Tài liệu Mạng và viễn thông P11 ppt

l1 Intelligent Networks and Services By storing a massive ‘memory’ of customer and service information in a network, and referring to it while setting up calls, and as a historical record of network use, a phenomenal new range of services becomes possible. The effect is almost as if the network had some degree of ‘intelligent’ power of thought. This chapter commences by describing the ‘intelligent networks’ as a concept, and then goes on to give examples of the new services that we can expect from it. 11.1 THE CONCEPT OF INTELLIGENT NETWORKS The concept and development of intelligent networks (INS) originated in North America. The forerunner was AT&T’s database 800 service, and AT&T continue to be a key driver of the technology. Subsequently much work has also originated from the RBOCs (the American Regional Bell Operating Companies, or local telephone com- panies), in conjunction with their jointly funded research arm, Bellcore. More recently, ETSI (the European Telecommunications Standards Institute) has been very active. The concept is based on the premise that all services can be broken down into elemental capabilities called functional components or service-independent building blocks (SIBs or SIBBs). For example, a simple service may include providing dial tone, collecting digits, performing number translation, switching the connection, and charg- ing at an appropriate rate. If we were now to examine a second service, then we would find that some of the functional components used in that service would overlap those already identified in the first. If a comprehensive set of these functional components (SIBs) could be implemented at every exchange (so-called service switchingpoint (SSP)) and if a suitable means of controlling the exchanges, from new powerful and remote computers called service control points (or SCPs), could be found, then new and much more powerful services could be implemented simply by writing software (a service script) for the SCP, enabling it to manipulate the SSP(s). 231 Networks and Telecommunications: Design and Operation, Second Edition. Martin P. Clark Copyright © 1991, 1997 John Wiley & Sons Ltd ISBNs: 0-471-97346-7 (Hardback); 0-470-84158-3 (Electronic) 232 INTELLIGENT NETWORKS AND SERVICES 11.2 INTELLIGENT NETWORK ARCHITECTURE In the past, each exchange had at least a small amount of ‘intelligence’, comprising software programs and related data for call routing and service control of ‘basic’ tele- phone services. However, when we speak of an intelligent network we mean a network equipped with a much larger information reference store and with software capable of controlling more powerful services. The intelligence can be added to the network on either a distributed or a centralized basis, according to the circumstances of the established network, the equipment to be used and the service to be provided. Here we compare and contrast the two architec- tures as a means of illustrating the scope of possibilities. In a network employing distributed intelligence the information required for advanced call routing and service control is spread over a large number of sites or exchanges. Each exchange stores a large store of information necessary for the set up and control of the wide range of services it is expected to offer. This will include a store of customer-specific data (the information pertinent to a given customer’s network), as well as some service logic to tell the exchange exactly how each sophisticated service works, and the procedure for setting up calls. This sort of intelligent network could be created by continual enhancement of today’s exchanges, progressively adding software and hardware to cope with new service needs. The advantage of such an approach (storing information at a large number of exchanges) is that the service becomes available at all existing exchanges and the call handling capacity is large. The disadvantages are that the exchange software becomes very complex and the job of keeping all the exchanges’ software up to date is unmanageable. Not only that, but the software and data duplication increases the risk of inconsistencies and may affect the service creation environment offline development environment (say 2-8 per network) - I ive environment public telephone exchange (Say 25 per network) point (SSP) (ideally a function included in most main exchanges) Figure 11.1 Intelligent network architecture THE SERVICE CONTROL POINT (SCP) 233 smooth running of both the service and the network as a whole. (For example, two exchanges may hold conflicting data because they were updated by different people at different times.) Figure 11.1 illustrates the standard ‘centralized’ intelligent network (IN) architecture. In the lowest tier of a centralized intelligent network are a number of service switching points (or SSPs). These contain a service switching function (SSF). These are enhanced telephone exchanges which have been developed to include a new intelligent network interface. The interface allows the exchange to refer the call control of advanced service calls to the service controlpoint (SCP), allowing the SCP (a centralized control point) to manipulate subsequent actions of the exchange. 11.3 THE SERVICE CONTROL POINT (SCP) The service control point (SCP) is a specialized computer, distinct and often remote from the exchange, connected by a signalling system number 7 (SS7, see Chapter 12) signalling link. The SCP comprises the service control function (SCF), the ‘knowledge’ of how a service works and the customer-specific data required to perform it. In response to an exchange request to deal with an ‘advanced service’ call attempt, the SCP sends a sequence ofprimitive commands to the exchange, using SS7 signalling. The commands direct the exchange to perform the necessary sequence of simple switching actions which combine to appear as a more complex service offering (e.g. ‘collect digits’, ‘connect switch path’). Thus the call control is carried out by the SCP rather than the exchange (SSP). However, the connection itself never passes through the SCP. Connections are always only switched by exchanges (the SSPs). During call set-up, call processing is suspended so that the SSP may refer to the SCP. The reference may reveal, for example, whether a given caller is permitted to be connected to a given number. Alternatively a credit card number might be validated before accepting call charges, a dialled freephone number might be interpreted into another ‘real’ telephone number, or some other ‘intelligent’ action may be undertaken. The SSP sends an SS7 message to the SCP containing the dialled number and any other known information about the called or calling party. The SCP interprets the call request using the received information and its own store of data, and then returns the sequence of commands back to the SSP. The specially developed user parts of SS7 signalling which enable this interaction are called the signalling connection and control part (SCCP) and the transaction capability application part (TCAP, ITU-T Q.771-Q.775) and the newly defined INAP (intelligent network application part) These are described in more detail in Chapter 12. The number of SCPs deployed in any given intelligent network depends on a number of factors, including the complexity of the service logic required to support the advanced services and the traffic demand for them. One option is to allocate one SCP for each individual advanced service, but for a large number of services we would need a large number of SCPs. Some experts therefore favour SCPs which are capable of handling a number of different services, so that the number of SCPs in a network can be kept down to a handful. In this case each will cater for a number of services, but each service will be duplicated over more than one SCP to prevent total loss of the service in the event of an SCP computer failure. 234 INTELLIGENT NETWORKS AND SERVICES 11.4 THE SERVICE SWITCHING POINT (SSP) The service switching point (SSP) or service switching function (SSF) is a modified telephone exchange. Over and above the normal functions of a telephone exchange it contains an ‘intelligent network’ functionality comprising 0 trigger tables 0 transaction capabilities 0 intelligent peripherals (IPs) Every telephone exchange has a number look-up table of some form to enable it to switch calls through to their correct destinations. In the case of an SSP trigger table, the information needed to complete the call set-up is not contained in the table itself; instead there is a trigger (typically activated by the dialled number) to commence a query transaction with the SCP. The SSP next collects all necessary information about the call (caller’s number, class of service, dialled number, etc.) and forwards this information to the SCP to request further control information. The information and short dialogue which then follows between SSP and SCP is called a transaction and is conducted using SS7 TCAP signalling (transaction capabilities application part). During the dialogue the SCP returns a number of control commands to the SSP to control its switching and charging functions, and also to activate any necessary intelligent peripherals (ZPs). Intelligent peripherals could be any number of different types of device affording different types of advanced service. At the simplest an IP might be a recorded announcement machine (say, thanking a televoting caller for his interest). At a more complex level it might be a voice interaction unit. 11.5 THE SERVICE MANAGEMENT SYSTEM (SMS) AND SERVICE CREATION ENVIRONMENT (SCE) The service management system (SMS) or service management point (SMP) appears above the SCP and is used to control the SCPs in a network. SMSs are ofline computer systems used to prepare database and configuration tables of network and customer- specific data before downloading them to the live SCPs. The SMS ensures that the data held in all SCPs is comprehensive and consistent. The fact that only one SMS exists, or a small number of SMSs, makes the manual task of administering data held within the network a great deal easier. The service risk of running only a single SMS is not material because it is only an ‘updating machine’. The service availability is affected mainly by the reliability of the SCPs and SSPs. The SCE (service creation environment) is the platform for SCP software develop- ment and testing (i.e. it is the tool with which new ‘intelligent’ services can be developed). Usually it comprises sophisticated software debugging tools, capable of ‘stepping’ through the programmed commands within a new software service script. These help the service designer ensure that the service is realized in the manner intended. BENEFITS OF INTELLIGENT NETWORKS 235 11.6 BENEFITS OF INTELLIGENT NETWORKS The main advantages of an intelligent network over predecessing public telephone networks is the ease with which complex, and particularly network-wide, services may be managed. Instead of having to configure routing tables and other network control elements which are distributed across many exchanges, the network operator only needs to maintain the data in the central SCP. This guarantees a higher level of data consistency within the network and thus of service reliability. In addition, the network operator is able to react faster in the introduction of new services. This leads to 0 minimal impact on existing network and switching equipment during the rapid introduction of new services (the introduction requires only the downloading of new service script software and configuration data to the SCP (from SCE and SMS)) 0 reduced cost of introducing and enhancing services 0 higher quality of service 0 the ability for rapid re-configuration of services, allowing continual retuning to meet changing market needs (the use of a single SMS means that the job of coordinating network upgrades is largely eliminated) 0 the ability to give the limited customer control and management facilities if required (by providing special customer terminals connected to the SMS, customers could be authorized to make some changes specific to their own networks) 11.7 INTELLIGENT NETWORK (IN) SERVICES Certain types of telephone services are best realized using an intelligent network. This applies to those types of service where either the charging requirements of the service are complicated (e.g. there is a need to charge the person called and not the caller), or where the handling is complicated (e.g. caller authorization is necessary or complicated translation of the dialled number is necessary, as for example by freephone numbers where a dialled 800 telephone number must be converted to the standard telephone number of the called party). Examples of intelligent network services include the following. Virtual private network (VPN) A service in which a company-specific network (a telephone closed user group with a specific telephone numbering plan) may be created for individual corporate customers of the public network. The public network thus appears to the corporate customer much as a private network would, with a ‘tailored’ company numbering plan. Freephone The intelligent network converts an 800 dialled freephone number into a standard telephone number allowing the SSP to complete the call set-up, while simultaneously 236 INTELLIGENT NETWORKS AND SERVICES creating a call charge record for the call receiver’s account (rather than for the caller’s account as is normal). Premium rate service The ability to charge a premium rate for calls over and above normal telephone charges so that the caller shall be charged for information services (e.g. weather forecast, traffic information, etc.). The extra charges collected are furthered to the information service provider. Calling card service A service which allows telephone company calling card holders (e.g. AT&T calling card) to make calls from any telephone in the public network, invoicing their call charges to their personal calling card account. At call set-up, IN verifies the card account number and requests caller authorization by means of his personal identification number (PIN). Televoting A service conceived to complement television game shows in which viewers are invited to call different telephone numbers to register their vote for the best participant in, for example, a television game show. IN counts the total number of calls to each dialled number and connects the caller to a recorded announcement which thanks him for his call. Universal number service This service enables customers of the public telephone network to move around the country while remaining available under the same telephone number. As the user moves to a new location, he must register with the SCP where he now is, so that future calls to his number may be furthered to him. This may become the basis of number portubility service, the ability for a customer to change his telephone network provider without being forced to change his telephone number. The difficulty caused by changing number, requiring one to print new letterheads and advise business partners, might otherwise dissuade a change of telephone network provider, so that number portubility is increasingly viewed as an essential enabler of competition between public telephone service providers. Universal personal telephone service This service is an extension of the universal number service, allowing the customer not only to roam within the ‘fixed’ telephone network but also to connections of mobile telephone and other types of telecommunication networks. 11.8 CALLING CARD Using network intelligence to validate culling curd or credit curd account numbers and as a historical record of transactions, an alternative means of paying for calls is possible. Calls made from any telephone can be charged to a special ‘calling card’ FREEPHONE SERVICE (OR 800 SERVICE) 237 account. The bill can then be sent to the card holders address. Maybe such a service will make obsolete the familiar public payphones, or at least the ones for which you need handfuls of coins to operate. There are three ways of initiating a call. In one the caller tells the operator the card number and the personal identiJication number (PIN). The operator types this information into a computer which interrogates the SCP to check that the card is valid, and subsequently charges the cost of the call to the appropriate account. An alternative is an automatic version that relies on the customer being prompted to dial in his card account number and PIN using a DTMF telephone. Finally, a specially designed telephone with a ‘card-wipe’ system might also be available. In this instance, a magnetic strip on the reverse of the card is ‘wiped’ through a narrow channel on the telephone. The telephone ‘reads’ the magnetic strip to derive the calling card (or standard credit card) type and number, and automatically validates the card, notes its expiry date and other details by using the network intelligence in the same way as above. If the card is not valid, or if the caller dials in the wrong PIN then the call is not permitted. The beauty of using central intelligence of the SCP to validate cards is the scope that it gives for tailoring calling capabilities of the card to its owner’s needs. A student’s parents can give their son a calling card with which he can only ‘call home’ (as in MCI’s ‘friends and family’ service). Other calls are at the student’s expense. Similarly, a company representative can be given the means to call his office. Calling card service is growing in popularity in countries where it is already available, and most major PTOs are planning to introduce it. Figure 11.2 illustrates an example of a telephone designed especially for automatic card validation. 11.9 FREEPHONE SERVICE (OR 800 SERVICE) Freephone, toil-free, nulltarif or 800 service is available in a number of countries. In the UK callers who dial a number in the 0800 range, and in the US callers who dial a 1-800 range number have those calls completed entirely free of charge. The call charge is paid by the recipient of the call. Freephone service gives companies a way of persuading people to call them. A company may wish to promote calls to follow-up an advertisement campaign, or to allow customers to call the service department, or maybe to allow their travelling representatives to call the office. Network intelligence plays two key roles in support of the freephone service. First, the 0800 number dialled (say, 0800 12345) must be converted into the receiving company’s actual number, say 071-246 8021, otherwise the normal telephone network will be incapable of completing the call. The second role is to record the total number and duration of calls made, so that the call recipient can be charged in due course. Figure 11.3 shows a diagram of automatic freephone service. The caller has dialled the number 0800 12345 into the network. The SSP sends the number to the SCP, which returns the normal telephone number to the network (to allow routing), and records the time of day, call origin and call duration, so that the recipient (071-246 8021) may be charged for the call by normal quarterly account. Figure 11.2 Credit card telephone. Telephone specially designed to allow payment for public telephone calls by credit or calling card. (Courtesy of British Telecom) 900 SERVICE 239 I SCP J Sends ‘0800’ f \ Returns actual directory number (071- 2L6 8021) Network 1 dials 0800 123L5 Network intelligence records cost of call. Costs chorged to recipient 1071-266 8021) Figure 11.3 Automatic freephone service 11.10 900 SERVICE The United States 900 service uses a similar intelligent network to that of the 800 service, but rather than calls being free to callers they are charged at a premium. The premium charge covers not only the cost of the call itself, but also the cost of value- added information provided during the call. Thus a typical 900 service might be ‘dial up weather forecast’ or ‘dial up sport news’. The value-added information is provided by a service independent of the PTO who pays for the provision of 900 service facilities but receives revenue from the PTO for each call made. The role of the SCP in the 900 service is to ensure translation of dialled 900 numbers and to record call attempts for later settlement of account between PTO and service provider. In other countries the service may be known under different names; the UK equivalent, for example, is the 0898 service. 11.11 CENTREX SERVICE AND VIRTUAL PRIVATE NETWORK Many companies run their own automatic telephone and data networks on their own premises, using automatic private branch exchanges (PBX$) and private packet switches, etc. Some of these companies also lease transmission capacity from public telecommunication operators (PTOs) to connect together a number of geograph.ically widespread sites into a single, company-wide, network. These private networks are always tailored to the company’s particular needs, often supporting service facilities which are not available from the public network. For example, on a company’s own telephone network, the allocation of extension numbers may be set according to departmental or company whim. In addition, other special features may’ be made available, such as ring buck w3hen free, conference culls and special call barring facilities (to prevent some extensions from dialling trunk or international calls). 240 INTELLIGENT NETWORKS AND SERVICES The decreasing cost of private networks equipment, coupled with the restricted service facilities of some public networks, has recently stimulated a rapid growth of private networks. If allowed to continue by the public telecommunication operators (PTOs), this could pose a threat to revenue income, as less income is available from leased circuits than from the equivalent public network service. From their point of view it will be worse still in countries whose governments allow the resale of private network services. Faced with this, a number of public telecommunications operators and main exchange manufacturers have been developing new services to protect their market shares. Centrex and virtual private network (VPN) services are both products of the counter-reaction. The centrex service provides facilities similar to that of a PBX, but from the public network's local exchange (or central ofice). This gives the customer benefits equivalent to owning an on-site PBX but without the 'up-front' capital investment, and without the ongoing need for expertise and accommodation to maintain it. All of the customer's 'on-site' telephones are connected directly to the public network's local exchange, which acts as if it were a PBX. For example, the customer may determine the extension numbering plan. In addition, features like call interrupt, or ring-back when free, etc., may be made available between extension numbers. Furthermore, just as in a PBX, only the extension number need be dialled to call other on-site company extensions. Figure 11.4 compares a centrex service with the comparable service provided using a PBX. To the user of extension number 2435, on either the centrex (Figure 11.4(b)) or the PBX network (Figure 11.4(a)), it is not apparent which type of network is being used as the network and special service capabilities are identical. This makes it feasible for a small company to consider first subscribing to centrex service from the public tele- communication operator, and later installing an on-site PBX, when its cost is justified. Corporate I customers' premises I i I l Company extension number plan I X2435 PBX I X2436 etc. I (a) PBX service Public corporate I Part ot local premises acts as if it network customers'l exchange Company extenslon number plan I Local X2435 "L' I I X2436 "e I etc. I +I Exchange I- I I Local I Exchange BSI I (b) centrex service Figure 11.4 Company extension number plan using PBX centrex service