Wireless And Mobile Communication

1. Paging and
Location Update
By: Abidullah Zarghoon

2. Some Terms:
• MSC/VLR - Mobile Switching Center / Visitor
Location Register
• HLR - Home Location Register
• PLMN - Public Land Mobile Network
• TMSI – Temporary Mobile Subscriber Identity
• LA - Location Area
• LAI - Location Area Identity
• LAC - Location Area Code
• LU – Location Update

3. • MS - The Mobile Station
• BSS - The Base Station Subsystem
• NSS - The Network Switching Subsystem
• OSS - The Operation Support Subsystem

4. Overview
• A GSM or UMTS network, like all cellular networks, is
basically a radio network of individual cells, known
as base stations.
• Each base station covers a small geographical
area which is part of a uniquely identified location
area.

5. Location Area
• A location area is a set of base stations that are
grouped together to optimize signaling
• Location Area is a group of cells and the subscriber
is paged in this area.
• One or more base station controllers are used to
serve each Location Area but by a single MSC.
• Each Location Area has a unique Location Area
Identity number.

6. Location Area Update
• The mobile station also performs location updating,
in order to indicate its current location, when it
moves to a new Location Area or a different Public
Land Mobile Network (PLMN). This location updating
message is sent to the new MSC/VLR, which gives
the location information to the subscriber's HLR. If
the mobile station is authorized in the new
MSC/VLR, the subscriber's HLR cancels the
registration of the mobile station with the old
MSC/VLR.

7. Location Update
Procedure
• The location update procedure allows a mobile
device to inform the cellular network, whenever it
moves from one location area to the next.
• Mobiles are responsible for detecting location area
codes.
• When mobile finds that location area code is
different from its last update, it performs another
update by sending to the network, a location
update request, together with its previous location
and TMSI (Temporary Mobile Subscriber Identity)

8. Periodic Location Update
• A location updating is also performed periodically.
If after the updating time period, the mobile station
has not registered, it is then deregistered.
• Each mobile is required to regularly report its
location at a set time interval using a periodic
location update.

9. Random Location Update
• Whenever a mobile moves from one location area
to the next while not on a call, a random location
update is required.
• This is also required of a stationary mobile that
reselects coverage from a cell in a different
location area, because of signal fade.

10. Continued…
• When a subscriber is paged in an attempt to deliver
a call or SMS and the subscriber does not reply to
that page then the subscriber is marked as absent
in both the Mobile Switching Center / Visitor
Location Register (MSC/VLR) and the Home
Location Register (HLR) (Mobile not reachable flag
MNRF is set). The next time the mobile performs a
location update the HLR is updated and the mobile
not reachable flag is cleared.

11. Paging
• Paging is the one-to-one communication between
the mobile and the base station
• Paging is a procedure the network uses to find out a
subscriber’s location before actual call
establishment.
• Paging is used to alert the mobile station of an
incoming call.

12. • Paging is initiated by the NSS (Network Subsystem)
and is based on the Location Registration
information the Mobile Subscriber has supplied
when performing the Location Update.

13. Paging Strategies
• Location Area Splitting in Paging Areas
o Mobile registers only when entering the Location Area; it doesn’t register
when moving between Paging Areas of one Location Area.
o For an incoming call, paging messages are broadcasted in the Paging
Areas according to a sequence determined by different strategies.

14. Location Area Splitting in
Paging Areas

15. Paging Strategies
• Multilayer Location Areas:
o Each mobile is assigned to a given group, and each group is assigned
one or several layers of Location Areas.
o Location Update traffic is distributed over all the cells.
o Multilayer Las solves the problem where Location Update traffic is mainly
concentrated in the cells of the Location Area border.

16. Multilayer Location
Areas:

17. Differences between Paging
and Location Update
• Mobility Management
based on pure Paging
o If a call arrives, terminal is
paged in all cells of the mobile
network
o Location update is not
required
o As paging must be executed
in all cells of the network for
each arriving call/SMS/data-
packet
• high signaling overhead
• high delay in
call/SMS/data-packet
delivery
• Mobility Management
based on pure Location
Update:
o Each time the user crosses cell
boundaries a location update
is triggered
o Paging is not required
o As location updates must be
initialized whenever crossing
cell boundaries
• high signaling and
database update
overhead
• high power consumption in
the terminals

18. • Location Update• Paging

19. Some Definitions
• TMSI:
o The Temporary Mobile Subscriber Identity (TMSI) is a temporary
identification number that is used in the GSM network instead of the IMSI
to ensure the privacy of the mobile subscriber
• LAI
o A Location Area Identity (LAI) is a globally unique number.
• LAC
o A Location Area Code (LAC) is only unique in a particular network

20. • Cell:
o Cell is the basic service area: one BTS covers one cell. Each cell is given a
Cell Global Identity (CGI), a number that uniquely identifies the cell.
• MSC/VLR Service Area:
o The area covered by one MSC is called the MSC/VLR service area.
• PLMN
o The area covered by one network operator is called PLMN. A PLMN can
contain one or more MSCs.
o A network that is established and operated by an administration or by
a recognized operating agency (ROA) for the specific purpose of
providing land mobile telecommunications services to the public

21. References:
• Advances in Network Management
o By Jianguo Ding – 2009