Information for IETF relevant to Carrier Slection / Preselection March 15 Regulatory requirements on carrier selection within a country or area are national matter. Thus, there is NO Recommendation approved in ITU-T on this topic. Attached for your information is a supplement which describes alternatives for Carrier Selection and Network Identification. -------------------------------------------------------------------------- Supplement 1 to Recommendation E.164 ALTERNATIVES FOR CARRIER SELECTION AND NETWORK IDENTIFICATION (Geneva, 1998) 1 Introduction The changing telecommunications environment has enhanced the importance of being able to choose the service providers which perform functions on a call. This ability to designate a specific service provider for a specific portion of a call may be achieved through the use of a prefix, presubscription, signalling, database analysis, or embedding the identification in the number itself. At each hand-off point of a call, the current provider must determine the next provider to which to route the call (provider determination). 2 Scope This supplement presents a summary of the potential methods for Carrier / Service provider selection and network identification on the public network. The guidance provided may be utilized for both international and national implementations. This supplement does not specifically address the class of provider determination methods based on contractual agreements, bilateral negotiations, transit routes, or previous traffic (proportional routing). These methods are used by individual providers in determining the next provider to which to route the call. 3 Assumptions The following is a list of basic assumptions used in generating this supplement. In considering Carrier Selection and Network Identification techniques methodologies that use information within the signalling should be considered. Information within this supplement is based on current needs and technologies but not at the expense of future needs and technology. Where a competitive environment is not present, normal call set-up should not be impacted by Carrier Selection techniques. 4 References - ITU-T Recommendation E.164 (1997), The international public telecommunication numbering plan. 5 Definitions The term carrier selection is used when the decision is controlled by the calling party, and the term network identification is used when the decision is controlled by the called party. This supplement uses a functional model of network services to provide a framework for examples of both carrier selection and network identification. The word "Carrier" in this supplement included both "Access Provider" and "Transport Provider". 6 Acronyms This supplement uses the following acronyms. ISP Intermediate Service Provider(s) ITP Intermediate Transport Provider(s) OAP Originating Access Provider(s) OASP Originating Access Service Provider(s) OSP Originating Service Provider(s) OTP Originating Transport Providers(s) TAP Terminating Access Provider(s) TASP Terminating Access Service Provider(s) TSP Terminating Service Provider(s) TTP Terminating Transport Provider(s) 7 Functional models +------+ +-----+ +-----+ +-----+ +------+ | OASP | | OSP | | ISP | | TSP | | TASP | +------+ +-----+ +-----+ +-----+ +------+ | | | | | | | | | | +------+ +-----+ +-----+ +-----+ +------+ ----> | OAP |---->| OTP |---->| ITP |---->| TTP |---->| TAP |----> Calling+------+ +-----+ +-----+ +-----+ +------+ Called Party party Figure 1 Functional model In discussing issues related to carrier selection/network identification, it is useful to address them in the context of a general model. The model shown (see Figure 1) illustrates the entities and relationships involved in a call. This is a functional model and hence the entities shown are not necessarily distinct companies. The functions provided in network service are: connection to/from the network, transport through the network, and service features. These functions are provided to the calling party (originating) and the called party (terminating). Each provider offering connection or transport may provide service features or access to an entity providing service features. For a call, the calling party connects to the network through the Originating Access Provider (OAP). The OAP determines the Originating Transport Provider (OTP) to carry the call forward via voice path or signalling. The OTP progresses the call to the Terminating Transport Provider (TTP) which could be done via an Intermediate Service Provider (ISP), (e.g. who may provide transit transport services). The TTP routes the call to the called party through the Terminating Access Provider(TAP). Any one or all of these connection providers could provide access to a service provider offering features to the calling or called parties. It is important to re-emphasize that these are functional entities. One carrier could function as multiple entities on a given call. There could be multiple instances of one entity on a given call. 8 Alternatives 8.1 General options for Carrier Selection and Network Identification in relation to E.164 numbers For Carriers and Networks, it may be necessary to identify the Carrier/Network which is providing a specific service. There are three basic methods that can be used to identify Carriers/Networks in relation to E.164 numbers. These options are: a) the implementation of Carrier Selection and Network Identification external to the E.164 number; b) the implementation of Network Identification internal to the E.164 Number; c) the implementation of the complete E.164 Number as a means of identification of the Carrier/Network. 8.1.1 General considerations for Network Identification in relation to the E.164 number The choice of implementation of one of the above methods should be done on the basis of evaluating each individual service. It will be selected based on service and operational requirements for each service application. In some applications, specific recommendations should be made for a preferred method of Carrier Selection and Network Identification using particular numbering resources. In other cases, specific recommendations on the Carrier Selection and Network Identification method should be left as a national matter. The following is a list of general issues to be evaluated when considering all three Carrier Selection and Network Identification methodologies. a) Timing and equipment availability The choice of a particular Carrier Selection and Network Identification approach can be impacted by the time frame (i.e. the requested date) when the service for which the numbering resources are required. This is because the availability of hardware and software to support the specific Carrier Selection and Network Identification scheme can have an impact on the Carrier Selection and Network Identification method that is selected. b) Impact on network interconnections and interworking In choosing a Carrier Selection and Network Identification methodology, the issues of network interconnection and interworking between networks and carriers should be considered. For example, should a subscriber dial an E.164 number destined to a Carrier or Network other than the network or carrier from which the call originates, then certain interworking arrangements must be in place for the call to be routed and billed. The apportionment of international traffic between Carriers/Networks may also be impacted once Carrier Selection and Network Identification is associated with an E.164 number. The transport of Carrier Selection and Network identification information between networks may also be necessary. c) Impact on retaining or discarding Carrier Selection and Network Identification information Carrier Selection and Network Identification information is necessary to determine the routing and settlement arrangements for international calls. The nature of a given call type (e.g. calling or called party paid) will determine the need to retain or discard the Carrier Selection and Network Identification information as an international call is routed to its destination address. 8.1.2 Considerations for Carrier Selection/Network Identification options The following subclauses contain specific considerations applying to each of the above three Carrier Selection and Network Identification options. 8.1.2.1 Considerations for applying the Carrier Selection and Network Identification external to the E.164 number It may be possible to use either prefixes or suffixes in dialling E.164 Numbers. The Carrier Selection and Network Identification may also take place in the call related signalling information external to the number. Presubscription to a carrier may be one method. Another method may be to allow a subscriber to change their presubscription by dialling a short code (on a semi-permanent basis). Some ramifications of this approach are: a) No portion of the numbering space is used for Carrier Selection and Network Identification, and therefore the carrier selection and network identification does not impact the quantity, format or makeup of the numbers. b) Additional digits may be dialled (e.g. a prefix or suffix). c) All digit combinations (used for the prefix or suffix) are available unless they are already assigned or apportioned for other uses. d) Service Provider Portability of Numbers is feasible under this Carrier Selection and Network Identification option. e) Modifications to existing signalling protocol may be required to transmit the Carrier Selection and Network Identification identifiers. This may be achieved by using the transit network selection parameter in existing signalling Recommendations. f) The calling party must dial the correct information in addition to the E.164 number. 8.1.2.2 Considerations for applying Network Identification internal to the E.164 number When identifying the Carrier Selection and Network Identification internal to the E.164 number for particular applications, the following implications should be considered: a) Impact on efficient use of the quantity of available numbers: If a portion of the E.164 number is used for Network Identification, then the numbering space is divided into some finite quantity of carrier or network identification groupings. Under each such grouping, a block of numbers is then assigned to individual networks. The efficient use of these E.164 number allocations is dependent on the utilization of the numbers under each network Identification allocation. Should some networks not assign many numbers, the overall efficiency in utilizing these resources may be low. This may lead to premature exhaust of the specific E.164 numbering resource. b) Trade off between Network Identifiers and quantity of subscriber numbers per Network: The designation for Network Identification purposes of some quantity of digits in the E.164 number reduces the number of available digits for subscriber numbers and limits the quantity of numbers that any one Network has available for assignment to its particular customer base. The quantity of Network specific numbers is inversely proportional to the number of networks that can be identified within the number. c) Service provider portability is precluded: When an E.164 number contains Network specific identification, the flexibility to change service providers and maintain the same number is lost. d) Routing to the appropriate network is facilitated in an efficient fashion. e) No additional digits are required when an E.164 number is dialled. f) From a subscriber's perspective, no additional signalling information is required from the calling user for Network Identification beyond the E.164 number. From a network perspective, no additional signalling information is required for Network Identification beyond the E.164 number if every network node involved in the call correctly interprets the internal E.164 field designated for network identification. g) No additional knowledge is required by the calling party beyond the number itself to convey Network Identification information. 8.1.2.3 Use of the complete E.164 number as a means to achieve Carrier Selection and Network Identification Recommendations E.164 and E.162 require networks to do analysis on seven (7) digits for international calls. Using the complete E.164 number as a means of achieving Carrier Selection and Network Identification requires that the originating network have the ability to analyze the entire Number (up to 15 digits) to determine the particular Carrier Selection and Network Identification. This may require a database lookup capability for E.164 numbers of up to 15 digits in length. a) No portion of the numbering space is used for Carrier Selection and Network Identification, and therefore the Carrier Selection and Network Identification does not impact the quantity, format or makeup of the numbers. b) All the E.164 numbers can be used and mapped for Carrier Selection and Network Identification unless they are already assigned to some other application. c) Service Provider Portability of Numbers is feasible under this Carrier Selection and Network Identification option. d) Modifications to existing signalling protocol may be required to transmit the Carrier Selection and Network Identification information. e) Routing to the appropriate carrier/network may need database lookup. f) No additional digits are required when an E.164 number is dialled. g) No additional knowledge is required by the calling party beyond the number itself to obtain Carrier Selection or Network Identification information. 8.2 Selection by calling party 8.2.1 Functional description The following diagrams utilize the functional model, showing implementations to clarify carrier selection. Each of the cases discussed shows only a voice-path between entities. Some applications may use signalling paths between entities, but these are determined by the same carrier selection methods shown here. We have shown only selection of the connection carriers for simplicity, it is assumed the service providers at each stage are either the same as the connection carrier or are determined by the connection carrier based on the selection information received. Table 1 summarizes various methods of selecting the different carriers shown in the functional model. Table 1 Carrier selection methods +-------------+-------------------------+------------------+---------------+ | Selection of| Based on | Identification in| Controlled by | +-------------+-------------------------+------------------+---------------+ | Originating | Presubscription(Figure2)| Subscriber Info | Calling Party | | Transport | Prefix(Figure 3) | Prefix,Signalling| Calling Party | | Provider | Number Analysis By OAP | Number | Calling Party | | (OTP) | (Figure 4) | | | +-------------+-------------------------+------------------+---------------+ 8.2.1.1 External to the number +-----+ | OSP | +------+ +-----+ | OASP | | +-----+ +------+ | | OSP | | +-----+ +-----+ | +--->| OTP | | +------+ | +-----+ | TEL ----> | OAP |----+ +-----+ +------+ | OTP | +-----+ +-----------------------------+ | Calling Party Number -->OTP | | Calling Party Number -->OTP | | Calling Party Number -->OTP | | Calling Party Number -->OTP | +-----------------------------+ OTP presubscription table Figure 2 Selection of OTP - Presubscription In Figure 2, the OAP performs the function of carrier selection through means of a provisioned presubscription table using the calling party number as the key. The data in this table is provisioned prior to the call being made on a line basis in the carrier providing the OAP function and is used to determine the default carrier providing the OTP function for a call. +-----+ | OSP | +------+ +-----+ | OASP | | +-----+ +------+ | | OSP | | +-----+ +-----+ | +--->| OTP | | +------+ | +-----+ | TEL ----> | OAP |----+ +-----+ Prefix +------+ | OTP | Prefix=OTP +-----+ Figure 3 Selection of OTP - Prefix In Figure 3, the OAP performs the function of carrier selection through means of a dialled prefix. In addition to being dialled, the carrier selection information could also be populated in the call set-up message by the calling party's equipment. The OAP translates this information to determine the requested OTP. 8.2.1.2 The complete number +-----+ | OSP | +------+ +-----+ | OASP | | +-----+ +------+ | | OSP | | +-----+ +-----+ | +--->| OTP | | +------+ | +-----+ | TEL ----> | OAP |----+ +-----+ +------+ | OTP | | ^ +-----+ Dialled Number | | OTP V | +------+ | DB | +------+ Figure 4 Selection of OTP- Number analysis by OAP In Figure 4, the OAP performs the function of carrier selection through means of analysis of the dialled number to determine the requested OTP. 8.3 Selection by the Called Party 8.3.1 Functional description The following diagrams utilize the functional model, showing implementations to clarify network identification. Each of the cases discussed shows only a voice-path between entities. Some applications may use signalling paths between entities, but these are determined by the same network identification methods shown here. We have shown only identification of the connection networks for simplicity ? it is assumed the service providers at each stage are either the same as the connection network or are determined by the connection network based on the identification information received. Table 2 summarizes various methods of network identification. Table 2 Network identification methods +-------------+-----------------------+------------------+---------------+ | Selection of| Based on | Identification in| Controlled by | +-------------+-----------------------+------------------+---------------+ | Terminating | Number Analysis By OAP| Number | Calling Party | | Transport | (Figure 6) | | choice of SP | | Provider | Destination Number | Number | Calling Party | | (TTP) | By OTP (Figure 5) | | choice of SP | +-------------+-----------------------+------------------+---------------+ 8.3.1.1 Internal to the number +-----+ | TSP | +------+ +-----+ | OSP | | +-----+ +------+ | | TSP | | +-----+ +-----+ | +--->| TTP | | +------+ | +-----+ | ----> | OTP |----+ +-----+ (CC)NDC SN +------+ | TTP | (CC)NDC=TTP +-----+ Figure 5 Identification of TTP - Destination number by OTP In Figure 5, the OTP performs the function of network identification through means of digit analysis of the destination number. The destination number contains a field which explicitly identifies the TTP. The OTP must recognize that the destination number contains explicit network identification, identify the field within the number containing that identification, and translate the value of the field to the appropriate TTP. 8.3.1.2 The complete number +-----+ | TSP | +------+ +-----+ | OSP | | +-----+ +------+ | | TSP | | +-----+ +-----+ | +--->| TTP | | +------+ | +-----+ | ----> | OTP |----+ +-----+ +------+ | TTP | | ^ +-----+ Dialled Number | | TTP V | +------+ | DB | +------+ Figure 6 Identification of TTP - Number analysis by OTP In Figure 6, the OTP performs the function of network identification through means of analysis of the entire dialled number. The OTP must recognize that the destination number must be analyzed to determine the appropriate TTP, and perform analysis on the entire number. --------------------------------------------------------------------------