1、CEPT T/S*43-12*E 8 232641.Y 0008152 7 T/S43-12 Page E 1 Recommendation T/S 43-12 (Edinburgh 1988) SIGNALLING REQUIREMENTS RELATING TO ROUTING OF CALLS TO MOBILE SUBSCRIBERS Recommendation proposed by Working Group T/WG 11 “Signalling, Protocols and Switching” (SPS) Text of the Recommendaioti ndopted
2、 by the “Telecommtinications” Commission: “The European Conference of Post and Telecommunications Administrations, considering - that it is intended to open a pan European mobile service, - that facilities have to be provided in order to route the calls to the actual location of the mobile subscribe
3、s, recommends that European Administration who wish to introduce this mobile service apply the following Recommendation.” Note. This Recommendation is also referenced as T/GSM 03-04. O 1. INTRODUCTION When a subscriber wants to call a mobile subscribes, the fixed network needs to know the actual loc
4、ation of the MS in order to route the connection to the relevant Mobile Services Switching Centre (see Recommen- dation T/GSM 03-12 on location registration). This recommendation presents the requirements the fixed network has to comply with for that purpose. The document considers the different ass
5、umptions concerning the capabilities of the xed exchanges to perform some procedures prior to call Set-up. This Recommendation assumes that the routing analysis requirements specified in CCITT Recommenda- tion Q.lO7bis are fulfilled. This Recommendation assumes that the ISDN number of the mobile con
6、tains a specific National Destina- tion Code. The cases where the mobile numbering plan is fully integrated in the fixed numbering plan may require additional or different routing features. 2. GENERAL ROUTING RULES The number dialled by the calling subscriber contains no indication concerning the ac
7、tual location of the called MS. Therefore, to set up the complete connection, it is necessary to know the location of the MS and the routing address to be used, i.e. the Mobile Station Roaming Number. The onLy equipment able to provide this information is the Home Location Register. Therefore, to ro
8、ute the call to the Mobile Services Switching Centre where the MS is located, it is necessary to interrogate the HLR. The preferred procedure with regard to signalling is the following: 1. When a subscriber wants to Cali a mobile subscriber he dials the ISDN number of this subscribes. 2. The local e
9、xchange (or a transit exchange) analyzes the number dialled and recognizes the mobile service National Destination Code indicating that the call is destinated to a mobile subscribes. In general, this complete routing analysis can be made for the national calk only: when the outgoing exchange recogni
10、zes that the calling subscribes dialled the international prex, it routes directly the call to the outgoing International Switching Centre (ISC) without any further analysis. This ISC can then recognize the mobile NDC. 3. If the result of routing analysis shows that it is necessary to get additional
11、 information to set up the complete connection to the MSC where the called MS is located, then this information must be obtained from the HLR in charge of the mobile subscribes. If the interrogation procedure is implemented in an exchange referred in 2.) above, this exchange then performs the interr
12、ogation of the Home Location Register. The HLR sends back the roaming number of the called MS. This procedure is supported by the Transaction Capabilities of the Signalling system No. 7. 4. The connection is then set up in the fixed network to the MSC according to the roaming number of the MS. . Edi
13、tion of January 15, 1989 - CEPT T/S*43-12*E 88 = 232b414 0008353 9 TIS 43-12 E Page 2 3. 4. 4.1. 4.2. 4.2.1. 4.2.2. 5. 5.1. GENERAL REQUIREMENTS FOR THE FIXED NETWORK To route a call up to a mobile subscriber, an interrogation of the HLR must be performed in order to get the roaming number allocated
14、 to that MS. This interrogation procedure is supported by the Transaction Capabilities of the signalling system No. 7. The preferred solution is that the local exchanges be adapted to TCAP and able to perform this interrogation: then, they can route the call directly to the called MS according to th
15、e roaming number they obtain from their interrogation of the HLR. The following section of this document shows possible solutions if this assumption is not fulfilled. As it is described below, in the case where there are no interrogation facilities in the fixed network, on recognition that a call is
16、 destinated to a mobile subscriber, the routing is first performed to a Gateway MSC. The interrogation of the HLR is then performed by this MSC and the call proceeds according to the Roaming Number received. Section 5. deals with the routing of calls to foreign mobile stations: usually, in this case
17、, the local exchange does not analyze the national part of the called address and routes directly to the outgoing International Switching Centre, which then performs the correct routing of the call. ROUTING OF CALL TO A MOBILE STATION MANAGED BY A HOME PLMN SITUATED IN THE SAME COUNTRY The originati
18、ng exchange is adapted to the interrogation procedure (Figure 1 (T/S 43-12) If the originating local exchange is able to perform the interrogation procedure, the call set-up occurs as it is specified in section 2. of this document. The originating exchange is not adapted to the interrogation procedu
19、re If the originating exchange is unable to use TCAP, the following cases can be considered: - the interrogation procedure is performed by a transit exchange; - the call is rerouted by a Gateway MSC. The interrogation is performed by a transit exchange (Figure 2 (T/S 43- 12) It the originating excha
20、nge is unable to perform the interrogation of the HLR, the connection is set up to a transit exchange. This latter analyzes the address received (the ISDN number of the subscriber) and notices that the call is destinated to a mobile subscriber. It performs then the interrogation of the HLR and route
21、s the call as it is described in section 2. The call is rerouted by a Gateway MSC (Figure 3 (T/S 43-12) If the fixed network is unable to interrogate the HLR in order to route the call to the actual location of the MS, the connection is set up to the Gateway MSC. The Gateway MSC interrogates the HLR
22、 of the called MS (using MAP in general case). It receives back the roaming number of the subscriber. With this address, the GMSC sets up a connection via the telephone (or ISDN) network to the MSC where the MS is located. If the called subscriber is abroad, the connection is normally set-up via the
23、 international network. ROUTING A CALL TO A FOREIGN NOBrLE SUBSCRIBER As for a normal telephone call, the calling subscriber, when he wants to call a foreign mobile subscriber, dials first the international access prefix. His local exchange, according to this prefix, routes directly the call to the
24、outgoing International Switching Centre without any further analysis of the number dialled. The routing of the call is then performed by the outgoing International Switching Centre. Two assumptions can be envisaged: - the outgoing International Switching Centre recognizes that the called party is a
25、mobile subscriber and - the outgoing International Switching Centre is unable to perform the interrogation of the HLR. The outgoing ISC can perform the interrogation of the HL,R (Figure 4 (T/S 43-12) When the outgoing International Switching Centre receives the call, it analyzes for routing the coun
26、try code and the first digits of the national significant number of the called party address. It can then notice that the call is destinated to an MS and needs a preliminary interrogation transaction prior to setting up the connection. can perform the interrogation of the HLR; Edition of January 15.
27、 1-L CEPT T/S*43-l12*E 88 W 2326434 0008354 O TfS 43-12 E Page 3 With the roaming number, the ISC routes then the call to the MSC where the MS is actually located. The connection is set up via the international network if the MS is not in the same country as the calling subscriber. 5.2. The outgoing
28、 ISC is unable to perform the interrogation of the HCR (Figure 5 (T/S 43-12) If the outgoing International Switching Centre is unable to perform the interrogation procedure, it routes the call to the incoming ISC of the country where the Home PLMN of the called mobile is situated according to the te
29、lephone (or the ISDN) number dialled by the calling subscriber. The incoming International Switching Centre receiving the call notices that it is destinated to a mobile. The following assumptions can be envisaged: - this ISC can perform the interrogation; - this ISC is unable to perform the interrog
30、ation: therefore, the interrogation has to be made either by In this assumption where the actual routing has to be made in the home country of the mobile, the connection may comprise two international links in tandem if the subscriber is roaming abroad. Therefore, it would be better that the interro
31、gation is performed in the outgoing country; this method would limit the length of the complete connection. The worst case will appear when the called MS is roaming in the country of the calling subscriber: the complete connection includes two international links in tandem instead of a simple nation
32、al routing. The International Switching Centre recognizes that it is a call to an MS but cannot perform the interrogation In this case, the International Switching Centre routes the call to a Gateway MSC which performs the interrogation. i) If the GMSC is accessed by the outgoing ISC: see Figure 6 (
33、T/S 43-12). ii) If the GMSC is accessed by the incoming ISC: see Figure 7 (T/S 43-12). a national transit exchange or by a Gateway MSC. 5.3. 6. ALTERNATIVE SOLUTION: REROUTING OF THE CALL AFTER CLEARING THE PREVIOUS CONNECTION (Figure 8 (T/S 43-12) The ISUP provides a backward message to indicate th
34、at the call should be rerouted and containing the new address. This facility may be used in the case where a foreign MS is called and no interrogation functions are available in the fixed network to get the Roaming Number from the HLR. A long international connection may be established before the lo
35、cation of the MS is determined but this facility could allow the call to be “dropped back” to the suitable MSC. 7. PARTICULAR CASES : IMPACT OF SUPPLEMENTARY SERVICES HANDLING 7.1. Call forwarding services - Call forwarding unconditional: if this service is activated, the address given back by the H
36、ome Location Register when it is interrogated will be the forwarded-to number given by the subscriber at the registration of the service. It is not a normal call forwarding but a call diversion from the interrogation exchange. - Other call forwarding services: in the other cases (on no reply, on MS
37、busy.), the call forwarding is performed according to the result of the call set-up in the MSC where the mobile is located. Therefore, the call has to be normally routed according to the roaming number given by the HLR. The call forwarding is then performed by the MSC according to parameters given b
38、y its VLR. 7.2. Closed user group The closed user group parameters concerning a mobile subscriber are stored in the HLR. When the interrogation is performed, the HLR can check the closed user group parameters and give the right answer to the originating exchange. If the answer is positive, the HLR g
39、ives back the roaming number of the MS. If the compatibility check does not give a positive result, an unsuccessful indication is given to the originating exchange. r - Edition of January 15, 1989 CEPT T/S*43-32*E 88 2326434 0008355 2 TIS 43-12 E Page 4 7.3. Barring of incoming calls When this servi
40、ce is activated, the relevant indicator is stored in the HLR. When a call is set up to this mobile, the HLR will return an unsuccessful indication to the originating network. The indication given to the calling subscriber will discourage the repeat attemps (e.g. sending of Special Information Tone).
41、 7.4. Supplementary Service incompatibility Is an indication given in the interrogation message to the HLR shows an incompatibility with one of the supplementary services activated by the mobile subscriber, an unsuccessful indication is given back to the originating network. The indication given to
42、the subscriber will discourage a repeat attempt in the same conditions. 8. UNSUCCESSFUL CALL SET-UP 8-1. Roaming not allowed If the MS is roaming in an area where is not allowed to have calls, the location is not stored in the HLR and an indicator is set. When a call is set up to this subscriber, th
43、e HLR will return an unsuccessful indication to the originating exchange. 8.2. Restart of the HLR After a restart, the HLR considers that the informations coming from the back up are still valid. If an interrogation is related to a subscriber whose information are not yet restored, the HLR gives bac
44、k the Roaming Number it has in its tables. If there is a mistake, the restoration procedure specified in Recoin- mendation T/GSM 03-07 will re-establish the right information. Mobile Station Roaming Number unallocated If the incoming MSC receives a call which roaming number is declared unallocated b
45、y the VLR, it sends back an unsuccessful call set-up indication to the outgoing exchange. This situation may occur after a restart of the HLR or of the VLR (see Recommendation T/GSM 03-07). 8.3. Edition of January 15J99-rp- I ,F7 7 Edition of January 15, 1989 -y CEPT T/S*43-12*E 88 2326414 000815b 4
46、 c + i /- ISDN outgoing exchange Interrogation Actual PLMN -0- route Figure 1 (T/S 43-12). General interrogation procedure. Interrogation done by outgoing ISDN exchange. . /-o- ISDN 1. Transit ,/. Lo-/-/ b Actual Interrogation route Figure 2 (T/S 43-12). Interrogation is done by a transit exchange.
47、TIS 43-12 E Page 5 - CEPT T/S*43-32*E 88 232b434 0008357 b TIS 43-12 E Page 6 Outgoing exchange &-A -ft4.“s MSC) i i “i“ (gateway MSC MSC) Interrogation PLMN .*-./- Figure 3 (T/S 43-12). Routing to nearest MSC using call forwarding combined with interrogation within the PLMN. CEPT T/S*43-32*E 88 E 2
48、326434 0008358 8 TIS 43-12 E Page 7 Figure 5 (T/S 43-12). Rerouting by the incoming ISC. ISC. Edition of January 15, 1989 - CEPT T/S*43-22*E 88 U 2326424 00081159 T = TIS 43-12 E Page 8 Figure 7 (T/S 43-12). Rerouting by a GMSC, when accessed by the incoming ISC. . IAM -.-*- I ! Routing info I f interrogation J .e- i ( ISDN i -/ Country 3 t , Figure 8 (T/S 43-12). Rerouting by the ISDN of origin. Edition of January 15, 1989
