The interface between the SCP and the SSP is G.703 digital trunk. The MTR, SCCP, TCAP and INAP protocols of the CCS7 protocol stack are defined in this interface.
Service Control Point (SCP)
The SCP is a fault-tolerant online computer system. It communicates with the SSPs and the IP for providing guidelines on handling IN service calls. The physical interface to the SSPs is G.703 digital trunk. It communicates with the IP via the requesting SSP for connecting specialized resources.
SCP stores large amounts of data concerning the network, service logic, and the IN customers. For this, secondary storage and I/O devices are supported. For more details refer to the chapter on the “SCP Architecture”.
As has been commented before, the service programs and the data at the SCP are updated from the SMP.
Service Management Point (SMP)
The SMP, which is a computer system, is the front-end to the SCP and provides the user interface. It is sometimes referred to as the Service Management System (SMS). It updates the SCP with new data and programs (service logic) and collects statistics from it. The SMP also enables the service subscriber to control his own service parameters via a remote terminal connected through dial-up connection or X.25 PSPDN. This modification is filtered or validated by the network operator before replicating it on the SCP.
The SMP may contain the service creation environment as well. In that case the new services are created and validated first on the SMP before downloading to the SCP.
One SMP may be used to manage more than one SCPs.
Intelligent Peripheral (IP)
The IP provides enhanced services to all the SSPs in an IN under the control of the SCP. It is centralized since it is more economical for several users to share the specialized resources available in the IP which may be too expensive to replicate in all the SSPs. The following are examples of resources that may be provided by an IP:
- Voice response system
- Voice mail boxes
- Speech recognition system
- Text-to-speech converters
- The IP is switch based or is a specialized computer. It interfaces to the SSPs via ISDN Primary Rate Interface or G.703 interface at which ISUP, INAP, TCAP, SCCP and MTP protocols of the CCS7 protocol stack are defined.
The IN architecture is depicted in Fig.1.
4 Distributed Functional Plane
Functional model of IN contains nine functional entities (FE’s) which are distributed over various physical entities (PE’s) described in the previous section. A functional entity is a set of unique functions. Brief description of the FE’s is given below :
Call Control Agent Function, gives users access to the network.
Call Control Function provides the basic facility for connecting the transport (e.g. speech). It involves the basic switching function and trigger function for handling the criteria relating to the use of IN (Intelligent Network).
Service Switching Function is used to switch calls based on the advice of the SCF at the SCP. This function provides a service independent interface.
It contains the service logic components and advises the SSF at SSP on further call handling.
Service Data Function contains the user related data and data internal to the network.
Specialized Resources Function covers all types of specialized resources other than the connection resources that are in the exchange (e.g. recorded announcements, tones, conference bridges, etc.).
Service Creation Environment Function specifies, develops, tests and deploys the services on the network.
Service Management Access Function provides an interface between service management function and the service manager who may be an operator.
Service Management Function enables a service to be deployed and used on IN. Fig. 2 depicts the distribution and interconnection of the various functional entities.
The distribution of functional entities over the physical entities and their inter-connection is summarized in Tables 1 and 2 below. It may be noted that all the physical entities may not be present in all INs as the choice of functional entities to be provisioned is entirely up to the service provider.
Table 1 Distribution of FE’s over PE’s
|Physical Entity||Possible Functional Entities|
|SSP||CCF, SSF, CCAF|
|SMP||SCEF, SMF, SMAF|
Table 2 FE-FE Relationship to PE-PE Relationship
|SSF-SCF||SSP-SCP||INAP, TCAP, SCCP, and MTP|
|SCF-SDF||SCP-SDP||X.25 or Proprietary|
|INAP, TCAP, SCCP and MTP
ISUP, INAP, TCAP, SCCP and MTP
|SRF-SSF||SSP-IP||ISUP and MTP|
5 IN Services
The IN services proposed to be introduced in the Indian network have been derived from ITU-T recommendations. Q.1211 (April ’92). This document briefly gives the description of 25 services mentioned in Capability set no. 1 (CS1) of above mentioned ITU-T recommendations. CS1 basically deals with single ended services (which ITU-T calls as Type-A services). Single needed services apply to only one party in the call.
1) ABD – Abbreviated dialing
The subscriber can register a short dialing code and use the same for access to any PSTN Number.
2) ACC – Account Card Calling
- A special telephone instrument is required.
- The user dials an access code and gets an acceptance tone.
- Then he dials a PIN (personal identification no.) code and dials the called no. The Exchange reads the account number from the card.
- The Billing is debited to an account number (Telephone no.) as defined by the card.
- In another variation of the service, the account number can be given through a DTMF telephone instrument.
- The follow-on feature facilitates the subscriber to dial another number without disconnecting the call and without need to dial PIN and account number again.
3) AAB – Automatic Alternative Billing
- Call can be initiated by any user and any instrument.
- The call charges are billed in the user’s account and that account need not be a calling or a called party.
- The user first dials access code.
- Receives an announcement to dial account code and PIN (which is given by management).
- The account code and PIN are validated to check its correctness and expired credit limit.
- On getting acceptance tone the user dials the called number.
- In another variation of the service, the called party may be billed based on his concurrence.
4) CD – Call Distribution
- This service allows subscribers to have I/C calls routed to different destinations according to allocation law specified by management (The Subscriber has multiple installations).
- Three types of laws exist :
- Uniform load distribution
- % Load distribution
- Priority list distribution
- In case of congestion or fault, the alternative over flow is specified.
5) CFU – Call Forwarding Unconditional