Ver 1.0.0 Dated: 25/12/01
CALL MANAGEMENT LESSON OBJECTIVES: Upon completion of this unit , you should be able to:
•Describe the steps of a Mobile Originated Call. •Describe the steps of a Mobile Terminated Call. The basic call types that we discuss in this section are: •Mobile-to- Land call •Land-to- Mobile call •Mobile-to- Mobile call
Prepared By: Manish Garg Help : To quit press Esc
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MOBILE -TO -LAND CALL SCENARIO RADIO CHANNEL
BSS
VOICE TRUNK
MSC
VOICE TRUNK
PHASES OF A MOBILE -TO LAND CALL :
(1) REQUEST FOR SERVICE (2) EQUIPMENT VALIDATION
(3) CALL SET UP (4) RELEASE
PSTN
LINE
(1) REQUEST FOR SERVICE
It is assumed that the MS is already registered with the system. A mobile originated call starts when the user enters the directory number digits, associated with the person to be called, on the mobile station handset .The user presses the send key after all digits have been entered .
Um
BSS
A
MSC
B
VLR
CHANNEL REQUEST (1)
(2)
( RACH)
DEDICATED SIGNALING CHANNEL ASSIGNMENT (AGCH)
(3)
SERVICE REQUEST (SDCCH)
(1)MS transmits a channel request message over a common access channel, Random Access Channel (RACH) . (2)Once the BSS receives the channel request message, it allocates a SDCCH and forwards this channel assignment information to the MS over the AGCH. It is over the SDCCH that the MS will communicate with the BSS and MSC until a TCH is assigned . (3) The MS transmits a service request message to the base station over the SDCCH . Included in this message is the mobile station TMSI and the Location Area Identification (LAI) .
Um
BSS
A
MSC
B
CHANNEL REQUEST (1)
(2) (3)
( RACH)
(4) DEDICATED SIGNALING CHANNEL ASSIGNMENT (AGCH) SERVICE REQUEST
SERVICE REQUEST
(5)
SERVICE REQUEST
(SDCCH)
(4) The base station forwards the service request message to the MSC . (5) The MSC informs its VLR that a particular mobile station is requesting service .
VLR
(2) EQUIPMENT VALIDATION At this point, the mobile station has been authenticated and the radio channel is being encrypted.
Two events will occur in parallel: •The MSC interrogates the mobile station for its equipment number ie. International mobile identity number(IMEI) and checks the equipment against information in the Equipment Identity Register(EIR). •The Mobile station,after receiving the cipher command,forwards a cal setup request to the MSC.
(3) CALL SETUP
There are two steps in setting up voice path for a call from the mobile to a PSTN subscriber.
•The call set up with mobile- where a voice path is created between the MS and the MSC by allocating a radio traffic channel and a voice trunk.
•The call set up with a land network - Where a voice path is established between the MSC and the PSTN network.
CALL SETUP-WITH MOBILE Um (10)
BSS
A
MSC
C
VLR
CALL SETUP REQUEST (SDCCH)
(11) REQUEST FOR MSRN (12)
(15)
D
HLR
CALL PROCEE`DING
(14)
MSRN
PROVIDE MSRN FOR MSISDN
(13)
MSRN
SDCCH
(10)The mobile station transmits a call set up request message to the MSC.Included this request message are the dialed digits. (11)The MSC , upon receiving the call set up request, will request the HLR supply subscriber parameters and MSRN necessary for handling the call. The HLR will check for call barring conditions and other required parameters.For the present case we assume that there is no call barring for the specified call. (12) HLR using the VLR address and MSISDN then requests to VLR to allocate a MSRN. (13) VLR allocates a MSRN to the MS identified by the MSISDN and informs the HLR. (14) The gateway MSC receives the MSRN from HLR and route the call accordingly. (15) The MSC informs the mobile station that the call is proceeding.
Um
BSS (14)
(15) (16)
A
MSC
B
VLR
ASSIGN TRUNK & RADIO (TN)
ASSIGN RADIO CHANNEL (TCH)
SDCCH
RADIO ASSIGNMENT COMPLETE SDCCH (17)
TRUNK &RADIO ASSIGNMENT COMPLETE
The next four steps involve establishing a voice path between MSC and mobile station : (14) The MSC allocates a trunk to the BSS currently serving to the mobile station. The MSC sends a message to the BSS supplying it with the trunk number allocated (TN), and request the BSS to allocate a radio traffic channel (TCH) for the MS.
(15) The BSS allocates a radio traffic channel and transmits this assignment to to the mobile station over the SDCCH. (16) The mobile station tuned to assigned radio channel and transmits an acknowledgement to BSS.
(17) The BSS connects the radio traffic channel to the assigned trunk of the MSC. The BSS then transmits a trunk and radio assignment complete message to the MSC .
CALL SETUP-WITH PSTN MSC (18) (19) (20)
PSTN NETWORK SETUP (DD..) NETWORK ALERTING
ALERTING
Following steps are involved in call setup with PSTN : (18)The MSC sends a network setup message to the PSTN requesting that a call be setup. This includes the MS’s dialed digits and details specifying which trunk should be used for call.
(19) The local exchange will generate the ringing tone over the trunk to the MSC. At this point in time the mobile station will hear ringing tone. The PSTN notifies the MSC with a network alerting message when this event occurs. (20) The MSC informs the mobile station that the destination number is being altered.
PSTN
MSC (18)
(20)
ALERTING
(19)
(21) (22) (23)
NETWORK SETUP (DD..) NETWORK ALERTING
CONNECT (ANSWER)
CONNECT CONNECT ACKNOWLEDGMENT
(21) When the destination party goes off-hook the PSTN will inform the MSC of this event. This event usually triggers the beginning of billing. At this point the mobile station will be connected to the destination party.
(22) The MSC informs the mobile station that the connection has been established. (23) The mobile station acknowledges the receipt of the contact message.
(4) RELEASE-MOBILE INITIATED
Under normal conditions, the termination of a call is : • Mobile initiated • Network initiated Here we assume that the mobile initiates the release of the call .
Um
(24)
A
BSS
PSTN
MSC
DISCONNECT (TCH)
(25)
(26)
NETWORK RELEASE
RELEASE (TCH)
(24) The mobile user initiated the release of the call by pressing the end button on the mobile station . The mobile station sends a disconnect message to the MSC . (25) The PSTN party is notified of the termination of the call by a release message from the MSC . The end- to- end connection is terminated . (26) When the MSC determines that the call has no more reason to exist a release message is sent to the mobile station .
Um
(27)
BSS
A
MSC
RELEASE COMPLETE (TCH)
(28) (29)
CLEAR COMMAND
CHANNEL RELEASE (TCH)
(30)
CLEAR COMPLETE
(27) The MS answers back with release complete message . (28) The voice trunk between the MSC and the BSS is released . (29) The traffic channel is cleared . (30) The release of the resources is completed .
PSTN
LAND -TO -MOBILE CALL LINE
PSTN
VOICE TRUNK
MSC
VOICE TRUNK
BSS
PHASES OF LAND- TO- MOBILE CALL : (1) ROUTING ANALYSIS (2) PAGING (3) CALL SETUP (4) RELEASE
RADIO CHANNEL
(1) ROUTING ANALYSIS`
The following shows the scenario of Land-to-Mobile call. It is assumed that the mobile station is already registered with the system and has been allocated a Temporary Mobile Identity Number (TMSI) . It is assumed that the mobile station is visiting its home system .A land subscriber dials the directory number of a mobile subscriber .
HOME MSC
PSTN (1)
C
HLR
VLR
INCOMING CALL (MSISDN)
(2)
GET ROUTE (MSISDN)
(3)
ROUTING INFORMATION
(4) (5)
INCOMING CALL MSRN
PERFORM PAGE (LAI,IMSI)
(1) The PSTN routes the call to the home MSC of the mobile subscriber’s ISDN number (MSISDN) . (2) The MSC, not knowing whether this MS is roaming in its own service area or not , sends a message , with the MSISDN in it , to the HLR requesting it to provide routing information about this MS . (3) The HLR returns to the MSC a directory number where the MS can be reached , which is referred to as the Mobile Station Roaming Number (MSRN) . (4) The MSC then informs the VLR that a call is to be terminated to a mobile station . Included in this message is MSRN . (5) The VLR responds to the MSC by specifying the location area in which the mobile station is located and its IMSI .
(2) PAGING Um
BSS (6)
(7)
PAGE
A
HOME OR VISITED MSC
B
HOME OR VISITED VLR
PERFORM PAGE (TMSI)
(PCH)
CHANNEL REQUEST (8)
(RACH)
DEDICATED SIGNALING (9) CHANNEL ASSIGNMENT ( AGCH)
(6) The MSC uses the location area identity, provided by the VLR, to determine which BSSs should page the MS . The MSC transmits a message which includes the TMSI of the MS to each of these BSSs requesting that a page be performed . (7) Each of the BSSs broadcasts the IMSI of the mobile in a page message of the paging channel . (8) When a MS detects its IMSI, broadcast on the paging channel it responds with a channel request message over a common access channel,Random Access Channel (RACH) . (9) Once the base station receives the Channel Request message , it allocates a SDCCH and forwards this channel assignment information to the MS over the AGCH .
Um
(10)
BSS
A
HOME OR VISITED MSC
B
HOME OR VISITED VLR
PAGE RESPONSE (IMSI, LAI), (SDCCH)
(11)
PAGE RESPONSE (12)
PAGE RESPONSE
(10) The MS transmits a page response message to the BSS over the SDCCH. Included in this message is the mobile station IMSI & LAI .
(11) The BSS forwards the page response message to the MSC .
(12) The MSC informs its VLR that a particular MS is responding to a page .
(3) CALL SETUP
There are two steps in setting up voice path for a call from the PSTN to the mobile subscriber.
•The call set up with mobile- where a voice path is created between the MS and the MSC by allocating a radio traffic channel and a voice trunk.
•The call set up with a land network - Where a voice path is established between the MSC and the PSTN network.
CALL SETUP-WITH MOBILE HOME OR VISITED MSC
BSS CALL SETUP
(13) SDCCH
(14)
CALL SETUP CONFIRM SDCCH
(15)
ASSIGN RADIO & TRUNK CHANNEL
(13) After the MSC receives the Encipher Complete message from the mobile station, the mobile station is informed that the call will be set up via a set up message.
(14) The MS upon receiving a set up message performs compatibility checking and then acknowledges the call setup message with a setup confirm message. (15) The MSC selects a trunk (terrestrial channel) to the BSS. The MSC than sends a assignment request message to BSS requesting it to assign a radio resource.
HOME OR VISITED MSC
BSS (15) (16) (17)
ASSIGN RADIO & TRUNK CHANNEL
ASSIGN RADIO CHANNEL(SDCCH) RADIO ASSIGNMENT COMPLETE (SDCCH) (18)
TRUNK &RADIO ASSIGNMENT COMPLETE
(16) The BSS, upon receiving an Assignment Request Message, allocates a radio traffic channel and transmits an Assignment Command over the (SDCCH) to the mobile station informing it to tune to a new radio channel configuration.
(17) The Mobile Station tunes to the specified traffic channel and transmits an assignment complete message back to BSS.
(18) The BSS upon receiving the assignment complete message connects the assigned traffic channel to the trunk ( terrestrial facility)that was allocated by MSC. The BSS places the SDCCH on a free list and transmits an assignment complete message to the MSC .
CALL SETUP-WITH PSTN HOME OR VISITED MSC
PSTN (19) (21)
MOBILE ALERTING CONNECT (TCH)
(20) (22)
(23)
NETWORK ALERTING CONNECT
CONNECT ACKNOWLEDGE
(19) The mobile station will begin alerting the user after it receive a traffic channel assignment and sends an alerting message to the MSC. (20) The MSC upon receiving an alerting indication from the MS would begin generating audible ringing to the calling party and sends a network alerting to the PSTN.
(21) It is assumed that the mobile subscriber answers the phone . Now the MS stops alerting and sends a connect message to the MSC.
(22) The MSC removes audible to the PSTN and connects the PSTN trunk to the BSS trunk .
(23) The MSC sends the MS a connect acknowledgement message .
(4) RELEASE-NETWORK INITIATED Um
(25)
BSS
MSC (24)
DISCONNECT (TCH)
PSTN NETWORK RELEASE
RELEASE
(26) (27)
A
(TCH)
RELEASE COMPLETE (TCH)
(28) (29)
CLEAR COMMAND
CHANNEL RELEASE (TCH)
(30)
CLEAR COMPLETE
(24) The MSC receives a release message from the network to terminate the end-to-end connection . (25) This causes the sending of disconnect message towards the MS .
(26) The MS answers by a release message . (27) This is acknowledgement by a release complete from the MSC . (28) The voice trunk between the MSC and the BSS is cleared . (29) The traffic channel is released . (30) The resources are completely released .
MOBILE-TO-MOBILE CALL RADIO CHANNEL
BSS
VOICE TRUNK
MSC
VOICE TRUNK
BSS
RADIO CHANNEL
The call origination follows the following phases : •Request for service •Equipment validation •Call setup •Release The process of call origination is similar to the call being transferred from a mobile to land station . The call termination follows the following phases : •Routing analysis •Paging •Equipment validation •Call setup •Release The process of call termination is similar to the call being transferred from a land to mobile station .
