WPCL 2BJ|x ` H   x|@  6'6' Recommendation Q.1005 8HANDOVER PROCEDURES A =Contentsă A A H1.Introduction 2.Functional composition of MSCs and interface for handover 3.Initiation   4.General description of the procedures for handover to another MSC 5.Detailed procedures in MSCA 6.Detailed procedures in MSCB 7.Authentication 8.Handling of supplementary services 9.Location updating after handover Recommendation Q.1005 h=HANDOVER PROCEDURES H1.HIntroduction HThis Recommendation contains a detailed description of handover procedures to be used in PLMNs. HThe following cases are considered: Hi)h  handover between radio channels of the same base station;   HX Note: This capability is mandatory and could be used in the following situations: H  when the radio channel carrying the call is subject to interference or other disturbances, and/or  8 H  when a radio channel or channel equipment carrying a call has to be taken out of service for maintenance or other reasons;   Hii)  handover between base stations of the same MSC in order to ensure HH continuity of the connection when an MS moves from one BS area to ` another;  `    HHX HHiii) handover between base stations of different MSCs of the same PLMN; and Hiv)  handover between base stations of MSCs in different PLMNs. HThe same procedures can be used on the radio path for all four cases. HCases i) and ii) involve only one MSC. NoteĠDepending on the handover criteria, case ii) may involve measurements in other MSCs. HCases iii) and iv) involve more than one MSC. For these cases, two procedures are defined requiring the use of the mobile application part: Ha)h  basic handover procedure where the call is handed over from the controlling MSC (MSCA) to another MSC (MSCB); and Hb)h  subsequent handover procedure where the call is handed over from MSCB to MSCA or from MSCB to a third MSC (MSCB'). HIn most respects case iv) is similar to case iii). However, any additional aspects of case iv) not covered by the specification of caseiii) will not be included in this Recommendation for the time being. HThe procedures in the mobile application part for supporting handover are specified in Recommendation Q.1051. HIn the following, the controlling MSC will be referred to as MSCA also when the handover only involves this MSC (cases i) and ii) above). For casesiii) and iv), the controlling MSC (MSCA) is the MSC on which the call was originally established. HAll MSCs should be capable of acting as MSCA and MSCB. 2.HFunctional composition of MSCs and interfaces for handover 2.1HMSCA HFor handover the controlling MSC can be regarded as being composed of functional units as shown in Figure 1/Q.1005. HSignalling functions  8 HH1.h  The BS/MSC (MS/BS) procedures MSCA for signalling between the MSC and the BS and between the MSC and the MS. The functional unit interfaces the BSs through interfacesA' (to the previous BS) and, for case ii), also through interfaceA'' (to the new BS). Interworking with other functional units takes place through the internal interface x.  `    HH2.h  The call control procedures MSCA for normal call control functions (interface B') and for signalling and call control of connections to other MSCs (interfacesB'' and B'''). InterfacesB'' and B''' apply only to handover casesiii) and iv) where interfaceB''' is required for subsequent handover.  `   H HH3.h  The handover control procedures MSCA for overall control of the handover including interworking with other functional units (interfaces x, y and z).  `   ,Ԍ=(recoup)   HH4.h  The MAP procedures MSCA for information exchange with other MSCs and location registers. This function is required for handovercases iii) and iv). The external interface   HHX is interfacec and the internal interface to the handover control functions is interfacez. InterfaceC represents the interface to all entities with which MSCA is communicating during handover (other MSCs, location registers).  `   ( NoteĠThis functional unit may also be required for casesi) and ii) if measurements have to be performed in other MSCs for determining the new BS (see below). HSwitching functions  X HH5.h  The switch and handover device MSCA for connecting the new path. This function is additional to normal switching functions in the MSC. The handover device has interfaces to the previous BS (interface A') and the new BS (interface A'') for handover case ii). Interface B' represents the original connection with the fixed network and interface B'' represents the new connection to and MSCB for handover between MSCs (cases iii) and iv)). Interface B''' represents the connection to a third MSC (MSCB') for subsequent handover from MSCB to MSCB'. The connections which can exist in the handover device are shown in Figure2/Q.1005.  `   ( HThe connection via interface A' is released after completion of a successful handover (Figures2a and 2b/Q.1005). HFor MS to MS calls in the same MSC the configuration in Figure2b/Q.1005 applies. Then interface B'' is not to another MSC but internal to MSCA. XJ X5CaseInitial connectionResulting connection X<Figure2a)/Q.1005A'toB'A''toB' X<Figure2b)/Q.1005A'toB'B'toB'' XJ X;Figure2c)/Q.1005B'toB'B'toB''' 2.2HMSCB  X HThe functional composition of an MSC acting as MSCB is essentially the same as that of MSCA. However, there are some differences. The functional units are as follows (see Figure 3/Q.1005). HSignalling functions  8 HH1.h  The BS/MSC (MS/BS) procedures MSCB for signalling between the MSC and the new BS and between the MSC and the MS (interface A'').  `  =(recoup) =(recoup)   HH2.h  The call control procedures MSCB for normal call control functions and for signalling between MSCA and MSCB.  `    HH3.h  The handover control procedures MSCB for control of the handover in MSCB.  `   H HH4.h  The MAP procedures MSCB for information exchange with MSCA and the VLR of MSCB.  `  HSwitching functions   HH5.h  The switch MSCB for connecting the circuit from MSCA (interfaceB'') to the circuit to the BS (interfaceA'').  `   H HMSCB will also require a handover device for subsequent handovers to BSs (or to another channel of the same BS) in the MSC area of MSCB. Subsequent handovers to other MSCs will not require switching in MSCB (see below). 3.HInitiation HThe decision that a handover shall take place can be made by both the MS and the BS by monitoring the channel quality. If the decision is made by the MS, a handover request message should be provided to the BS. HDepending on the radio subsystem arrangement the new BS, to which the call is to be handed over, can either be determined by the MS or the MSC. If determined by the MS, the indication of the BS candidates will be providing to the MSC by signalling on the radio path. HIf the new BS is to be determined by the MSC, this may require measurements on its own BSs and BSs in other MSCs. Procedures defined in RecommendationQ.1051 are used for initiating measurements on BSs in other MSCs. HThe initiation procedures are for further study. 4.HGeneral description of the procedures for handover to another MSC 4.1HBasic handover procedure HThe procedure which takes place after initiation, i.e. after the identity of the new BS has been determined, is shown in Figure 4/Q.1005 for a successful handover. The procedure makes use of messages of the Mobile Application Part (MAP) of Recommendation Q.1051. ,Ԍ HFirstly, MSCA sends a radio channel request message to MSCB. The message will contain all parameters needed by MSCB for allocating a radio channel (see RecommendationQ.1051). The message will also identify the BS to which the call is to be handed over. MSCB will return the radio channel acknowledge message after having received the mobile station roaming number from its VLR (exchange of the messages request for handover number and handover number acknowledge). The roaming number is to be used for routing the call from MSCA to MSCB. If a traffic channel is available in MSCB the radio channel acknowledge message will contain the identity of the new radio channel and the mobile station roaming number. Other parameters may also be included (see RecommendationQ.1051). HIf there is no free traffic channel in MSCB, this will be indicated to MSCA and MSCA will terminate the handover procedure. The existing connection to the MS will not be cleared. HAt this point, MSCA establishes a connection between MSCA and MSCB by signalling procedures supported by the network to which MSCA is connected. In Figure4/Q.1005 this is illustrated by the messages IAM (Initial Address Message) and the ACM (Address Complete Message) of Signalling System No.7. MSCB initiates the handover procedure on the radio path when the ACM is sent and MSCB initiates the procedure when the ACM is received (illustrated by HB and HAINDICATION, respectively). HThe connection is throughconnected in MSCA by use of a handover device. The throughconnection is done and the old radio channel is released when MSCA receives an acknowledgement from the MS (HACONFIRM) or when the successful handover message is received from MSCB. MSCB sends this message when it receives an acknowledgement from the MS (HBCONFIRM). HIn order not to conflict with the PSTN/ISDN signalling system(s) used between MSCA and MSCB, MSCB must generate an answer signal when HBCONFIRM is received. HIf the connection between MSCA and MSCB cannot be established (e.g.an unsuccessful backward message is received instead of the ACM), MSCA terminates the procedure without clearing the radio path. HMSCA will have the overall call control until the call is cleared by the fixed subscriber or the MS and there are no further call control functions to be performed (e.g.servicing waiting calls). MSCA then releases the connection to MSCB and also sends an end signal message which terminates the MAP procedure. When receiving this message MSCB will release all call control functions and send the message remove handover number to its VLR. HMSCA may terminate the procedure at any time by sending the MAP message handover cancellation to MSCB. If establishment of the physical connection between MSCA and MSCB has been initiated, the physical connection must also be cleared by procedures defined for the signalling system used between MSCA and the fixed network. The VLR of MSCB is also informed by using the remove handover number message. HThe handover cancellation message is sent when MSCA detects clearing or interruption of the radio path before the call has been established on MSCB. The message is also sent in order to terminate the MAP procedure in MSCB when it is not possible to establish a connection between MSCA and MSCB. 4.2HProcedure for subsequent handover HWhen an MS, after the call has been handed over from MSCA to MSCB, leaves the area of MSCB during the same call, subsequent handover is necessary in order to continue the connection. HThe following cases are identified: Hi) the MS moves back to the area of MSCA, and Hii) the MS moves into the area of a third MSC (MSCB'). HIn both cases the call is redirected in MSCA using the handover device; the connection between MSCA and MSCB can be released after a successful subsequent handover has been performed. 4.2.1HDescription of subsequent handover procedure i) : MSCB to MSCA HThe procedure which takes place after the initiation procedure has indicated that a handover has to be made back to MSCA is shown in Figure5/Q.1005 for the case of successful handover.  ,Ԍ HJ(recoup) HThe procedure is as follows. HMSCB sends the subsequent handover request message to MSCA indicating that the new MSC is MSCA. Because MSCA is the call controlling MSC, this MSC needs no roaming number for routing purposes; MSCA can directly search for a free radio channel at the desired BS. HWhen a radio channel can be assigned in time, MSCA will return the subsequent handover acknowledgement message containing the new radio channel number and possibly other information to MSCB. If a radio channel cannot be assigned, a no channel available indication will be given to MSCB and MSCB has to maintain the connection with the MS as long as possible. HIf a radio channel has been reserved in MSCA, both MSCA and MSCB can start the handover procedure on the radio path (in Figure 5/Q.1005 indicated by the interworking messages HBINDICATION and HAINDICATION respectively). HAfter handover, MSCA has to release the connection with MSCB by the procedures relevant to the PSTN/ISDN signalling system(s) used between MSCA and MSCB. HMSCA must also terminate the MAP procedure for the basic handover between MSCA and MSCB. This is done by MSCA by sending the end signal message to MSCB. When receiving this signal, MSCB sends the remove handover number message to its VLR. 4.2.2HDescription of the subsequent handover procedure ii) : MSCB to MSCB' HThe procedure which takes place after the initiation procedure has indicated that the call has to be handed over to MSCB' is shown in Figure6/Q.1005 in the case of successful handover. HThe procedure consists of two parts: H subsequent handover as described in 4.2.1 between MSCA and MSCB, and H a basic handover procedure as described in 4.1 between MSCA and MSCB'. HMSCB sends the subsequent handover request message to MSCA indicating a new MSC which is not MSCA. The message contains the identity of MSCB' and of the new BS. MSCA then starts a basic handover procedure towards MSCB'. HWhen MSCA receives the ACM from MSCB', MSCA informs MSCB that MSCB' has started the handover procedure on the radio path by sending the subsequent handover acknowledgement message to MSCB containing the new radio channel number. Now MSCB can start the procedure on the radio path. HFor MSCA the handover is completed when it has received the successful handover message from MSCB'. The connection between MSCA and MSCB is  h released by normal clearing procedures applicable for the PSTN/ISDN signalling system(s) on the connection between MSCA and MSCB. MSCA also sends the end signal message to MSCB in order to terminate the original handover procedure between MSCA and MSCB. Receiving this message, MSCB releases the radio path. HIn case no radio channel can be allocated in time or the connection between MSCA and MSCB' cannot be established, MSCA informs MSCB by a congestion message. MSCB has then to maintain the existing connection with the MS as long as possible. When necessary, MSCA sends the handover cancellation message to MSCB'. HWhen the MS again passes the MSC boundary, MSCB' is considered as an MSCB so that the subsequent handover procedures given above are applicable for any series of handover between MSCs. 4.3HHandover procedure using subscriber information transfer (optional procedures) HThis procedure is a handover procedure with subscriber information transfer during handover. To realize this handover procedure, only the following additional procedure will be needed. 4.3.1HBasic handover procedure (optional) HIn addition to the basic handover procedure, described in 4.1, this optional procedure is illustrated in Figure 7/Q.1005. MSCA sends a handover completion message which contains subscriber information as soon as MSCA receives the successful handover message. MSCB informs its VLR to send a roaming number to the HLR to support supplementary services (e.g., call waiting), after receiving the handover completion message. 8GInsert Figure 6/Q.1005 4.3.2HSubsequent handover procedure (optional) HHX H4.3.2.1 i)MSCB to MSCA HIn addition to the subsequent handover procedure, described in 4.21, this optional procedure is illustrated in Figure 8/Q.1005. When receiving the end signal, MSCB sends the remove handover number message to its VLR and the handover completion message to MSCA. MSCA informs its VLR to send a roaming number to the HLR, after receiving the handover completion message. HHX H4.3.3.2 ii)MSCB to MSCB' HIn addition to the subsequent handover procedure, described in 4.2.2, this optional procedure is illustrated in Figure 9/Q.1005. After receiving the end signal, MSCB releases the radio path and sends handover completion message to MSCB'. MSCB' informs its VLR to send a roaming number to the HLR, after receiving the handover completion message. Note Implementation of this procedure requires careful consideration of the , handling of some supplementary services (e.g., call waiting, conference calling or call commpletion to busy subscriber) at handover, since these aspects have not been studied in detail. The procedure is not included in the current version of the MAP (Recommendation Q.1051). 8KFIGURE 7/Q.1005 8R 8FBasic handover procedureă 8KFIGURE 8/Q.1005ă 8R 8BSubsequent handover procedure i):ă 8?successful handover from MSCB to MSCAă 8N(recoup) 5.HDetailed procedures in MSCA 5.1HBS/MSC (MS/BS) procedures MSCA (functional unit 1) HThe handover procedures in this functional unit consist of: Hi)h  signalling between the MS and the MSC; and Hii)  signalling between the BS and the MSC for H  initiation of quality measurements, and H  access management. HSignals sent to and received from functional unit 3 (handover control procedures MSCA) are indicated in 5.3 below. 5.2HCall control procedures MSCA (functional unit 2) HRelated to handover the call control procedures in MSCA can be divided into two functional entities. HThe first entity is the call control procedure as part of the normal interworking between the PSTN/ISDN and the PLMN; for an MS originating call MSCA is the originating exchange, for an MS terminating call MSCA is the destination exchange. HThe second entity is the call control procedure for the connection between MSCA and MSCB in case of a handover from MSCA to MSCB. For the latter call control procedure the following applies. Call set up HThe connection to MSCB is set up by procedures relevant to the signalling system used in the PSTN/ISDN to which MSCA is connected. The call is set up by using the MS roaming number received from MSCB as part of the MAP procedures. HThe call setup direction will always be from MSCA to MSCB, i.e.also when the call was originally established by the MS. Functional unit 2 should therefore keep information on call setup direction in order to be able to correctly interpret any clearing signals (see below). HThe unit should indicate the addresscomplete condition to functional unit3 and through connect without waiting for the answer signal from MSCB. This applies also to signalling systems where addresscomplete signals are not supported. In such cases, an artificial address complete is established by functionalunit2. Call clearing ,Ԍ HThe call clearing consists of two parts after inter MSC handover, clearing of the BSMS connection and clearing of the inter MSC connection. HThe MAP is used to transfer information between MSCB and MSCA in order to maintain full control with MSCA. MSCA determines, based on information received from MSCB, the appropriate signals to be sent to the MS, and sends this information to MSCB. HMSCA shall initiate inter MSC connection release and send the end signal to release any resource attached to the call. HThe clearing of the connection is by procedures relevant to the signalling system in the PSTN/ISDN to which MSCA is connected. HWhen the signalling system No. 7 ISDN User Part is used, the normal symmetric release procedures apply on both the connection to the fixed network and to MSCB. HWhen a signalling system is used with a symmetric release possibility, some notice should be given to the clearforward and clearback procedures. HFor MS terminating calls the following conditions apply on clear forward and clearback: H when a clearforward signal is received on interfaceB' (see Figure1/Q.1005), MSCA clears the circuit to MSCB by normal clearforward procedures; and H when a clearback signal is received from MSCB, MSCA starts normal clearback procedures towards the fixed network (interfaceB') and sends the clearforward signal on interfaceB'' in order to clear the connection with MSCB. HX Note: This case corresponds to a fault situation. O&M actions are for further study. HFor MS originated calls the following applies: H when an MSCA receives a clearback signal from MSCB, this signal must be interpreted as indicating clearforward condition. MSCA then clears both the connection on interfaceB' (see Figure1/Q.1005) and to MSCB by normal clearforward procedures; and HX Note: This case corresponds to a fault situation. O&M actions are for further study. H when MSCA receives a clearback signal on interfaceB',   HHX MSCA should distinguish between national and international connections:  `   8 H  for international connections MSCA sends a clearforward signal on both interfaceB' to the fixed network and interfaceB'' to MSCB; and H  for national connections a timer is started according to national practice for clearback supervision and MSCA proceeds as follows: H i)if a clearback signal is received from MSCB, MSCA HHX X  interprets this as indicating a clearforward condition and proceeds by clearing the connections on interface B' and to MSCB by normal clearforward procedures, or  `   8 H X ii)if the timer expires, MSCA proceeds by normal clear forward of the connections on interfaceB' to MSCB. 5.3HHandover control procedures MSCA (functional unit3)   HThe procedures of functional unit3 are given in terms of SDL diagrams in Figure10/Q.1005. For all signals sent to or received from another functional unit the source or sink of the signal is indicated (e.g.from 4, to 2,etc.). HThe procedures of functional unit 3 include the following. Hi)h  Initiation (states1, 2 and 3). The initiation condition is shown by the signal HAREQUEST. This may either be generated by the MS or the BS depending on the initiation condition (see 3). The diagram includes all possibilities described in 3, i.e.the MS identifies the new BS, or the new BS is identified by the MSC by measurements in adjacent BSs. These may include BSs in other MSCs. HX The diagram also includes queuing when there is no channel available. Calls for which handover had been initiated should be queued with priority higher than normal calls. They should have lower priority than emergency calls. Hii)  Handover of calls within the area of MSCA, i.e.handover casesi) and ii) (states1, 2, 3 and 4). MSCA controls the procedures on both the previous and the new radio channel. Both signals HAINDICATION and HBINDICATION are required. The handover procedure is completed when HBCONFIRM is received. If this signal is not received, the radio path and the connection on interfaceB' are either released or the original connection is maintained depending on national choice. HX The handover device is first set up so that all interfacesA', A'' and B' are connected (illustrated by the signal set up handover device). This is done when HAINDICATION is sent. The device is connected in its final position (i.e.A'' to B' for caseii)) (illustrated by the signal connect handover device) either when HACONFIRM is received or when HBCONFIRM is received. HHX HHiii) Handover to MSCB (states1, 2, 5, 6 and 7). This procedure is the one described in 4.1. The handover device is set up when MSCA send the HAINDICATION, i.e.the interfacesA', B' and B'' are connected. The device is connected in its final position (i.e.B' to B'') when either the HACONFIRM signal is received from the MS or the successful procedure indication is received from functional unit4. Hiv)  Subsequent handover to MSCA (states7 and 9). This procedure is described in 4.2. When a handover to MSCA indication is received from functional unit4, the handover device is set up so that interfacesB', B'' and A' are connected. When HBCONFIRM is received, the device is connected in its final position (i.e.B' to A'). HX If HBCONFIRM is not received (expiry of timerT104), the handover device releases interfaceA' and returns to a position where B' and B'' are connected. A congestion indication is returned via functional unit4 to MSCB.  ,ԌHv)h  Subsequent handover to a third MSC (MSCB') (states7 and 8). The procedure is described in 4.2. The handover device is set up in its initial position, i.e.interconnection of interfacesB', B'' and B''', when the connection to MSCB' has been established (indicate by the signal connection established from functional unit2). MSCB is informed via functional unit4 (send acknowledge) that the connection has been established and that the procedure on the radio path can be initiated. The device is connected in its final position (i.e.B' to B''') when a successful procedure indication in received from functional unit4. MSCB is informed that all procedures in MSCB can be terminated (illustrated by the sendend signal indication). The device returns to the state where B' and B'' are connected if the subsequent handover procedure fails. Timers in MSCA HThe procedures are supervised by timers in order to avoid deadlock when responses are not received or the procedures fail. The following timers are defined. T100:HThis timer supervises the time between sending a request for measurements to a BS or an MSC and the receipt of the results. Results received after time out are ignored. T100 = (FS) T101:HThis timer supervises the queuing time for a free channel. If T101 expires, a no channel indication is generated. T101 = (FS) T102:HThis timer supervises the time for handover completion for handover between BSs in MSCA. If T102 expires, the radio path and the connection on interfaceB' are released. T102 = (FS) T103:HThis timer supervises the time between issuing a HAINDICATION in MSCA and receiving a successful procedure indication from MSCB. If T103 expires, the handover procedure is cancelled and either the radio channel is released (if HACONFIRM has been received) or it continues on the old channel (if HACONFIRM has not been received). T103 = (FS) T104:HThis timer supervises the time between sending an HBINDICATION and receiving the HBCONFIRM for a subsequent handover from MSCB to MSCA. If T104 expires, the new radio channel is released and the existing handover device connection to MSCB is maintained. T104 = (FS) 5.4HMAP procedures in MSCA (functional unit4) HThe MAP procedures for handover are defined in RecommendationQ.1051. They include: H requesting measurements in other MSCs; H procedures for basic handover; and H procedures for subsequent handover. HThese procedures are as outlined in 4. 6.HDetailed procedures in MSCB 6.1HBS/MSC (MS/BS) procedures MSCB (functional unit1) HThe handover procedures in this functional unit consist of: Hi)h  signalling between the MS and the MSC; and Hii)  signalling between the BS and the MSC for H  initiation of quality measurements, and H  access management. HSignals exchanged with functional unit3 are indicated in 6.3 below. 6.2HCall control procedures MSCB (functional unit2) HThese procedures relate to the call control in MSCB of the "handover" connection with MSCA. For these procedures the following apply. Call setup HThe connection is setup by MSCA. MSCB should provide, if possible, the following backward signals: H signals indicating unsuccessful call set up and, if possible, the cause of call failure; H address complete signal; and H answer signal (see note). NoteĠThe answer signal is not related to answering by the MS and if has no meaning in the handover procedure between MSCA and MSCB. But after successful handover this signal is needed for bringing the connection in the answered state in the intermediate PSTN/ISDN exchanges. HThere will be no indication that the call applies to a handover. This information has to be derived from the MS roaming number received during call set up in relation to the earlier radio channel request/radio channel acknowledgement procedure between MSCA and MSCB (MAPprocedure). HWhen the connection has been established an indication should be given to functional unit3 (illustrated by the signal "connection established" in Figure11/Q.1005). Call clearing HThe call clearing consists of two parts after inter MSC handover, clearing of the BSMS connection and clearing of the inter MSC connection. HThe MAP is used to transfer information between MSCB and MSCA in order to make it possible for MSCB to send the appropriate signals and still leave the call control to MSCA. HMSCA initiates release of the connection between MSCA and MSCB. HMSCB is only allowed to initiate inter MSC connection release after the end signal is received. HWhen the Signalling System No. 7 ISDN User Part is used, the normal symmetric release procedures apply. HWhen a signalling system is used without a symmetric release possibility, the following applies. ,Ԍ H When MSCB receives a clearforward signal from MSCA, it shall release the radio path. H In fault situations, e.g. machine malfunction or loss of the connection on interface A, MSCB may send a clearback signal to MSCA. 6.3HHandover control procedures MSCB (functional unit3) HThe procedures of functional unit3 are given in the form of SDL diagrams in Figure 11/Q.1005. For all signals sent to or received from another functional unit the source or sink of the signal is indicated (e.g.from 4, to2, etc.). HThe procedures in functional unit3 include the following. Hi)h  Handover from MSCA (states1, 2, 3 and 4). This case includes initiation by MSCA (indicated by the allocate radio channel signal received from functional unit4) and allocation and establishment of the new radio channel. The procedure is outlined in 4.1. Hii)  Subsequent handover within the area controlled by MSCB (states4, 5, 6 and 7). This procedure is essentially the same as that of ii) of 5.3.  x HHX HHiii) Subsequent handover to another MSC (MSCA or MSCB') (states4, 8 and 9). The initiation procedure is essentially the same as that of i) of 5.3. The HAINDICATION is now generated by MSCB after a subsequent handover accepted indication is received from MSCA (via functional unit4). The procedure is terminated in MSCB when MSCB receives a terminate procedure indication from functional unit 4. Timers in MSCB HThe procedures are supervised by timers in order to avoid deadlock when responses are not received or the procedures fail. The following timers are defined. T200:HThis timer is the same as T100 (5.3). T201:  This timer is the same as T101 (5.3). T202:HThis timer is the same as T102 (5.3). T204:HThis timer is the same as T104 (5.3). T210:HThis timer is used to supervise the time for establishing a connection from MSCA to MSCB after an allocate radio channel request has been received. When T210 expires, the allocated channel in MSCB is released. T210 = (FS) T211:HThis timer is used to control the time between requesting a subsequent handover and receiving the response from MSCA. If T211 expires, the existing connection with the MS is maintained. T211 = (FS) 6.4HMAP procedures MSCB (functional unit4) HThe MAP procedures for handover are defined in RecommendationQ.1051. They include: H requesting measurements in other MSCs, H procedures for basic handover, H procedures for subsequent handover, and H procedures for obtaining and releasing MS roaming number for handover from the VLR. HThese procedures are outlined in 4. 7.HAuthentication HAuthentication will be performed after handover (for further study). 8.HHandling of supplementary services HThis is for further study. MAP procedures for supporting such functions are contained in RecommendationQ.1051. HMSCA will maintain call control until all operations, i.e.the existing call and any supplementary service operation have been terminated. At this instant, MSCB is informed by the end signal message of the MAP that all functions in MSCB can be released. HIf the call waiting service is provided for the called MS, and there are calls waiting at the time of a handover to another MSC, these calls should be established by MSCA using normal call forwarding to MSCB. If the MS requests holding of the existing call and connection of a waiting call, the MAP is used to provide the necessary exchange of information between MSCA and the MS. 9.HLocation updating after handover HMSCB (or VLRB) should not initiate automatic updating of the HLR at the end of the call. The procedures in the MS should be such that the MS should initiate updating after the call has been completed and the MS has tuned to a common control channel. HAutomatic updating by MSCB (or VLRB) is for further study. L(Recoup 17 pages)