l 1 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 r
Trang 1l 1 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
The concept and development of intelligent networks ( I N S ) 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 ( S S P ) )
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)
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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)
Trang 2232 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
Trang 3THE 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 ( I N ) 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 ( S S F ) 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 ( S C P ) , allowing the SCP (a centralized control point) to
manipulate subsequent actions of the exchange
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 ( S C F ) , 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 p a r t ( S C C P ) and the transaction capability application part ( T C A P , ITU-T
Q.771-Q.775) and the newly defined I N A P (intelligent network application p a r t ) 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
Trang 4234 INTELLIGENT NETWORKS AND SERVICES
The service switching point ( S S P ) or service switching function ( S S F ) 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 ( S M S ) or service management point ( S M P ) 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 S M S 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
Trang 5BENEFITS OF INTELLIGENT NETWORKS 235
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
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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
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’
Trang 7FREEPHONE 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 ( P I N ) 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 DT MF 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
Trang 8Figure 11.2 Credit card telephone Telephone specially designed to allow payment for public telephone calls
by credit or calling card (Courtesy of British Telecom)
Trang 9900 SERVICE 239
I SCP J
Sends ‘0800’ f \ Returns actual
directory number
(071- 2L6 8021)
dials 0800 1 2 3 L 5
Network intelligence records cost of call
Costs chorged to recipient 1071-266 8021)
Figure 11.3 Automatic freephone 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)
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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 ( V P N ) 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
X2435
X2436
etc
I
(a) PBX service
Public corporate I Part ot local
premises acts a s if it network customers'l exchange
Company extenslon
Exchange
I - I
I
Local
I Exchange
B S I
I
( b ) centrex service Figure 11.4 Company extension number plan using PBX centrex service