IMSI Detach - Discount Coupons · PDF fileIMSI Detach The MS must inform the network when it is entering an inactive state (detach). 1. At power off or when the SIM card is taken out,

IMSI Detach

The MS must inform the network when it is entering an

inactive state (detach).

1. At power off or when the SIM card is taken out, the MS asks for a signaling channel

2. The MS uses this signaling channel to send the IMSI detach message to the MSC/VLR.

3. In the VLR, an IMSI detach flag is set for the subscriber which is used to reject incoming calls to the MS.

The detach will not be acknowledged.

Section 5 – Call Handling

Only the VLR is updated with the “detached” information.


IMSI Attach

The attach procedure is performed only when the MS is turned on and is in the same LA as it was when it sent the detach message. If the MS changes location area while being switched off, it is forced to do a normal location update. The procedure is as follows

1. The MS requesting a signaling channel.

2. The MSC/VLR receives the IMSI attach message from the MS.

3. The MSC/VLR sets the IMSI attach in the VLR, that is, the mobile is ready for normal call handling.

4. The VLR returns an acknowledgment to the MS.



Periodic Location Update

To avoid unnecessary paging of the MS in case the MSC never got the IMSI detach message, there is another type of location updating called periodic registration.

The procedure is controlled by timers both in the MS and in the MSC.

If the MS does not register within the determined interval plus a guard time, then the scanning function in the MSC detects this and the MS will be marked detached.


Paging

A call to MS is routed to the MSC/ VLR and send a paging message to the MS. This message is broadcast all over the Location Area (LA), which means that all BTSs with in the LA will send a paging message to the mobile. The MS, moving in the LA and listening to the CCCH information, will hear the paging message and answer it immediately.


Paging Capacity

Paging capacity is the number of mobiles that can be paged per second

This depends on: • CCCH configuration • AGCH blocks reservation • Type of paging message used • Paging message takes 4 bursts

(1 CCCH block) • This can page up to 4 mobiles

depending on the message type used


Paging Message Types

Type 1: can address up to two mobiles using either IMSI or TMSI

Type 2: can address up to 3 mobiles, one by IMSI and other 2 by TMSI.

Type 3: can address up to 4 mobiles using the TMSI only.

If the network does not use TMSI then only type 1 is used in the network.


Calculation Of Paging Capacity

X = number of mobiles paged per paging message (1 to 4)

Y = number of possible paging messages per multiframe

Duration of channel multiframe = 0.235 seconds (235 ms)

• X depends on paging message type

• Y depends on CCCH configuration in the multiframe (e.g. 3 or 9) and the number of AGCH blocks reserved


PCH Dimensioning

Paging channel requirement in blocks per multiframe is given by:

Calls = Number of calls predicted for the location area during busy hour

MT = Fraction of calls which are mobile terminated

PF = Paging Factor = number of pages required per call

M = safety margin

PMF = Paging Message Factor = number of pages per message

Number of control channel multiframes per second = 4.25


Example

A particular location area contains 50 000 subscribers. It is predicted that 30% of these will receive a call during the busy hour. On average 2 pages are needed per call and only type 3 paging messages (TMSI) are used.

This gives the following data: Calls = 50 000 MT = 0.3 PF = 2 PMF = 4


A typical safety margin for peak variations in number of calls is 1.2

• 1 PCH block per multiframe will be adequate


Paging Control

The MSC has to initiate the paging procedure, as it holds the information on the last MS location update.

MSC sends a paging message to BSC and sets a timer for response from the MS, which is send as a part of service request message. The paging message from the MSC contains a cell list identifier, identifying the cells in which paging message is to be transmitted.


Call From MS (Mobile to PSTN)

cb

VLR

MSC Exch PSTN

PLMN


Call From MS Overview

• Mobile is active and idle, wants to set up a call

• User dial the number and press send, at first moment it sends on RACH

• MSC/VLR assigns a dedicated channel

• If the calling MS is allowed to make a call MSC/VLR acknowledges the access request

• Depending on whether a fixed or a mobile subscriber is called, number is analyzed directly in the MSC/VLR.

• Call setup message is acknowledged as soon as the link is ready.

• MS is also assigned to move to a dedicated traffic channel TCH.


Signaling Interfaces

BSC

VLR

MSC

LAPDm

LAPD

DTAP

BSSMAP

PLMN ISDN/PSTN

ISUP/TUP


Point Of Interconnect (POI) Location

In case of long distance mobile to PSTN call, circuits define to route a call in the switch should be such that, call can travel maximum distance on the airtime and minimum on the land line to enhance the revenue.

Call should handover to the POI as near as possible to the subscriber location.


Call to MS (PSTN to Mobile)

GMSC

GSM/PLMN

PSTN MSISDN

Link is setup from local exchange to the GMSC


GMSC

GSM/PLMN

PSTN

HLR

signaling No.7: Interrogation function used by GMSC

MSISDN + MSRN request


GMSC

GSM/PLMN

PSTN

HLR

VLR

MSC

signaling No7: Request for MSRN to VLR

IMSI


GMSC

GSM/PLMN

PSTN

HLR

VLR

MSC

IMSI

MSRN in VLR. signaling No 7: MSRN send to GMSC

MSRN request + IMSI MSRN


GSM/PLMN

PSTN

VLR

MSC GMSC

Link is setup from GMSC to MSC/VLR

HLR


GSM/PLMN

PSTN

VLR

MSC GMSC HLR BSC

signaling No7: Paging message is sent to the BSS


GSM/PLMN

PSTN

VLR

MSC GMSC

HLR

BSC

Air path signaling: Paging message is sent over the air path to MS. The MS answers.


GSM/PLMN

PSTN

VLR

MSC GMSC

HLR

BSC

The link is setup from the MSC/VLR to the MS, completing the connection from subscriber to subscriber


Signaling Interfaces

BSC

VLR

MSC

LAPDm

LAPD

DTAP

BSSMAP

PLMN ISDN/PSTN

ISUP/TUP

HLR

GMSC

MAP

ISUP/TUP


Mobile to Mobile (Mobile Originated)

MS BTS BSC MSC Channel Request

rn Channel Request

rn+fn+TA

SDDCH Allocation

TA+SDDCH+power

Channel Activation

SCCP Connection Req

Immediate assign (AGCH) Immediate assign commd

Switch to SDDCH

rn+fn+TA+ SDCCH

Channel Activation Ack

SABM

Establish Indication

SCCP Connection Confirm

Service Request

Service Request

UA

Cm+Service Request


MS BTS BSC MSC

Setup (SDCCH)

Tele/bearer service called party no.

Layer 3CC Layer 3CC

Layer 3CC Layer 3CC Call proceeding

Assignment request

Channel type+cm TCH allocation

Physical context request

Physical context confirm

Power+TA Channel activation

TCH+TA+cipher+DTX+power

SACCH

TA+power updates

Channel activation ack

Assignment command (SDCCH)

Release SDCCH


MS BTS BSC MSC

SABM (FACCH)

Establish indication

UA (FACCH) Set transcoder

Assignment complete (FACCH)

Set switching path

alerting

connect

Layer 3CC

Layer 3CC

Layer 3CC

Layer 3CC

Layer 3CC

Connect ack

Initiate SDCCH release


Mobile to Mobile (Mobile Terminated)

MS BTS BSC MSC

Paging

TMSI/IMSI+cell list Paging command

TMSI/IMSI paging group+ channel no TMSI/IMSI

Paging request (PCH)

Paging request (RACH)

Channel required

Radio and Link Establishment Procedure


MS BTS BSC MSC

Layer 3CC Layer 3CC Setup

Tele/bearer service

Layer 3CC Layer 3CC

Call confirmed (SDCCH) bearer service

Normal Assignment Procedure for TCH

alerting Layer 3CC

Layer 3CC

Layer 3CC Layer 3CC

connect

Layer 3CC Layer 3CC Connect acknowledge

Ring tone

User answer


SMS Point to Point

The Short Message Service, SMS, provides means of sending text messages, to and from GSM mobile station. SMS makes use of service centre, which acts a store and forward center for short messages.


Mobile Terminated SMS

SMS - C SMS - GMSC MSC/VLR

HLR


SMS –C has the capability to transfer the short messages and also

provides the information about the delivery.

1. A user sends a message to an SMS – C

2. SMS – C sends the message to the SMS – GMSC

3. SMS – GMSC interrogates the HLR for routing information

4. HLR interrogates MSC/VLR for a roaming number

5. MSC/VLR returns a MSRN to the SMS – GMSC via HLR

6. SMS – GMSC reroutes the message to MSC/VLR

Continued…..


7. MS is paged and a connection is setup between MS and the

network.

8. If authentication was successful the MSC/VLR delivers the message to the MS. It is transmitted on the allocated SDCCH

9. If the delivery was successful a delivery report is sent from MSC/VLR to the SMS – C.

In the case of an unsuccessful delivery the service messages waiting will provide the HLR and VLR with the information that there is a message in the originating SMS – C waiting to be delivered to the MS.


Documents

IMSI Detach - Discount Coupons · PDF fileIMSI Detach The MS must inform the network when it is entering an inactive state (detach). 1. At power off or when the SIM card is taken out,