The document provides information on various GSM traffic cases including call setup, location updating, and call handover. It describes the processes for mobile originated and mobile terminated calls. Location updating includes normal location updating, IMSI attach, and periodic registration. It also outlines different types of call handover such as intra-BTS, inter-BTS intra-BSC, inter-BSC, and inter-MSC handovers.

1. GSM Traffic Cases
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING
(2016-2017)
TAE- 3
Technical PowerPoint Presentation
Subject:
Wireless Communication
Year/Semester: 4td Year | 7th Sem | Section: ‘C’
Submitted By:
Adarsh Pisey (24) | Akash J. Shahu(26) | Amol Wagh (27) |
Ashish M. Pandey (30) Mandar Muley (33)

2. GSM Traffic Cases
Introduction:
• The Traffic cases will include calls and the
operation that supports a Subscriber Mobility:
1. Location Updating Operations.
2. Handover Cases.
• All the possible GSM traffic cases consists of:
1. Call Establishments
2. Data Calls
3. Short Message Services.
GSM Traffic Cases
Cont..

3. GSM Traffic Cases
Introduction:
• The Mobile Station can be powered ‘off’, or the SIM card
can be removed from the mobile, or the mobile can be ‘on’
but located in an area without service.
• In all these cases, the mobile station is considered to be in
Detached condition.
• Otherwise, the mobile station can powered ‘on’ within the
GSM system and will subsequently enter into an attached
relationship with the system.
• The Mobile station is attached in Two different ways:
1. Ideal State
2. Active or Dedicated State
GSM Traffic Cases
Cont..

4. GSM Traffic Cases
Concept:
• In the Attached mode mobile station may
changes from Ideal to Active Mode.
• As the result of call setup, short message
service transfer, location updating or
supplementary service procedure.
GSM Traffic Cases

5. Types of GSM Traffic Cases
1. Call Setup
2. Location Updating
3. Call Handover
GSM Traffic Cases

6. CALL Setup
Call set up can be classified into two major
categories, they are:
1. Call From MS (Mobile Originated
call) (MOC).
2. Call to MS (Mobile Terminated call) ( MTC).
GSM Traffic Cases

7. CALL Setup
Call From MS (Mobile Originated call) (MOC).
• Mobile Originated call is possible when the
MS is attached with the MSC/VLR and is
listening to the system information.
1. The MS requests a SDCCH using RACH (
Point 1, 2a, 2b, 2c of Normal Location
Updating all are also occurred internally
or in background.)
2. The MS indicates that it wants to set up
a call. The identity of the MS, IMSI is
analyzed and the MS is marked as busy in
the VLR.
GSM Traffic Cases

8. CALL Setup
Call From MS (Mobile Originated call) (MOC).
3. Authentication is performed.
4. Ciphering may be initiated.
5. The MSC receives a setup message
from the MS. This includes the kind
of service the MS wants and the B-
number. MSC verify that the MS
doesn’t have services like barring of
outgoing calls. If the MS is not
barred, the setup of call proceeds.
GSM Traffic Cases

9. CALL Setup
Call From MS (Mobile Originated call) (MOC).
6. Between the MSC and the BSC a link
is established and a PCM time slot is
seized. The MSC sends a request to
the BSC to assign a TCH. The BSC
assigns a TCH to the call (if there is
an idle TCH available) and tells the
BTS to activate the channel. The BTS
sends an acknowledgement when
the activation is completed and the
BSC orders the MS to switch over to
the TCH. The BSC informs the MSC
when the assignment is complete.
GSM Traffic Cases

10. CALL Setup
Call From MS (Mobile Originated call) (MOC).
7. An alert message is sent to the MS
indicating that a ringing tone has been
generated on the other side. The
ringing tone generated in the
exchange on the B- subscriber side is
sent t the MS via the group switch in
the MSC.
8. When the B subscriber answers, the
network sends a connect message to
the MS indicating that the call is
accepted . The MS returns a connect
acknowledgement which completes
the call set-up.
GSM Traffic Cases

11. CALL Setup
Call to MS (Mobile Terminated call) ( MTC).
1. The number dialed by the calling party is
called the Mobile station ISDN number
(MSISDN). If the call is being made from a
PSTN exchange, the exchange analyses the
number and decides that the call is for a
GSM subscriber
2. From PSTN, the call is routed to the
GMSC in the home PLMN of the called MS.
3. By analyzing the MSISDN, the GMSC finds
out which HLR the subscriber is registered
in. GMSC asks the HLR for information so
the call can be routed to the MSC/VLR
where the MS is temporarily registered.
GSM Traffic Cases

12. CALL Setup
Call to MS (Mobile Terminated call) ( MTC).
4. The HLR contacts the VLR and gets the
roaming number.
5. The HLR forwards the roaming number to
the GMSC.
6. With the help of the roaming number (MSRN)
, the GMSC can route the call to the
appropriate MSC. The call is routed to the
MSC.
7. The MSC knows which location area the MS is
located in and sends a paging message to the
BSCs handling this location area.
8. The BSC distributes the paging message to
the BTSs in the LAI.
9. The BTSs page the MS using IMSI .
GSM Traffic Cases

13. Location Updating
 Need for Location updating:
• It should be possible for the MS to receive a call from the network at any
time at any location.
• While the MS moves freely within a network, the network should know
about its whereabouts, in terms of its location and the cell with which it is
attached.
• The MS should update the network whenever it changes the location and
is called Location Updating.
• Three types of location updating:
1. Location updating normal.
2. IMSI attach.
3. Periodic Registration.
GSM Traffic Cases

14. Location updating Normal.
Normal:
• A location area is the area handled by
one or more BTSs where the MS can
move around without updating the
network.
• A location area is controlled by one or
more BSCs but strictly by one MSC.
• MS gets the location area identity of the
serving cell, through listening the BCCH.
• MS compares the Location Area Identity
(LAI) to the one stored in the MS
through the SIM card & if LAI differs
from the one stored in the SIM card, the
MS decides to do a location update,
type normal.
GSM Traffic Cases

15. Location updating Normal.
Normal:
1. The MS listens to the system information
on BCCH Channel, compares the LAI
with the one stored in SIM card. When it
finds the difference, it decides to do an
location update.
2a. The MS sends a channel request
message through RACH channel.
2b. The message received by the BTS is
forwarded to the BSC. The BSC allocates
a SDCCH, if there is one idle, and tells
the BTS to activate it.
2c. BTS give acknowledgement on AGCH
channel.
GSM Traffic Cases

16. Location updating Normal.
Normal:
3. The MS sends a location updating
request message which contains the
identity of the MS, the identity of the
old location area and the type of
updating.
4a. The authentication parameter is sent to
the MS. If the MS is not already
registered in this MSC/VLR the
appropriate HLR or the previously used
MSC/VLR must be contacted to retrieve
MS subscriber data and authentication
parameters.
4b. MS sends an answer calculated using
the received authentication parameter.
GSM Traffic Cases

17. Location updating Normal.
Normal:
5. If authentication is successful, the VLR is
updated.
6. The MS receives an acceptance of the
location updating.
7a. The BTS is told to release the SDCCH.
7b. The MS is told to release the SDCCH and
switches to idle mode.
GSM Traffic Cases
During the location change, if the MS is busy in
call, it receives the information about the new
LAI on the SDCCH. The location updating (above
said procedure) takes place after the call is
released.

18. Location Updating IMSI attach
•MSI attach is used by the MS to notify
the system that it was powered on,
provided it is still
•in the same location area as it was
when it entered the detached state.
•This procedure is to be used only
when the IMSI detach flag is set in the
VLR.
•If the flag is set in the HLR, switching
to active mode
•requires a normal location updating of
the MS.
GSM Traffic Cases

19. Location Updating IMSI attach
1. The MS requests a SDCCH ( The
point number 1 , 2a, 2b , 2c all are
same as in Normal Updating).
2. The system receives the IMSI attach
message from the MS.
3. The MSC sends the IMSI attach
message to the VLR. The VLR
removes the IMSI detached flag and
resumes normal call handling for the
MS.
4. The VLR returns the IMSI attach
acknowledge message to the MSC.
5. The MS also receives an
acknowledge message.
GSM Traffic Cases

20. Location Updating Periodic
Registration
• Periodic registration is a type of location
updating procedure that is used to avoid
unnecessary paging of the mobile in
cases where the MSC never receives the
IMSI detach message and also to prevent
damage in case of database failure.
GSM Traffic Cases
1. The MS is informed via the system information if periodic registration is used in
the cell. If periodic registration is used, the MS is told how often it must register.
The time is set by a counter where the values are 0 to 255 deci-hours (a unit of six
minutes).
If the parameter is set to zero means periodic registration is not used, if the
parameter is set to twenty for example, then MS must register every two hours.

21. Location Updating Periodic
Registration
2. The procedure is controlled by a timer
both in the MS and in MS.
3. When the timer in the MS expires, the
MS performs a location updating, type
periodic registration and the timers in
MS and MSC restart.
4. In the MSC there is a time scanning
function for the MS, if the MS does not
register within the determined interval
plus a guard time, then the scanning
function in MSC detects this and the MS
is flagged as detached .
GSM Traffic Cases

22. Call Handover
GSM Traffic Cases
The process of handover or handoff within any cellular system is of great importance.
It is a critical process and if performed incorrectly handover can result in the loss of the
call.
Dropped calls are particularly annoying to users and if the number of dropped calls
rises, customer dissatisfaction increases and they are likely to change to another network.
Accordingly GSM handover was an area to which particular attention was paid when
developing the standard.
Types of Handover:
1. Intra-BTS handover:
2. Inter-BTS Intra BSC handover:
3. Inter-BSC handover:
4. Inter-MSC handover:

23. Call Handover
GSM Traffic Cases
Intra-BTS handover: This form of GSM handover occurs if it is required to change the
frequency or slot being used by a mobile because of interference, or other reasons. In this
form of GSM handover, the mobile remains attached to the same base station transceiver,
but changes the channel or slot.
Inter-BTS Intra BSC handover: This for of GSM handover or GSM handoff occurs when
the mobile moves out of the coverage area of one BTS but into another controlled by the
same BSC. In this instance the BSC is able to perform the handover and it assigns a new
channel and slot to the mobile, before releasing the old BTS from communicating with the
mobile.
Inter-BSC handover: When the mobile moves out of the range of cells controlled by one
BSC, a more involved form of handover has to be performed, handing over not only from
one BTS to another but one BSC to another. For this the handover is controlled by the
MSC.
Inter-MSC handover: This form of handover occurs when changing between networks.
The two MSCs involved negotiate to control the handover.