignoring the

limitations of TDM networks.● It’s an open topology which may transport voice-based

services as well as data services.● It dissociates the control and transport parts, enabling

them to evolve separately and breaking the monolithiccommunication structure.

● It uses open interfaces between all elements, allowing anetwork operator to buy the best products from the bestmanufacturers for each part of its NGN network.

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Layers of Telephony NGN

BTS BSC

Access

Control Media Gateway Controller

Media Gateway

Adaptation

Transport

Router/Switch

Application Application ServerSCP

Telephony NGNDeploying an NGN infrastructure starts with the consideration of the transport layer whichmay be IP/ATM or ATM based. In the future, new technologies may exist such as IP/SDH orIP/D-WDM. ATM as the service transport layer is not a long term solution because ATM isconnection oriented and lacks scalability for the establishment of millions of switched virtualcircuits (SVCs) as in PSTN. IP is connectionless and therefore is more scalable.The second step is considering the various legacy equipment to interconnect to thisbackbone. This later is called the access layer. The operator will first start trying emulatingonly telephony with NGN called Telephony NGN.Initially, the network operator may consider removing its class 4 switches and replacingthem by NGN (IP or ATM transport). Then, the replacement of class 5 switches will takeplace. The same will apply to GSM since TDM is used in GSM. To interconnect legacyequipment, we need gateways that belong to the adaptation layer. The gateway onlyconverts voice signals in packets or cells.In PSTN, a switch contains both the signaling (Signaling point) and transport (fabric)functions. Moreover an internal interface enables the SP controlling the Fabric. In NGN,there two functions are separated to enable standardizing the interface and to permit theNGN market to be more open. On the one side, we have the controller called MGC (MediaGateway Controller); on the other side, we have the MGW (Media Gateway). In addition, wemay have various kinds of Gateways (e.g., Residential Gateway) and in this case a uniqueMGC may control hundreds of thousands of MGWs. MGCs belong to the control layer. Thecontrol protocol used by the MGC to control the MGW is called MGCP or MEGACO.Finally, we have to consider the application layer. Since we only want to emulatetelephony services, this layer contains IN SCPs or CAMEL CSEs. The protocol used isINAP or CAP. The MGC contains an SSP function to activate services. In fact TelephonyMGC = SP of a PSTN switch + MEGACO

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Layers of Multimedia NGN

Media Gateway

Adaptation

Transport

Router/SwitchBTS BSC

Access

Control Media Gateway Controller

Application Application ServerSCPMultimediaApplication

Server

Deploying initially a Telephony NGN enables a smooth migration to theMultimedia NGN. To reach this multimedia target, we have to enable IPphones or multimedia enabled PCs to connect to NGN. This leads to theprovisioning of new advanced applications (e.g., unified messaging,videoconferencing).IP phones or multimedia PCs will use a multimedia signaling protocol. Thislatter may be H.323 proposed by ITU-T or SIP from IETF. Therefore theMGC should be able to control not only MGWs by means ofMEGACO/MGCP but also IP Phones by using H.323/SIP.That is the reason the MGC equipment will include an MGC function tocontrol the MGWs, a proxy server function to control SIP enabledterminals and a Gatekeeper function to control H.323 enabled terminals.The MGC equipment is generally called MMCS (Multimedia Call Server)NGN multimedia = NGN Telephony + IP Telephony.IP Telephony = SIP or H.323In the context of multimedia NGN there is a need of advanced application.New application servers are required. These are called MMAS(Multimedia Application Servers). They interface with the MMCS through aSIP or PARLAY interface.

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NGN : Three Generations● 1st Generation : 1999; Class 4 NGN with proprietary interfaces.● 2nd Generation : Mid 2001; Class 4 and Class 5 NGN but only

for telephony emulation without any multimedia features.Standardized interfaces.

● 3rd Generation : Beginning 2003; Multimedia NGN.● NGN Vendors :

● Ericsson : Engine Bridgehead (1); Engine Integral (2); EngineMultimedia (3).

● Alcatel : Softswitch Release 1 (1); Softswitch Rel. 2 (2); SoftswitchRel. 3 (3)

● Nortel : Succession● Siemens : Surpass● Lucent : Softswitch● Sonus Networks : Softswitch

1st Generation : Telephony NGN, Class 4 (1999)• Control protocol between MGC and MGW proprietary or IPDC. The MGW ismainly a Trunking Gateway• Either MGCs are running on pure Unix Workstations (Lucent, Sonus) or the callcontrol is based on the signaling of the PSTN switch and the bearer control runs onUnix workstation (Nortel, Siemens, Ericsson). MGC supplies 1 Million BHCA• Mainly ATM transport due to lack of scalable IP QoS Mechanisms2nd Generation : Telephony NGN, Class 5 (Mid 2001)• Control protocol between MGC and MGW is MGCP (US) or MEGACO (Europe).MGWs are either TGWs or AGWs or RGWs.•ATM or IP transport. MGC supplies 1,5 to 5 Millions BHCA.3rd Generation : Multimedia NGN (Beginning 2003)• Control protocol is MEGACO•MGCs based on UNIX workstations (Multimedia Call Servers)• IP transport•Multiprotocol MGCs (include SIP and H.323 signaling); 4 to 6 Millions BHCA.

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NGN Class 4 (Telephony)

TGWFaxFax

IP/ATM Network

Class 5Switch

MEGACO/H.248

MEGACO/H.248

SCP

TGW

VoiceCircuits

ISUP

MGC INAP CS-1

ISUP

Class 5Switch

SS7 SS7

VoiceCircuits

ISUP : ISDN User PartMGC : Media Gateway ControllerSCP : Service Control PointTGW : Trunking Gateway

Phone Phone

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ALCATEL NGN Components

A1000 Softswitch ALCATEL 7470 MG

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Networks Relationships

TransmissionNetwork

SwitchingNetwork

SignalingNetwork

IntelligentNetwork

ManagementNetwork : EMS+OSS

MUX

STP STP

SCP SCP

Optic Fiber

Switch

Multiplexer

SS7

SP

OSOS

BillingSystem

Customer Care

BSS

SP SP

EMS : Element Management SystemOSS : Operation Support SystemOS : Operation System

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Acronyms (1)● ADM : Add and Drop Multiplexer● ADSL : Asymmetric Digital Subscriber Line● AGW : Access Gateway● AMPS : Advanced Mobile Phone System● ATM: Asynchronous Transfer Mode● BSC : Base Controller Station● BSS : Base Station Subsystem● BSS : Business Support System● BTS : Base Transceiver Station● CAMEL: Customized Application for Mobile network

Enhanced Logic● CAP: Camel Application Part● CIC : Circuit Identification Code● DSL : Digital Subscriber Line● D-WDM : Dense - Wavelength Division Multiplexing● FR : Frame Relay● GGSN : Gateway GPRS support node● GK : Gatekeeper● GMSC: Gateway MSC● GPRS : General Packet Radio Service● GW: Gateway● HDSL : High Speed Digital Subscriber Line● HLR: Home Location Register● IMEI : International Mobile Equipment Identity● IMSI : International Mobile Subscriber Identity

● IN: Intelligent Network● INAP: Intelligent Network Application Protocol● IP: Intelligent Peripheral● IP : Internet Protocol● ISDN: Integrated Service Digital Network● ISUP : ISDN User Part● ITU: International Telecommunication Union● LAI : Location Area Identitifier● LEC: Local Exchange = Class 5 Switch● MAP: Mobile application Part● MEGACO : Media Gateway Control Protocol● MGW : Media Gateway● MGC : Media Gateway Controller● MIB : Management Information Base● MS: Mobile Station● MSC: Mobile Switching Center● MSISDN : Mobile Station ISDN Number● MSRN : Mobile Station Roaming Number● NGN : Next Generation Network● NSS : Network Subsystem● OSS : Operation support system● PDH : Plesiochronous Digital Hierarchy● PSTN: Public Switched Telephone Network● PVC : Permanent Virtual Circuit● RNC : Radio Network Controller

90Copyright - EFORT

Acronyms (2)● SCE: Service Creation Environment● SDH : Synchronous Digital Hierarchy● SG : Signaling Gateway● SGSN : Serving GPRS support node● SIP: Session Initiation Protocol● SMSC : Short Message Service Center● SP : Signaling Point● SS7: signaling System N°7● SSP: Service Switching Point● SRP : Specialized Resource Point● STP : Signaling Transfer Point TCAP : Transaction

Capabilities Application Part● TCP : Transmission control Protocol● TGW : Trunking Gateway● TMF : TeleManagement Forum● TMSI : Temporary IMSI● TOM : Transaction Oriented Middleware● TOM : Telecom Operations Map● TMN: Telecommunications Management Network● UDP : User Datagram Protocol● UMTS: Universal Mobile Telecommunications System● VLR: Visitor Location Register● VP : Virtual Path● VPC : Virtual Path Connection● VPN: Virtual Private Network● WDM : Wavelength Digital Multiplexing